The recycling of heavy metal contaminants from wastewater as a source of valuable products perfec... more The recycling of heavy metal contaminants from wastewater as a source of valuable products perfectly fits with the principles of a Circular Economy system in view of restoring pollutants back into the system endowed with new social and economic benefits. Heavy metals are often present in such a low concentration that it makes the removal efficiency difficult to realize through the conventional physicochemical methods with high selectivity. Biosorption, conversely, by EPSs (extracellular polymeric substances) produced by several bacterial cells’ strains, is gaining a great deal of attention as an economic, efficient and sustainable depolluting process of wastewater from metal cations such as copper. Metal coordination to EPS components was thus deeply investigated by 1H NMR titration experiments. The 1,10–Phenanthroline–copper complex was exploited for quantifying the ability of different strains to sequester copper by a practical UV-Vis spectrophotometric method. The obtained data d...
World Journal of Microbiology and Biotechnology, 2019
Iron-and sulfur-oxidizing bacteria inhabiting rice rhizoplane play a significant role on arsenic ... more Iron-and sulfur-oxidizing bacteria inhabiting rice rhizoplane play a significant role on arsenic biogeochemistry in flooded rice paddies, influencing arsenic translocation to rice grains. In the present study, the selective pressure of arsenic species on these microbial populations was evaluated. Rice roots from continuously flooded plants were incubated in iron sulfide (FeS) gradient tubes and exposed to either arsenate or arsenite. The biomass developed in the visible iron-oxidation band of the enrichments was analyzed by Scanning Electron Microscopy and Energy-Dispersive Spectroscopy (SEM-EDS) and the bacterial communities were characterized by 16S rRNA gene sequencing. Different Proteobacteria communities were selected depending on exposure to arsenate and arsenite. Arsenate addition favored the versatile iron-oxidizers Dechloromonas and Azospira, associated to putative iron (hydr)oxide crystals. Arsenite exposure decreased the diversity in the enrichments, with the development of the sulfur-oxidizer Thiobacillus thioparus, likely growing on sulfide released by FeS. Whereas sulfur-oxidizers were observed in all treatments, iron-oxidizers disappeared when exposed to arsenite. These results reveal a strong impact of different inorganic arsenics on rhizospheric ironoxidizers as well as a crucial role of sulfur-oxidizing bacteria in establishing rice rhizosphere communities under arsenic pressure.
The genus Thioalkalivibrio includes haloalkaliphilic chemolithoautotrophic sulfur-oxidizing bacte... more The genus Thioalkalivibrio includes haloalkaliphilic chemolithoautotrophic sulfur-oxidizing bacteria isolated from various soda lakes worldwide. Some of these lakes possess in addition to their extreme haloalkaline environment also other harsh conditions, to which Thioalkalivibrio needs to adapt. An example is arsenic in soda lakes in eastern California, which is found there in concentrations up to 3000 µM. Arsenic is a widespread element that can be an environmental issue, as it is highly toxic to most organisms. However, resistance mechanisms in the form of detoxification are widespread and some prokaryotes can even use arsenic as an energy source. We first screened the genomes of 76 Thioalkalivibrio strains for the presence of known arsenic oxidoreductases and found 15 putative ArxA (arsenite oxidase) and two putative ArrA (arsenate reductase). Subsequently, we studied the resistance to arsenite in detail in Thioalkalivibrio jannaschii ALM2 T , and Thioalkalivibrio thiocyanoxidans ARh2 T by comparative genomics and by growing them at different arsenite concentrations followed by arsenic species and transcriptomic analysis. Tv. jannaschii ALM2 T , which has been isolated from Mono Lake, an arsenic-rich soda lake, could resist up to 5 mM arsenite, whereas Tv. thiocyanoxidans ARh2 T , which was isolated from a Kenyan soda lake, could only grow up to 0.1 mM arsenite. Interestingly, both species oxidized arsenite to arsenate under aerobic conditions, although Tv. thiocyanoxidans ARh2 T does not contain any known arsenite oxidases, and in Tv. jannaschii ALM2 T , only arxB2 was clearly upregulated. However, we found the expression of a SoeABC-like gene, which we assume might have been involved in arsenite oxidation. Other arsenite stress responses for both strains were the upregulation of the vitamin B 12 synthesis pathway, which can be linked to antioxidant activity, and the up-and downregulation of different DsrE/F-like genes whose roles are still unclear. Moreover, Tv. jannaschii ALM2 T induced the ars gene operon and
The possible generation of oxidative stress induced by aromatic hydrocarbon degradation suggests ... more The possible generation of oxidative stress induced by aromatic hydrocarbon degradation suggests that ancillary enzyme activities could facilitate the utilization of polycyclic aromatic hydrocarbons as sole carbon source. To investigate the metabolic profiles of low molecular weight polycyclic aromatic hydrocarbon-degrading strains of Sphingobium chlorophenolicum, Rhodococcus aetherovorans, Rhodococcus opacus and Mycobacterium smegmatis, the determination of the activity of putative detoxifying enzymes (rhodanese-like and glutathione S-transferase proteins) was combined with genetic analyses. All the studied strains were able to utilize phenanthrene or naphthalene. Glutathione S-transferase activity was found in S. chlorophenolicum strains grown on phenanthrene and it was related to the presence of the bphK gene, since modulation of glutathione S-transferase activity by phenanthrene paralleled the induction of glutathione S-transferase transcript in the S. chlorophenolicum strains. No glutathione S-transferase activity was detectable in R. aetherovorans, R. opacus and in M. smegmatis strains. All strains showed 3-mercaptopyruvate:cyanide sulfurtransferase activity. A rhodanese-like SseA protein was immunodetected in R. aetherovorans, R. opacus and in M. smegmatis strains, where increase of 3-mercaptopyruvate:cyanide sulfurtransferase activity was significantly induced by growth on phenanthrene.
