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Ecosystems Dynamics in a Polar Desert: The McMurdo Dry Valleys, Antarctica. Antarctic Research Series, Vol. 72. John C. Priscu, ed. American Geophysical Union, Washington, DC, 1998. 369 pp., illus., CD-ROM. [...]

Green sulfur bacteria (GSB) (Chlorobiaceae) are primary producers that are important in global carbon and sulfur cycling in natural environments. An almost complete genome sequence for a single, dominant GSB species (‘C-Ace’) was assembled from shotgun sequence data of an environmental sample taken from the O2–H2S interface of the water column of Ace Lake, Antarctica. Approximately 34 Mb of DNA sequence data were assembled into nine scaffolds totaling 1.79 Mb, representing approximately 19-fold coverage for the C-Ace composite genome. A high level (∼31%) of metaproteomic coverage was achieved using matched biomass. The metaproteogenomic approach provided unique insight into the protein complement required for dominating the microbial community under cold, nutrient-limited, oxygen-limited and extremely varied annual light conditions. C-Ace shows physiological traits that promote its ability to compete very effectively with other GSB and gain dominance (for example, specific bacteriochlorophylls, mechanisms of cold adaptation) as well as a syntrophic relationship with sulfate-reducing bacteria that provides a mechanism for the exchange of sulfur compounds. As a result we are able to propose an explanation of the active biological processes promoted by cold-adapted GSB and the adaptive strategies they use to thrive under the severe physiochemical conditions prevailing in polar environments. [ABSTRACT FROM AUTHOR]

Evidence is provided from a sediment core from saline Abraxas Lake, Vestfold Hills, that indicates that the lake existed through the Last Glacial Maximum. It can therefore be concluded that at least part of the Vestfold Hills also remained ice-free through the Last Glacial Maximum, or at most was covered by a thin, non-erosive cold-based ice sheet. The evidence for the continued existence of Abraxas Lake includes a 14C date that significantly predates the Last Glacial Maximum (though this cannot be considered direct proof of the existence of the lake prior to the Last Glacial Maximum); the presence of saline porewater throughout the core, including in compacted sediments deposited during the glacial period, which implies that the lake obtained its salt prior to any Holocene marine highstand; and the occurrence of marine-derived fauna from the onset of significant biological activity late in the Pleistocene. The occurrence of ice-free land in the Vestfold Hills and similar oases suggests that the margin of the polar ice cap did not reach far beyond its current position at the Last Glacial Maximum, at least in regions now occupied by these oases. [ABSTRACT FROM AUTHOR]

New evidence regarding the origins of the Crustacea of Antarctic lakes is reviewed. Palaeolimnological data indicates that the cladoceran Daphniopsis studeri has been present in Lake Reid, Larsemann Hills, for over 120 000 yr. This is the first direct evidence of a continental lacustrine refugium during the last glacial maximum. There are strong indications that the calanoid copepod Boeckella poppei maintained populations over the same period in lakes of the Amery Oasis, and the rapid post-glacial colonization by this species of newly formed lakes on the Antarctic Peninsula and Signy Island argues for a local rather than an extra-continental source. Evidence for the entry of marine-derived species into the longer term fauna of the continent is also presented, it is concluded that many of the Crustacea in Antarctic lakes are likely to have had a long association with the continent. [ABSTRACT FROM AUTHOR]

The origins of the freshwater fauna that inhabits Antarctic lakes are poorly known. The species present today could be relict species that have survived Quaternary glaciations on the continent, or Holocene migrants from more temperate regions. One approach to investigating these questions is to study faunal microfossils in lake sediment. This approach was applied to a 293 cm sediment core from Lake Boeckella, located at the northern tip of the Antarctic Peninsula. The microfossils indicated that most of the metazoan species that occur in the lake today have been present since soon after the lake's formation c. 5.5 ka ago. In particular, the centropagid copepod Boeckella poppei (Mrázek) has been present throughout the lake's history, suggesting a local source for this species. The development of biodiversity in the lake with time was in general more consistent with local (Antarctic) rather than distant (South American) sources, though an alternative explanation is that dispersal to Antarctica was more efficient in the mid-Holocene. Evidence of dispersal from extra-continental sites comes from the scattered occurrence throughout the core of Eubosmina chilensis (Daday), a South American species that does not reach the Antarctic or the sub-Antarctic islands at present, and which failed to establish a permanent population in the lake. [ABSTRACT FROM AUTHOR]

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The presence of crustaceans in some Antarctic lakes adds a level of complexity to the food webs of these environments. The grazing pressure of the crustaceans on phytoplankton and other protists, and the role they play in controlling food web structure, has not yet been examined in any detail. This paper presents the first data on grazing pressure of crustacean zooplankton in continental Antarctic lakes. In this study the grazing rates of Paralabidocera antarctica in saline Ace Lake, Vestfold Hills, were assessed using a radio-tracer method. Clearance rates ranged from approximately 1 to 8 ml ind.-1 day-1, depending on developmental stage. Due to their high abundance, nauplii exhibited the highest daily carbon ingestion rates. The population cleared about 3% of the water column per day, accounting for a significant fraction of primary production. P. antarctica has a considerable impact on the carbon cycle in Ace Lake and, by inference, in the other lakes in which it occurs. [ABSTRACT FROM AUTHOR]

In nature, the complexity and structure of microbial communities varies widely, ranging from a few species to thousands of species, and from highly structured to highly unstructured communities. Here, we describe the identity and functional capacity of microbial populations within distinct layers of a pristine, marine-derived, meromictic (stratified) lake (Ace Lake) in Antarctica. Nine million open reading frames were analyzed, representing microbial samples taken from six depths of the lake size fractionated on sequential 3.0, 0.8 and 0.1 μm filters, and including metaproteome data from matching 0.1 μm filters. We determine how the interactions of members of this highly structured and moderately complex community define the biogeochemical fluxes throughout the entire lake. Our view is that the health of this delicate ecosystem is dictated by the effects of the polar light cycle on the dominant role of green sulfur bacteria in primary production and nutrient cycling, and the influence of viruses/phage and phage resistance on the cooperation between members of the microbial community right throughout the lake. To test our assertions, and develop a framework applicable to other microbially driven ecosystems, we developed a mathematical model that describes how cooperation within a microbial system is impacted by periodic fluctuations in environmental parameters on key populations of microorganisms. Our study reveals a mutualistic structure within the microbial community throughout the lake that has arisen as the result of mechanistic interactions between the physico-chemical parameters and the selection of individual members of the community. By exhaustively describing and modelling interactions in Ace Lake, we have developed an approach that may be applicable to learning how environmental perturbations affect the microbial dynamics in more complex aquatic systems.

The major phospholipids of Halorubrum lacusprofundi grown at 25 degrees C were archaeol phosphatidylglycerol, archaeol phosphatidylglycerylsulphate and archaeol phosphatidylglycerylphosphate methyl ester. Glycolipids included a monoglycosyl archaeol and the sulphate ester of a diglycosyl archaeol. Cultures grown at 12 degrees C contained the same suite of phospho- and glycolipids, with the addition of a series of unsaturated analogues with up to six double bonds. The patterns of unsaturation were similar for all the phospholipid series, but a different pattern occurred in the glycolipids. The analytical techniques used in this study allow facile detection of unsaturated archaeal cell membrane lipids that are degraded by commonly used chemical derivatization procedures.