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Light underneath Antarctic sea-ice is below detectable limits for up to 4 months of the year. The ability of Antarctic sea-ice diatoms to survive this prolonged darkness relies on their metabolic capability. This study is the first to examine the proteome of a prominent sea-ice diatom in response to extended darkness, focusing on the protein-level mechanisms of dark survival. The Antarctic diatom Fragilariopsis cylindrus was grown under continuous light or darkness for 120 d. The whole cell proteome was quantitatively analysed by nano-LC-MS/MS to investigate metabolic changes that occur during sustained darkness and during recovery under illumination. Enzymes of metabolic pathways, particularly those involved in respiratory processes, tricarboxylic acid cycle, glycolysis, the Entner-Doudoroff pathway, the urea cycle and the mitochondrial electron transport chain became more abundant in the dark. Within the plastid, carbon fixation halted while the upper sections of the glycolysis, gluconeogenesis and pentose phosphate pathways became less active. We have discovered how F. cylindrus utilises an ancient alternative metabolic mechanism that enables its capacity for long-term dark survival. By sustaining essential metabolic processes in the dark, F. cylindrus retains the functionality of the photosynthetic apparatus, ensuring rapid recovery upon re-illumination., (© 2019 The Authors. New Phytologist © 2019 New Phytologist Trust.)

Sea ice is a highly dynamic and productive environment that includes a diverse array of psychrophilic prokaryotic and eukaryotic taxa distinct from the underlying water column. Because sea ice has only been extensive on Earth since the mid-Eocene, it has been hypothesized that bacteria highly adapted to inhabit sea ice have traits that have been acquired through horizontal gene transfer (HGT). Here we compared the genomes of the psychrophilic bacterium Psychroflexus torquis ATCC 700755(T), associated with both Antarctic and Arctic sea ice, and its closely related nonpsychrophilic sister species, P. gondwanensis ACAM 44(T). Results show that HGT has occurred much more extensively in P. torquis in comparison to P. gondwanensis. Genetic features that can be linked to the psychrophilic and sea ice-specific lifestyle of P. torquis include genes for exopolysaccharide (EPS) and polyunsaturated fatty acid (PUFA) biosynthesis, numerous specific modes of nutrient acquisition, and proteins putatively associated with ice-binding, light-sensing (bacteriophytochromes), and programmed cell death (metacaspases). Proteomic analysis showed that several genes associated with these traits are highly translated, especially those involved with EPS and PUFA production. Because most of the genes relating to the ability of P. torquis to dwell in sea-ice ecosystems occur on genomic islands that are absent in closely related P. gondwanensis, its adaptation to the sea-ice environment appears driven mainly by HGT. The genomic islands are rich in pseudogenes, insertional elements, and addiction modules, suggesting that gene acquisition is being followed by a process of genome reduction potentially indicative of evolving ecosystem specialism.

A real-time polymerase chain reaction (PCR) method to quantify the proportion of microorganisms containing alkane monooxygenase was developed and used to follow changes in the microbial community in hydrocarbon-contaminated Antarctic soil during a bioremediation field trial. Assays for the alkB and rpoB genes were validated and found to be both sensitive and reproducible (less than 2% intrarun variation and 25-38% interrun variation). Results from the real-time PCR analysis were compared to analysis of the microbial population by a culture-based technique [most probable number (MPN) counts]. Both types of analysis indicated that fertilizer addition to hydrocarbon-contaminated soil stimulated the indigenous bacterial population within 1 year. The proportion of alkB containing microorganisms was positively correlated to the concentration of n-alkanes in the soil. After the concentration of n-alkanes in the soil decreased, the proportion of alkane-degrading microorganisms decreased, but the proportion of total hydrocarbon-degrading microorganisms increased, indicating another shift in the microbial community structure and ongoing biodegradation.

