The perennial ice-covered lakes of the Antarctic McMurdo Dry Valleys harbour oligotrophic microbial communities that are separated geographically from other aquatic systems. Their microbiomes include planktonic microbes as well as lift-off mat communities that emerge from the ice. We used the ShortBRED protein family profiler to quantify the antibiotic resistance genes (ARGs) from metagenomes of lift-off mats emerging from ice and from filtered water samples of Lake Fryxell and Lake Bonney. The overall proportion of ARG hits was similar to that found in temperate-zone rural ponds with moderate human inputs. Specific ARGs showed distinct distributions for the two lakes and for mat vs planktonic sources. Metagenomic taxa distributions showed that mat phototrophs consisted mainly of cyanobacteria or Betaproteobacteria, whereas the water column phototrophs were mainly protists. An enrichment culture of the Betaproteobacterium Rhodoferax antarcticus from a Lake Fryxell mat sample showed an unusual mat-forming phenotype not previously reported for this species. Its genome showed no ARGs associated with Betaproteobacteria but had ARGs consistent with a minor Pseudomonas component. The Antarctic lake mats and water showed specific ARGs distinctive to the mat and water sources, but overall ARG levels were similar to those of temperate water bodies with moderate human inputs.

Since March 2001, samples of the remaining oil from the wreck of the “Erika” have been collected along the Atlantic coastline in order to assess the natural degradation rate. Four years after the sinking of the tanker, chemical analyses of the oil revealed the influence of environmental parameters on the degradation kinetics. Among the diverse parameters controlling the fate of oil in the environment, biodegradation by microorganisms is known to play an important role. To investigate the role of microorganisms on “Erika” oil degradation, microbial mats from the Guérande salt marches were maintained in slurries containing the pollutant. From these slurries experiments, a low biodegradation rate of the “Erika” oil was detected indicating the degradation capacities of microbial mats. Biodiversity studies were conducted to further understand the biodegradation processes. Microbial mats from the Guérande salterns were maintained in microcosms to evaluate the impact of “Erika” oil on bacterial communities. Molecular analysis based on 16S rRNA and pufM encoding genes allowed fingerprinting of the bacterial and purple anoxygenic bacterial (PAB) communities respectively. These studies revealed bacterial diversity and communities changes showing the adaptation of microorganisms to the “Erika”.

A mathematical model was used to simulate interannual patterns of biomass accumulation within benthic microbial mats of two Antarctic lakes. Lakes Hoare and Vanda are in the Dry Valley region of Southern Victoria Land, and are both perennially ice covered. The model combines experimentally derived observations of light/photosynthesis relationships and rates of respiration of mats from a range of depths in these lakes, with data on incident radiation and the optical properties of the ice and water column. The model was used to estimate daily and annual production and, using measured carbon content, the potential vertical accumulation of the mats over a year. An annual pattern of photosynthesis was predicted for both lakes, with net production from October to February and net respiration at other times. Predicted rates and patterns of net photosynthesis were remarkably similar in the two lakes, despite differences in light climate: the ice of Lake Hoare transmits 1–4% incident radiation, whereas that of Lake Vanda transmits up to 20%. Maximum daily rates of 15–20 μg carbon cm−2 were predicted to occur at approximately 10 m depth in both lakes. Maximum annual rates of carbon fixation (at 10–12 m depth) in both lakes were c. 1.2 mg carbon cm−2 equating to approximately 0.1–4 mm vertical accumulation of mat each year. Experimental studies of microbial mats in the lakes revealed horizontal laminations of similar thickness to model estimates, supporting the hypothesis that these were annual layers. Differences between model estimates and observations were found in deeper water in Lake Vanda, where considerably more material accumulated than was predicted.

The discovery of subsurface communities has encouraged speculation that such communities might be present on planetary bodies exposed to harsh surface conditions, including the early Earth. While the astrobiology community has focused on the deep subsurface, near-subsurface environments are unique in that they provide some protection while allowing partial access to photosynthetically active radiation. Previously we identified near-surface microbial communities based on photosynthesis. Here we assess the productivity of such an ecosystem by measuring in situ carbon fixation rates in an intertidal marine beach through a diurnal cycle, and find them surprisingly productive. Gross fixation along a transect (99×1 m) perpendicular to the shore was highly variable and depended on factors such as moisture and mat type, with a mean of ~41 mg C fixed m−2 day−1. In contrast, an adjacent well-established cyanobacterial mat dominated by Lyngbya aestuarii was ~12 times as productive (~500 mg C fixed m−2 day−1). Measurements made of the Lyngbya mat at several times per year revealed a correlation between total hours of daylight and gross daily production. From these data, annual gross fixation was estimated for the Lyngbya mat and yielded a value of ~1.3×105 g m−2 yr−1. An analysis of pulse-chase data obtained in the study in conjunction with published literature on similar ecosystems suggests that subsurface interstitial mats may be an overlooked endogenous source of organic carbon, mostly in the form of excreted fixed carbon.