Project description:Because of severe abiotic limitations, Antarctic soils represent simplified ecosystems, where microorganisms are the principle drivers of nutrient cycling. This relative simplicity makes these ecosystems particularly vulnerable to perturbations, like global warming, and the Antarctic Peninsula is among the most rapidly warming regions on the planet. However, the consequences of the ongoing warming of Antarctica on microorganisms and the processes they mediate are unknown. Here, using 16S rRNA gene pyrosequencing and qPCR, we report a number of highly consistent changes in microbial community structure and abundance across very disparate sub-Antarctic and Antarctic environments following three years of experimental field warming (+ 0.5-2°C). Specifically, we found significant increases in the abundance of fungi and bacteria and in the Alphaproteobacteria-to-Acidobacteria ratio. These alterations were linked to a significant increase in soil respiration. Furthermore, the shifts toward generalist or opportunistic bacterial communities following warming weakened the linkage between bacterial diversity and functional diversity. Warming also increased the abundance of some organisms related to the N-cycle, detected as an increase in the relative abundance of nitrogenase genes via GeoChip microarray analyses. Our results demonstrate that soil microorganisms across a range of sub-Antarctic and Antarctic environments can respond consistently and rapidly to increasing temperatures, thereby potentially disrupting soil functioning. We conducted in situ warming experiments for three years using open-top chambers (OTCs) at one sub-Antarctic (Falkland Islands, 52ºS) and two Antarctic locations (Signy and Anchorage Islands, 60ºS and 67ºS respectively) (see Supplementary Fig. 1 for a map). OTCs increased annual soil temperature by an average of 0.8°C (at a depth of 5 cm), resulting in 8-43% increase in positive-degree days annually and a decrease in freeze-thaw cycle frequency by an average of 15 cycles per year (8). At each location, we included densely vegetated and bare fell-field soils in the experimental design for a total of six environments. Densely vegetated and bare environments represent two contrasting environments for Antarctic soil microorganisms, with large differences in terms of C and N inputs to soils. Massively parallel pyrosequencing (Roche 454 GS FLX Titanium) of 16S rRNA gene amplicons was used to follow bacterial diversity and community composition [GenBank Accession Numbers: HM641909-HM744649], and functional gene microarrays (GeoChip 2.0)(11) were used to assess changes in functional gene distribution. Bacterial and fungal communities were also quantified using real-time PCR.

Project description:Abstract Hypersaline lakes are of immense ecological value as they niche some of the most exclusive extremophilic communities dominated by bacterial and archaeal domains, with few eukaryotic algal representatives. A handful reports describe Picocystis as a key primary producer with great production rates in extremely saline habitats. An extremely haloalkaliphilic picoalgal strain, Picocystis salinarum SLJS6 isolated from hypersaline lake Sambhar, Rajasthan, India, grew robustly in an enriched soda lake medium containing mainly Na2CO3, 50 g/L; NaHCO3, 50g/L, NaCl, 50 g/L (salinity ≈150 ‰) at pH 10. To elucidate the molecular basis of such tolerance to high inorganic carbon and NaCl concentrations, a high-throughput LFQ (label-free quantitation) based quantitative proteomics approach was applied. Out of the total 383 proteins identified in treated samples, 225 were Differentially abundant proteins (DAPs), of which 150 were statistically significant (p value <0.05) including 70 upregulated and 64 downregulated proteins after 3 days of salt and alkalinity stress. Gene ontology analysis was done to annotate and classify the DAPs into functional groups. The analysis linked most DAPs to photosynthesis, oxidative phosphorylation, glucose metabolism and ribosomal structural components envisaging that photosynthesis and ATP synthesis were central to the alkalinity-salinity response. Key components of photosynthetic machinery like photosystem reaction centres, ATP synthase, Rubisco, Fructose-bisphosphate aldolase were significantly upregulated. Enzymes Peptidylprolyl isomerases (PPIase), important for correct protein folding showed remarkable marked-up regulation along with other chaperon proteins indicating their role in alleviating stress. Enhanced photosynthetic activity exhibited by Picocystis salinarum in highly saline-alkaline condition is noteworthy as photosynthesis is suppressed by salt stress in most photosynthetic organisms. This study provided the first evidence of a tailored regulatory mechanism of alkalinity and salt tolerance in extremophilic alga P. salinarum, potentially unraveling the basis of resilience in this not so known organism and paves the way for a promising future production host and model or¬ganism for deciphering the molecular mechanisms of os¬motic stress responses.

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Soil metagenome

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