Membrane proteome of Acinetobacter radioresistens S13 during aromatic exposure

Study of the bacterial membrane proteome, though in its early stages, is a field of growing interest in-the search for information about nutrient transport and processing. We tested different strategies and chemical compounds to extract proteins from the membranes (inner and outer) of Acinetobacter radioresistens S13, a Gram-negative bacterium selected for its ability to degrade aromatics. A. radioresistens S13 was monitored under different growth substrate conditions, using acetate,. benzoate or phenol as sole carbon source. Two-dimensional gel electrophoresis map analysis of membrane extracts from benzoate- and phenol-grown cells reveals differences versus controls (acetate-grown cultures). Primarily, a different pattern of spots was observed and, in particular, some proteins were only expressed in the presence of aromatic substrate. Among these, we detected a Na+/H+ antiporter, whose function is likely to be regulation of intracellular pH, and an ABC type sugar transport system, probably involved in capsular polysaccharide translocation. We also identified other proteins, detectable in acetate-grown but over-expressed in aromatic-grown cells. These include: (1) an outer membrane protein ascribable to an OmpA-like protein, recently described in the literature as "alasan", a bioemulsifying agent involved in solubilizing and enhancing bioavailability of hydrocarbons; (2) a trimeric porin of the PhoE family also belonging to the outer membrane and involved in facilitating the transport of anions (especially phosphate); and (3) two glycosyl transferases probably involved in capsules and/or lipopolysaccharide biosynthesis. Study of the bacterial membrane proteome helps to elucidate the role of the membrane as modulable site enabling communication between internal and external environments.