The genetic relationships of nine strains of Chlorella saccharophila were determined by DNA hybri... more The genetic relationships of nine strains of Chlorella saccharophila were determined by DNA hybridization techniques. Four strains are closely related to the type strain 211-9a and one strain seems to be moderately related, whereas the taxonomic position of the remaining three strains is not clear. C. saccharophila, like C. sorokiniana, is another species of Chlorella containing strains which are heterogeneous in their overall DNA base sequence and partly also in morphological, biochemical and physiological characters.
Although intracellular associations with mycorrhizal fungi are known for Ginkgo biloba, no other ... more Although intracellular associations with mycorrhizal fungi are known for Ginkgo biloba, no other endosymbiotic relationships have ever been reported for this ''living fossil.'' A protoplast culture derived from haploid explants has now revealed the existence of a green alga in vitro, whose eukaryotic status was confirmed by transmission electron microscopic studies. Phylogenetic 18S rDNA sequence analyses showed this alga to be closely related to the lichen photobiont Coccomyxa. Algae, which in host cells exist as more or less undifferentiated ''precursor'' forms, proliferated within necrosing G. biloba cells of a subculture derived from a zygotic embryo and were finally released into the medium. Light and electron microscopic observations showed that G. biloba cells rapidly filled up with countless green particles whose number increased up to the bursting of the hypertrophic host cells. At the beginning of reproduction no algae were visible in the nutritive medium, demonstrating that the proliferation started inside the G. biloba cells and excluding the possibility of an exogenous contamination. Occasionally, mature algae together with their precursor forms were detected by transmission electron microscopy in intact host cells of a green callus. The algae were easily identified by their similarity to the cultured algae. Eukaryotic algae have never been reported to date to reside inside higher plant cells, whereas several algal associations are well known from the animal kingdom.
Forty-six strains of 15 taxa of Chlorella having 11 known physiological and biochemical character... more Forty-six strains of 15 taxa of Chlorella having 11 known physiological and biochemical characters were examined for their ability to form stable symbioses with a Swiss strain of aposymbiotic Hydra viridis. Eighteen strains of 6 taxa: C. saccharophila var. ellipsoidea, C. saccharophila var. saccharophila, C. fusca var. vacuolata, C. kessleri, C. luteoviridis, and C. protothecoides formed stable symbioses with this hydra. Six strains persisted in the cells of hydra for several weeks before they disappeared, and 22 strains were lost from the hydra within 6 days. Among the 11 physiological and biochemical characteristics known in these Chlorella species, it was only their ability to grow in vitro at or below a pH of 4.0 that correlated with the ability to live as endosymbionts in hydra. These results suggest that acid tolerance of the algae is a prerequisite for symbiosis with hydra. The fact that some strains which grew at pH 3.5-4.0 did not form a stable symbiosis, however, indicates that growth at low pH is not the only characteristic needed for the successful establishment of symbiosis with aposymbiotic hydra.
In the summer of 2003, a microalga strain was isolated from a massive green microalgae bloom in w... more In the summer of 2003, a microalga strain was isolated from a massive green microalgae bloom in wastewater stabilization ponds at the treatment facility of La Paz, B.C.S., Mexico. Prevailing environmental conditions were air temperatures over 40°C, water temperature of 37°C, and insolation of up to 2400 lmol m 2 s À1 at midday for several hours at the water surface for four months. The microalga was identified as Chlorella sorokiniana Shih. et Krauss, based on sequencing its entire 18S rRNA gene. In a controlled photo-bioreactor, this strain can grow to high population densities in synthetic wastewater at temperatures of 40-42°C and light intensity of 2500 lmol m 2 s À1 for 5 h daily and efficiently remove ammonium from the wastewater under these conditions better than under normal lower temperature (28°C) and lower light intensity (60 lmol m 2 s À1). When co-immobilized with the bacterium Azospirillum brasilense that promotes growth of microalgae, the population of microalga grew faster and removed even more ammonium. Under exposure to extreme growth conditions, the quantity of four photosynthetic pigments increased in the co-immobilized cultures. This strain of microalga has potential as a wastewater treatment agent under extreme conditions of temperature and light intensity.
