![]() ![]() To increase protein flexibility at low temperatures, proteins of subzero-growing bacteria are composed of more serine and less proline and acidic residues than mesophilic bacteria 16. Glycine betaine accumulated in cytosol contributed to an improvement in cold tolerance and osmotolerance in psychrophilic bacteria 15. bgaS gene encoding Β-galactosidase in Arthrobacter species isolated from Antarctica was identified as cold-active and increased 5.0-fold at 0–18 ☌, in comparison to mesophilic bacteria (such as Escherichia coli) at 10–20 ☌ 14. AtcJ protein of Shewanella oneidensis, a functional J-domain protein (JDP) in co-chaperone protein networks, was essential in maintaining proteostasis and bacterial growth at low temperatures 13. Oleispira antarctica RB-8 at 4 ☌ employed the primary protein-folding system by using chaperone Cpn60 as a single heptameric barrel unlike the typical double-barrel structure formed at 16 ☌ 12. PAMC21119 isolated from Antarctic soil upregulated proteins involved in protein folding, metabolite transport, acetyl-CoA metabolism, and membrane fluidity, and downregulated proteins related to heme synthesis, energy conversion, and production in cold environments 11. This increases the composition of unsaturated lipids to improve membrane fluidity, express helicases, cold shock proteins to stabilize DNA/RNA, and utilize carotenoid pigments for protection from solar radiation 10. One strategy psychrophilic bacteria use to counter this is to upregulate cold-activity enzymes. Microbes in cold habitats must prevent temperature stress from disrupting enzyme activity and protein stability 9. All psychrotolerant and psychrophilic Actinobacteria including Arthrobacter and Pseudarthrobacter species must have specific survival strategies to cope with the extreme environmental conditions in Antarctica 3, 8. Interestingly, many Actinobacteria genomes also possess genes involved in carbon dioxide fixation through the Clavin-Benson-Bassham (CBB) cycle to gain metabolic energy under limited carbon and nitrogen circumstances 5, 7. Notably, distinct clusters belonging to Actinobacteria play key roles in ecosystem function, such as global carbon cycling, plant productivity, and bioactive compound production 6. A substantial variety of bacterial groups ( Actinobacteria, Proteobacteria, Firmicutes, and Chloroflexi) has been discovered in Antarctic regions 3, 4, 5. However, relatively low microbial diversity and reduced microbe-mediated ecosystem functions, such as carbon and nitrogen cycles, are prevalent in Antarctic soil due to unfavorable conditions for microbial activity 2. Taken together, our data highlights the cellular filamentation and protein homeostasis of a psychrophilic YJ56 strain in coping with high-temperature stress.Ĭold environments such as the Arctic Ocean, glaciers, ice caps, permafrost, and sea ice having low temperatures below 5 ☌ throughout the years account for approximately 80% of the Earth’s environments, which implies their important contribution to the biogeochemical cycle on the Earth 1. Level of proteins involved in the assembly of 50S ribosomal proteins and L29 in 50S ribosomal proteins increased at 13 ☌, which suggested distinct roles of many ribosomal proteins under different conditions. Our proteomic data suggested that Actinobacteria cells experienced physiological stresses at 25 ☌, showing the upregulation of chaperone proteins, GroEL and catalase, KatE. Comparative genomics of strain YJ56 with other genera in the phylum Actinobacteria indicate remarkable copy numbers of rimJ genes that are possibly involved in dual functions, acetylation of ribosomal proteins, and stabilization of ribosomes by direct binding. Unlike a single rod-shaped cell at 13 ☌, strain YJ56 at 25 ☌ was morphologically shifted into a filamentous bacterium with several branches. The psychrophilic Pseudarthrobacter psychrotolerans YJ56 had superior growth at 13 ☌, but could not grow at 30 ☌, compared to other bacteria isolated from the same Antarctic soil. Both culture-independent and culture-dependent analyses using Nanopore-based 16S rRNA sequencing showed that short-term exposure of Antarctic soils to low temperature increased biomass with lower bacterial diversity and maintained high numbers of the phylum Proteobacteria, Firmicute, and Actinobacteria including Pseudarthrobacter species.
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