Mangrove sediment, a new source of potential biosurfactant-producing bacteria

Biosurfactant-producing bacteria were isolated from mangrove sediment samples collected in the southern part of Thailand by an enrichment-culture technique in which lubricating oil was the sole carbon source. A total of 1,600 colonies were obtained, which were screened for biosurfactant production using the qualitative dropcollapsing test in a mineral salts medium containing 1% of different carbon sources (commercial sugar, glucose, molasses, and used lubricating oil). Ninety-five isolates were positive for biosurfactant production based on the results of this test, among which 20 could reduce the surface tension of the 48-h culture supernatant. The phylogenetic position of these 20 isolates was evaluated by 16S rRNA gene sequence analysis. The production of biosurfactants was determined for strains representative of eight different bacterial genera. Leucobacter komagatae 183, one of the newly isolated strains showing biosurfactant production, produced extracellular biosurfactants which reduced the surface tension of the culture supernatant from 72.0 to 32.0 m/Nm. Eighteen strains released extracellular emulsifiers able to stabilize the emulsion formed. Among these, the strains L. komagatae 183 and Ochrobactrum anthropi 11/6 exhibited emulsification activities comparable to those of synthetic surfactants. Overall, the new biosurfactantproducing strains isolated in this study display promising features for the future development and use in economically efficient industrial-scale biotechnological processes.