Isolation and characterization of rhamnolipid-producing bacterial strains from a biodiesel facility

Novel strains of rhamnolipid-producing bacteria were isolated from soils at a biodiesel facility on the basis of their ability to grow on glycerol as a sole carbon source. Strains were identified as Acinetobacter calcoaceticus, Enterobacter asburiae, Enterobacter hormaechei, Pantoea stewartii, and Pseudomonas aeruginosa. The strains of the former five species were found to produce rhamnolipids in quantities the same as, or similar to, coisolated strains of P. aeruginosa. Measurements of surface tension revealed that that emulsifying properties of these strains were similar to levels displayed by rhamnolipids produced by P. aeruginosa. Results of matrix-assisted laser desorption/ionization time-of-flight MS analyses revealed that the predominant compounds made by all strains were C10-C10 mono- and dirhamnolipids. Notably, E. hormaechei and one strain of A. calcoaceticus produced rhamnolipids in amounts similar to the pseudomonads. As all strains examined were from the same taxonomic class of Proteobacteria, further examination of this group may reveal many additional species not previously known to produce rhamnolipids in addition to novel strains of species currently known to produce rhamnolipids.