A total of 1246 Pseudomonas strains were isolated from the rhizosphere of two perennial grasses (... more A total of 1246 Pseudomonas strains were isolated from the rhizosphere of two perennial grasses (Lolium perenne and Molinia coerulea) with different nitrogen requirements. The plants were grown in their native soil under ambient and elevated atmospheric CO 2 content (pCO 2) at the Swiss FACE (Free Air CO 2 Enrichment) facility. Root-, rhizosphere-, and non-rhizospheric soil-associated strains were characterized in terms of their ability to reduce nitrate during an in vitro assay and with respect to the genes encoding the membrane-bound (named NAR) and periplasmic (NAP) nitrate reductases so far described in the genus Pseudomonas. The diversity of corresponding genes was assessed by PCR-RFLP on narG and napA genes, which encode the catalytic subunit of nitrate reductases. The frequency of nitrate-dissimilating strains decreased with root proximity for both plants and was enhanced under elevated pCO 2 in the rhizosphere of L. perenne. NAR (54% of strains) as well as NAP (49%) forms were present in nitrate-reducing strains, 15.5% of the 439 strains tested harbouring both genes. The relative proportions of narG and napA detected in Pseudomonas strains were different according to root proximity and for both pCO 2 treatments: the NAR form was more abundant close to the root surface and for plants grown under elevated pCO 2. Putative denitrifiers harbored mainly the membrane-bound (NAR) form of nitrate reductase. Finally, both narG and napA sequences displayed a high level of diversity. Anyway, this diversity was correlated neither with the root proximity nor with the pCO 2 treatment.
CO concentrations were measured in the water of a eutrophic lake by a technique which allowed the... more CO concentrations were measured in the water of a eutrophic lake by a technique which allowed the detection of greater than or equal to 0.5 nl CO x liter/sup -1/ of water. In spring, when the lake was aerobic to the bottom, CO distribution was relatively homogeneous with concentrations of 40-130 nl x liter/sup -1/. In summer, CO concentrations ranged between 20 and 615 nl x liter/sup -1/ in the aerobic epilimnion and metalimnion, but reached values of >8000 nl x liter/sup -1/ in the anaerobic hypolimnion. CO increased during the morning and decreased during the afternoon in the upper water layers as well as in the dark hypolimnion. Incubation of lake water samples from different depths under daylight conditions resulted in a strong CO production. The light-dependent CO production was stimulated by the high numbers of Oscillatoria rubescens in the metalimnion, but also by material from the lake sediment. Incubation of lake water samples in darkness resulted in CO consumption under...
The highly thermophilic, hydrogen-oxidizing aerobic bacteria related to Hydrogenobaeter possess a... more The highly thermophilic, hydrogen-oxidizing aerobic bacteria related to Hydrogenobaeter possess a respiratory chain comprising a quinone and b-type (alpha band at 556 nm and 562 nm) and c-type (alpha band at 552nm) cytochromes. They have no aa3-type cytochromes and their terminal oxidase is an o-type cytochrome. A polarographic method with an oxygen electrode was used for the measurement of the hydrogenoxidizing activity. This activity was strongly inhibited by HQNO (2-N-heptyl-4-hydroxyquinoline N-oxide), an inhibitor of the respiratory chain in the quinonecytochrome b region, and by KCN, an inhibitor of the terminal cytochrome oxidase. This study shows that the electrons released from hydrogen oxidation by the membrane-bound hydrogenase probably enter the respiratory chain at the level of the quinone-cytochrome b region.
Heterotrophic pyruvate-limited steady-state continuous cultures of the bacterium Aquuspirillum ru... more Heterotrophic pyruvate-limited steady-state continuous cultures of the bacterium Aquuspirillum rurtotrophicum were perturbed with a pulse injection of a small volume of concentrated pyruvate solution. These cultures exhibited an instantaneous change in the growth dynamics, turning from steady state to apparently linear growth. These transient growth-responses had no lag phase and were clearly distinct from unlimited exponential growth according to the initial rates of increase of biomass and substrate disappearance kinetics. A linear accumulation with time of poly(P-hydroxybutyrate) was observed within the cells. Slopes of these linear responses were negatively correlated with the dilution rate. Physiological bases of linear growth are discussed in the light of the models of H. E. Kubitschek. Poly(P-hydroxybutyrate) synthesis in the absence of exogenous limitation may serve to protect the cells against a transient metabolic overfiow.
