Warming responses, antibiosis potentials, and ecological implications of cryo-adapted copiotrophs from a...

A Trans-Himalayan lake-desert ecosystem was explored for the low-to-high temperature adaptations of copiotrophic psychrophiles having potentials for substantive carbon remineralization under natural and/or anthropogenically-influenced conditions of high organic matter delivery to the environment. Overall 27 bacterial species were isolated from the brackish-water and sediment-surface of Tso Moriri (a massive lake on the Changthang plateau that remains frozen for approximately one third of the year), and the fine talus covering a lake-side rocky mountain. In Luria broth (LB), all isolates grew at 4 °C and 15 °C; at -10 °C, 13 could grow while others remained only metabolically-active. Catabolizing different complex-organic-compounds, all isolates achieved considerable growth at 4 °C; 20 accomplished low growth at -10 °C. LB-based growth dwindled with rising temperature: 23, 11, and none of the isolates grew at 28 °C, 37 °C, and 42 °C respectively. In agar-overlay assays, most actinobacterial isolates inhibited other mesophilic bacteria. The isolates’ genomes, and their habitats’ metagenomes, encompassed diverse genes for extreme-temperature adaptation, carbohydrate catabolism, antibiosis and antibiotic-resistance. All in-vitro findings collectively engender the following hypothesis, via contextual inferences pending field-study-based validations. Warming-induced cessation of organotrophic growth, within high-altitude cryospheres, would curb the production of simple-fatty-acids, CO2 and N2O. Short-supply of acetate and CO2 would, in turn, cut-back methanogenesis. Such negative-feedback control of greenhouse gas production at the micro-habitat level can add-up in the biome-scale to mitigate broader environmental warming; it, however, endangers the ecosystem from thermally-better-adapted foreign microbes that can usher positive-feedback cycles of warming. In the latter scenario, antibiosis potentials of native actinobacteria become pivotal to microbiome protection.