The processes of CO 2 acquisition were characterized for the acid-tolerant, free-living chlorophy... more The processes of CO 2 acquisition were characterized for the acid-tolerant, free-living chlorophyte alga, CPCC 508. rDNA data indicate an affiliation to the genus Coccomyxa, but distinct from other known members of the genus. The alga grows over a wide range of pH from 3.0 to 9.0. External carbonic anhydrase (CA) was detected in cells grown above pH 5, with the activity increasing marginally from pH 7 to 9, but most of the CA activity was internal. The capacity for HCO 3) uptake of cells treated with the CA inhibitor acetazolamide (AZA), was investigated by comparing the calculated rate of uncatalyzed CO 2 formation with the rate of photosynthesis. Active bicarbonate transport occurred in cells grown in media above pH 7.0. Monitoring CO 2 uptake and O 2 evolution by membrane-inlet mass spectrometry demonstrated that air-grown cells reduced the CO 2 concentration in the medium to an equilibrium concentration of 15 lM, but AZA-treated cells caused a drop in extracellular CO 2 concentration to a compensation concentration of 27 lM at pH 8.0. CO 2pulsing experiments with cells in the light indicated that the cells do not actively take up CO 2. An internal pool of unfixed inorganic carbon was not detected at the CO 2 compensation concentration, probably because of the lack of active CO 2 uptake, but was detectable at times before compensation point was reached. These results indicate that this free-living Coccomyxa possesses a CO 2-concentrating mechanism (CCM) due to an active bicarbonateuptake system, unlike the Coccomyxa sp. occurring in symbiotic association with lichens.
The genus Coccomyxa comprises green microalgae, which can be found worldwide in remarkably versat... more The genus Coccomyxa comprises green microalgae, which can be found worldwide in remarkably versatile aquatic and terrestrial ecosystems including symbiotic associations with a number of different hosts. In this study, we describe a new species, Coccomyxa onubensis, based on 18S and ITS ribosomal DNA (rDNA) sequence data. Coccomyxa onubensis was isolated from acidic water, and its ability to adapt to a wide range of acidic and alkaline pH values and to high salinity was analyzed. The long-term adaptation capacity of the microalga to such extreme conditions was evaluated by performing continuous repeated batches at selected salt concentrations and pH values. Adapted cultures of C. onubensis were found to yield high biomass productivities from pH 2.5 to 9, with maximum yields at acidic pH between 2.5 and 4.5. Moreover, C. onubensis was also found to adapt to salinities as high as 0.5 M NaCl, reaching biomass productivities that were similar to those of control cultures. Ultrastructural analysis by transmission electron microscopy of C. onubensis cells adapted to high salinity showed a robust response to hyperosmotic shock. Thus, C. onubensis was found to be acidotolerant and halotolerant. High biomass productivity over a wide range of pH and salinities denotes C. onubensis as an interesting candidate for various biotechnological applications including outdoor biomass production.
The species of the genus Chlorella exhibit considerable biochemical and physiological differences... more The species of the genus Chlorella exhibit considerable biochemical and physiological differences. Therefore, it is important to select for and utilize in research or biotechnology correctly identified strains of the species having the most favorable properties for the respective project. We examined the Chlorella strains of the University of Texas collection at Austin, Texas, according to species‐specific chemotaxonomic characters and assigned 58 strains to 10 well‐established species (only 17 of these strains were correctly named before).
Ranging from unicells to complex “plantlike” organisms that are adapted to habitats from subaeria... more Ranging from unicells to complex “plantlike” organisms that are adapted to habitats from subaerial or terrestrial to freshwater or marine, the green algae represent a diversity of life forms that offer a daunting challenge in the search for shared morphological characters. The ultrastuctural techniques that fueled the 1970s and early 1980s revolution in algal systematics revealed a suite of new morphological characters, but many were not global (i.e., present in all of the taxa). Controversy over the interpretation of the importance of ultrastructural features (e.g., of cell division versus flagellar apparatus) led to conflicting hypotheses. Also, different researchers studied different details of different taxa, and thus a data matrix reporting a complete set of morphological and ultrastructural characters over a wide range of algal taxa was not available. Thus, it is no wonder that many researchers interested in unraveling the mystery of green algal phylogeny embraced molecular systematics, hoping that its early promise of relatively simple access to ample global characters would lead, finally, to a “true” phylogeny. The extent to which this promise has been fulfilled, or is likely to be fulfilled, is the subject of this chapter.
Morphological, biochemical, and molecular data strongly suggest a common ancestry of land plants ... more Morphological, biochemical, and molecular data strongly suggest a common ancestry of land plants and Charophyceae sensu MATTOX & STEWART. Although it is now widely accepted that the Charophyceae are a sister group to the land plants, there is considerable disagreement over the systematics of different charophycean taxa and whether a Chara- or Coleochaete-like alga was ancestral to the land plants. Comparative analyses of complete 18S rRNA gene sequences of charophycean algae, together with sequences from bryophytes, pteridophytes and higher plants now confirm a common ancestry of charophytes and land plants. These data suggest that the Charales diverged early into a separate lineage, whereas other orders within the Charophyceae show close affinities to the bryophytes.