A thermophilic, chemolithoautotrophic, hydrogen-oxidizing sporeformer has been isolated from pond... more A thermophilic, chemolithoautotrophic, hydrogen-oxidizing sporeformer has been isolated from ponds in a solfatara in the geothermal area of Tuscany (Italy). Some physicochemical parameters of the habitat were determined. The habitat was characterized by the presence of molecular hydrogen in the escaping gases, a very low content of phosphate and organic matter. Temperature and water level in the ponds varied widely. The organism formed oval, subterminal spores, which swelled distinctly the sporangium. Optimal growth occured between pH 4.2 and 4.8 at 55~ It grew best under autotrophic conditions, but organic substrates including short chain fatty acids, amino acids and alcohols could also support heterotrophic growth. Sugars were not metabolized. The hydrogenase was soluble but did not reduce pyridine nucleotides. Based on its morphological and biochemical features, the organism belongs to the genus Bacillus, but differs from all the previously described species. It is therefore proposed as constituting a new species, Bacillus tusciae.
The fine structure of the cell envelope, of membrane systems and of cytoplasmic inclusions of Gra... more The fine structure of the cell envelope, of membrane systems and of cytoplasmic inclusions of Gram-negative aerobic hydrogen bacteria has been studied. The results have been tabulated, and three main groups could be recognized: Group 1: Alcaligenes eutrophus, A.paradoxus, A.ruhlandii, Pseudomonas facilis, P.flava, P.pseudoflava, P.palleronii, and Aquaspirillum autotrophicum; Group 2: "Corynebacterium" autotrophicum and strains MA 2 and SA 35; Group 3: Paracoccus denitrificans. Special structures related to the chemoautotrophic way of life of the hydrogen bacteria were not observed.
Thiobacillus denitrificans strain RT, an obligate sulfur-oxidizing chemolithoautotroph, was grown... more Thiobacillus denitrificans strain RT, an obligate sulfur-oxidizing chemolithoautotroph, was grown under microaerophilic conditions with thiosulfate as the only energy source. The rates of tetrathionate, thiosulfate, elemental sulfur (So) and sulfite oxidation were measured respirometrically with an oxygen electrode, using actively growing cells. Cells oxidized thiosulfate, elemental sulfur (So) and sulfite, but not tetrathionate. The thiosulfateoxidizing activity and elemental sulfur-oxidizing activity
The oxalate-carbonate pathway involves the oxidation of calcium oxalate to low-magnesium calcite ... more The oxalate-carbonate pathway involves the oxidation of calcium oxalate to low-magnesium calcite and represents a potential long-term terrestrial sink for atmospheric CO 2. In this pathway, bacterial oxalate degradation is associated with a strong local alkalinization and subsequent carbonate precipitation. In order to test whether this process occurs in soil, the role of bacteria, fungi and calcium oxalate amendments was studied using microcosms. In a model system with sterile soil amended with laboratory cultures of oxalotrophic bacteria and fungi, the addition of calcium oxalate induced a distinct pH shift and led to the final precipitation of calcite. However, the simultaneous presence of bacteria and fungi was essential to drive this pH shift. Growth of both oxalotrophic bacteria and fungi was confirmed by qPCR on the frc (oxalotrophic bacteria) and 16S rRNA genes, and the quantification of ergosterol (active fungal biomass) respectively. The experiment was replicated in microcosms with non-sterilized soil. In this case, the bacterial and fungal contribution to oxalate degradation was evaluated by treatments with specific biocides (cycloheximide and bronopol). Results showed that the autochthonous microflora oxidized calcium oxalate and induced a significant soil alkali-nization. Moreover, data confirmed the results from the model soil showing that bacteria are essentially responsible for the pH shift, but require the presence of fungi for their oxalotrophic activity. The combined results highlight that the interaction between bacteria and fungi is essential to drive metabolic processes in complex environments such as soil.