Achromobacter sp. strain N2 was isolated from a pyrite-cinder-contaminated soil and presented pla... more Achromobacter sp. strain N2 was isolated from a pyrite-cinder-contaminated soil and presented plant-growth promoting traits (ACC deaminase activity, production of indole-3-acetic and jasmonic acids, siderophores secretion and phosphate solubilization) and arsenic transformation abilities. Achromobacter sp. strain N2 was resistant to different metals and metalloids, including arsenate (100 mM) and arsenite (5 mM). The strain was resistant to ionic stressors (i.e. arsenate and NaCl), whereas bacterial growth was impaired by osmotic stress. Strain N2 was able to oxidize 1.0 mmol L-1 of arsenite to arsenate in 72 h. This evidence was supported by the retrieval of an arsenite oxidase AioA gene highly homologous to arsenite oxidases of Achromobacter and Alcaligenes species. Rice seeds of Oryza sativa (var. Loto) were bio-primed with ACCD-induced and noninduced cells in order to evaluate the effect of inoculation on rice seedlings growth and arsenic uptake. The bacterization with ACCD-induced cells significantly improved seed germination and seedling heights if compared with the seeds inoculated with noninduced cells and non-primed seeds. Enhanced arsenic uptake was evidenced in the presence of ACCD-induced cells, suggesting a role of ACCD activity on the mitigation of the toxicity of arsenic accumulated by the plant. This kind of responses should be taken into account when proposing PGP strains for improving plant growth in arsenicrich soils. See attachment.
A rhizobacterial community, associated with the roots of wild thistle Cirsium arvense (L.) growin... more A rhizobacterial community, associated with the roots of wild thistle Cirsium arvense (L.) growing in an arsenic polluted soil, was studied by fluorescence in situ hybridization (FISH) analysis in conjunction with cultivation-based methods. In the bulk, rhizosphere, and rhizoplane fractions of the soil, the qualitative picture obtained by FISH analysis of the main phylogenetic bacterial groups was similar and was predominantly comprised of Alphaproteobacteria, Betaproteobacteria, and Gammaproteobacteria. The arsenic-resistant isolates belonged to 13 genera, the most abundant being those of Bacillus, Achromobacter, Brevundimonas, Microbacterium, and Ochrobactrum. Most bacteria grew in the presence of high arsenic concentrations (over 100 mM arsenate and 10 mM arsenite). Most strains possessed the ArsC, ArsB and ACR3 genes homologous to arsenate reductase and to the two classes of arsenite efflux pumps, respectively, peculiar to the ars operon of the arsenic detoxification system. ArsB and ACR3 were present simultaneously in highly resistant strains. An inconsistency between 16S rRNA phylogenetic affiliations and the arsenate reductase sequences of the strains was observed, indicating possible horizontal transfer of arsenic resistance genes in the soil bacterial community. Several isolates were able to reduce arsenate and to oxidise arsenite. In particular, Ancylobacter dichloromethanicum strain As3-1b possessed both characteristics, and arsenite oxidation occurred in the strain also under chemoautotrophic conditions. Some rhizobacteria produced siderophores, indole acetic acid and 1-amino-cyclopropane-1-carboxylic acid deaminase, thus possessing potential plant growth-promoting traits.
A heterotrophic arsenite-oxidizing bacterium, strain 2WW, was isolated from a biofilter treating ... more A heterotrophic arsenite-oxidizing bacterium, strain 2WW, was isolated from a biofilter treating arsenic-rich groundwater. Comparative analysis of 16S rRNA gene sequences showed that it was closely related (98.7 %) to the alphaproteobacterium Aliihoeflea aesturari strain N8(T). However, it was physiologically different by its ability to grow at relatively low substrate concentrations, low temperatures and by its ability to oxidize arsenite. Here we describe the physiological features of strain 2WW and compare these to its most closely related relative, A. aestuari strain N8(T). In addition, we tested its efficiency to remove arsenic from groundwater in combination with Pf-ferritin. Strain 2WW oxidized arsenite to arsenate between pH 5.0 and 8.0, and from 4 to 30 °C. When the strain was used in combination with a Pf-ferritin-based material for arsenic removal from natural groundwater, the removal efficiency was significantly higher (73 %) than for Pf-ferritin alone (64 %). These resu...
Pseudomonas putida CM37, Pseudomonas aureofaciens CM32 and Pseudomonas putida CM23 degraded tolue... more Pseudomonas putida CM37, Pseudomonas aureofaciens CM32 and Pseudomonas putida CM23 degraded toluene through different pathways. CM37 carried xylA,M gene for xylene monooxygenase (TOL pathway), CM32 carried todC1 gene for toluene dioxygenase (TOD pathway) and CM23 carried both genes and was charac- terised by the contemporary presence of TOL and TOD pathways. In this study we com- pared the behaviour of
Journal of Environmental Science and Health . Part A: Environmental Science and Engineering and Toxicology, 1995
... (% average) Specific load (Kg C0D/m3d) HRT (h) Total biogas (L/d ... [2] Bull MA, Sterritt RM... more ... (% average) Specific load (Kg C0D/m3d) HRT (h) Total biogas (L/d ... [2] Bull MA, Sterritt RM and Lester JN An evaluation of four start-up regimes for anaerobic fluidized bed reactors. ... [5] Denac M. and Dunn IJ Packed-and fluidized-bed biofilm reactor performance for anaerobic ...
