Plesiocystis pacifica gen. nov., sp nov., a marine myxobacterium that contains dihydrogenated menaquinone, isolated from the Pacific coasts of Japan

Two strains of a novel myxobacterium (designated SIR-1(T) and SHI-1) were isolated from Japanese coasts located in the Pacific subtropical zone. Cells of both strains were Gram-negative, rodshaped and motile by gliding. The strains were chemoheterotrophic and strictly aerobic. They had the common characteristics associated with myxobacteria, such as bacteriolytic action and fruiting-body formation. The characteristic feature of the strains was a NaCl growth requirement with an optimum concentration of 2.0-3.0% (w/v), comparable to that of sea water. In addition, other cationic components of sea water, such as Mg2+, Ca2+ and K+, were needed for growth. The major respiratory quinone was MK-8(H-2). The cellular fatty acid profile was characterized by the predominance Of iso-C-15: 0. Characteristic fatty acids anteiSO-C-16: 0 and anteiso-C-17: 0, and a long-chain polyunsaturated fatty acid (C-20: 4), were also detected. The G + C content of the genomic DNA of strains SIR-1(T) and SHI-1 was between 69-3 and 70-0 mol% (as determined by HPLC). Strains SIR-1(T) and SHI-1 shared almost identical 16S rDNA sequences, and clustered with the genus Nannocystis as their closest relative upon phylogenetic analysis. However, the phylogenetic distance between the novel strains and the genus Nannocystis was large enough to warrant their different generic allocation. This finding was supported by significant phenotypic differences between the novel strains and Nannocystis. Thus, strains SIR-1(T) and SHI-1 represent a novel genus and species, for which the names Plesiocystis and Plesiocystis pacifica, respectively, are proposed. The type strain of the species is SIR-1(T) (=JCM 11591(T) = DSM 14875(T) =AJ 13960(T)).