Abstract
Marine bacteria display significant versatility in adaptation to variations in the environment and stress conditions, including temperature shifts. Shewanella baltica plays a major role in denitrification and bioremediation in the marine environment, but is also identified to be responsible for spoilage of ice-stored seafood. We aimed to characterize transcriptional response of S. baltica to cold stress in order to achieve a better insight into mechanisms governing its adaptation. We exposed bacterial cells to 8 °C for 90 and 180 min, and assessed changes in the bacterial transcriptome with RNA sequencing validated with the RT-qPCR method. We found that S. baltica general response to cold stress is associated with massive downregulation of gene expression, which covered about 70% of differentially expressed genes. Enrichment analysis revealed upregulation of only few pathways, including aminoacyl-tRNA biosynthesis, sulfur metabolism and the flagellar assembly process. Downregulation was observed for fatty acid degradation, amino acid metabolism and a bacterial secretion system. We found that the entire type II secretion system was transcriptionally shut down at low temperatures. We also observed transcriptional reprogramming through the induction of RpoE and repression of RpoD sigma factors to mediate the cold stress response. Our study revealed how diverse and complex the cold stress response in S. baltica is.
Highlights
Bacteria had evolved multiple mechanisms for efficient adaptation to changes in their habitats
Global transcription reprogramming was observed in cold-stressed S. baltica: expression of the rpoE gene, encoding the sigma E factor, was induced in response to the envelope and oxidative stress, while the housekeeping sigma factor, rpoD, expression decreased
Alterations in amino acid profiles during cold stress are apparently common in bacterial world, it may be assumed as a universal response mechanism ensuring adequate protein structural flexibility, stability and activity at low temperatures
Summary
Bacteria had evolved multiple mechanisms for efficient adaptation to changes in their habitats. Adaptation to the abrupt temperature downshift usually involves an acclimatization stage where the gene expression pattern is reprogrammed to shut down unnecessary processes and induce those beneficial for survival, which is followed by resuming of growth at a rate adapted to the altered condition. For mesophilic bacteria, such adaptation typically involves upregulation of the synthesis of cold shock proteins (Csp) which serve as RNA chaperones, transcription modulators and DNA topology organizers [8,9]. Function of the transmembrane transporters is adjusted
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