Two new motile phototrophic consortia: "Chlorochromatium lunatum" and "Pelochromatium selenoides".

Two new phototrophic consortia, "Chlorochromatium lunatum" and "Pelochromatium selenoides", were observed and collected in the hypolimnion of several dimictic lakes in Wisconsin and Michigan (USA). The two consortia had the same morphology but different pigment composition. The cells of the photosynthetic components of the consortia were half-moon-shaped. This morphology was used to differentiate them from the previously described motile phototrophic consortia "Chlorochromatium aggregatum" and "Pelochromatium roseum". These phototrophic cells did not resemble any described unicellular green sulfur bacteria. The predominant pigments detected were bacteriochlorophyll d and chlorobactene for the green-colored "Clc. lunatum", and bacteriochlorophyll e and isorenieratene for the brown-colored "Plc. selenoides". Their pigment compositions and the presence of chlorosomes attached to the inner face of the cytoplasmic membrane in both kinds of photosynthetic cells confirmed this new half-moon-shaped morphotype as a green sulfur bacterium. Both consortia were found thriving in lakes with low concentrations of sulfide (< 60 &mgr;M), below the layers of "Clc. aggregatum" and "Plc. roseum". The green consortia were observed in lakes where the oxic-anoxic interface was located at shallow depths (2-7 m), while the brown consortia were found at greater depths (8-16 m). The two newly described consortia were never detected together at the same depth in any lake.