Antarctic Saline Lakes Research Articles

Plasmids of archaea as possible ancestors of DNA-containing viruses

Тhе kingdom Archaea, as well as Bacteria, belongs to the overkingdom Prokaryota. Halophilic archaea (Halorubrum lacusprofundi) isolated from Antarctic saline lakes contain plasmids (pR1SE) that code proteins taking part in the formation of membranes of archaea vesicles. The molecular and biological properties of pR1SE and the peculiarity of its interaction with sensitive cells are considered in this article. The role of structural proteins coded by pR1S in the process of formation of vesicle membrane complex is paid special attention. Plasmid-containing archaea vesicles model some properties of viruses. Archaea plasmids can be viewed as possible ancestors of DNA-containing viruses.

Detection of a novel ecotype of Pfiesteria piscicida (Dinophyceae) in an Antarctic saline lake by real-time PCR

The heterotrophic dinoflagellate Pfiesteria piscicida was detected in Ace Lake in the Vestfold Hills, eastern Antarctica by using real-time PCR based on 18S rDNA sequences. Antarctic water samples collected in 2004 were tested by species-specific real-time PCR assays for the identification of P. piscicida and P. shumwayae. Positive results were shown with P. piscicida-specific real-time PCR, and PCR products were examined by sequence analysis for confirmation. A phylogenetic tree made from partial 18S rDNA sequences showed that the Antarctic clone clustered with P. piscicida. This result suggests that P. piscicida is present in the extreme conditions of an Antarctic saline lake which has not contained fish for thousands of years.

Viral dynamics and patterns of lysogeny in saline Antarctic lakes

Antarctic lakes are extreme ecosystems with microbially dominated food webs, in which viruses may be important in controlling community dynamics. A year long investigation of two Antarctic saline lakes (Ace and Pendant Lakes) revealed high concentrations of virus like particles (VLP) (0.20–1.26 × 108 ml−1), high VLP: bacteria ratios (maximum 70.6) and a seasonal pattern of lysogeny differing from that seen at lower latitudes. Highest rates of lysogeny (up to 32% in Pendant Lake and 71% in Ace Lake) occurred in winter and spring, with low or no lysogeny in summer. Rates of virus production (range 0.176–0.823 × 106 viruses ml−1 h−1) were comparable to lower latitude freshwater lakes. In Ace Lake VLP did not correlate with bacterial cell concentration or bacterial production but correlated positively with primary production, while in Pendant Lake VLP abundance correlated positively with both bacterial cell numbers and bacterial production but not with primary production. In terms of virus and bacterial dynamics the two saline Antarctic lakes studied appear distinct from other aquatic ecosystems investigated so far, in having very high viral to bacterial ratios (VBR) and a very high occurrence of lysogeny in winter.

Depth distribution of euryhaline halophilic bacteria in Suribati Ike, a meromictic lake in East Antarctica

Euryhaline halophiles grow over a wide range of salinity, from 15% NaCl and even saturation level (about 30% NaCl). Several species of euryhaline halophiles occur worldwide, especially in marine environments and also in aquatic and terrestrial habitats of the Antarctic ice-free areas. A biogeographic view of Antarctic halophiles is that their migration among lakes on land is more difficult than in marine setting. Ponds and lakes on land may thus serve as “islands” which facilitate the selection and separation of unique species. We isolated euryhaline halophiles from the saline lake, Suribati Ike, near Syowa Station and placed them into seven groups, each demonstrating a clear depth-related distribution. Six of the seven groups probably represent new species of the genera Halomonas and Marinobacter. This result suggests that Antarctic saline lakes exhibit high selectivity of unique euryhaline halophiles and possibly of other microbial groups.

Flagellate nutritional versatility as a key to survival in two contrasting Antarctic saline lakes

Summary1. Seasonal patterns of grazing and photosynthesis were investigated in two saline Antarctic lakes (Highway and Ace) in the Vestfold Hills (68°S). The phototrophic nanoflagellate (PNAN) community was dominated by Pyramimonas gelidicola and two morphological forms of a cryptophyte species that occurred throughout the year. Both species were mixotrophic on bacteria, and in Highway Lake they also exploited dissolved organic carbon as determined by the uptake of fluorescently labelled dextrans.2. Clearance rates ranged between 0.02 and 0.21 nL h−1 cell−1 in Ace Lake and 0.004–1.05 nL h−1 cell−1 in Highway Lake. On occasion cryptophyte grazing equalled that of the heterotrophic nanoflagellates (HNAN).3. Photosynthetic rates showed similar trends in both lakes, but there were differences in chlorophyll a specific rates and photosynthetic efficiency, probably related to the meromictic characteristic of Ace Lake. Primary production was measurable in winter and peaked in summer following the maxima of mixotroph grazing.4. The HNAN community of Highway Lake achieved clearance rates of 0.02–1.80 nL h−1 cell−1 and removing between 50 and 693 ng bacterial carbon L−1 day−1, with highest impact in winter when HNAN were most abundant. The HNAN also ingested fluorescently labelled dextrans showing a preference for 4 and 500 kDa molecules. The more diverse HNAN community of Ace Lake had lower clearance rates (0.04–0.37 nL h−1 cell−1) and exerted a lower grazing pressure on bacterioplankton. In Highway Lake, where the HNAN community was dominated by the choanoflagellate Diaphanoeca grandis, there was a significant correlation between mean cell volume and clearance rate.5. The major feature was that the microbial plankton functioned throughout the year by employing nutritional versatility.

