The diversity of gas vesicle genes in Planktothrix rubescens from Lake Zurich

Part of the gas vesicle gene cluster was amplified by PCR from three strain s of Planktothrix rubescens isolated from Lake Zurich, Switzerland. Each co ntains multiple alternating copies of gvpA and gvpC. All of the gvpA sequen ces in the different strains are identical. There are two types of gvpC: gv pC(20), of length 516 bp, encodes a 20 kDa protein of 172 amino acid residu es (whose N-terminal amino acid sequence is homologous with the sequence of GvpC in Planktothrix [Oscillatoria] agardhii); gvpC(16), of length 417 bp, encodes a 16 kDa protein of 139 amino acid residues that differs in lackin g an internal 33-residue section. An untranslated 72 bp fragment from the 3 ' end of gvpC, designated Omega C, is also present in some strains. The two types of gvpC and presence of Omega C could be distinguished by the differ ent lengths of PCR amplification products obtained using pairs of oligonucl eotide primers homologous to internal sequences in gvpC and gvpA. Three gen otype classes were found: GV1, containing only gvpC(20); GV2, containing gv pC(20) and Omega C; and GV3, containing gvpC(16), gvpC(20) and Omega cC. Su bclasses of GV2 and GV3 contained either one or two copies of Omega C. The accompanying paper by D. I, Bright & A. E. Walsby (Microbiology 145, 2769-2 775) shows that strains of the GV3 genotype produce gas vesicles with a hig her critical pressure than those of GV1 and GV2. A PCR survey of 185 clonal cultures of P. rubescens isolated from Lake Zurich revealed that 3 isolate s were of genotype GV1, 73 were of GV2 and 109 were of GV3. The PCR techniq ue was used to distinguish the gas vesicle genotype, and thence the associa ted critical-pressure phenotype, of single filaments selected from lakewate r samples. Sequence analysis of the 16S rDNA and of regions within the oper ons encoding phycoerythrin, phycocyanin and Rubisco confirmed that these st rains of Planktothrix form a tight phylogenetic group.