Several orange- and yellow-pigmented, halophilic, strictly aerobic, chemoheterotrophic, Gram-negative strains were isolated during investigations of maritime Antarctic habitats, including coastal fast sea-ice brine and algae, crustaceans and quartz stone sublithic cyanobacterial biofilms. Isolates investigated in this study belonged to the marine clade of the family Flavobacteriaceae and represented lineages that were either distinct from species with validly published names or appeared to be distinct species within existing genera. A polyphasic taxonomic analysis demonstrated the novelty of these strains, and several new taxa are proposed. Strains from quartz stone sublithic communities were grouped into two new genera designated Subsaximicrobium gen. nov. and Subsaxibacter gen. nov. The genus Subsaximicrobium included the species Subsaximicrobium wynnwilliamsii sp. nov. (type species; type strain G#7(T)=ACAM 1070(T)=CIP 108525(T)) and Subsaximicrobium saxinquilinus sp. nov. (type strain Y4-5(T)=ACAM 1063(T)=CIP 108526(T)). The genus Subsaxibacter contained a single species designated Subsaxibacter broadyi sp. nov. (type strain P7(T)=ACAM 1064(T)=CIP 108527(T)). A novel bacterial strain isolated from the lake-dwelling, calanoid copepod Paralabidocera antarctica was given the name Lacinutrix copepodicola gen. nov., sp. nov. (type strain DJ3(T)=ACAM 1055(T)=CIP 108538(T)). Four novel species of the genus Bizionia were discovered, Bizionia algoritergicola sp. nov. (type strain APA-1(T)=ACAM 1056(T)=CIP 108533(T)) and Bizionia myxarmorum sp. nov. (type strain ADA-4(T)=ACAM 1058(T)=CIP 108535(T)), which were isolated from the carapace surfaces of sea-ice algae-feeding amphipods, and Bizionia gelidisalsuginis sp. nov. (type strain IC164(T)=ACAM 1057(T)=CIP 108536(T)) and Bizionia saleffrena sp. nov. (type strain HFD(T)=ACAM 1059(T)=CIP 108534(T)), which were isolated from sea-ice brines. Several other novel species were also isolated from sea-ice samples, including two novel species of the genus Gelidibacter, Gelidibacter gilvus sp. nov. (type strain IC158(T)=ACAM 1054(T)=CIP 108531(T)) and Gelidibacter salicanalis sp. nov. (type strain IC162(T)=ACAM 1053(T)=CIP 108532(T)), as well as three novel species of the genus Gillisia, Gillisia illustrilutea sp. nov. (type strain IC157(T)=ACAM 1062(T)=CIP 108530(T)), Gillisia sandarakina sp. nov. (type strain IC148(T)=ACAM 1060(T)=CIP 108529(T)) and Gillisia hiemivivida sp. nov. (type strain IC154(T)=ACAM 1061(T)=CIP 108528(T)).

Exopolysaccharides (EPSs) are high molecular weight carbohydrate polymers that make up a substantial component of the extracellular polymers surrounding most microbial cells in the marine environment. EPSs constitute a large fraction of the reduced carbon reservoir in the ocean and enhance the survival of marine bacteria by influencing the physicochemical environment around the bacterial cell. Microbial EPSs are abundant in the Antarctic marine environment, for example, in sea ice and ocean particles, where they may assist microbial communities to endure extremes of temperature, salinity, and nutrient availability. The microbial biodiversity of Antarctic ecosystems is relatively unexplored. Deep-sea hydrothermal vent environments are characterized by high pressure, extreme temperature, and heavy metals. The commercial value of microbial EPSs from these habitats has been established recently. Extreme environments offer novel microbial biodiversity that produces varied and promising EPSs. The biotechnological potential of these biopolymers from hydrothermal vent environments as well as from Antarctic marine ecosystems remains largely untapped.

