Putative Roles of Cold Inducible Proteins in Low Temperature Growth

The temperature regulates the growth rate, the level of biosynthesis, metabolism, and survival (Price and Sowers 2004). Comparison of the proteomic profiles of different psychroactive bacteria grown at low temperatures involves the up-regulation of the similar proteins.

Protein profiles of strains P cryohalolentis K5 and E. sibiricum 255-15 following cold adaptation showed overexpression of translation elongation factor Ts involved in gene expression, and F1/F0-type ATP-synthase B subunit important for energy production (Qiu et al. 2006; Bakermans et al. 2007). The overexpression of translation elongation factor Tu was observed in two Psychrobacter strains studied (Bakermans et al. 2007; Zheng et al. 2007). The proteins involved in gene expression, e.g., CSPs, transcriptional regulators, ribosomal proteins, RNA chaperones and elongation factors, are known to be induced in the response to low temperature in order to decrease stress on transcription, translation initiation and elongation (Mihoub et al. 2003). Low-temperature-induced synthesis and accumulation of CIPs in the cells allows bacteria to maintain energy and constructive metabolism under unfavorable environmental conditions.

Bacteria of the genus Exiguobacterium are non-spore-forming bacteria; however, the elevated level of the sporulation control protein was observed in both Exiguobacterium strains studied, suggesting that cold-stressed bacteria may enter cyst-like resting states that enhance their survivability (Chong et al. 2000; Qiu et al. 2006; Soina et al. 2004). Growth at low temperatures has been shown to require more energy and be less efficient (Bakermans et al. 2003; Bakermans and Nealson 2004). Both Exiguobacterium strains showed low-temperature overexpression of triosephosphate isomerase that involved glycolysis which might be maximally induced under cold growth (Wouters et al. 2000). Some bacteria use different pathways at different growth temperatures; for example, psychrotrophic Rhizobium strains switched from respiration to lactate glycolysis in order to generate energy effectively at low temperatures (Sardesai and Babu 2000). Temperature-specific carbon source utilization has also been observed in E. sibiricum 255-15 and P. arcticus 273-4 (Ponder et al. 2005). Various carbon sources may differentially influence the protein production, suggesting that cells grown with one carbon source may be stressed by low temperatures to a greater extent than cells grown with another (Barbaro et al. 2002). The suggested induction of the glycolysis at low temperature has been further supported by observation of up-regulation the enzymes of the glycolytic pathway, e.g. malate/lactate dehydrogenases, in P. cryo-halolentis K5 (Bakermans et al. 2007).

The affinity to substrate decreases at low temperatures; therefore the changes in transport systems are required to counteract lower rates of diffusion and solute transport across the membrane (Nedwell 1999). Bacteria of the genera Exiguobacterium and Psychrobacter were shown to be able to grow at temperatures below 0°C, therefore the processes of substrate sequestration from the environment and excretion of spent solutes from cells turn out to be very important for growth at the low temperatures. A number of transport-related proteins and membrane-associated proteins were up-regulated by cold in these strains (Chong et al. 2000; Qiu et al. 2006; Bakermans et al. 2007; Zheng et al. 2007). The drop of a temperature below 0°C leads to ice formation within the cell which might lead to cell lysis, and leads to the increase of salinity outside the cell followed by the consequent increase of an osmotic gradient across the cell membrane. The cold-shock induced ice nucleation activity in different psychroactive bacteria including E. sibiricum 7-3 (Ponder et al. 2005), and induced synthesis of the ice nucleation proteins which can act as a template for ice formation (Kawahara 2002). Another stress that bacteria encounter at low temperatures is oxidative stress, because oxygen radicals accumulate to higher concentrations, given that oxygen is more soluble and reduced respiration rates consume oxygen more slowly. The CIPs of diverse functions including chemotaxis, hydroperoxide detoxification, and surface proteins may maintain cell integrity and functioning during this stress (Bakermans et al. 2007).

The psychrotrophic bacteria harbored antibiotic multiresistant traits, and this feature increased with cold (Munsch-Alatossava and Alatossava 2007). While E. sibiricum 255-15 showed a decrease in resistance to chloramphenicol and tetracyclin at 4°C (penicillin was not tested) (Ponder et al. 2005), the high overexpression level of penicillin tolerance protein was detected in this bacterium at 4°C (Qiu et al. 2006).

During the growth at low temperatures, cells cope with amino acid starvation, oxidative stress, aberrant protein synthesis, cell-surface remodeling, alterations in degradative metabolism, and induction of global regulatory responses. A life in less than ideal environmental conditions leads to changes in the physiological state and the biochemical activity of bacterial cells, and these changes bind directly to protein synthesis.

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