A rhizobacterial community, associated with the roots of wild thistle Cirsium arvense (L.) growin... more A rhizobacterial community, associated with the roots of wild thistle Cirsium arvense (L.) growing in an arsenic polluted soil, was studied by fluorescence in situ hybridization (FISH) analysis in conjunction with cultivation-based methods. In the bulk, rhizosphere, and rhizoplane fractions of the soil, the qualitative picture obtained by FISH analysis of the main phylogenetic bacterial groups was similar and was predominantly comprised of Alphaproteobacteria, Betaproteobacteria, and Gammaproteobacteria. The arsenic-resistant isolates belonged to 13 genera, the most abundant being those of Bacillus, Achromobacter, Brevundimonas, Microbacterium, and Ochrobactrum. Most bacteria grew in the presence of high arsenic concentrations (over 100 mM arsenate and 10 mM arsenite). Most strains possessed the ArsC, ArsB and ACR3 genes homologous to arsenate reductase and to the two classes of arsenite efflux pumps, respectively, peculiar to the ars operon of the arsenic detoxification system. ArsB and ACR3 were present simultaneously in highly resistant strains. An inconsistency between 16S rRNA phylogenetic affiliations and the arsenate reductase sequences of the strains was observed, indicating possible horizontal transfer of arsenic resistance genes in the soil bacterial community. Several isolates were able to reduce arsenate and to oxidise arsenite. In particular, Ancylobacter dichloromethanicum strain As3-1b possessed both characteristics, and arsenite oxidation occurred in the strain also under chemoautotrophic conditions. Some rhizobacteria produced siderophores, indole acetic acid and 1-amino-cyclopropane-1-carboxylic acid deaminase, thus possessing potential plant growth-promoting traits.
This study reports the isolation from an agricultural metal impacted soil of a cadmium-resistant ... more This study reports the isolation from an agricultural metal impacted soil of a cadmium-resistant bacterium and its ability to bioprecipitate cadmium and zinc ions in solution. From the biomass of the cadmium-tolerant population, among the most dominant bacterial colonies, a Pseudomonas putida strain B14 was isolated and identified. The microorganism showed a simultaneous resistance to Cd, Zn, Pb, Co, Ni and Cu. P. putida B14 in the presence with either 1 mmol L-1 Cd(II) or Zn(II) removed the Cd(II) almost completely and about 80% of the Zn(II) from the aqueous solution, precipitating them as crystals. Cadmium was removed mainly as CdCO3 by a gratuitous mechanism in conse- quence of the CO2-generating metabolism. The possibility of using multiple-metal resist- ant bacteria to immobilise heavy metals, and facilitate their removal, could contribute to the implementation of a strategy of bioremediation for polluted waters and industrial waste waters.
Enrichment cultures on naphtha solvent were used to select aromatic hydrocarbon-degrading bacteri... more Enrichment cultures on naphtha solvent were used to select aromatic hydrocarbon-degrading bacteria from a BTEX (benzene, toluene, ethylbenzene, xylene)-contaminated subsoil obtained from beneath a paint factory located in Milan, Italy. Fifteen isolated strains were studied for their different biodegradative capacities. Among these, 13 were able to grow on naphtha solvent. Ten were identified as Pseudomonas putida and three as Pseudomonas aureofaciens. Two other degraders were identified as Pseudomonas aeruginosa and Alcaligenes xylosoxidans subsp. denitrificans. Further molecular characterization of the isolates was carried out by randomly amplified polymorphic DNA analysis to ascertain that all the studied strains belonged to different haplotypes. The isolates were characterized for the presence of genes encoding for toluene dioxygenase, xylene monooxygenase and catechol 2,3-dioxygenase by polymerase chain reaction analysis and by Southern analysis. P. putida strain CM23, which showed homology with xylA,M, xylE and todC1C2BA genes, possessed multiple pathways which enabled the strain to grow on benzene, toluene and m-xylene.
A selected mixed culture and a strain of Alcaligenes eutrophus TCP were able to totally degrade 2... more A selected mixed culture and a strain of Alcaligenes eutrophus TCP were able to totally degrade 2,4,6-TCP with stoichiometric release of Cl − . In cultures of Alc. eutrophus TCP, a dioxygenated dichlorinated metabolite was detected after 48 h of incubation. Experiments conducted with soil microcosms gave evidence that : the degradative process had a biotic nature and was accompanied by microbial growth ; the soil used presented an intrinsic degradative capacity versus 2,4,6-TCP ; the specialized organism used as inoculum was effective in degrading 2,4,6-TCP in a short time. These results could be utilized for the adoption of appropriate remediation techniques for contaminated soil.
Journal of Environmental Science and Health, Part B, 1994
Laboratory experiments were conducted to study the degradation of acifluorfen 5-[2-chloro-4-(trif... more Laboratory experiments were conducted to study the degradation of acifluorfen 5-[2-chloro-4-(trifluoromethyl)-phenoxyl]-2-nitrobenzoic acid by a mixed microbial population. Concentrations of acifluorfen up to 100 mg/l had no inhibitory effect on the growth of microbial culture. The microorganisms degraded acifluorfen through a cometabolic process in presence of 2-nitrobenzoate. The degradation rate of acifluorfen, determined by liquid chromatography analysis in batch cultures incubated under oxygen-limited conditions were compared. The degradation was slower under oxygen than oxygen-limited conditions. Aminoacifluorfen was produced in both conditions.