Thermophilic hydrogen-oxidizing strains forming round, terminal endospores were isolated from geo... more Thermophilic hydrogen-oxidizing strains forming round, terminal endospores were isolated from geothermal areas. They were neutrophilic and facultatively autotrophic. They resembledBacillus schlegelii, a thermophilic hydrogen bacterium found so far only in cold environments. Phenotypic similarities, as well as DNA G+C content and DNA:DNA homologies, clearly revealed that the isolated strains belonged to the taxospeciesB. schlegelii. Hence, the strains ofB. schlegelii found in cold environments are probably allochthonous, their origin being geothermal and volcanic areas.
Thiobacillus novellus (type strain) was grown chemolithoautrophically on thiosulfate in batch cul... more Thiobacillus novellus (type strain) was grown chemolithoautrophically on thiosulfate in batch cultures under microaerophilic conditions. Under these conditions,T. novellus grew exponentially (µ=0.05–0.06 h-1). The respiratory oxidation rates of tetrathionate, thiosulfate, elemental sulfur (So), and sulfite were measured respirometrically with an oxygen electrode, with exponentially growing cells. Cells growing on thiosulfate as the unique energy source retain thiosulfate-oxidizing activity, So-oxidizing activity
Studies on the diversity of environmental culturable Pseudomonas populations are dependent on the... more Studies on the diversity of environmental culturable Pseudomonas populations are dependent on the isolation procedure.This procedure includes the use of selective media which may influence the recovery of strains and thus the diversity described.In this study, we assessed the use of two agar isolation media for describing the diversity of soil- and root-inhabiting Pseudomonas associated with the perennial grass Molinia
A total of 1246 Pseudomonas strains were isolated from the rhizosphere of two perennial grasses (... more A total of 1246 Pseudomonas strains were isolated from the rhizosphere of two perennial grasses (Lolium perenne and Molinia coerulea) with different nitrogen requirements. The plants were grown in their native soil under ambient and elevated atmospheric CO 2 content (pCO 2) at the Swiss FACE (Free Air CO 2 Enrichment) facility. Root-, rhizosphere-, and non-rhizospheric soil-associated strains were characterized in terms of their ability to reduce nitrate during an in vitro assay and with respect to the genes encoding the membrane-bound (named NAR) and periplasmic (NAP) nitrate reductases so far described in the genus Pseudomonas. The diversity of corresponding genes was assessed by PCR-RFLP on narG and napA genes, which encode the catalytic subunit of nitrate reductases. The frequency of nitrate-dissimilating strains decreased with root proximity for both plants and was enhanced under elevated pCO 2 in the rhizosphere of L. perenne. NAR (54% of strains) as well as NAP (49%) forms were present in nitrate-reducing strains, 15.5% of the 439 strains tested harbouring both genes. The relative proportions of narG and napA detected in Pseudomonas strains were different according to root proximity and for both pCO 2 treatments: the NAR form was more abundant close to the root surface and for plants grown under elevated pCO 2. Putative denitrifiers harbored mainly the membrane-bound (NAR) form of nitrate reductase. Finally, both narG and napA sequences displayed a high level of diversity. Anyway, this diversity was correlated neither with the root proximity nor with the pCO 2 treatment.