The sea ice microbial community plays a key role in the productivity of the Southern Ocean. Exopolysaccharide (EPS) is a major component of the exopolymer secreted by many marine bacteria to enhance survival and is abundant in sea ice brine channels, but little is known about its function there. This study investigated the effects of temperature on EPS production in batch culture by CAM025, a marine bacterium isolated from sea ice sampled from the Southern Ocean. Previous studies have shown that CAM025 is a member of the genus Pseudoalteromonas and therefore belongs to a group found to be abundant in sea ice by culture-dependent and -independent techniques. Batch cultures were grown at -2 degrees C, 10 degrees C, and 20 degrees C, and cell number, optical density, pH, glucose concentration, and viscosity were monitored. The yield of EPS at -2 degrees C and 10 degrees C was 30 times higher than at 20 degrees C, which is the optimum growth temperature for many psychrotolerant strains. EPS may have a cryoprotective role in brine channels of sea ice, where extremes of high salinity and low temperature impose pressures on microbial growth and survival. The EPS produced at -2 degrees C and 10 degrees C had a higher uronic acid content than that produced at 20 degrees C. The availability of iron as a trace metal is of critical importance in the Southern Ocean, where it is known to limit primary production. EPS from strain CAM025 is polyanionic and may bind dissolved cations such at trace metals, and therefore the presence of bacterial EPS in the Antarctic marine environment may have important ecological implications.

Exopolysaccharides (EPS) may have an important role in the Antarctic marine environment, possibly acting as ligands for trace metal nutrients such as iron or providing cryoprotection for growth at low temperature and high salinity. Ten bacterial strains, isolated from Southern Ocean particulate material or from sea ice, were characterized. Whole cell fatty acid profiles and 16S rRNA gene sequences showed that the isolates included representatives of the genera Pseudoalteromonas, Shewanella, Polaribacter, and Flavobacterium as well as one strain, which constituted a new bacterial genus in the family Flavobacteriaceae. The isolates are, therefore, members of the "Gammaproteobacteria" and Cytophaga-Flexibacter-Bacteroides, the taxonomic groups that have been shown to dominate polar sea ice and seawater microbial communities. Exopolysaccharides produced by Antarctic isolates were characterized. Chemical composition and molecular weight data revealed that these EPS were very diverse, even among six closely related Pseudoalteromonas isolates. Most of the EPS contained charged uronic acid residues; several also contained sulfate groups. Some strain produced unusually large polymers (molecular weight up to 5.7 MDa) including one strain in which EPS synthesis is stimulated by low temperature. This study represents a first step in the understanding of the role of bacterial EPS in the Antarctic marine environment.

The abundance, spatial distribution and diversity of class Flavobacteria were investigated in the Southern Ocean euphotic zone across a latitudinal transect and in the ice pack off Eastern Antarctica. Surface seawater samples filter-fractionated into 0.8 mum particulate and 0.2 m planktonic fractions were investigated with different molecular techniques. The abundance of particle-associated Flavobacteria, ascertained with real-time PCR and DGGE band analysis using Flavobacteria-specific primers, was found to be significantly higher in Polar Front Zone (PFZ) and Antarctic Zone (AZ) water samples than in nutrient limited Temperate Zone (TZ) and Sub-Antarctic Zone (SAZ) waters. Abundance of particle-associated Flavobacteria correlated positively with seawater chlorophyll a and nutrient concentrations, suggesting that increased Flavobacteria abundance may relate to enhanced primary production in the PFZ and AZ. This is supported by comparison of DGGE profiles that demonstrated significant differences in the total Flavobacteria community structure and 16S rRNA gene diversity between samples from the PFZ and AZ and those from TZ and SAZ. Sequence analysis revealed a broad diversity amongst class Flavobacteria in the Southern Ocean with several Flavobacteria clades detected in PFZ and AZ waters not detected in TZ and SAZ waters that putatively represent psychrophilic taxa. Sequence data included a large, so far uncultivated, cosmopolitan phylogenetic clade ("DE cluster 2") that is distributed throughout the Southern Ocean.

