Cellular Hydrophobicity is Not Determinant of Water-In-Oil Emulsification Breaking by Bacteria
Rita de Cássia Rocha Fernandes, Arnaldo Chaer Borges, Marcos Rogério Tótola

Abstract
We evaluated if the capability of bacterial isolates to break water-in-oil (W/O) emulsions depends on cell surface hydrophobicity. Among 12 bacterial isolates obtained from enrichment of solid waste compost in mineral-paraffin medium, four were shown to be efficient in breaking W/O emulsion. These strains were identified as Acinetobacter sp. and Pseudomonas mendocina. W/O emulsion-breaking activity (EBA) decreased with culture age. EBA of young cultures (22 hours of growth) was dependent on the presence of cells, and soluble deemulsifier(s) did not have significant effect at this stage. In contrast, EBA of older cultures (198 hours of growth) was attributed to the presence of non-surfactant deemulsifier compound(s) in the culture broth. Experiments with Acinetobacter sp. LBBMA LU3 revealed that cell integrity is not required for EBA. EBA was insensitive to variation of pH (3-8) or salt concentration (0-150 g l-1 NaCl), but increased linearly with temperature (30-60°C). Correlation between cell surface hydrophobicity and EBA was either absent, negative or positive, depending on the microbial strain or on previous growth condition for a particular strain. We conclude that hydrophobicity is not a primary factor determining EBA of bacterial cells.

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