A eukaryotic alga from picoplankton of Lake Baikal: morphology, ultrastructure and rDNA sequence data

An eukaryotic alga (strain BAC 9708) from the picoplankton of Lake Baikal (Eastern Siberia) has been cultivated in order to investigate its morphology, ultrastructure, growth requirements, pigment composition and nuclear-encoded 18S and chloroplast-encoded 16S rDNA sequences. Cells of strain BAC 9708 contain a nucleus, a single chloroplast without a pyrenoid, one mitochondrion, a poorly visible dictyosome, a large vacuole and a cell wall with an outer sporopollenin-containing layer. Ellipsoidal cells, 1.5-2.0 x 1.0-1.5 mum in size, propagate usually by two, or infrequently by four autospores. Sequence analysis of nuclear-encoded rDNA showed that all 581 nucleotides of the 5'-end of the 18S rDNA were identical to that of Choricystis minor (Skuja) Fott (Chlorococcales, Chlorophyta) obtained earlier (Krienitz et al., 1996). The chloroplast-encoded rDNA sequence of this strain showed identity with one of three chloroplast sequences, selected by PCR-amplification with 16S rDNA specific primers from total picoplanktonic DNA, obtained previously.