Aims: This study was undertaken to examine and characterize Antarctic marine bacterial isolates and the exopolysaccharides (EPS) they produce in laboratory culture., Methods and Results: Two EPS-producing bacterial strains CAM025 and CAM036 were isolated from particulate material sampled from seawater and sea ice in the southern ocean. Analyses of 16S rDNA sequences placed these isolates in the genus Pseudoalteromonas. In batch culture, both strains produced EPS. The yield of EPS produced by CAM025 was 30-fold higher at -2 and 10 degrees C than at 20 degrees C. Crude chemical analyses showed that these EPS were composed primarily of neutral sugars and uronic acids with sulphates. Gas chromatographic analysis of monosaccharides confirmed these gross compositional findings and molar ratios of monosaccharides revealed differences between the two EPS., Conclusions: The EPS produced by Antarctic bacterial isolates examined in this study appeared to be polyanionic and, therefore, 'sticky' with respect to cations such as trace metals., Significance and Impact of the Study: As the availability of iron as a trace metal is of critical importance in the southern ocean where it is know to limit primary production, the role of these bacterial EPS in the Antarctic marine environment has important ecological implications.

16S ribosomal DNA (rDNA) clone library analysis was conducted to assess prokaryotic diversity and community structural changes within a surficial sediment core obtained from an Antarctic continental shelf area (depth, 761 m) within the Mertz Glacier Polynya (MGP) region. Libraries were created from three separate horizons of the core (0- to 0.4-cm, 1.5- to 2.5-cm, and 20- to 21-cm depth positions). The results indicated that at the oxic sediment surface (depth, 0 to 0.4 cm) the microbial community appeared to be dominated by a small subset of potentially r-strategist (fast-growing, opportunistic) species, resulting in a lower-than-expected species richness of 442 operational taxonomic units (OTUs). At a depth of 1.5 to 2.5 cm, the species richness (1,128 OTUs) was much higher, with the community dominated by numerous gamma and delta proteobacterial phylotypes. At a depth of 20 to 21 cm, a clear decline in species richness (541 OTUs) occurred, accompanied by a larger number of more phylogenetically divergent phylotypes and a decline in the predominance of Proteobacteria. Based on rRNA and clonal abundance as well as sequence comparisons, syntrophic cycling of oxidized and reduced sulfur compounds appeared to be the dominant process in surficial MGP sediment, as phylotype groups putatively linked to these processes made up a large proportion of clones throughout the core. Between 18 and 65% of 16S rDNA phylotypes detected in a wide range of coastal and open ocean sediments possessed high levels of sequence similarity (>95%) with the MGP sediment phylotypes, indicating that many sediment prokaryote phylotype groups defined in this study are ubiquitous in marine sediment.

The prokaryote community activity and structural characteristics within marine sediment sampled across a continental shelf area located off eastern Antarctica (66 degrees S, 143 degrees E; depth range, 709 to 964 m) were studied. Correlations were found between microbial biomass and aminopeptidase and chitinase rates, which were used as proxies for microbial activity. Biomass and activity were maximal within the 0- to 3-cm depth range and declined rapidly with sediment depths below 5 cm. Most-probable-number counting using a dilute carbohydrate-containing medium recovered 1.7 to 3.8% of the sediment total bacterial count, with mostly facultatively anaerobic psychrophiles cultured. The median optimal growth temperature for the sediment isolates was 15 degrees C. Many of the isolates identified belonged to genera characteristic of deep-sea habitats, although most appear to be novel species. Phospholipid fatty acid (PLFA) and isoprenoid glycerol dialkyl glycerol tetraether analyses indicated that the samples contained lipid components typical of marine sediments, with profiles varying little between samples at the same depth; however, significant differences in PLFA profiles were found between depths of 0 to 1 cm and 13 to 15 cm, reflecting the presence of a different microbial community. Denaturing gradient gel electrophoresis (DGGE) analysis of amplified bacterial 16S rRNA genes revealed that between samples and across sediment core depths of 1 to 4 cm, the community structure appeared homogenous; however, principal-component analysis of DGGE patterns revealed that at greater sediment depths, successional shifts in community structure were evident. Sequencing of DGGE bands and rRNA probe hybridization analysis revealed that the major community members belonged to delta proteobacteria, putative sulfide oxidizers of the gamma proteobacteria, Flavobacteria, Planctomycetales, and Archaea. rRNA hybridization analyses also indicated that these groups were present at similar levels in the top layer across the shelf region.

