Biosurfactant biosynthesis by Alcanivorax borkumensis and its role in oil biodegradation

The marine bacterium Alcanivorax borkumensis degrades alkanes derived from phytoplankton, natural hydrocarbon seeps and oil spills. We study the biosynthesis and function of a glycine-glucolipid biosurfactant from A. borkumensis for alkane degradation and identify a gene cluster encoding a nonribosomal peptide synthetase, glycosyltransferase and phosphopantetheinyl transferase. Analyses of A. borkumensis mutants and expression studies reveal that the nonribosomal peptide synthetase catalyzes the synthesis of the aglycone (tetra-D-3-hydroxydecanoyl-glycine) from glycine and D-3-hydroxydecanoyl-CoA, to which a glucose moiety is added by the glycosyltransferase. Deficiency in glycine-glucolipid impairs the ability of mutant cells to attach to the oil-water interface, compromises growth on hexadecane and affects carbon storage. The glycine-glucolipid is essential for biofilm formation on oil droplets and uptake of alkanes. The high incidence of Alcanivorax at oil-polluted sites can in part be explained by the accumulation of the glycine-glucolipid on the cell surface, effectively making the cells themselves act as biosurfactants.