Journal of Environmental Science and Health, Part A, 1998
Anaerobic digestion of winery effluents derived from two different wine making processes was comp... more Anaerobic digestion of winery effluents derived from two different wine making processes was compared in a laboratory scale upflow filter. White winery effluents (WWE) were more easily degradable (average soluble COD removal=92%) than red winery effluents (RWE) (average soluble COD removal = 85%). Differences in the reactor microbial populations for the two effluents were also observed. Both aceticlastic and hydrogenotrophic methanogens in the circulating fractions were significantly higher during the treatment of WWE than during that of RWE. With both wastewaters, the reactor promptly reacted to volumetric organic load (Bv) stress (tripling from 4 to 12 g COD L d). Following the Bv perturbation, COD removal decreased to 50%. However, after two weeks the COD removal values were as before perturbation. Volatile fatty acids, especially total VFAs and butyrate measured on the second day after the imposed Bv perturbation, were good indicators of process imbalance. Coenzyme F420 determination and scanning electron microscopy revealed the presence of Methanosaeta like cells embedded to extracellular polymers in a uniform slime matrix in the biofilm. The main methanogens observed in the effluents were Methanosarcina and Methanobrevibacter cells.
Different soil samples characterised by a long-term Hg-pollution were studied for Hg total conten... more Different soil samples characterised by a long-term Hg-pollution were studied for Hg total content, fractionation, phytotoxicity and influence on the bacterial community. Hg pollution ranged from 1 to 50 mg kg À1 and most of it was speciated in scarcely soluble forms. In agreement with this, the biochemical quality indexes were investigated (biomass, enzyme activities) and the bacterial community (viable heterotrophic (VH) bacteria, functional diversity) apparently was not influenced by the degree of Hg pollution. In particular, the investigated soils exhibited a low percentage of Hg-resistant (Hg R ) bacteria ranging from less than 0.001% to 0.25% of the VH and the addition of available Hg in the form of HgCl 2 induced an enrichment of resistant Hg R populations. The general biodiversity of the bacterial community was evaluated by denaturing gradient gel electrophoresis of DNA of Hg spiked soil microcosms and of control soils. Hg R bacteria capable to grow in a minimal medium containing HgCl 2 were also isolated and identified. MerA and merB gene PCR fragments were obtained from different Hg R strains and the range of similarities at the DNA level and at the deduced amino acid level showed that they carried mercuric reductase and lyase. Differently from bacteria, some influence of soil Hg content on seeds' germination and root elongation was observed for Lepidium sativum L. and Solanum lycopersicum L. In conclusion, most of the Hg in these long-term polluted soils was scarcely mobile and available and did not significantly influence the soil bacterial community. The risk of potential Hg remobilisation over time, that could be naturally favoured by the activity of plant roots or other inorganic processes occurring in soil, can be extenuated since bacterial community was resistant and resilient to subsequent Hg stress.
The survival and activity of Rhodococcus sp. strain 1BN, inoculated into naphthalenecontaminated ... more The survival and activity of Rhodococcus sp. strain 1BN, inoculated into naphthalenecontaminated sandy-loam soil microcosms, were studied using classical and molecular methods. Methods and Results: The naphthalene-degrading activity of 1BN in microcosms was examined through viable counts, CO 2 production and naphthalene consumption, while its survival after inoculation was monitored by detecting the contemporary presence of alkane and naphthalene degradative genes and by analysing the 16S rDNA specific restriction profile. The inoculation of 1BN did not significantly enhance naphthalene degradation in the naphthalenecontaminated native soil, where 1BN maintained its catabolic activity also when in the presence of indigenous microflora. Instead the rate of naphthalene degradation by the inoculated 1BN was greater in sterile naphthalene-contaminated soil. The level of 1BN was only slightly higher after inoculation regardless of whether indigenous naphthalene-degrading bacteria were present or not and 1BN remained viable even when the substrate was depleted.
International Biodeterioration & Biodegradation, 2011
The aim of the research was to verify if a Sphingobium chlorophenolicum strain C3R was effective ... more The aim of the research was to verify if a Sphingobium chlorophenolicum strain C3R was effective in the degradation of phenanthrene (Ph) in agricultural soil co-contaminated by metals and mixtures of PAHs. The presence of PAHs in mixtures produced interactive effects which could either increase or decrease the utilization rate of Ph by C3R and by the native bacterial microflora. Bioaugmentation significantly improved the biodegradation rate of Ph in the presence of both cadmium and arsenic and PAH mixtures. The augmented C3R strain persisted in inoculated microcosms as monitored by the DGGE analysis and outcompeted some indigenous bacteria. The potential role of the soil bacteria in PAH degradation could be envisaged. The results indicate the applicability of S. chlorophenolicum C3R toward in situ bioremediation of sites contaminated with phenanthrene alone or co-contaminated with low molecular weight PAHs and with cadmium and arsenate.
Rhodococcus sp. 1BN was isolated from a contaminated site and showed various biodegradative capab... more Rhodococcus sp. 1BN was isolated from a contaminated site and showed various biodegradative capabilities. Besides naphthalene, strain 1BN degraded medium-(C 6 ) and long-chain alkanes (C 16 ±C 28 ), benzene and toluene, alone or when the hydrocarbons were mixed in equal proportions. The nucleotide sequence of an alk polymerase chain reaction (PCR) fragment revealed a 59% nucleotide homology to the Pseudomonas oleovorans alkB gene. The nar fragments were highly homologous to genes coding for large and small subunits of cis-naphthalene 1,2-dioxygenase (narAa and narAb) and to cis-naphthalene dihydrodiol dehydrogenase (narB) from other rhodococci. The oxidation of indene to cis-(1S,2R)-1,2dihydroxyindan by toluene-induced cells allows to hypothesize that strain 1BN also carries a toluene dioxygenase-like system.
