System. App!. Microbio!. 20, 209-215 (1997) © Gustav Fischer Verlag Psychrobacter giacincoia sp. nov., a Halotolerant, Psychrophilic Bacterium Isolated from Antarctic Sea Ice JOHN P. BOWMAN, DAVID S. NICHOLS and TOM A. McMEEKIN Antarctic CRC and Department of Agricultural Science, University of Tasmania, Hobart, Tasmania Australia Received October 22, 1996 Summary Two groups of halotolerant, strictly oxidative, non-motile bacterial strains with a distinct coccoidal mor- phology were isolated from predominantly congelation sea ice collected from the Vestfold Hills area (69 oS 78 °E) and from anchor ice of the Amery Ice Shelf (69 oS 71 °E) in Eastern Antarctica. One group of strains were found to be phenotypically similar to the species Psychrobacter immobilis. This relationship was confirmed by DNA:DNA hybridization which showed representative strains shared 74-92% DNA homology with Psychrobacter immobilis ACAM 52F (T, type strain). A second group of strains possessed an optimal temperature for growth of 13-15 °C, and required seawater for optimal growth and failed to form acid from carbohydrates. These strains were also halotolerant growing in the presence of NaCI con- centrations up to 1.8-2.1 M. Further characterization studies determined that the strains belonged to a single distinct taxon within the genus Psychrobacter which differed phenotypically and genotypically from other Psychrobacter species isolated from Antarctica and other environments. Psychrobacter urativorans ACAM 534 T was the closest phylogenetic relative to the novel sea ice taxa in terms of 16S rDNA sequence similarity of 96.7%. The sea ice strains thus represent a novel species within the genus Psychrobacter with the proposed name, Psychrobacter glacincola sp. nov. (type strain = ACAM 483 T ). Key words: Antarctic bacteria - marine bacteria - psychrophilic bacteria - Psychrobacter - Moraxella- ceae - sea Ice Introduction The genus Psychrobacter includes gram negative cells with a coccoidal or rod-like morphology which lack motility and possess a strictly oxidative metabolism (JUNI and HEYM, 1986). 16S rDNA sequence and rRNA:DNA hybridization analyses have shown the genus Psy- chrobacter belongs to the family Moraxellaceae (ROSSAU et aI., 1991; BOWMAN et al. 1996) which also includes the genera Moraxella and Acinetobacter. Psychrobacter species are characteristically halotolerant and psy- chrotrophic and have been isolated from a wide range of habitats including food and clinical sources; the skin, gills, and intestines of fish; and seawater (JUNI, 1991). Recently ornithogenic soils in active penguin colonies of Antarctica have been found to harbour high populations of two recently described Psychrobacter species with low growth temperature optima (BOWMAN et aI., 1996). Antarctic sea ice represents a mostly transient but vast habitat for a wide variety of organisms, including di- atoms, flagellates, protozoa, and bacteria. Though sea ice is a stressful invironment which combines both con- stantly low temperatures and highly variable water activ- ity, a rich diversity of bacterial life has been discovered there (SULLIVAN and PALMISANO, 1984). Sea ice contains an active microbial loop (KOTTMEIER and SULLIVAN, 1990), and bacterial activity and productivity have been investigated in several studies (PALMISANO and GARRISON, 1993; GROSSMANN and DIECKMANN, 1994). Sea ice bacte- rial communties have been shown to be vertically strati- fied and the highest populations usually correspond with highest ice algae biomass (KOTTMEIER and SULLIVAN, 1990; HELMKE and WEYLAND, 1995). The photosynthetic based primary production of ice algae blooms has been found to be tightly coupled to bacterial heterotrophy. During an investigation into the bacterial biodiversity of Antarctic sea ice, gram-negative, coccoidal cells were frequently observed and several strains were isolated. In this study the characterization of these strains is detailed and shows some of the strains represent a novel species within the genus Psychrobacter, Psychrobacter glacincola sp. nov.