Cold adaptation in the marine bacterium, Sphingopyxis alaskensis, assessed using quantitative proteomics

Summary The cold marine environment constitutes a large pro- portion of the Earth's biosphere. Sphingopyxis alaskensis was isolated as a numerically abundant bacterium from several cold marine locations, and has been extensively studied as a model marine bacte- rium. Recently, a metabolic labelling platform was developed to comprehensively identify and quantify proteins from S. alaskensis. The approach incorpo- rated data normalization and statistical validation for the purpose of generating highly confident quantita- tive proteomics data. Using this approach, we deter- mined quantitative differences between cells grown at 10°C (low temperature) and 30°C (high temperature). Cold adaptation was linked to specific aspects of gene expression: a dedicated protein-folding system using GroESL, DnaK, DnaJ, GrpE, SecB, ClpB and PPIase; polyhydroxyalkanoate-associated storage materials; a link between enzymes in fatty acid metabolism and energy generation; de novo synthesis of polyunsatu- rated fatty acids in the membrane and cell wall; inor- ganic phosphate ion transport by a phosphate import PstB homologue; TonB-dependent receptor and bac- terioferritin in iron homeostasis; histidine, tryptophan and proline amino acid metabolism; and a large number of proteins without annotated functions. This study provides a new level of understanding on how important marine bacteria can adapt to compete effec- tively in cold marine environments. This study is also a benchmark for comparative proteomic analyses with other important marine bacteria and other cold- adapted organisms.