The recycling of heavy metal contaminants from wastewater as a source of valuable products perfec... more The recycling of heavy metal contaminants from wastewater as a source of valuable products perfectly fits with the principles of a Circular Economy system in view of restoring pollutants back into the system endowed with new social and economic benefits. Heavy metals are often present in such a low concentration that it makes the removal efficiency difficult to realize through the conventional physicochemical methods with high selectivity. Biosorption, conversely, by EPSs (extracellular polymeric substances) produced by several bacterial cells’ strains, is gaining a great deal of attention as an economic, efficient and sustainable depolluting process of wastewater from metal cations such as copper. Metal coordination to EPS components was thus deeply investigated by 1H NMR titration experiments. The 1,10–Phenanthroline–copper complex was exploited for quantifying the ability of different strains to sequester copper by a practical UV-Vis spectrophotometric method. The obtained data d...
World Journal of Microbiology and Biotechnology, 2019
Iron-and sulfur-oxidizing bacteria inhabiting rice rhizoplane play a significant role on arsenic ... more Iron-and sulfur-oxidizing bacteria inhabiting rice rhizoplane play a significant role on arsenic biogeochemistry in flooded rice paddies, influencing arsenic translocation to rice grains. In the present study, the selective pressure of arsenic species on these microbial populations was evaluated. Rice roots from continuously flooded plants were incubated in iron sulfide (FeS) gradient tubes and exposed to either arsenate or arsenite. The biomass developed in the visible iron-oxidation band of the enrichments was analyzed by Scanning Electron Microscopy and Energy-Dispersive Spectroscopy (SEM-EDS) and the bacterial communities were characterized by 16S rRNA gene sequencing. Different Proteobacteria communities were selected depending on exposure to arsenate and arsenite. Arsenate addition favored the versatile iron-oxidizers Dechloromonas and Azospira, associated to putative iron (hydr)oxide crystals. Arsenite exposure decreased the diversity in the enrichments, with the development of the sulfur-oxidizer Thiobacillus thioparus, likely growing on sulfide released by FeS. Whereas sulfur-oxidizers were observed in all treatments, iron-oxidizers disappeared when exposed to arsenite. These results reveal a strong impact of different inorganic arsenics on rhizospheric ironoxidizers as well as a crucial role of sulfur-oxidizing bacteria in establishing rice rhizosphere communities under arsenic pressure.
The genus Thioalkalivibrio includes haloalkaliphilic chemolithoautotrophic sulfur-oxidizing bacte... more The genus Thioalkalivibrio includes haloalkaliphilic chemolithoautotrophic sulfur-oxidizing bacteria isolated from various soda lakes worldwide. Some of these lakes possess in addition to their extreme haloalkaline environment also other harsh conditions, to which Thioalkalivibrio needs to adapt. An example is arsenic in soda lakes in eastern California, which is found there in concentrations up to 3000 µM. Arsenic is a widespread element that can be an environmental issue, as it is highly toxic to most organisms. However, resistance mechanisms in the form of detoxification are widespread and some prokaryotes can even use arsenic as an energy source. We first screened the genomes of 76 Thioalkalivibrio strains for the presence of known arsenic oxidoreductases and found 15 putative ArxA (arsenite oxidase) and two putative ArrA (arsenate reductase). Subsequently, we studied the resistance to arsenite in detail in Thioalkalivibrio jannaschii ALM2 T , and Thioalkalivibrio thiocyanoxidans ARh2 T by comparative genomics and by growing them at different arsenite concentrations followed by arsenic species and transcriptomic analysis. Tv. jannaschii ALM2 T , which has been isolated from Mono Lake, an arsenic-rich soda lake, could resist up to 5 mM arsenite, whereas Tv. thiocyanoxidans ARh2 T , which was isolated from a Kenyan soda lake, could only grow up to 0.1 mM arsenite. Interestingly, both species oxidized arsenite to arsenate under aerobic conditions, although Tv. thiocyanoxidans ARh2 T does not contain any known arsenite oxidases, and in Tv. jannaschii ALM2 T , only arxB2 was clearly upregulated. However, we found the expression of a SoeABC-like gene, which we assume might have been involved in arsenite oxidation. Other arsenite stress responses for both strains were the upregulation of the vitamin B 12 synthesis pathway, which can be linked to antioxidant activity, and the up-and downregulation of different DsrE/F-like genes whose roles are still unclear. Moreover, Tv. jannaschii ALM2 T induced the ars gene operon and
The possible generation of oxidative stress induced by aromatic hydrocarbon degradation suggests ... more The possible generation of oxidative stress induced by aromatic hydrocarbon degradation suggests that ancillary enzyme activities could facilitate the utilization of polycyclic aromatic hydrocarbons as sole carbon source. To investigate the metabolic profiles of low molecular weight polycyclic aromatic hydrocarbon-degrading strains of Sphingobium chlorophenolicum, Rhodococcus aetherovorans, Rhodococcus opacus and Mycobacterium smegmatis, the determination of the activity of putative detoxifying enzymes (rhodanese-like and glutathione S-transferase proteins) was combined with genetic analyses. All the studied strains were able to utilize phenanthrene or naphthalene. Glutathione S-transferase activity was found in S. chlorophenolicum strains grown on phenanthrene and it was related to the presence of the bphK gene, since modulation of glutathione S-transferase activity by phenanthrene paralleled the induction of glutathione S-transferase transcript in the S. chlorophenolicum strains. No glutathione S-transferase activity was detectable in R. aetherovorans, R. opacus and in M. smegmatis strains. All strains showed 3-mercaptopyruvate:cyanide sulfurtransferase activity. A rhodanese-like SseA protein was immunodetected in R. aetherovorans, R. opacus and in M. smegmatis strains, where increase of 3-mercaptopyruvate:cyanide sulfurtransferase activity was significantly induced by growth on phenanthrene.
