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Electrochemical characterization of adhesion mechanism in Acinetobacter strains degrading fuel oil

We investigated interfacial properties of a bacterial strain Acinetobacter venetianus VE-C3 isolated from polluted surface waters of Venice Lagoon, that can utilize fuel oil (n-alkanes mixture) as sole carbon source. The initial step of degradation involves bacterial adhesion onto hydrophobic oil droplets dispersed in seawater. Artificial fluid interface: mercury drop electrode/aqueous electrolyte solution is used as a model hydrophobic interface and a probe responding simultaneously to adhesion of bacteria onto n-alkane droplets. Degradation of fuel oil and n-hexadecane (model molecule) by Acinetobacter venetianus VE-C3 were compared with Acinetobacter sp. RAG-1. The latter is known to produce a surfactant lipopolysaccharide, emulsan.. The two strains, VE-C3 and RAG-1, have the same catabolic genes (alk operons) so the same catabolic pathway to degrade n-alkanes. But, the two strains resulted different as regards the electrophoretic mobility and mecahnism of adhesion. Acinetobacter venetianus VE-C3 was hydrophilic in a complex medium, whereas it become hydrophobic when was grown in the presence of n-hexadecane and fuel oil as carbon sources. Acinetobacter sp. RAG-1 was always hydrophobic. The hydrophobicity of the Acinetobacter venetianus VE-C3 was attributed to the inducible production of an exopolysaccharide capsule. VE-C3 strain was found to be more efficient in degrading fuel oil and n-hexadecane and in biofilm formation than Acinetobacter sp. RAG-1. Ability of VE-C3 strain to degradate n-alkanes is not based on direct interaction of bacterial cells with oil/sewater interface, but on production of surface-active polysaccharides that mediate the interaction.

biodegradation; adhesion; marine bacteria; fuel oil

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