Colwellia demingiae sp. nov., Colwellia hornerae sp. nov., Colwellia rossensis sp. nov. and Colwellia psychrotropica sp. nov.: psychrophilic Antarctic species with the ability to synthesize docosahexaenoic acid (22: 63)

As part of a general survey of the biodiversity and inherent ecophysiology of bacteria associated with coastal Antarctic sea-ice diatom assemblages, eight strains were identified by 16S rRNA sequence analysis as belonging to the genus Colwellia. The isolates were non-pigmented, curved rod-like cells which exhibited psychrophilic and facultative anaerobic growth and possessed an absolute requirement for sea water. One isolate was able to form gas vesicles. All strains synthesized the ω3 polyunsaturated fatty acid (PUFA) docosahexaenoic acid (22:6ω3, DHA) (0·7–8·0% of total fatty acids). Previously, DHA has only been detected in strains isolated from deep-sea benthic and faunal habitats and is associated with enhanced survival in permanently cold habitats. The G+C content of the DNA from the Antarctic Colwellia strains ranged from 35 to 42 mol% and DNA-DNA hybridization analyses indicated that the isolates formed five genospecies, including the species Colwellia psychrerythraea (ACAM 550T). 16S rRNA sequence analysis indicated that the strains formed a cluster in the γ-subclass of the Proteobacteria with Colwellia psychrerythraea. Sequence similarities ranged from 95·2 to 100% between the various Antarctic Colwellia isolates. Phenotypic characterization confirmed distinct differences between the different genospecies. These studies indicate that the DHA-producing Antarctic isolates consist of five different Colwellia species: Colwellia psychrerythraea and four novel species with the proposed names Colwellia demingiae sp. nov. (ACAM 459T), Colwellia psychrotropica sp. nov. (ACAM 179T), Colwellia rossensis sp. nov. (ACAM 608T) and Colwellia hornerae sp. nov. (ACAM 607T).