Temperature - A critical abiotic paradigm that governs bacterial heterogeneity in natural ecological system.

A baseline data has been presented here to prove that among the abiotic factors, temperature is the most critical factor that regulates and governs the bacterial diversity in a natural ecosystem. Present study in Yumesamdong hot springs riverine vicinity (Sikkim), parades a gamut of bacterial communities in it and hosts them from semi-frigid region (- 4-10 °C) to fervid region (50-60 °C) via an intermediate region (25-37 °C) within the same ecosystem. This is an extremely rare intriguing natural ecosystem that has no anthropogenic disturbances nor any artificial regulation of temperature. We scanned the bacterial flora through both the culture-dependent and culture-independent techniques in this naturally complex thermally graded habitat. High-throughput sequencing gave bacterial and archaeal phyla representatives of over 2000 species showcasing their biodiversity. Proteobacteria, Firmicutes, Bacteroidetes and Chloroflexi were the predominant phyla. A concave down-curve significance was found in temperature-abundance correlation as the number of microbial taxa decreased when the temperature increased from warm (35 °C) to hot (60 °C). Firmicutes showed significant linear increase from cold to hot environment whereas Proteobacteria followed the opposite trend. No significant correlation was observed for physicochemical parameters against the bacterial diversity. However, only temperature has shown significant positive correlation to the predominant phyla at their respective thermal gradients. The antibiotic resistance patterns correlated with temperature gradient where the prevalence of antibiotic resistance was higher in case of mesophiles than that of psychrophiles and there was no resistance in thermophiles. The antibiotic resistant genes obtained were solely from mesophiles as it conferred high resistance at mesophilic conditions enabling them to adapt and metabolically compete for survival. Our study concludes that the temperature is a major factor that plays a significant contribution in shaping the bacterial community structure in any thermal gradient edifice.