Community survival strategies under environmental extremes
To understand community survival strategies under extreme temperature and geochemical gradients, we selected genes in our metagenomes that are involved with stress response, DNA repair, protein biosynthesis, and transport and chemotaxis. Although communities from all samples were equally abundant in genes related to stress response, very distinct patterns of specific responses were observed accordingly environmental temperature (Figure 4). The oxidative stress response was markedly higher in the fumarole at 98 oC, mainly represented by glutaredoxins, glutathione (redox cycle) and rubrerythrin functions (all with p < 0.001 in comparison with other samples). Contrastingly, osmotic stress genes were prevalent in glaciers samples, represented mainly by functions such as osmoregulation (p< 0.001), osmoprotectant (yehX ) (p = 0.01), aquaporin Z (p = 0.05) and synthesis of osmoregulated periplasmatic glucans (p < 0.001). The abundance of genes related to heat and cold responses (thermal response) was distinctly distributed among fumaroles and glaciers. General function of heat-shock proteins (including hsp70 /dnaK ) were prevalent in glaciers and <80 oC fumaroles (p< 0.001), whereas specific archaeal thermal responses dominated the 98 oC fumarole, such as thermosome chaperonin (p < 0.001, 0.7% of total relative abundance), as were bacterial and archaeal heat-shocksgroEL /groES (p < 0.001). The relative abundance of cold shock cspA was higher in <80oC fumaroles, followed by glaciers (p< 0.001). Glaciers and <80 oC fumaroles exhibited the highest abundance of dormancy and sporulation function (p < 0.01) and all fumaroles had a prevalence of the universal stress protein family (p < 0.01) (Figure 4).
Differences in abundance patterns of DNA repair, protein biosynthesis, transport and chemotaxis were also observed across environmental temperatures (Supplementary Figure 2). Base excision repair, recombination through recU and reverse gyrase (all with p< 0.01) were the main strategies of DNA positive supercoiling and repair notably found in communities of the highest temperature fumarole (98 oC). Strategies of DNA repair usinguvrABC complex, recombination through recA and photolyase were dominant in <80 oC fumaroles and glaciers (all with p < 0.001). Protein biosynthesis genes were dominant in the highest temperature fumarole (98oC); functions such as universal GTPases (p< 0.01) and translation elongation factors in Archaea (p < 0.001) were significantly higher when compared to the other samples. Chemotaxis genes were also prevalent in the highest temperature fumarole (98 oC) (p < 0.001), as were several transport systems (transport of Ni, Co, and Zn) and ABC transporters (e.g. branched-chain amino acid, oligopeptide and tungstate) (all with at least p < 0.05). Mn transport and the ABC transporters of iron and peptides were significantly higher in <80 oC fumaroles (all with at leastp < 0.05) (Supplementary Figure 2).