Proteomic analysis of Marinobacter hydrocarbonoclasticus SP17 biofilm formation at the alkane-water interface reveals novel proteins and cellular processes involved in hexadecane assimilation

Many hydrocarbon-degrading bacteria form biofilms at the hydrocarbon-water interface to overcome the weak accessibility of these poorly water-soluble substrates. In order to gain insight into the cellular functions involved, we undertook a proteomic analysis of Marinobacter hydrocarbonoclasticus SP17 biofilm developing at the hexadecane-water interface. Biofilm formation on hexadecane led to a global change in cell physiology involving modulation of the expression of 576 out of 1144 detected proteins when compared with planktonic cells growing on acetate. Biofilm cells overproduced a protein encoded by MARHY0478 that contains a conserved domain belonging to the family of the outer membrane transporters of hydrophobic compounds. Homologs of MARHY0478 were exclusively found in marine bacteria degrading alkanes or possessing alkane degradation genes, and hence presumably constitute a family of alkane transporters specific to marine bacteria. Interestingly, we also found that sessile cells growing on hexadecane overexpressed type VI secretion system components. This secretion system has been identified as a key factor in virulence and in symbiotic interaction with host organisms. This observation is the first experimental evidence of the contribution of a type VI secretion system to environmental adaptation, and raises the intriguing question about the role of this secretion machine in alkane assimilation.