Frigidly Concentrated Seawater and the Evolution of Antarctic Saline Lakes

The frigidly concentrated seawater and the evolution of Antarctic saline lakes were discussed. The concentration of the major ions of the saline lakes was accurately quantified. The current state of salt mineral equilibria in the brines was determined. The analysis showed that the major ion composition of saline lakes was modified accurately using a closed-basin brine evolution model based on seawater freezing.

The biology and evolution of Antarctic saline lakes in relation to salinity and trophy

Five brackish to hypersaline lakes (Highway, Ace, Pendent, Williams and Rookery) in the Vestfold Hills, eastern Antarctica were investigated during the austral summer of 1999/2000. The aims were to characterise the functional dynamics of the plankton and gain an understanding of how the different environments in the lakes have led to the evolution of different communities. The plankton was dominated by microorganisms and differed across the salinity spectrum in relation to trophy, age and the presence of meromixis. However, some elements of the plankton were common to all of the lakes, e.g. the mixtrophic ciliate, Mesodinium ruhrum, which reached abundances of 2.7 x 10(5) l(-1) and spanned a salinity gradient of 4-63parts per thousand. Marine dinoflagellate species also occurred in all of the lakes, often at high abundances in Highway Lake, Pendent Lake and Lake Williams. During December (midsummer), primary production showed an increase along the salinity gradient from Highway Lake to Lake Williams; however, it was low in hyper-nutrified Rookery Lake because of the turbidity of the waters. Bacterial production followed the same trend and was extremely high in Rookery Lake (327 mug l(-1) h(-1) in January). The lakes possessed a marine microbial plankton that has become very simplified through time, and now contains a small number of highly successful species, which were pre-adapted to surviving in extreme Antarctic lakes.

00/00867 Behavior of organic matter from Callovian shales during low-temperature air oxidation

The phospholipid ester-linked fatty acids (PLFA) from members of the family Halomonadaceae and the genus Flavobacterium were analyzed in detail by capillary GC and GC-MS. Precise monounsaturated double bond position and geometry was determined by GC-MS analysis of the dimethyl disulphide adducts of the monounsaturated fatty acids. No clear distinction was observed between members of the two genera Halomonas and Deleya based upon PLFA composition. The major PLFAs detected in strains from the two genera were 18 : 1w7c, 16: 1w7c and 16 : 0. These three fatty acids accounted for greater than 95% of the total PLFA detected. The PLFA profiles of “Flavobacterium salegens” (ACAM 48) and “Flavobacterium gondwanense” (ACAM 44), proposed new species of moderately halophilic bacteria isolated from Organic Lake, Antarctica, were characterized by high abundances of i15 : 0, a15 : 0, 15 : 0, i15 : 1w10c, a15 : 1w10c and i16 : 0. The two species were distinguishable from each other based on their PLFA and hydroxy fatty acid profiles. The position of the double bond in the branched C15 monoununsaturated fatty acids is unusual, and may be a taxonomic feature of these bacteria. It may also be possible to use these signature fatty acids (i and a15 : 1w10c) in microbial ecology studies of antarctic saline lakes where the presence and relative importance of these bacteria is being investigated.

The plankton community of a young, eutrophic, Antarctic saline lake

A shallow, saline lake (Rookery Lake) close to the sea and surrounded by a penguin rookery was investigated during the austral spring and summer of 1996/1997. The proximity to the sea means that the lake is likely to have been formed recently during isostatic uplift. Inputs of carbon and nutrients from the penguin rookery have rendered Rookery Lake eutrophic compared with other brackish and saline lakes in the Vestfold Hills. Chlorophyll a concentration, bacterioplankton, heterotrophic nanoflagellate and phototrophic nanoflagellate abundances were all significantly higher than in other non-enriched lakes. The high productivity created seasonal anoxia during winter and spring below ice cover. The ciliate community resembled the marine community, and was dissimilar to that seen in older saline lakes within the Vestfold Hills. Thus Rookery Lake provides valuable evidence of the impact of natural eutrophication on an Antarctic lake, as well as of the evolution of the typical microbial community which dominates the older lakes of the Vestfold Hills.