Several strains isolated from Antarctic winter sea water, sea-ice algal assemblages and quartz stone subliths were found to belong to a novel 16S rDNA sequence cluster within the family Flavobacteriaceae (Cytophaga-Flavobacterium-Bacteroides division). The strains were gram-negative, non-motile, psychrotolerant, strictly aerobic, chemoheterotrophic rod-shaped cells that contained orange or yellow carotenoid pigments and required yeast extract when grown in defined mineral-salts media. The requirement for sodium ions varied between strains. Results of DNA-DNA hybridization analysis were used to divide the strains into four distinct genospecies, which were differentiated by physiological and nutritional characteristics. The DNA G+C content of the strains was 33-39 mol%. The fatty acid profiles of representative strains were very similar, with major constituents including i15:1omega10c, a15:1omega10c, i15:0, a15:0, i16:1omega6c, i17:1omega5c and 3-OH i16:0. The novel genus Aequorivita gen. nov., which has widespread distribution in the Antarctic region, is proposed. The genus comprises four species: the type species Aequorivita antarctica sp. nov. (type strain SW49T = ACAM 640T = DSM 14231T), Aequorivita lipolytica sp. nov. (type strain Y10-2T = ACAM 641T = DSM 14236T), Aequorivita crocea sp. nov. (type strain Y12-2T = ACAM 642T = DSM 14239T) and Aequorivita sublithincola sp. nov. (type strain 9-3T= ACAM 643T = DSM 14238T).

A group of strains with potent extracellular enzymic activity were isolated from the surfaces of the chain-forming sea-ice diatom Melosira and from an unidentified macrophyte collected from the Eastern Antarctic coastal zone. 16S rDNA sequence analysis indicated that the strains belonged to the genus Cellulophaga and showed greatest similarity to the species Cellulophaga baltica (sequence similarity 97%). Phenotypic characteristics, DNA base composition and DNA-DNA hybridization values clearly separate the Antarctic strains from Cellulophaga baltica and other Cellulophaga species. Thus, the strains form a distinct and novel species and have the proposed name Cellulophaga algicola sp. nov. (type strain IC166T = ACAM 630T). In addition, it was recognized that the species Cytophaga uliginosa (ZoBell and Upham 1944) Reichenbach 1989, a species phylogenetically remote from the type species of the genus Cytophaga, possessed 16S rDNA sequences and phenotypic and chemotaxonomic traits similar to those of other Cellulophaga species. Thus, it was proposed that the species Cytophaga uliginosa be renamed as Cellulophaga uliginosa comb. nov.

A suite of six sterols, lanosterol, lanost-8(9)-en-3beta-ol, 4, 4-dimethylcholesta-8(14),24-dien-3beta-ol, 4, 4-dimethylcholest-8(14)-en-3beta-ol, 4-methylcholesta-8(14), 24-dien-3beta-ol and 4-methylcholest-8(14)-en-3beta-ol, were identified in the psychrophilic methanotrophic bacterium, Methylosphaera hansonii. Their presence suggests that the capacity for sterol biosynthesis in methanotrophic bacteria is limited to the family Methylococcaceae but which have widely different optimal growth temperatures.

16S rRNA phylogenetic analysis of a number of yellow- and orange-pigmented strains isolated from a variety of Antarctic habitats including sea ice, lakewater and cyanobacterial mats indicated a close relationship to the genus Flavobacterium but distinct from known Flavobacterium species. Phenotypic properties, DNA G+C content and whole-cell fatty acid profiles of the Antarctic strains were consistent with those of the genus Flavobacterium. DNA-DNA hybridization analysis indicated the presence of two distinct and novel genospecies each isolated from a different Antarctic habitat. From polyphasic taxonomic data it is proposed that the two groups represent new species with the following proposed names: Flavobacterium gillisiae (ACAM 601T) and Flavobacterium tegetincola (ACAM 602T). In addition polyphasic analysis of the species '[Cytophaga] xantha' (Inoue and Komagata 1976), isolated from Antarctic mud, indicated it was a distinct member of the genus Flavobacterium and was thus revived as Flavobacterium xanthum. Phylogenetic and fatty acid analyses also indicate that the species [Flavobacterium] salegens (Dobson et al. 1993), from Organic Lake, Antarctica, is misclassified at the genus level. It is proposed that this species belongs to a new genus, Salegentibacter salegens gen. nov., comb. nov.