Achromobacter sp. strain N2 was isolated from a pyrite-cinder-contaminated soil and presented pla... more Achromobacter sp. strain N2 was isolated from a pyrite-cinder-contaminated soil and presented plant-growth promoting traits (ACC deaminase activity, production of indole-3-acetic and jasmonic acids, siderophores secretion and phosphate solubilization) and arsenic transformation abilities. Achromobacter sp. strain N2 was resistant to different metals and metalloids, including arsenate (100 mM) and arsenite (5 mM). The strain was resistant to ionic stressors (i.e. arsenate and NaCl), whereas bacterial growth was impaired by osmotic stress. Strain N2 was able to oxidize 1.0 mmol L-1 of arsenite to arsenate in 72 h. This evidence was supported by the retrieval of an arsenite oxidase AioA gene highly homologous to arsenite oxidases of Achromobacter and Alcaligenes species. Rice seeds of Oryza sativa (var. Loto) were bio-primed with ACCD-induced and noninduced cells in order to evaluate the effect of inoculation on rice seedlings growth and arsenic uptake. The bacterization with ACCD-induced cells significantly improved seed germination and seedling heights if compared with the seeds inoculated with noninduced cells and non-primed seeds. Enhanced arsenic uptake was evidenced in the presence of ACCD-induced cells, suggesting a role of ACCD activity on the mitigation of the toxicity of arsenic accumulated by the plant. This kind of responses should be taken into account when proposing PGP strains for improving plant growth in arsenicrich soils. See attachment.
A rhizobacterial community, associated with the roots of wild thistle Cirsium arvense (L.) growin... more A rhizobacterial community, associated with the roots of wild thistle Cirsium arvense (L.) growing in an arsenic polluted soil, was studied by fluorescence in situ hybridization (FISH) analysis in conjunction with cultivation-based methods. In the bulk, rhizosphere, and rhizoplane fractions of the soil, the qualitative picture obtained by FISH analysis of the main phylogenetic bacterial groups was similar and was predominantly comprised of Alphaproteobacteria, Betaproteobacteria, and Gammaproteobacteria. The arsenic-resistant isolates belonged to 13 genera, the most abundant being those of Bacillus, Achromobacter, Brevundimonas, Microbacterium, and Ochrobactrum. Most bacteria grew in the presence of high arsenic concentrations (over 100 mM arsenate and 10 mM arsenite). Most strains possessed the ArsC, ArsB and ACR3 genes homologous to arsenate reductase and to the two classes of arsenite efflux pumps, respectively, peculiar to the ars operon of the arsenic detoxification system. ArsB and ACR3 were present simultaneously in highly resistant strains. An inconsistency between 16S rRNA phylogenetic affiliations and the arsenate reductase sequences of the strains was observed, indicating possible horizontal transfer of arsenic resistance genes in the soil bacterial community. Several isolates were able to reduce arsenate and to oxidise arsenite. In particular, Ancylobacter dichloromethanicum strain As3-1b possessed both characteristics, and arsenite oxidation occurred in the strain also under chemoautotrophic conditions. Some rhizobacteria produced siderophores, indole acetic acid and 1-amino-cyclopropane-1-carboxylic acid deaminase, thus possessing potential plant growth-promoting traits.
A heterotrophic arsenite-oxidizing bacterium, strain 2WW, was isolated from a biofilter treating ... more A heterotrophic arsenite-oxidizing bacterium, strain 2WW, was isolated from a biofilter treating arsenic-rich groundwater. Comparative analysis of 16S rRNA gene sequences showed that it was closely related (98.7 %) to the alphaproteobacterium Aliihoeflea aesturari strain N8(T). However, it was physiologically different by its ability to grow at relatively low substrate concentrations, low temperatures and by its ability to oxidize arsenite. Here we describe the physiological features of strain 2WW and compare these to its most closely related relative, A. aestuari strain N8(T). In addition, we tested its efficiency to remove arsenic from groundwater in combination with Pf-ferritin. Strain 2WW oxidized arsenite to arsenate between pH 5.0 and 8.0, and from 4 to 30 °C. When the strain was used in combination with a Pf-ferritin-based material for arsenic removal from natural groundwater, the removal efficiency was significantly higher (73 %) than for Pf-ferritin alone (64 %). These resu...
Pseudomonas putida CM37, Pseudomonas aureofaciens CM32 and Pseudomonas putida CM23 degraded tolue... more Pseudomonas putida CM37, Pseudomonas aureofaciens CM32 and Pseudomonas putida CM23 degraded toluene through different pathways. CM37 carried xylA,M gene for xylene monooxygenase (TOL pathway), CM32 carried todC1 gene for toluene dioxygenase (TOD pathway) and CM23 carried both genes and was charac- terised by the contemporary presence of TOL and TOD pathways. In this study we com- pared the behaviour of
Journal of Environmental Science and Health . Part A: Environmental Science and Engineering and Toxicology, 1995
... (% average) Specific load (Kg C0D/m3d) HRT (h) Total biogas (L/d ... [2] Bull MA, Sterritt RM... more ... (% average) Specific load (Kg C0D/m3d) HRT (h) Total biogas (L/d ... [2] Bull MA, Sterritt RM and Lester JN An evaluation of four start-up regimes for anaerobic fluidized bed reactors. ... [5] Denac M. and Dunn IJ Packed-and fluidized-bed biofilm reactor performance for anaerobic ...
