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Characterization of purple sulfur bacteria from the South Andros Black Hole cave system: highlights taxonomic problems for ecological studies among the genera Allochromatium and Thiocapsa
Author(s) -
Herbert Rodney A.,
RanchouPeyruse Anthony,
Duran Robert,
Guyoneaud Rémy,
Schwabe Stephanie
Publication year - 2005
Publication title -
environmental microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.954
H-Index - 188
eISSN - 1462-2920
pISSN - 1462-2912
DOI - 10.1111/j.1462-2920.2005.00815.x
Subject(s) - biology , phototroph , anoxygenic photosynthesis , botany , purple bacteria , halophile , chlorosome , bacteriochlorophyll , 16s ribosomal rna , ecology , zoology , bacteria , photosynthesis , paleontology , photosynthetic reaction centre
Summary A dense 1 m thick layer of phototrophic purple sulfur bacteria is present at the pycnocline (17.8 m depth) in the meromictic South Andros Black Hole cave system (Bahamas). Two purple sulfur bacteria present in samples collected from this layer have been identified as belonging to the family Chromatiaceae . One isolate (BH‐1), pink coloured, is non‐motile, non‐gas vacuolated, 2–3 µm in diameter and surrounded by a capsule. The other isolates (BH‐2 and BH‐2.4), reddish‐brown coloured, are small celled (4 µm × 2 µm), motile by means of a single polar flagellum. In both isolates (BH‐1 and BH‐2), the intracellular photosynthetic membranes are of the vesicular type and bacteriochlorophyll a and carotenoids of the normal spirilloxanthin series are present. Both isolates grow well in the presence of sulfide and carbon dioxide in the light. During photoautotrophic growth sulfur globules are stored intracellularily as intermediate oxidation products. According to the 16S rRNA gene sequence data the isolates belong to the genera Thiocapsa and Allochromatium . However, at the species level a number of inconsistencies exist between the phenotypic and phylogenetic data, highlighting taxonomic problems within these genera. These inconsistencies may have implications for microbiologists studying the ecology of anoxygenic phototrophs. For ecologists studying the functioning of an ecosystem it may not be particularily important to know whether a specific isolate belongs to one species or another. However, if one wants to study the role of different populations within a particular functional group then the species concept is important. This study demonstrates that further work is still required on the taxonomy of purple sulfur bacteria in order that microbial ecologists are able to accurately identify a population/species isolated from hitherto undescribed aquatic ecosystems.