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).