A rhizobacterial community, associated with the roots of wild thistle Cirsium arvense (L.) growin... more A rhizobacterial community, associated with the roots of wild thistle Cirsium arvense (L.) growing in an arsenic polluted soil, was studied by fluorescence in situ hybridization (FISH) analysis in conjunction with cultivation-based methods. In the bulk, rhizosphere, and rhizoplane fractions of the soil, the qualitative picture obtained by FISH analysis of the main phylogenetic bacterial groups was similar and was predominantly comprised of Alphaproteobacteria, Betaproteobacteria, and Gammaproteobacteria. The arsenic-resistant isolates belonged to 13 genera, the most abundant being those of Bacillus, Achromobacter, Brevundimonas, Microbacterium, and Ochrobactrum. Most bacteria grew in the presence of high arsenic concentrations (over 100 mM arsenate and 10 mM arsenite). Most strains possessed the ArsC, ArsB and ACR3 genes homologous to arsenate reductase and to the two classes of arsenite efflux pumps, respectively, peculiar to the ars operon of the arsenic detoxification system. ArsB and ACR3 were present simultaneously in highly resistant strains. An inconsistency between 16S rRNA phylogenetic affiliations and the arsenate reductase sequences of the strains was observed, indicating possible horizontal transfer of arsenic resistance genes in the soil bacterial community. Several isolates were able to reduce arsenate and to oxidise arsenite. In particular, Ancylobacter dichloromethanicum strain As3-1b possessed both characteristics, and arsenite oxidation occurred in the strain also under chemoautotrophic conditions. Some rhizobacteria produced siderophores, indole acetic acid and 1-amino-cyclopropane-1-carboxylic acid deaminase, thus possessing potential plant growth-promoting traits.
This study reports the isolation from an agricultural metal impacted soil of a cadmium-resistant ... more This study reports the isolation from an agricultural metal impacted soil of a cadmium-resistant bacterium and its ability to bioprecipitate cadmium and zinc ions in solution. From the biomass of the cadmium-tolerant population, among the most dominant bacterial colonies, a Pseudomonas putida strain B14 was isolated and identified. The microorganism showed a simultaneous resistance to Cd, Zn, Pb, Co, Ni and Cu. P. putida B14 in the presence with either 1 mmol L-1 Cd(II) or Zn(II) removed the Cd(II) almost completely and about 80% of the Zn(II) from the aqueous solution, precipitating them as crystals. Cadmium was removed mainly as CdCO3 by a gratuitous mechanism in conse- quence of the CO2-generating metabolism. The possibility of using multiple-metal resist- ant bacteria to immobilise heavy metals, and facilitate their removal, could contribute to the implementation of a strategy of bioremediation for polluted waters and industrial waste waters.
Enrichment cultures on naphtha solvent were used to select aromatic hydrocarbon-degrading bacteri... more Enrichment cultures on naphtha solvent were used to select aromatic hydrocarbon-degrading bacteria from a BTEX (benzene, toluene, ethylbenzene, xylene)-contaminated subsoil obtained from beneath a paint factory located in Milan, Italy. Fifteen isolated strains were studied for their different biodegradative capacities. Among these, 13 were able to grow on naphtha solvent. Ten were identified as Pseudomonas putida and three as Pseudomonas aureofaciens. Two other degraders were identified as Pseudomonas aeruginosa and Alcaligenes xylosoxidans subsp. denitrificans. Further molecular characterization of the isolates was carried out by randomly amplified polymorphic DNA analysis to ascertain that all the studied strains belonged to different haplotypes. The isolates were characterized for the presence of genes encoding for toluene dioxygenase, xylene monooxygenase and catechol 2,3-dioxygenase by polymerase chain reaction analysis and by Southern analysis. P. putida strain CM23, which showed homology with xylA,M, xylE and todC1C2BA genes, possessed multiple pathways which enabled the strain to grow on benzene, toluene and m-xylene.
A selected mixed culture and a strain of Alcaligenes eutrophus TCP were able to totally degrade 2... more A selected mixed culture and a strain of Alcaligenes eutrophus TCP were able to totally degrade 2,4,6-TCP with stoichiometric release of Cl − . In cultures of Alc. eutrophus TCP, a dioxygenated dichlorinated metabolite was detected after 48 h of incubation. Experiments conducted with soil microcosms gave evidence that : the degradative process had a biotic nature and was accompanied by microbial growth ; the soil used presented an intrinsic degradative capacity versus 2,4,6-TCP ; the specialized organism used as inoculum was effective in degrading 2,4,6-TCP in a short time. These results could be utilized for the adoption of appropriate remediation techniques for contaminated soil.
Journal of Environmental Science and Health, Part B, 1994
Laboratory experiments were conducted to study the degradation of acifluorfen 5-[2-chloro-4-(trif... more Laboratory experiments were conducted to study the degradation of acifluorfen 5-[2-chloro-4-(trifluoromethyl)-phenoxyl]-2-nitrobenzoic acid by a mixed microbial population. Concentrations of acifluorfen up to 100 mg/l had no inhibitory effect on the growth of microbial culture. The microorganisms degraded acifluorfen through a cometabolic process in presence of 2-nitrobenzoate. The degradation rate of acifluorfen, determined by liquid chromatography analysis in batch cultures incubated under oxygen-limited conditions were compared. The degradation was slower under oxygen than oxygen-limited conditions. Aminoacifluorfen was produced in both conditions.