Seasonal abundance of Halomonas meridiana, Halomonas subglaciescola, Flavobacterium gondwanense and Flavobacterium salegens in four Antarctic lakes

Indirect immunofluorescence was used to quantify the seasonal variation of four halophilic aerobic Antarctic bacteria in Antarctic saline lakes from July 1990 to January 1991. Antibodies were raised against type strains from the Australian Collection of Antarctic Microorganisms. During summer, all four serogroups were identified in the aerobic waters of lakes with total dissolved salts above 61%. Maximal abundances of Halomonas meridiana, H. subglaciescola and Flavobacterium gondwanense serogroups were observed at discrete depths within the water column in the two most hypersaline lakes at about midsummer, coincident with the time of maximum sunlight and the commencement of the summer thaw. At this time the Halomonas spp. serogroups comprised up to 40% of the total bacteria and the F. gondwanense serogroup up to 10% of the total bacteria. The F. salegens serogroup was in low numbers (>2% of total bacteria) in some aerobic waters. Up to 2% of the total bacterial populations in the lakes were autofluorescent or stained non-specifically. Dissolved organic carbon values were measured throughout the sampling period and correlated well with total bacterial numbers but not with changes in species composition. Change in species abundance, as indicated by immunofluorescence, was not reflected in the total bacterial count, indicating compositional change of the total bacterial population.

Biology and biotechnological potential of halotolerant bacteria from Antarctic saline lakes

The saline lakes of the Vestfold Hills, Antarctica, are unique ecosystems in which microorganisms survive and grow in cold, saline and often anaerobic conditions. A polyphasic approach to taxonomy of the microbiota has extended the known range of microbial diversity through description of nine new species including bacteria and archaea. Low temperature and reduced water activity are the major constraints on microbial growth in the lakes. Bělhradek-type models provide a good description of temperature dependence and indicate the potential of the microbiota to colonise their natural habitats. Physiological traits of the microbiota selected by the physical and chemical characteristics of the saline lakes suggest biotechnological potential in areas such as polyunsaturated fatty acid production and hydrocarbon degradation.

The Phospholipid Ester-linked Fatty Acid Composition of Members of the Family Halomonadaceae and Genus Flavobacterium: A Chemotaxonomic Guide

Summary The phospholipid ester-linked fatty acids (PLFA) from members of the family Halomonadaceae and the genus Flavobacterium were analyzed in detail by capillary GC and GC-MS. Precise monounsaturated double bond position and geometry was determined by GC-MS analysis of the dimethyl disulphide adducts of the monounsaturated fatty acids. No clear distinction was observed between members of the two genera Halomonas and Deleya based upon PLFA composition. The major PLFAs detected in strains from the two genera were 18 : 1 w 7c, 16: 1 w 7c and 16 : 0. These three fatty acids accounted for greater than 95% of the total PLFA detected. The PLFA profiles of “ Flavobacterium salegens ” (ACAM 48) and “ Flavobacterium gondwanense ” (ACAM 44), proposed new species of moderately halophilic bacteria isolated from Organic Lake, Antarctica, were characterized by high abundances of i15 : 0, a15 : 0, 15 : 0, i15 : 1 w 10c, a15 : 1 w 10c and i16 : 0. The two species were distinguishable from each other based on their PLFA and hydroxy fatty acid profiles. The position of the double bond in the branched C 15 monoununsaturated fatty acids is unusual, and may be a taxonomic feature of these bacteria. It may also be possible to use these signature fatty acids (i and a15 : 1 w 10c) in microbial ecology studies of antarctic saline lakes where the presence and relative importance of these bacteria is being investigated.

Iodine distribution in an antarctic meromictic saline lake

Water samples collected from a range of depths in Ace Lake in the Vestfold Hills, Antarctica were analysed for iodine species by a polarographic method. Contrary to thermodynamic prediction, iodide was the predominant species in oxic surface waters. Total dissolved iodine was closely correlated with bacterial density down the water column. This observation and other data are used to postulate a scheme for the biological mediation of iodine distribution in the lake.

Effect of temperature on the growth rates of halotolerant and halophilic bacteria isolated from Antarctic saline lakes

The effect of temperature on the growth rates of Halomonas subglaciescola and a Halobacterium sp., halotolerant and halophilic bacteria isolated from Antarctic saline lakes, was predicted accurately by models which propose a linear relationship between temperature and the square root of the reciprocal of the growth rate. The cardinal temperatures of the strains examined were in general 5–10°C lower than those of taxonomic counterparts isolated from temperate and tropical environments. Temperature dependence data for strains of the Halobacterium sp. and annual temperature profiles of Deep Lake allowed estimation of the in situ potential for growth.

Pathway and distribution of trace elements in Lake Vanda, Antarctica

Lake Vanda, an Antarctic saline lake, situated in the Dry Valleys area, Victoria Land, has a unique distribution of temperature, chlorinity and nutrient matters. Although the origins of these properties and major elements have been discussed previously1–6, only a few geochemical studies have been undertaken on trace elements7,8. We report here concentrations of 14 trace elements, including 7 elements not previously measured (Sc, Cr, Co, Rb, Sb, Cs and Th), in the lake that were determined by instrumental neutron activation and atomic absorption methods. The concentration of every element except for aluminium increased abruptly in the highly stratified deep layer. The chemical composition of inflow water was the same as those of tropospheric aerosol particles9,10 and snow11,12 at Antarctica. We suggest that the pathway of the trace elements observed in Lake Vanda was: tropospheric aerosol particles→precipitation→glacier→glacial melt water→Lake Vanda. The composition of these elements in the highly stratified layer has been secondary transformed by the reduction, removal and ion-exchange processes.