Intracellular symbioses involving eukaryotic microalgae and a variety of heterotrophic protists a... more Intracellular symbioses involving eukaryotic microalgae and a variety of heterotrophic protists and invertebrates are widespread, but are unknown in higher plants. Recently, we reported the isolation and molecular identiWcation of a Coccomyxa-like green alga from in vitro cell cultures of Ginkgo biloba L. This alga resides intracellularly in an immature "precursor" form with a nonfunctional chloroplast, implying that algal photosynthetic activity has no role in this endosymbiosis. In necrotizing Ginkgo cells, precursors evolved into mature algae, proliferated, and were liberated into the culture medium after host cell bursting. In the present paper we demonstrate by molecular methods a worldwide distribution of the alga in planta. Endosymbiont-speciWc sequences of ribosomal DNA could be traced in Ginkgo tissues of each specimen examined from diVerent geographic locations in Europe, North America, and Asia. The Ginkgo/Coccomyca association represents a new kind of intracellular, vertically inherited symbiosis. Storage bodies, probably of lipid nature, present in the cytoplasm of each partner suggest a possible involvement of the endosymbiont in metabolic pathways of its host.
Little is known about phytoplankton communities inhabiting low pH environments such as volcanic a... more Little is known about phytoplankton communities inhabiting low pH environments such as volcanic and geothermal sites or acidic waters. Only specialised organisms are able to tolerate such extreme conditions. There is, thus, low species diversity. We have characterised the previously isolated acid tolerant Chlorella-like microalgae Viridiella fridericiana and Chlorella protothecoides var. acidicola by microscopical and biomolecular methods in order to assess their phylogenetic relationships. Both isolates belong to the trebouxiophycean lineage of chlorophytes. 18S and ITS1 sequence data clearly confirm that Viridiella fridericiana constitutes a new genus apart from the morphologically similar and likewise acid tolerant microalga Chlorella saccharophila. Chlorella protothecoides var. acidicola on the other hand is not a variety of Chlorella protothecoides but falls within a heterogeneous cluster consisting of Nannochloris, "Chlorella" spec. Yanaqocha, and Koliella, and is mo...
The green alga Scenedesmus pupukensis and the red alga Porphyra spiralis contain large group-IC1 ... more The green alga Scenedesmus pupukensis and the red alga Porphyra spiralis contain large group-IC1 introns in their nuclear small subunit ribosomal RNA genes due to the presence of open reading frames at the 5' end of the introns. The putative 555 amino-acid Scenedesmus-encoded protein harbors a sequence motif resembling the bacterial S9 ribosomal proteins. The Porphyra intron self-splices in vitro, and generates both ligated exons and a full-length intron RNA circle. The Porphyra intron has an unusual structural organization by encoding a potential 149 amino-acid homing-endonuclease-like protein on the complementary strand. A comparison between related group-I introns in the Bangiophyceae revealed homing-endonuclease-like pseudogenes due to frame-shifts and deletions in Porphyra and Bangia. The Scenedesmus and Porphyra introns provide new insights into the evolution and possible novel functions of nuclear group-I intron proteins.
Phylogenetic relationships within the genusChlorella were studied by means of DNA/DNA hybridizati... more Phylogenetic relationships within the genusChlorella were studied by means of DNA/DNA hybridization under both optimal and relaxed reassociation conditions as well as by determination of the thermal stability of hybrid DNA duplexes. The results indicate a relationship betweenC. fusca var.fusca, C. fusca var.rubescens, C. fusca var.vacuolata, and the genusScenedesmus. In addition, the strains endosymbiotic withParamecium bursaria seem to be related
Chlorella, the archetype of unicellular green algae, is a high-performance primary producer in aq... more Chlorella, the archetype of unicellular green algae, is a high-performance primary producer in aquatic and terrestrial ecosystems. Under the simple spherical morphology of Chlorella, many other 'green balls' unfolded as independent phylogenetic lineages as a result of convergent evolution. By contrast, green algae with strikingly different phenotypes were unmasked as close relatives of Chlorella by modern molecular techniques. Here, we point to the increasing impact of these diverse protists on ecology, evolution, and biotechnology in the light of integrative taxonomy.