Journal of Environmental Science and Health, Part A, 1998
Anaerobic digestion of winery effluents derived from two different wine making processes was comp... more Anaerobic digestion of winery effluents derived from two different wine making processes was compared in a laboratory scale upflow filter. White winery effluents (WWE) were more easily degradable (average soluble COD removal=92%) than red winery effluents (RWE) (average soluble COD removal = 85%). Differences in the reactor microbial populations for the two effluents were also observed. Both aceticlastic and hydrogenotrophic methanogens in the circulating fractions were significantly higher during the treatment of WWE than during that of RWE. With both wastewaters, the reactor promptly reacted to volumetric organic load (Bv) stress (tripling from 4 to 12 g COD L d). Following the Bv perturbation, COD removal decreased to 50%. However, after two weeks the COD removal values were as before perturbation. Volatile fatty acids, especially total VFAs and butyrate measured on the second day after the imposed Bv perturbation, were good indicators of process imbalance. Coenzyme F420 determination and scanning electron microscopy revealed the presence of Methanosaeta like cells embedded to extracellular polymers in a uniform slime matrix in the biofilm. The main methanogens observed in the effluents were Methanosarcina and Methanobrevibacter cells.
Different soil samples characterised by a long-term Hg-pollution were studied for Hg total conten... more Different soil samples characterised by a long-term Hg-pollution were studied for Hg total content, fractionation, phytotoxicity and influence on the bacterial community. Hg pollution ranged from 1 to 50 mg kg À1 and most of it was speciated in scarcely soluble forms. In agreement with this, the biochemical quality indexes were investigated (biomass, enzyme activities) and the bacterial community (viable heterotrophic (VH) bacteria, functional diversity) apparently was not influenced by the degree of Hg pollution. In particular, the investigated soils exhibited a low percentage of Hg-resistant (Hg R ) bacteria ranging from less than 0.001% to 0.25% of the VH and the addition of available Hg in the form of HgCl 2 induced an enrichment of resistant Hg R populations. The general biodiversity of the bacterial community was evaluated by denaturing gradient gel electrophoresis of DNA of Hg spiked soil microcosms and of control soils. Hg R bacteria capable to grow in a minimal medium containing HgCl 2 were also isolated and identified. MerA and merB gene PCR fragments were obtained from different Hg R strains and the range of similarities at the DNA level and at the deduced amino acid level showed that they carried mercuric reductase and lyase. Differently from bacteria, some influence of soil Hg content on seeds' germination and root elongation was observed for Lepidium sativum L. and Solanum lycopersicum L. In conclusion, most of the Hg in these long-term polluted soils was scarcely mobile and available and did not significantly influence the soil bacterial community. The risk of potential Hg remobilisation over time, that could be naturally favoured by the activity of plant roots or other inorganic processes occurring in soil, can be extenuated since bacterial community was resistant and resilient to subsequent Hg stress.
The survival and activity of Rhodococcus sp. strain 1BN, inoculated into naphthalenecontaminated ... more The survival and activity of Rhodococcus sp. strain 1BN, inoculated into naphthalenecontaminated sandy-loam soil microcosms, were studied using classical and molecular methods. Methods and Results: The naphthalene-degrading activity of 1BN in microcosms was examined through viable counts, CO 2 production and naphthalene consumption, while its survival after inoculation was monitored by detecting the contemporary presence of alkane and naphthalene degradative genes and by analysing the 16S rDNA specific restriction profile. The inoculation of 1BN did not significantly enhance naphthalene degradation in the naphthalenecontaminated native soil, where 1BN maintained its catabolic activity also when in the presence of indigenous microflora. Instead the rate of naphthalene degradation by the inoculated 1BN was greater in sterile naphthalene-contaminated soil. The level of 1BN was only slightly higher after inoculation regardless of whether indigenous naphthalene-degrading bacteria were present or not and 1BN remained viable even when the substrate was depleted.
International Biodeterioration & Biodegradation, 2011
The aim of the research was to verify if a Sphingobium chlorophenolicum strain C3R was effective ... more The aim of the research was to verify if a Sphingobium chlorophenolicum strain C3R was effective in the degradation of phenanthrene (Ph) in agricultural soil co-contaminated by metals and mixtures of PAHs. The presence of PAHs in mixtures produced interactive effects which could either increase or decrease the utilization rate of Ph by C3R and by the native bacterial microflora. Bioaugmentation significantly improved the biodegradation rate of Ph in the presence of both cadmium and arsenic and PAH mixtures. The augmented C3R strain persisted in inoculated microcosms as monitored by the DGGE analysis and outcompeted some indigenous bacteria. The potential role of the soil bacteria in PAH degradation could be envisaged. The results indicate the applicability of S. chlorophenolicum C3R toward in situ bioremediation of sites contaminated with phenanthrene alone or co-contaminated with low molecular weight PAHs and with cadmium and arsenate.
Rhodococcus sp. 1BN was isolated from a contaminated site and showed various biodegradative capab... more Rhodococcus sp. 1BN was isolated from a contaminated site and showed various biodegradative capabilities. Besides naphthalene, strain 1BN degraded medium-(C 6 ) and long-chain alkanes (C 16 ±C 28 ), benzene and toluene, alone or when the hydrocarbons were mixed in equal proportions. The nucleotide sequence of an alk polymerase chain reaction (PCR) fragment revealed a 59% nucleotide homology to the Pseudomonas oleovorans alkB gene. The nar fragments were highly homologous to genes coding for large and small subunits of cis-naphthalene 1,2-dioxygenase (narAa and narAb) and to cis-naphthalene dihydrodiol dehydrogenase (narB) from other rhodococci. The oxidation of indene to cis-(1S,2R)-1,2dihydroxyindan by toluene-induced cells allows to hypothesize that strain 1BN also carries a toluene dioxygenase-like system.
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