# Adaptation of the Marine Bacterium _Shewanella baltica_ to Low Temperature Stress  
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1 Department of Medical Biology and Genetics, Faculty of Biology, University of Gdarsk, Wita Stwosza 59, 80-308 Gdarsk, Poland 1  
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2 Department of Bacterial Molecular Genetics, Faculty of Biology, University of Gdarsk, Wita Stwosza 59, 80-308 Gdarsk, Poland; [EMAIL_ADDRESS] (G.M.C. ); [EMAIL_ADDRESS] (M.S. ); [EMAIL_ADDRESS] (K.K. ); [EMAIL_ADDRESS] (A.S.-P) 2  
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3345773345  
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]. As the low temperature affects bacterial membrane stability and permeability, one of the described responses is related to decreased lipid saturation to prevent membrane stiffness [10; 11]. Metabolic changes under cold stress involve repression of typical glycolysis and the tricarboxylic acid (TCA) cycle, in favor of secondary and alternate pathways [10]. Accumulation of specific compatible solutes (glycine, betaine, glycerol, trehalose, sucrose, mannitol, sorbitol) plays an important role in cryoprotection, preventing protein aggregation, free radical accumulation and membrane stabilization [12]. In this process, function of the transmembrane transporters is adjusted accordingly. Marine bacteria inhabiting the temperate and cold climate zones tend to develop psychrotolerant phenotypes, enabling them not only to survive but also thrive at the suboptimal temperatures. This is achieved by traits allowing for optimization of growth, enzyme functioning, motility and macromolecule synthesis [13; 14; 15]. Cold adaptation that leads to their optimal activity involves changes in the cell membrane structure and fluidity, protein folding with the help of chaperones, and changes in the nucleic acids topology that affect both, replication and gene expression [16; 17; 18]. The _Shewanella_ genus is one of the most abundant \(\gamma\)-proteobacteria in the marine and fresh water environment. Its metabolic versatility and ability to utilize a variety of extracellular electron acceptors is a key feature in its role in the turnover of organic matter, denitrification and bioremediation [19; 20]. In addition, _Shewanella_ species are known for their spoilage and decomposing potential even at low temperatures, which indicates that their metabolic processes are active under those conditions [21]. Despite of the reported psychrotrophic features of the _Shewanella_ genus representatives, the detailed molecular processes underlying their survival and metabolic activity at low temperature has been studied mostly only for the best known species, such as _Shewanella oneidensis_, for the deep-sea dwelling _Shewanella piezotolerans_, and for the Antarctic species _Shewanella livingstonensis_[22; 23; 24; 25], while other _Shewanella_ species provided mostly only some information on the cold-adapted enzymes and relevant processes [26; 27]. _Shewanella baltica_ is a representative of the _Shewanella_ genus inhabiting the Baltic Sea, where it is considered as the main player in reducing nitrates at the redox transition interface and its dominant role in denitrification of this habitat was reported [28; 29]. A study of the response of _S. baltica_ to various stressors revealed that upon nutrient limitation, heat shock and DNA damage these bacteria induce the stringent response--a global reaction to stress--as one of the ways of dealing with the challenging conditions [30].