CO concentrations were measured in the water of a eutrophic lake by a technique which allowed the... more CO concentrations were measured in the water of a eutrophic lake by a technique which allowed the detection of greater than or equal to 0.5 nl CO x liter/sup -1/ of water. In spring, when the lake was aerobic to the bottom, CO distribution was relatively homogeneous with concentrations of 40-130 nl x liter/sup -1/. In summer, CO concentrations ranged between 20 and 615 nl x liter/sup -1/ in the aerobic epilimnion and metalimnion, but reached values of >8000 nl x liter/sup -1/ in the anaerobic hypolimnion. CO increased during the morning and decreased during the afternoon in the upper water layers as well as in the dark hypolimnion. Incubation of lake water samples from different depths under daylight conditions resulted in a strong CO production. The light-dependent CO production was stimulated by the high numbers of Oscillatoria rubescens in the metalimnion, but also by material from the lake sediment. Incubation of lake water samples in darkness resulted in CO consumption under...
The highly thermophilic, hydrogen-oxidizing aerobic bacteria related to Hydrogenobaeter possess a... more The highly thermophilic, hydrogen-oxidizing aerobic bacteria related to Hydrogenobaeter possess a respiratory chain comprising a quinone and b-type (alpha band at 556 nm and 562 nm) and c-type (alpha band at 552nm) cytochromes. They have no aa3-type cytochromes and their terminal oxidase is an o-type cytochrome. A polarographic method with an oxygen electrode was used for the measurement of the hydrogenoxidizing activity. This activity was strongly inhibited by HQNO (2-N-heptyl-4-hydroxyquinoline N-oxide), an inhibitor of the respiratory chain in the quinonecytochrome b region, and by KCN, an inhibitor of the terminal cytochrome oxidase. This study shows that the electrons released from hydrogen oxidation by the membrane-bound hydrogenase probably enter the respiratory chain at the level of the quinone-cytochrome b region.
Heterotrophic pyruvate-limited steady-state continuous cultures of the bacterium Aquuspirillum ru... more Heterotrophic pyruvate-limited steady-state continuous cultures of the bacterium Aquuspirillum rurtotrophicum were perturbed with a pulse injection of a small volume of concentrated pyruvate solution. These cultures exhibited an instantaneous change in the growth dynamics, turning from steady state to apparently linear growth. These transient growth-responses had no lag phase and were clearly distinct from unlimited exponential growth according to the initial rates of increase of biomass and substrate disappearance kinetics. A linear accumulation with time of poly(P-hydroxybutyrate) was observed within the cells. Slopes of these linear responses were negatively correlated with the dilution rate. Physiological bases of linear growth are discussed in the light of the models of H. E. Kubitschek. Poly(P-hydroxybutyrate) synthesis in the absence of exogenous limitation may serve to protect the cells against a transient metabolic overfiow.
A thermophilic, chemolithoautotrophic, hydrogen-oxidizing sporeformer has been isolated from pond... more A thermophilic, chemolithoautotrophic, hydrogen-oxidizing sporeformer has been isolated from ponds in a solfatara in the geothermal area of Tuscany (Italy). Some physicochemical parameters of the habitat were determined. The habitat was characterized by the presence of molecular hydrogen in the escaping gases, a very low content of phosphate and organic matter. Temperature and water level in the ponds varied widely. The organism formed oval, subterminal spores, which swelled distinctly the sporangium. Optimal growth occured between pH 4.2 and 4.8 at 55~ It grew best under autotrophic conditions, but organic substrates including short chain fatty acids, amino acids and alcohols could also support heterotrophic growth. Sugars were not metabolized. The hydrogenase was soluble but did not reduce pyridine nucleotides. Based on its morphological and biochemical features, the organism belongs to the genus Bacillus, but differs from all the previously described species. It is therefore proposed as constituting a new species, Bacillus tusciae.
The fine structure of the cell envelope, of membrane systems and of cytoplasmic inclusions of Gra... more The fine structure of the cell envelope, of membrane systems and of cytoplasmic inclusions of Gram-negative aerobic hydrogen bacteria has been studied. The results have been tabulated, and three main groups could be recognized: Group 1: Alcaligenes eutrophus, A.paradoxus, A.ruhlandii, Pseudomonas facilis, P.flava, P.pseudoflava, P.palleronii, and Aquaspirillum autotrophicum; Group 2: "Corynebacterium" autotrophicum and strains MA 2 and SA 35; Group 3: Paracoccus denitrificans. Special structures related to the chemoautotrophic way of life of the hydrogen bacteria were not observed.