16S rDNA clone library analysis was used to examine the biodiversity and community structure within anoxic sediments of several marine-type salinity meromictic lakes and a coastal marine basin located in the Vestfolds Hills area of Eastern Antarctica. From 69 to 130 (555 total) 16S rDNA clones were analysed from each sediment sample, and restriction fragment length polymorphism (RFLP) and sequence analysis grouped the clones into 202 distinct phylotypes (a clone group with sequence similarity of >0.98). A number of phylotypes and phylotype groups predominated in all libraries, with a group of 10 phylotypes (31% of clones) forming a novel deep branch within the low G+C Gram-positive division. Other abundant phylotypes detected in several different clone libraries grouped with Prochlorococcus cyanobacteria, diatom chloroplasts, delta proteobacteria (Desulfosarcina group, Syntrophus and Geobacterl Pelobacter/Desulphuromonas group), order Chlamydiales (Parachlamydiaceae) and Spirochaetales (wall-less Antarctic spirochaetes). Most archaeal clones detected (3.1% of clones) belonged to a highly diverged group of Euryarchaeota clustering with clones previously detected in rice soil, aquifer sediments and hydrothermal vent material. Little similarity existed between the phylotypes detected in this study and other clone libraries based on marine sediment, suggesting that an enormous prokaryotic diversity occurs within marine and marine-derived sediments.

16S rRNA clone library analysis was used to examine the biodiversity and community structure within the sediments of three hypersaline Antarctic lakes. Compared to sediment of low to moderate salinity Antarctic lakes the species richness of the hypersaline lake sediments was 2-20 times lower. The community of Deep Lake (32% salinity, average sediment temperature -15 degrees C) was made up almost entirely of halophilic Archaea. The sediment communities of two meromictic hypersaline lakes, Organic Lake (20% salinity, -7 degrees C) and Ekho Lake (15% salinity, 15 degrees C) were more complex, containing phylotypes clustering within the Proteobacteria and Cytophagales divisions and with algal chloroplasts. Many phylotypes of these lakes were related to taxa more adapted to marine-like salinity and perhaps derive from bacteria exported into the sediment from the lower salinity surface waters. The Ekho Lake clone library contained several major phylotypes related to the Haloanaerobiales, the growth of which appears to be promoted by the comparatively high in situ temperature of this lake.

Four freshwater Antarctic lakes were examined for the presence of beta-galactosidase-producing bacteria using mineral medium enrichments and lactose. Enrichments from only one of the lakes produced growth and two strains were isolated that were very similar in phenotype and fatty acid profile, and shared considerable homology in their DNA (DNA-DNA hybridization = 93 +/- 7%). The strains were psychrotrophic with theoretical Tmax, Tmin and Topt of 30-31, -7 degrees and 26 degrees C, respectively. The beta-galactosidase in cell extracts had an optimal activity at 39 degrees C. The strains were Gram-negative rods, showed gliding motility, contained branched and hydroxy fatty acids, and menaquinone 6 as the major respiratory quinone. The strains did not form microcysts and utilized lactose while using ammonium ions as a source of nitrogen, and a range of other sugars. The G + C content of the DNA was 34 mol%. Phylogenetic analysis of one of the strains, by comparison of 16S rDNA sequences, showed that it was most similar, but not identical to, Flavobacterium columnare and '[Sporocytophaga] cauliformis'. Both species could be differentiated phenotypically from the Antarctic isolates. DNA-DNA hybridization of the Antarctic isolate with six different members of the Flavobacterium 16S rDNA cluster showed no strain with greater than 18% relatedness. The nearest type species to the Antarctic isolate in the phylogenetic analysis was Flavobacterium aquatile. The name Flavobacterium hibernum is proposed for the Antarctic strains, and the type strain is ATCC 51468T (= ACAM 376T).