The genetic relationships of nine strains of Chlorella saccharophila were determined by DNA hybri... more The genetic relationships of nine strains of Chlorella saccharophila were determined by DNA hybridization techniques. Four strains are closely related to the type strain 211-9a and one strain seems to be moderately related, whereas the taxonomic position of the remaining three strains is not clear. C. saccharophila, like C. sorokiniana, is another species of Chlorella containing strains which are heterogeneous in their overall DNA base sequence and partly also in morphological, biochemical and physiological characters.
Although intracellular associations with mycorrhizal fungi are known for Ginkgo biloba, no other ... more Although intracellular associations with mycorrhizal fungi are known for Ginkgo biloba, no other endosymbiotic relationships have ever been reported for this ''living fossil.'' A protoplast culture derived from haploid explants has now revealed the existence of a green alga in vitro, whose eukaryotic status was confirmed by transmission electron microscopic studies. Phylogenetic 18S rDNA sequence analyses showed this alga to be closely related to the lichen photobiont Coccomyxa. Algae, which in host cells exist as more or less undifferentiated ''precursor'' forms, proliferated within necrosing G. biloba cells of a subculture derived from a zygotic embryo and were finally released into the medium. Light and electron microscopic observations showed that G. biloba cells rapidly filled up with countless green particles whose number increased up to the bursting of the hypertrophic host cells. At the beginning of reproduction no algae were visible in the nutritive medium, demonstrating that the proliferation started inside the G. biloba cells and excluding the possibility of an exogenous contamination. Occasionally, mature algae together with their precursor forms were detected by transmission electron microscopy in intact host cells of a green callus. The algae were easily identified by their similarity to the cultured algae. Eukaryotic algae have never been reported to date to reside inside higher plant cells, whereas several algal associations are well known from the animal kingdom.
Forty-six strains of 15 taxa of Chlorella having 11 known physiological and biochemical character... more Forty-six strains of 15 taxa of Chlorella having 11 known physiological and biochemical characters were examined for their ability to form stable symbioses with a Swiss strain of aposymbiotic Hydra viridis. Eighteen strains of 6 taxa: C. saccharophila var. ellipsoidea, C. saccharophila var. saccharophila, C. fusca var. vacuolata, C. kessleri, C. luteoviridis, and C. protothecoides formed stable symbioses with this hydra. Six strains persisted in the cells of hydra for several weeks before they disappeared, and 22 strains were lost from the hydra within 6 days. Among the 11 physiological and biochemical characteristics known in these Chlorella species, it was only their ability to grow in vitro at or below a pH of 4.0 that correlated with the ability to live as endosymbionts in hydra. These results suggest that acid tolerance of the algae is a prerequisite for symbiosis with hydra. The fact that some strains which grew at pH 3.5-4.0 did not form a stable symbiosis, however, indicates that growth at low pH is not the only characteristic needed for the successful establishment of symbiosis with aposymbiotic hydra.
In the summer of 2003, a microalga strain was isolated from a massive green microalgae bloom in w... more In the summer of 2003, a microalga strain was isolated from a massive green microalgae bloom in wastewater stabilization ponds at the treatment facility of La Paz, B.C.S., Mexico. Prevailing environmental conditions were air temperatures over 40°C, water temperature of 37°C, and insolation of up to 2400 lmol m 2 s À1 at midday for several hours at the water surface for four months. The microalga was identified as Chlorella sorokiniana Shih. et Krauss, based on sequencing its entire 18S rRNA gene. In a controlled photo-bioreactor, this strain can grow to high population densities in synthetic wastewater at temperatures of 40-42°C and light intensity of 2500 lmol m 2 s À1 for 5 h daily and efficiently remove ammonium from the wastewater under these conditions better than under normal lower temperature (28°C) and lower light intensity (60 lmol m 2 s À1). When co-immobilized with the bacterium Azospirillum brasilense that promotes growth of microalgae, the population of microalga grew faster and removed even more ammonium. Under exposure to extreme growth conditions, the quantity of four photosynthetic pigments increased in the co-immobilized cultures. This strain of microalga has potential as a wastewater treatment agent under extreme conditions of temperature and light intensity.