Thiobacillus denitrificans strain RT, an obligate sulfur-oxidizing chemolithoautotroph, was grown... more Thiobacillus denitrificans strain RT, an obligate sulfur-oxidizing chemolithoautotroph, was grown under microaerophilic conditions with thiosulfate as the only energy source. The rates of tetrathionate, thiosulfate, elemental sulfur (So) and sulfite oxidation were measured respirometrically with an oxygen electrode, using actively growing cells. Cells oxidized thiosulfate, elemental sulfur (So) and sulfite, but not tetrathionate. The thiosulfateoxidizing activity and elemental sulfur-oxidizing activity
The oxalate-carbonate pathway involves the oxidation of calcium oxalate to low-magnesium calcite ... more The oxalate-carbonate pathway involves the oxidation of calcium oxalate to low-magnesium calcite and represents a potential long-term terrestrial sink for atmospheric CO 2. In this pathway, bacterial oxalate degradation is associated with a strong local alkalinization and subsequent carbonate precipitation. In order to test whether this process occurs in soil, the role of bacteria, fungi and calcium oxalate amendments was studied using microcosms. In a model system with sterile soil amended with laboratory cultures of oxalotrophic bacteria and fungi, the addition of calcium oxalate induced a distinct pH shift and led to the final precipitation of calcite. However, the simultaneous presence of bacteria and fungi was essential to drive this pH shift. Growth of both oxalotrophic bacteria and fungi was confirmed by qPCR on the frc (oxalotrophic bacteria) and 16S rRNA genes, and the quantification of ergosterol (active fungal biomass) respectively. The experiment was replicated in microcosms with non-sterilized soil. In this case, the bacterial and fungal contribution to oxalate degradation was evaluated by treatments with specific biocides (cycloheximide and bronopol). Results showed that the autochthonous microflora oxidized calcium oxalate and induced a significant soil alkali-nization. Moreover, data confirmed the results from the model soil showing that bacteria are essentially responsible for the pH shift, but require the presence of fungi for their oxalotrophic activity. The combined results highlight that the interaction between bacteria and fungi is essential to drive metabolic processes in complex environments such as soil.
Thermophilic hydrogen-oxidizing strains forming round, terminal endospores were isolated from geo... more Thermophilic hydrogen-oxidizing strains forming round, terminal endospores were isolated from geothermal areas. They were neutrophilic and facultatively autotrophic. They resembledBacillus schlegelii, a thermophilic hydrogen bacterium found so far only in cold environments. Phenotypic similarities, as well as DNA G+C content and DNA:DNA homologies, clearly revealed that the isolated strains belonged to the taxospeciesB. schlegelii. Hence, the strains ofB. schlegelii found in cold environments are probably allochthonous, their origin being geothermal and volcanic areas.
Thiobacillus novellus (type strain) was grown chemolithoautrophically on thiosulfate in batch cul... more Thiobacillus novellus (type strain) was grown chemolithoautrophically on thiosulfate in batch cultures under microaerophilic conditions. Under these conditions,T. novellus grew exponentially (µ=0.05–0.06 h-1). The respiratory oxidation rates of tetrathionate, thiosulfate, elemental sulfur (So), and sulfite were measured respirometrically with an oxygen electrode, with exponentially growing cells. Cells growing on thiosulfate as the unique energy source retain thiosulfate-oxidizing activity, So-oxidizing activity
Studies on the diversity of environmental culturable Pseudomonas populations are dependent on the... more Studies on the diversity of environmental culturable Pseudomonas populations are dependent on the isolation procedure.This procedure includes the use of selective media which may influence the recovery of strains and thus the diversity described.In this study, we assessed the use of two agar isolation media for describing the diversity of soil- and root-inhabiting Pseudomonas associated with the perennial grass Molinia
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