Species of the genus Pseudoalteromonas are frequently isolated from marine ecosystems and appear to be particularly abundant in Antarctic coastal waters. Most Pseudoalteromonas strains isolated form sea ice and underlying seawater samples are phenotypically similar to the species Pseudoalteromonas antarctica and Pseudoalteromonas nigrifaciens. However, a minority of isolates were recognized by phenotypic, DNA-DNA hybridization and 16S rRNA-based phylogenetic studies to represent a distinct genospecies clustering at the periphery of the non-pigmented, Pseudoalteromonas species clade. These strains are non-pigmented, halotolerant psychrotrophs that are capable of hydrolysing starch and chitin, and possess a DNA G+C content of 38-39 mol%. It is proposed that this group represents a novel species, Pseudoalteromonas prydzensis sp. nov., for which the type strain is ACAM 620(T).

A group of sea-ice-derived psychrophilic bacterial strains possessing the unusual ability to synthesize the polyunsaturated fatty acids eicosapentaenoic acid (20:5 omega 3) and arachidonic acid (20:4 omega 6) belong to the Family Flavobacteriaceae (Flexibacter-Bacteroides-Flavobacterium phylum), according to 16S rRNA sequence analysis. Surprisingly, the isolates were also found to cluster closely to the moderately halophilic and psychrotrophic species [Flavobacterium] gondwanense (sequence similarity 97.8-98.1%). The whole-cell fatty acid profiles of this group and [Flavobacterium] gondwanense were very similar and distinct from other related flavobacteria. The sea ice strains and [Flavobacterium] gondwanense differed substantially in terms of ecophysiology, possibly representing divergent adaptations to sympagic and planktonic marine habitats, respectively. Evidence based on phylogeny and fatty acid profiles supports the conclusion that the taxa are close relatives distinct from other bacterial groups. It is thus proposed that the sea ice strains represent a novel taxon designated Psychroflexus torquis gen. nov., sp. nov. (type strain ACAM 623T) while [Flavobacterium] gondwanense becomes Psychroflexus gondwanense gen. nov., comb. nov.

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).

The bacterial populations associated with sea ice sampled from Antarctic coastal areas were investigated by use of a phenotypic approach and a phylogenetic approach based on genes encoding 16S rRNA (16S rDNA). The diversity of bacteria associated with sea ice was also compared with the bacterial diversity of seawater underlying sea ice. Psychrophilic (optimal growth temperature, < or = 15 degrees C; no growth occurring at 20 degrees C) bacterial diversity was found to be significantly enriched in sea ice samples possessing platelet and bottom ice diatom assemblages, with 2 to 9 distinct (average, 5.6 +/- 1.8) psychrophilic taxa isolated per sample. Substantially fewer psychrophilic isolates were recovered from ice cores with a low or negligible population of ice diatoms or from under-ice seawater samples (less than one distinct taxon isolated per sample). In addition, psychrophilic taxa that were isolated from under-ice seawater samples were in general phylogenetically distinct from psychrophilic taxa isolated from sea ice cores. The taxonomic distributions of psychrotrophic bacterial isolates (optimal growth temperature, > 20 degrees C; growth can occur at approximately 4 degrees C) isolated from sea ice cores and under-ice seawater were quite similar. Overall, bacterial isolates from Antarctic sea ice were found to belong to four phylogenetic groups, the alpha and gamma subdivisions of the Proteobacteria, the gram-positive branch, and the Flexibacter-Bacteroides-Cytophaga phylum. Most of the sea ice strains examined appeared to be novel taxa based on phylogenetic comparisons, with 45% of the strains being psychrophilic. 16S rDNA sequence analysis revealed that psychrophilic strains belonged to the genera Colwellia, Shewanella, Marinobacter, Planococcus, and novel phylogenetic lineages adjacent to Colwellia and Alteromonas and within the Flexibacter-Bacteroides-Cytophaga phylum. Psychrotrophic strains were found to be members of the genera Pseudoalteromonas, Psychrobacter, Halomonas, Pseudomonas, Hyphomonas, Sphingomonas, Arthrobacter, Planococcus, and Halobacillus. From this survey, it is proposed that ice diatom assemblages provide niches conducive to the proliferation of a diverse array of psychrophilic bacterial species.

