Elucidation of the gas vesicle gene clusters in cyanobacteria of the genus Arthrospira (Oscillatoriales, Cyanophyta) and correlation with ITS phylogeny

The genus Arthrospira comprises filamentous cyanobacteria in which the trichomes form an open helix and contain gas vacuoles. The gas vesicle gene cluster of five Arthrospira strains was amplified by PCR and sequenced. The genes are organized in one operon, in the order gvpA1-gvpC1-gvpA2-gvpC2-gvpA3-gvpC3-gvpN. In Arthrospira sp. strain PCC 8005, the genes gvpJ, gvpK, gvpV and gvpW were also identified. Each of the three copies of gvpA encodes a protein of 71 amino acids. In the case of gvpC, there are two different length variants. Each of the two shorter genes, gvpC1 and gvpC2, encodes a putative protein of 151 amino acids, while the longer one, gvpC3, codes for a putative protein of 284 residues. The amino acid sequences of GvpC1 and GvpC2 are identical to the N-terminal part of GvpC3. In spite of the presence of stop codons downstream of gvpC1 and gvpC2, the deduced amino acid sequences in these regions are highly similar to the C-terminal part of GvpC3 (residues 160 to 229). The GvpC1, GvpC2 and GvpC3 proteins contain contiguous repeats of 33 amino acids as previously reported for other cyanobacteria. The sequences of the gvpA1, gvpC1, gvpA2 and gvpC2 genes were not found in the genome data of Arthrospira sp. PCC 8005, A. maxima CS-328, and A. platensis NIES-39 as a result of incomplete assembly. The genes gvpN and gvpJ located downstream of gvpC3, encode putative proteins of 394 and 127 amino acids, respectively. The deduced amino acid sequences of gvpK, gvpV and gvpW contain 151, 112 and 227 residues, respectively. The analysis of gvp sequences of five strains of Arthrospira revealed the presence of polymorphic positions, which distinguished the strains in agreement with their previous assignments to ITS clusters I and II. This is the first report of gvp genes in members of the genus Arthrospira.