Photobacterium proteolyticum sp. nov., a protease-producing bacterium isolated from ocean sediments of Laizhou Bay

A protease-producing bacterial strain, 13-12T, was isolated from the ocean sediment of Laizhou Bay, PR China and systematically studied. The bacterium was Gram-stain negative, non spore-forming rods, which were motile with two flagella. It was positive for oxidase, the hydrolysis of starch, agar and gelatin, and for nitrate reduction. It was negative for catalase, esterase and the degradation of CM-cellulose. Optimum growth was observed at 28 °C, pH 6.5-7.0 and in the presence of 2-3 % (w/v) NaCl. Phylogenetic analysis of the 16S rRNA gene, and whole genome data, affiliated it to the genus Photobacterium. It was most closely related to Photobacterium jeanii R-40508T (96.7 % 16S rRNA gene similarity). Strain 13-12T was found to have less than 86.1 % similarities with the type strains of its most closely related species in multi-locus sequence analysis, less than 75.2 % using genome average nucleotide identities (ANI), and less than 18.5 % in DNA-DNA relatedness studies. Q8 was the predominant respiratory menaquinone. Phosphatidylethanolamine, phosphoaminolipid and phospholipid were the major polar phospholipids and summed feature 3 (48.2 %), C16 : 0 (18.4 %) and C18 : 1ω5c (14.1 %) the major fatty acids. The combined phenotypic, phylogenetic, genomic and chemotaxonomic data support this strain representing a novel species of the genus Photobacterium, for which the name Photobacterium proteolyticum sp. nov. is proposed, with 13-12T (=KCTC 42764T=CGMCC 1.14970) as the type strain. The genome size of 13-12T is 6.2 Mbp, comprising 5806 predicted genes and the DNA G+C content is 47.9 mol%.