Psychrophilic, yellow-pigmented, seawater-requiring bacteria isolated from the pycnocline of meromictic Burton Lake and from sea ice cores obtained in the Vestfold Hills (68 degrees S, 78 degrees E) in eastern Antarctica were characterized. Phenotypic analysis showed that the strains isolated formed two distinct taxa. The first taxon included nonmotile, nutritionally fastidious strains that were isolated from the pycnocline of Burton Lake. The cells of these strains were morphologically variant, ranging from vibrioid to ring shaped to coiled and filamentous; in addition, the strains were unable to metabolise carbohydrates or polysaccharides and had DNA G + C contents of 27 to 29 mol%. The strains of the second taxon, which were isolated from sea ice cores and from ice aigal biomass, were saccharolytic, exhibited rapid gliding motility, were rodlike to filamentous, and had DNA G + C contents of 36 to 38 mol%. A 16S ribosomal DNA (rDNA) sequence analysis revealed that the two Antarctic taxa formed related but distinct lineages within the [Flexibacter] maritimus rRNA branch of the family Flavobacteriacrae. The levels of 16S rDNA sequence similarity between the taxa were 90.5 to 91.3%, while the levels of similarity to other members of the [F.] maritimus rRNA branch were 85 to 90%. The whole-cell lipid profiles of the Antarctic strains were mainly comprised of branched and unbranched monounsaturated C15 to C17 fatty acids. The presence of significant levels of the lipids a 15:1 omega 10c and a17:1 omega 7c appeared to be useful biomarkers for the new Antarctic taxa and for differentiating these organisms from other members of the family Flavobacteriaceae. On the basis of polyphasic taxonomic data we propose that the new taxa are novel bacterial species designated Psychroserpens burtonensis gen. nov., sp. nov. (type strain, ACAM 188) and Gelidibacter algens gen. nov., sp. nov. (type strain, ACAM 536).

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).

Ornithogenic soil is derived from the deposition of the fecal matter of various species of birds and is a major source of nutrient input in the Antarctic marine ecosystem. A significant proportion of microbiota of ornithogenic soil collected from an Adélie penguin colony in eastern Antarctica (Vestfold Hills ice-free zone) consisted of gram-negative, coccoid bacteria identified on the basis of their phospholipid ester-linked fatty acid and lipid class profiles as Psychrobacter strains. Phenotypic, genotypic, and 16S ribosomal DNA phylogenetic analyses revealed that the Antarctic psychrobacters belonged to three distinct groups. Comparisons with Psychrobacter immobilis and Moraxella phenylpyruvica reference cultures isolated from fish, seawater, poultry, and human clinical specimens revealed the relationships of these groups within the genus Psychrobacter. Two of the groups represent the following two novel species: Psychrobacter urativorans sp. nov. (type strain, strain ACAM 534) and Psychrobacter frigidicola sp. nov. (type strain, strain ACAM 304). The third group of strains included members of the previously described species P. immobilis (Juni and Heym 1986). In addition, M. phenylpyruvica (Bøvre and Henriksen 1967) is renamed Psychrobacter phenylpyruvicus comb. nov. (type strain, strain ACAM 535) on the basis of 16S ribosomal DNA phylogenetic data. In general, the genus Psychrobacter could be differentiated from the related genera Moraxella and Acinetobacter by the fact that the members of the genus Psychrobacter are psychrotolerant or psychrophilic and halotolerant, which reflects the ubiquitous distribution of the genus in both marine and terrestrial environments. On the basis of the results of this and previous studies, the genus Psychrobacter is the predominant genus in ornithogenic soils in Antarctica and is diverse.