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 . 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 3 polyunsaturated fatty acid (PUFA) docosahexaenoic acid (22:63, 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 strains ranged from 35 to 42 mol% and DNA-DNA hybridization analyses indicated that the isolates formed five genospecies, including the species (ACAM 550). 16S rRNA sequence analysis indicated that the strains formed a cluster in the gM-subclass of the with . Sequence similarities ranged from 95·2 to 100% between the various Antarctic isolates. Phenotypic characterization confirmed distinct differences between the different genospecies. These studies indicate that the DHA-producing Antarctic isolates consist of five different species: and four novel species with the proposed names sp. nov. (ACAM 459), sp. nov. (ACAM 179), sp. nov. (ACAM 608) and sp. nov. (ACAM 607).


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