Photobacterium toruni sp. nov., a bacterium isolated from diseased farmed fish.

Abstract

Three bacterial strains were isolated from liver and spleen of diseased farmed redbanded seabream (Pagrus auriga) in south-west Spain. Their partial 16S rRNA gene sequences clustered within those of the genus Photobacterium, showing high similarity (98.6-99.3 %) to the type strains of Photobacterium iliopiscarium, P. piscicola, P. kishitanii, P. aquimaris and P. phosphoreum. Multilocus sequence analysis using six housekeeping genes (gapA, topA, mreB, ftsZ, gyrB and 16S rRNA) confirmed the new strains as forming an independent branch with a bootstrap value of 100, likely to represent a novel species. To confirm this, we used whole genome sequencing and genomic analysis (ANIb, ANIm and in silico DNA-DNA hybridization) obtaining values well below the thresholds for species delineation. In addition, a phenotypic characterization was performed to support the description and differentiation of the novel strains from related taxa. Cells were Gram-stain-negative, motile bacilli, chemo-organotrophic and facultatively anaerobic. They fermented glucose, as well as galactose and d-mannose, without production of gas. Oxidase and catalase were positive. The predominant cellular fatty acids were C16 : 1ω7c/C16 : 1ω6c and C16 : 0. The predominant respiratory quinone (Q-8) and major polar lipids (phosphatidylethanolamine, phosphatidylglycerol and diphosphatidylglycerol) were inferred from annotated genes in the genome of strain H01100410BT, which had a G+C content of 38.6 mol%. The results obtained demonstrate that the three strains represent a novel species, for which the name Photobacterium toruni sp. nov. is proposed. The type strain is H01100410BT (=CECT 9189T=LMG 29991T).