Psychrophilic and cryophilic bacterial copiotrophs from a Trans-Himalayan lake-desert ecosystem as biogeothermometers of warming, mitigators of perturbation, and candidates for biodegradation

Abstract

A Trans-Himalayan lake-desert ecosystem was explored for the low-to-high temperature adaptations of native copiotrophic psychrophiles that have the potentials for rendering substantive carbon remineralization under natural and/or anthropogenically influenced conditions of high organic matter delivery to the environment. Overall 27 species, classified across 15 genera of Actinomycetota, Bacillota, Bacteroidota, and Pseudomonadota, were isolated from the brackish-water and sediment-surface of Tso Moriri (a massive lacustrine body 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, all the isolates grew at 4{degrees}C and 15{degrees}C; 13 of them grew, while 14 retained 19-99% cells in metabolically-active state, at -10{degrees}C; 23, 11, and none grew at 28{degrees}C, 37{degrees}C, and 42{degrees}C respectively. A Cryobacterium was most heat-susceptible, whereas some -10{degrees}C-growing Arthrobacter, Microbacterium, Paenarthrobacter, Pseudomonas and Streptomyces were most warming-resilient, among the present isolates. Catabolizing different simple/complex organic compounds, all isolates accomplished low/moderate/high growths at 4{degrees}C; 20 performed low growths at -10{degrees}C. Taxonomy/phylogeny did not determine the isolates growth/survival across the temperature-range tested. Lake-water and rock-dust isolates had the widest, while lake-sediment-dwellers had the narrowest, temperature-window for growth/survival. Rock-dust and lake-water isolates had more genes for low and high temperature adaptations, compared to the lake-sediment isolates. In co-cultures, most actinobacterial isolates inhibited the growth of mesophilic bacteria from warmer ecosystems, plus non-actinobacteria and actinobacteria from native/adjoining habitats. The data hold implications for biodegradation in cold/frigid territories, negative feedback control/reversal of warming, and microbiome protection from infiltration amidst climate change. IMPORTANCEPhylogenetically diverse, cold-adapted copiotrophic bacteria were retrieved from a Trans-Himalayan lake-desert ecosystem, and tested for chemoorganoheterotrophic growth at temperatures between -10{degrees}C and 42{degrees}C. Albeit growth dwindled at [≥]28{degrees}C, most of the isolates thrived on simple as well as complex organic substances under freezing condition, which makes them prospective constituents of biodegradation reactors suitable for high-altitude/latitude deployment. In the natural habitats of the psychrophilic isolates, cessation of organotrophic activities at elevated temperatures would stop simple fatty acids and CO2 production, which in turn would preempt methanogenesis, undo greenhouse effect, and reverse environmental thawing (usher cooling). Such negative feedback control of homeostasis is fraught with the danger of microbiome takeover by thermally-better-adapted foreign organisms. Consequently, ecosystem preservation rests on the native microfloras ability to resist external invasion. At 28{degrees}C, majority of the actinobacterial isolates inhibited bacteria from discrete higher-temperature ecosystems; they can, therefore, be viewed as the defenders of the cold/frigid ecosystem.