The processes of CO 2 acquisition were characterized for the acid-tolerant, free-living chlorophy... more The processes of CO 2 acquisition were characterized for the acid-tolerant, free-living chlorophyte alga, CPCC 508. rDNA data indicate an affiliation to the genus Coccomyxa, but distinct from other known members of the genus. The alga grows over a wide range of pH from 3.0 to 9.0. External carbonic anhydrase (CA) was detected in cells grown above pH 5, with the activity increasing marginally from pH 7 to 9, but most of the CA activity was internal. The capacity for HCO 3) uptake of cells treated with the CA inhibitor acetazolamide (AZA), was investigated by comparing the calculated rate of uncatalyzed CO 2 formation with the rate of photosynthesis. Active bicarbonate transport occurred in cells grown in media above pH 7.0. Monitoring CO 2 uptake and O 2 evolution by membrane-inlet mass spectrometry demonstrated that air-grown cells reduced the CO 2 concentration in the medium to an equilibrium concentration of 15 lM, but AZA-treated cells caused a drop in extracellular CO 2 concentration to a compensation concentration of 27 lM at pH 8.0. CO 2pulsing experiments with cells in the light indicated that the cells do not actively take up CO 2. An internal pool of unfixed inorganic carbon was not detected at the CO 2 compensation concentration, probably because of the lack of active CO 2 uptake, but was detectable at times before compensation point was reached. These results indicate that this free-living Coccomyxa possesses a CO 2-concentrating mechanism (CCM) due to an active bicarbonateuptake system, unlike the Coccomyxa sp. occurring in symbiotic association with lichens.
The genus Coccomyxa comprises green microalgae, which can be found worldwide in remarkably versat... more The genus Coccomyxa comprises green microalgae, which can be found worldwide in remarkably versatile aquatic and terrestrial ecosystems including symbiotic associations with a number of different hosts. In this study, we describe a new species, Coccomyxa onubensis, based on 18S and ITS ribosomal DNA (rDNA) sequence data. Coccomyxa onubensis was isolated from acidic water, and its ability to adapt to a wide range of acidic and alkaline pH values and to high salinity was analyzed. The long-term adaptation capacity of the microalga to such extreme conditions was evaluated by performing continuous repeated batches at selected salt concentrations and pH values. Adapted cultures of C. onubensis were found to yield high biomass productivities from pH 2.5 to 9, with maximum yields at acidic pH between 2.5 and 4.5. Moreover, C. onubensis was also found to adapt to salinities as high as 0.5 M NaCl, reaching biomass productivities that were similar to those of control cultures. Ultrastructural analysis by transmission electron microscopy of C. onubensis cells adapted to high salinity showed a robust response to hyperosmotic shock. Thus, C. onubensis was found to be acidotolerant and halotolerant. High biomass productivity over a wide range of pH and salinities denotes C. onubensis as an interesting candidate for various biotechnological applications including outdoor biomass production.
The species of the genus Chlorella exhibit considerable biochemical and physiological differences... more The species of the genus Chlorella exhibit considerable biochemical and physiological differences. Therefore, it is important to select for and utilize in research or biotechnology correctly identified strains of the species having the most favorable properties for the respective project. We examined the Chlorella strains of the University of Texas collection at Austin, Texas, according to species‐specific chemotaxonomic characters and assigned 58 strains to 10 well‐established species (only 17 of these strains were correctly named before).
Ranging from unicells to complex “plantlike” organisms that are adapted to habitats from subaeria... more Ranging from unicells to complex “plantlike” organisms that are adapted to habitats from subaerial or terrestrial to freshwater or marine, the green algae represent a diversity of life forms that offer a daunting challenge in the search for shared morphological characters. The ultrastuctural techniques that fueled the 1970s and early 1980s revolution in algal systematics revealed a suite of new morphological characters, but many were not global (i.e., present in all of the taxa). Controversy over the interpretation of the importance of ultrastructural features (e.g., of cell division versus flagellar apparatus) led to conflicting hypotheses. Also, different researchers studied different details of different taxa, and thus a data matrix reporting a complete set of morphological and ultrastructural characters over a wide range of algal taxa was not available. Thus, it is no wonder that many researchers interested in unraveling the mystery of green algal phylogeny embraced molecular systematics, hoping that its early promise of relatively simple access to ample global characters would lead, finally, to a “true” phylogeny. The extent to which this promise has been fulfilled, or is likely to be fulfilled, is the subject of this chapter.
Morphological, biochemical, and molecular data strongly suggest a common ancestry of land plants ... more Morphological, biochemical, and molecular data strongly suggest a common ancestry of land plants and Charophyceae sensu MATTOX & STEWART. Although it is now widely accepted that the Charophyceae are a sister group to the land plants, there is considerable disagreement over the systematics of different charophycean taxa and whether a Chara- or Coleochaete-like alga was ancestral to the land plants. Comparative analyses of complete 18S rRNA gene sequences of charophycean algae, together with sequences from bryophytes, pteridophytes and higher plants now confirm a common ancestry of charophytes and land plants. These data suggest that the Charales diverged early into a separate lineage, whereas other orders within the Charophyceae show close affinities to the bryophytes.
