The gene rhlG and the synthesis of rhamnolipids: they are related to each other?

There are differences in the literature regarding the relationship of RhlG protein and rhamnolipids production. Campos-Garcia et al. (1998) report that expression of protein from rhlG gene was responsible for the synthesis of the rhamnolipid lipid portion. However, Rock and Zhu (2008) corroborate Déziel et al. (2003) results, whose proposed that hydroxyalkanoic acids (AHA) formation occurs only in the presence of RhlA protein. The authors suggest that the lipid moiety is synthesized by the classical route for the synthesis of fatty acids from two carbon units (FASII). The present study proposes the evaluating of the relationship of rhlG gene with rhamnolipids production. Mutants deleted in the gene mentioned above and the parental strain, Pseudomonas aeruginosa PAOI, were used for rhamnolipids production, using hydrophobic compounds as carbon source. The bacteria growth and rhamnolipids production was assed by gravimetric method and HPLC, respectively. The results showed a significant difference between the maximum biossurfactant concentrations achieved by the microorganisms. The parental strain produced 22.9 and 21.6 with soybean and sunflower oil, while the mutant synthesized 13.4 and 3.7, respectively. These results show that rhlG gene expression is related to rhamnolipids production when hydrophobic sources are used.