Proteomic analysis of cold adaptation in a Siberian permafrost bacterium - Exiguobacterium sibiricum 255-15 by two-dimensional liquid separation coupled with mass spectrometry

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Abstract
Bacterial cold adaptation in Exiguobacterium sibiricum 255–15 was studied on a proteomic scale using a 2‐D liquid phase separation coupled with MS technology. Whole‐cell lysates of E. sibiricum 255–15 grown at 4°C and 25°C were first fractionated according to pI by chromatofocusing (CF), and further separated based on hydrophobicity by nonporous silica RP HPLC (NPS‐RP‐HPLC) which was on‐line coupled with an ESI‐TOF MS for intact protein Mr measurement and quantitative interlysate comparison. Mass maps were created to visualize the differences in protein expression between different growth temperatures. The differentially expressed proteins were then identified by PMF using a MALDI‐TOF MS and peptide sequencing by MS/MS with a MALDI quadrupole IT TOF mass spectrometer (MALDI‐QIT‐TOF MS). A total of over 500 proteins were detected in this study, of which 256 were identified. Among these proteins 39 were cold acclimation proteins (Caps) that were preferentially or uniquely expressed at 4°C and three were homologous cold shock proteins (Csps). The homologous Csps were found to be similarly expressed at 4°C and 25°C, where these three homologous Csps represent about 10% of the total soluble proteins at both 4°C and 25°C.