Intracellular symbioses involving eukaryotic microalgae and a variety of heterotrophic protists a... more Intracellular symbioses involving eukaryotic microalgae and a variety of heterotrophic protists and invertebrates are widespread, but are unknown in higher plants. Recently, we reported the isolation and molecular identiWcation of a Coccomyxa-like green alga from in vitro cell cultures of Ginkgo biloba L. This alga resides intracellularly in an immature "precursor" form with a nonfunctional chloroplast, implying that algal photosynthetic activity has no role in this endosymbiosis. In necrotizing Ginkgo cells, precursors evolved into mature algae, proliferated, and were liberated into the culture medium after host cell bursting. In the present paper we demonstrate by molecular methods a worldwide distribution of the alga in planta. Endosymbiont-speciWc sequences of ribosomal DNA could be traced in Ginkgo tissues of each specimen examined from diVerent geographic locations in Europe, North America, and Asia. The Ginkgo/Coccomyca association represents a new kind of intracellular, vertically inherited symbiosis. Storage bodies, probably of lipid nature, present in the cytoplasm of each partner suggest a possible involvement of the endosymbiont in metabolic pathways of its host.
Little is known about phytoplankton communities inhabiting low pH environments such as volcanic a... more Little is known about phytoplankton communities inhabiting low pH environments such as volcanic and geothermal sites or acidic waters. Only specialised organisms are able to tolerate such extreme conditions. There is, thus, low species diversity. We have characterised the previously isolated acid tolerant Chlorella-like microalgae Viridiella fridericiana and Chlorella protothecoides var. acidicola by microscopical and biomolecular methods in order to assess their phylogenetic relationships. Both isolates belong to the trebouxiophycean lineage of chlorophytes. 18S and ITS1 sequence data clearly confirm that Viridiella fridericiana constitutes a new genus apart from the morphologically similar and likewise acid tolerant microalga Chlorella saccharophila. Chlorella protothecoides var. acidicola on the other hand is not a variety of Chlorella protothecoides but falls within a heterogeneous cluster consisting of Nannochloris, "Chlorella" spec. Yanaqocha, and Koliella, and is mo...
The green alga Scenedesmus pupukensis and the red alga Porphyra spiralis contain large group-IC1 ... more The green alga Scenedesmus pupukensis and the red alga Porphyra spiralis contain large group-IC1 introns in their nuclear small subunit ribosomal RNA genes due to the presence of open reading frames at the 5' end of the introns. The putative 555 amino-acid Scenedesmus-encoded protein harbors a sequence motif resembling the bacterial S9 ribosomal proteins. The Porphyra intron self-splices in vitro, and generates both ligated exons and a full-length intron RNA circle. The Porphyra intron has an unusual structural organization by encoding a potential 149 amino-acid homing-endonuclease-like protein on the complementary strand. A comparison between related group-I introns in the Bangiophyceae revealed homing-endonuclease-like pseudogenes due to frame-shifts and deletions in Porphyra and Bangia. The Scenedesmus and Porphyra introns provide new insights into the evolution and possible novel functions of nuclear group-I intron proteins.
Phylogenetic relationships within the genusChlorella were studied by means of DNA/DNA hybridizati... more Phylogenetic relationships within the genusChlorella were studied by means of DNA/DNA hybridization under both optimal and relaxed reassociation conditions as well as by determination of the thermal stability of hybrid DNA duplexes. The results indicate a relationship betweenC. fusca var.fusca, C. fusca var.rubescens, C. fusca var.vacuolata, and the genusScenedesmus. In addition, the strains endosymbiotic withParamecium bursaria seem to be related
Chlorella, the archetype of unicellular green algae, is a high-performance primary producer in aq... more Chlorella, the archetype of unicellular green algae, is a high-performance primary producer in aquatic and terrestrial ecosystems. Under the simple spherical morphology of Chlorella, many other 'green balls' unfolded as independent phylogenetic lineages as a result of convergent evolution. By contrast, green algae with strikingly different phenotypes were unmasked as close relatives of Chlorella by modern molecular techniques. Here, we point to the increasing impact of these diverse protists on ecology, evolution, and biotechnology in the light of integrative taxonomy.
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Papers by Volker Huss