J Skerratt

Shewanella gelidimarina sp. nov. and Shewanella frigidimarina sp. nov., novel Antarctic species with the ability to produce eicosapentaenoic acid (20:5 omega 3) and grow anaerobically by dissimilatory Fe(III) reduction

A polyphasic taxonomic study was performed to characterize dissimilatory iron-reducing strains mostly isolated from Antarctic sea ice. The strains were isolated from samples of congelated (land-fast) sea ice, grease ice, and ice algal biomass collected from the coastal areas of the Vestfold Hills in eastern Antarctica (68 degrees S 78 degrees E). The strains were facultatively anaerobic, motile, and rod shaped, were capable of anaerobic growth either by fermentation of carbohydrates or by anaerobic respiration, and utilized a variety of electron acceptors, including nitrate, ferric compounds, and trimethylamine N-oxide. A phylogenetic analysis performed with 16S rRNA sequences showed that the isolates formed two groups representing novel lineages in the genus Shewanella. The first novel group included seawater-requiring, psychrophilic, chitinolytic strains which had DNA G + C contents of 48 mol%. The members of the second strain group were psychrotrophic and did not require seawater but could tolerate up to 9% NaCl. The strains of this group were also unable to degrade polysaccharides but could utilize a number of monosaccharides and disaccharides and had G + C contents of 40 to 43 mol%. The whole-cell-derived fatty acid profiles of the sea ice isolates were found to be similar to the profiles obtained for other Shewanella species. The omega-3 polyunsaturated fatty acid eicosapentaenoic acid (EPA) (20:5 omega 3) was detected in all of the sea ice isolates at levels ranging from 2 to 16% of the total fatty acids. EPA was also found at high levels in Shewanella hanedai (19 to 22%) and Shewanella benthica (16 to 18%) but was absent in Shewanella alga and Shewanella putrefaciens. On the basis of polyphasic taxonomic data, the Antarctic iron-reducing strains are placed in two new species, Shewanella frigidimarina sp. nov. (type strain, ACAM 591) and Shewanella gelidimarina sp. nov. (type strain, ACAM 456).

Methylosphaera hansonii gen. nov., sp. nov., a psychrophilic, group I methanotroph from Antarctic marine salinity, meromictic lakes

Methanotrophic bacteria were enumerated and isolated from the chemocline and surface sediments of marine-salinity Antarctic meromictic lakes located in the Vestfold Hills, Antarctica (68 degrees S 78 degrees E). Most probable number (MPN) analysis indicated that at the chemocline of Ace Lake the methanotroph population made up only a small proportion of the total microbial population and was sharply stratified, with higher populations detected in the surface sediments collected at the edge of Ace Lake and Burton Lake. Methanotrophs were not detected in Pendant Lake. Only a single phenotypic group of methanotrophs was successfully enriched, enumerated and isolated into pure culture from the lake samples. Strains of this group were non-motile, coccoidal in morphology, did not form resting cells, reproduced by constriction, and required seawater for growth. The strains were also psychrophilic, with optimal growth occurring at 10-13 degrees C and maximum growth temperatures of 16-21 degrees C. The ribulose monophosphate pathway but not the serine pathway for incorporation of C1 compounds was detectable in the strains. The guanine plus cytosine (G + C) content of the genomic DNA was 43-46 mol%. Whole-cell fatty acid analysis indicated that 16:1 omega 8c (37-41%), 16:1 omega 6c (17-19%), 16:1 omega 7c (15-19%) and 16:0 (14-15%) were the major fatty acids in the strains. 16s rDNA sequence analysis revealed that the strains form a distinct line of descent in the family Methylococcaceae (group I methanotrophs), with the closest relative being the Louisiana Slope methanotrophic mytilid endosymbiont (91.8-92.3% sequence similarity). On the basis of polyphasic taxonomic characteristics the Antarctic lake isolates represent a novel group I methanotrophic genus with the proposed name Methylosphaera hansonii (type strain ACAM 549).

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 : 6 omega 3)

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 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 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 gM-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).

Seasonal and inter-annual changes in planktonic biomass and community structure in eastern Antarctica using signature lipids

The total lipid, fatty acid, sterol and pigment composition of water column particulates collected near the Australian Antarctic Base, Davis Station, were analysed over five summer seasons (1988–93) using capillary GC, GC-MS, TLC-FID and HPLC. Maximum lipid concentrations usually occurred in samples collected in December and January and corresponded with increased algal biomass. Polar lipids were the dominant lipid class. Both lipid profiles and microscopic observations showed significant variation in biomass and community structure in the water column both intra- and interannually. During the period of diatom blooms (predominantly Nitzschia spp.) the dominant sterol and fatty acid were trans-22-dehydrocholesterol and 20:5 ω3, respectively, which were accompanied by a high 16:1 ω7c to 16:0 ratio. Very high polyunsaturated fatty acid and total lipid concentrations were measured during diatom blooms in the area. Bacterial markers increased in concentration after the summer algal blooms in each year. C30 sterols also increased in concentration during the latter half of all summers. Samples collected from the fjords contained greater biomass and diversity in algal and bacterial markers than samples from coastal sites. Signature lipids for the prymnesiophyte Phaeocystis sp., thought to be seasonally abundant in Antarctic waters, were identified in field samples over the five summer seasons studied. Blooms of this alga exhibited high 14:0, brassicasterol, low levels of polyunsaturated fatty acids and a low 16:1ω7c to 16:0 ratio. Based on the lipid profiles, the overall abundance of Phaeocystis sp. throughout the five summer seasons was sporadic and in most summers the abundance was low; these findings suggest Phaeocystis sp. is not always a major alga in this coastal region of Antarctica.

Nutrient stress gradient in the bottom 5 cm of fast ice, McMurdo Sound, Antarctica

Abstract One-centimeter-scale vertical sampling of fast ice from McMurdo Sound, Antarctica reveals evidence of progressive nutrient limitation with distance above the ice/water interface. Over the bottom 6 cm photosynthetically active radiation increases by between 1.8 and 3 times, C:N increases from 6.8 to 19.8 and δ13C increases from −18 to −12. Fatty acid composition also changes with a consistent decline in polyunsaturated fatty acids and a rise in saturated fatty acids. These factors all suggest severe and progressive nutrient limitation with distance from the ice/water interface.

Site Holds Promise for Ecosystem and Biogeochemical Investigations

Ellis Fjord, located in the Vestfold Hills of East Antarctica (68.5°S, 78°E), exhibits a range of environments, from essentially marine at its sea-ward end, to permanently stratified basins with hypersaline brines at its inland end. The drainage basin of the fjord contains small areas of mosses and lichens, but no higher plants, and supplies fresh water to the fjord in ephemeral summer melt streams. Direct anthropogenic inputs are negligible or non-existent, as are those from other mammals and birds. The fjord exhibits unusual biological and chemical properties, and offers the opportunity to study oceanic processes in isolation and at small scales. It also has the logistical advantage of proximity to the facilities of Australias year-round Davis research station.