We compared the spatial distribution and diversity of autotrophic microbial communities among four permanently ice-covered, chemically stratified lakes located in the Taylor (Lakes Bonney-east and west lobes, Fryxell), and Wright (Lake Vanda) Valleys of the McMurdo Dry Valleys (Victoria Land, Antarctica). Clone libraries were constructed for major carbon fixation genes (rbcL isoforms IA/B and ID; cbbM; nifJ). Real time quantitative polymerase chain reaction assays were also developed for each of these markers of autotrophy to assess the influence of lake physicochemical factors on spatial trends in major photosynthetic and chemolithoautotrophic groups. Both lobes of Lake Bonney were dominated by Ribulose-1, 5-bisphosphate carboxylase oxygenase (RubisCO) form ID rbcL (haptophytes and stramenopiles), while Lake Fryxell was dominated by rbcL form ID-harboring cryptophytes. Lake Vanda was the least productive lake and was dominated by form IA/B rbcL (cyanobacteria and chlorophytes) and form ID rbcL (stramenopiles). Autotrophic carbon fixation genes from photosynthetic organisms were generally positively correlated with light availability. Chemolithoautotrophic organisms harboring form II RubisCO were detected in only two of the four lakes (west lobe Lake Bonney and Fryxell) and were associated with the presence of either sulfide (Fryxell) or dimethylated sulfur compounds (west lobe Lake Bonney).

No abstract

Permanently cold habitats dominate our planet and psychrophilic microorganisms thrive in cold environments. Environmental adaptations unique to psychrophilic microorganisms have been thoroughly described; however, the vast majority of studies to date have focused on cold-adapted bacteria. The combination of low temperatures in the presence of light is one of the most damaging environmental stresses for a photosynthetic organism: in order to survive, photopsychrophiles (i.e. photosynthetic organisms adapted to low temperatures) balance temperature-independent reactions of light energy capture/transduction with downstream temperature-dependent metabolic processes such as carbon fixation. Here, we review research on photopsychrophiles with a focus on an emerging model organism, Chlamydomonas raudensis UWO241 (UWO241). UWO241 is a psychrophilic green algal species and is a member of the photosynthetic microbial eukaryote community that provides the majority of fixed carbon for ice-covered lake ecosystems located in the McMurdo Dry Valleys, Antarctica. The water column exerts a range of environmental stressors on the phytoplankton community that inhabits this aquatic ecosystem, including low temperatures, extreme shade of an unusual spectral range (blue-green), high salinity, nutrient deprivation and extremes in seasonal photoperiod. More than two decades of work on UWO241 have produced one of our most comprehensive views of environmental adaptation in a cold-adapted, photosynthetic microbial eukaryote.

The permanently ice‐covered lakes of the McMurdo Dry Valleys, Antarctica, harbor microbially dominated food webs. These organisms are adapted to a variety of unusual environmental extremes, including low temperature, low light, and permanently stratified water columns with strong chemo‐ and oxy‐clines. Owing to the low light levels during summer caused by thick ice cover as well as 6 months of darkness during the polar winter, chemolithoautotrophic microorganisms could play a key role in the production of new carbon for the lake ecosystems. We used clone library sequencing and real‐time quantitative PCR of the gene encoding form II Ribulose 1, 5‐bisphosphate carboxylase/oxygenase to determine spatial and seasonal changes in the chemolithoautotrophic community in Lake Bonney, a 40‐m‐deep lake covered by c. 4 m of permanent ice. Our results revealed that chemolithoautotrophs harboring the cbbM gene are restricted to layers just above the chemo‐ and oxi‐cline (≤ 15 m) in the west lobe of Lake Bonney (WLB). Our data reveal that the WLB is inhabited by a unique chemolithoautotrophic community that resides in the suboxic layers of the lake where there are ample sources of alternative electron sources such as ammonium, reduced iron and reduced biogenic sulfur species.