2 NEW MOTILE PHOTOTROPHIC CONSORTIA - CHLOROCHROMATIUM-LUNATUM AND PELOCHROMATIUM-SELENOIDES

Two new phototrophic consortia, ''Chlorochromatium lunatum'' and ''Pel ochromatium seleizoides'', were observed and collected in the hypolimn ion 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 p reviously described motile phototrophic consortia ''Chlorochromatium a ggregatum'' and ''Pelochromatium roseum''. These phototrophic cells di d not resemble any described unicellular green sulfur bacteria. The pr edominant pigments detected were bacteriochlorophyll ct and chlorobact ene for the green-colored ''Clc. lunatum'', and bacteriochlorophyll e and isorenieratene for the brown-colored ''Plc. selenoides''. Their pi gment compositions and the presence of chlorosomes attached to the inn er face of the cytoplasmic membrane in both kinds of photosynthetic ce lls confirmed this new half-moon-shaped morphotype as a green sulfur b acterium. Both consortia were found thriving in lakes with low concent rations of sulfide (< 60 mu M), below the layers of ''Clc. aggregatum' ' and ''Plc. roseum''. The green consortia were observed in lakes wher e the oxic-anoxic interface was located at shallow depths (2-7 m), whi le the brown consortia were found at greater depths (8-16 m). The two newly described consortia were never detected together at the same dep th in any lake.