Abstract
BackgroundMany microorganisms have a wide temperature growth range and versatility to tolerate large thermal fluctuations in diverse environments, however not many have been fully explored over their entire growth temperature range through a holistic view of its physiology, genome, and transcriptome. We used Exiguobacterium sibiricum strain 255-15, a psychrotrophic bacterium from 3 million year old Siberian permafrost that grows from -5°C to 39°C to study its thermal adaptation.ResultsThe E. sibiricum genome has one chromosome and two small plasmids with a total of 3,015 protein-encoding genes (CDS), and a GC content of 47.7%. The genome and transcriptome analysis along with the organism's known physiology was used to better understand its thermal adaptation. A total of 27%, 3.2%, and 5.2% of E. sibiricum CDS spotted on the DNA microarray detected differentially expressed genes in cells grown at -2.5°C, 10°C, and 39°C, respectively, when compared to cells grown at 28°C. The hypothetical and unknown genes represented 10.6%, 0.89%, and 2.3% of the CDS differentially expressed when grown at -2.5°C, 10°C, and 39°C versus 28°C, respectively.ConclusionThe results show that E. sibiricum is constitutively adapted to cold temperatures stressful to mesophiles since little differential gene expression was observed between 4°C and 28°C, but at the extremities of its Arrhenius growth profile, namely -2.5°C and 39°C, several physiological and metabolic adaptations associated with stress responses were observed.
Highlights
Many microorganisms have a wide temperature growth range and versatility to tolerate large thermal fluctuations in diverse environments, not many have been fully explored over their entire growth temperature range through a holistic view of its physiology, genome, and transcriptome
The genome size and the GC content of E. sibiricum were similar to Psychrobacter arcticus 2734, a Gram-negative microorganism isolated from the Siberian permafrost
This work demonstrates that this microorganism is constitutively adapted to cold temperatures since at stressful temperatures for mesophiles, such as 4°C and 10°C, genes related to temperature stress are not differentially expressed
Summary
Many microorganisms have a wide temperature growth range and versatility to tolerate large thermal fluctuations in diverse environments, not many have been fully explored over their entire growth temperature range through a holistic view of its physiology, genome, and transcriptome. Psychrophilic together with psychrotolerant bacteria comprise the cold-adapted microorganisms. These microbes have been isolated and characterized from various environments such as polar sediments and soils, as well as open oceans [2,3]. Most of the studies examining the cold and heat stress responses were done in mesophilic bacteria and a range of mechanisms has been identified. These mechanisms involve preserving the flexibility, topology, and interactions of macromolecules such as DNA, RNA and proteins, maintaining the homeoviscous adaption of the cell membrane, protecting the cell from disruption by producing osmoprotectants, and maintaining the diffusion rate and enzyme kinetics inside the cell [11,12,13]
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