Shewanella hafniensis sp nov and Shewanella morhuae sp nov., isolated from marine fish of the Baltic Sea

Two novel species belonging to the genus Shewanella are described on the basis of their phenotypic characteristics, phylogenetic analyses of 16S rRNA and gyrB gene sequences and levels of DNA-DNA hybridization. A total of 47 strains belonging to two novel Gram-negative, psychrotolerant, H2S-producing bacterial species were isolated from marine fish (cod and flounder) caught from the Baltic Sea off Denmark. The phenotypic characteristics of strains belonging to group 1 (14 strains) indicated that these represented a non-sucrose-assimilating variant of Shewanella baltica with a DNA G + C content of 47.0 mol%. Strains of group 2 (33 isolates) did not utilize the carbon substrates assimilated by S. baltica except gluconate, N-acetylglucosamine and malate. Their DNA G + C content was 44.0 mol%. Phylogenetic analysis of the 16S rRNA gene sequence data placed the two novel species within the genus Shewanella. Group 1 strains showed greatest sequence similarity to Shewanella putrefaciens ATCC 8071(T) (99.0%) and with S. baltica NCTC 10375(T) (98.3%). However, gyrB gene sequence analysis showed these isolates to share only 90.0% sequence similarity with S. putrefaciens ATCC 8071(T) and 93.9% with S. baltica NCTC 10375(T). Similarly, DNA-DNA hybridization experiments revealed DNA relatedness levels of 38% between the group 1 isolates and S. putrefaciens ATCC 8071(T) and 43% with S. baltica NCTC 10375(T). The group 2 strains shared less than 97% 16S rRNA gene sequence similarities with recognized Shewanella species. Comparisons between the two novel species indicated 16S rRNA gene sequence similarity of similar to 98%, gyrB gene sequence similarity of similar to 89% and DNA-DNA reassociation values of 20-34%. Based on the evidence presented, two novel species, Shewanella hafniensis sp. nov. (type strain P010(T) = ATCC BAA-1207(T) = NBRC 100975(T)) and Shewanella morhuae sp. nov. (type strain U 1417(T) = ATCC BAA-1205(T) = NBRC 100978(T)), are described.