Differential protein expression during growth on linear versus branched alkanes in the obligate marine hydrocarbon-degrading bacterium Alcanivorax borkumensis SK2T

Alcanivorax borkumensis SK2(T) is an important obligate hydrocarbonoclastic bacterium (OHCB) that can dominate microbial communities following marine oil spills. It possesses the ability to degrade branched alkanes which provides it a competitive advantage over many other marine alkane degraders that can only degrade linear alkanes. We used LC-MS/MS shotgun proteomics to identify proteins involved in aerobic alkane degradation during growth on linear (n-C-14) or branched (pristane) alkanes. During growth on n-C-14, A. borkumensis expressed a complete pathway for the terminal oxidation of n-alkanes to their corresponding acyl-CoA derivatives including AlkB and AlmA, two CYP153 cytochrome P450s, an alcohol dehydrogenase and an aldehyde dehydrogenase. In contrast, during growth on pristane, an alternative alkane degradation pathway was expressed including a different cytochrome P450, an alcohol oxidase and an alcohol dehydrogenase. A. borkumensis also expressed a different set of enzymes for beta-oxidation of the resultant fatty acids depending on the growth substrate utilized. This study significantly enhances our understanding of the fundamental physiology of A. borkumensis SK2(T) by identifying the key enzymes expressed and involved in terminal oxidation of both linear and branched alkanes. It has also highlights the differential expression of sets of beta-oxidation proteins to overcome steric hinderance from branched substrates.