Description of Shewanella glacialipiscicola sp. nov. and Shewanella algidipiscicola sp. nov., isolated from marine fish of the Danish Baltic Sea, and proposal that Shewanella affinis is a later heterotypic synonym of Shewanella colwelliana

Abstract

Two novel species belonging to the genusShewanellaare described on the basis of a polyphasic taxonomic approach. A total of 40 strains of Gram-negative, psychrotolerant, H2S-producing bacteria were isolated from marine fish (cod and plaice) caught in the Baltic Sea off Denmark. Strains belonging to group 1 (seven strains) were a lactate-assimilating variant ofShewanella morhuaewith a G+C content of 44 mol%. The strains of group 2 (33 strains) utilized lactate,N-acetylglucosamine and malate but did not produce DNase or ornithine decarboxylase. Their G+C content was 47 mol%. Phylogenetic analysis of the 16S rRNA gene sequence data placed the two novel species within the genusShewanella. Group 1 showed greatest sequence similarity withS. morhuaeATCC BAA-1205T(99.9 %). However,gyrBgene sequence analysis and DNA–DNA hybridization differentiated these isolates fromS. morhuae, with 95.6 % sequence similarity and less than 57 % DNA relatedness, respectively. Group 2 strains shared more than 99 % 16S rRNA gene sequence similarity with the type strains ofShewanella colwellianaandShewanella affinis, butgyrBsequence similarity (~85 %) and the results of DNA hybridization (~28 %) indicated that the new isolates represented a novel species. Furthermore, when compared to each other, the type strains ofS. colwellianaandS. affinishad almost identicalgyrBsequences and significantly high DNA reassociation values (76–83 %), indicating that they belonged to the same species. Based on the conclusions of this study, we propose the novel speciesShewanella glacialipiscicolasp. nov. (type strain T147T=LMG 23744T=NBRC 102030T) for group 1 strains andShewanella algidipiscicolasp. nov. (type strain S13T=LMG 23746T=NBRC 102032T) for group 2 strains, and we propose thatShewanella affinisas a later heterotypic synonym ofShewanella colwelliana.