Microbiome and ecology of a hot spring-microbialite system on the Trans-Himalayan Plateau
Chayan Roy, Moidu Jameela Rameez, Prabir Kumar Haldar, Aditya Peketi, Nibendu Mondal, Utpal Bakshi, Tarunendu Mapder, Prosenjit Pyne, Svetlana Fernandes, Sabyasachi Bhattacharya, Rimi Roy, Subhrangshu Mandal, William K. O’Neill, Aninda Mazumdar, Subhra Kanti Mukhopadhyay, Ambarish Mukherjee, Ranadhir Chakraborty, John E. Hallsworth, Wriddhiman Ghosh
Abstract
Little is known about life in the boron-rich hot springs of Trans-Himalayas. Here, we explore the geomicrobiology of a 4438-m-high spring which emanates ~70 °C-water from a boratic microbialite called Shivlinga. Due to low atmospheric pressure, the vent-water is close to boiling point so can entropically destabilize biomacromolecular systems. Starting from the vent, Shivlinga's geomicrobiology was revealed along the thermal gradients of an outflow-channel and a progressively-drying mineral matrix that has no running water; ecosystem constraints were then considered in relation to those of entropically comparable environments. The spring-water chemistry and sinter mineralogy were dominated by borates, sodium, thiosulfate, sulfate, sulfite, sulfide, bicarbonate, and other macromolecule-stabilizing (kosmotropic) substances. Microbial diversity was high along both of the hydrothermal gradients. Bacteria, Eukarya and Archaea constituted >98%, ~1% and <1% of Shivlinga's microbiome, respectively. Temperature constrained the biodiversity at ~50 °C and ~60 °C, but not below 46 °C. Along each thermal gradient, in the vent-to-apron trajectory, communities were dominated by Aquificae/Deinococcus-Thermus, then Chlorobi/Chloroflexi/Cyanobacteria, and finally Bacteroidetes/Proteobacteria/Firmicutes. Interestingly, sites of >45 °C were inhabited by phylogenetic relatives of taxa for which laboratory growth is not known at >45 °C. Shivlinga's geomicrobiology highlights the possibility that the system's kosmotrope-dominated chemistry mitigates against the biomacromolecule-disordering effects of its thermal water.