Pseudomonas aeruginosa biosurfactant production in culture with glucose as carbon source

A rhamnolipid producing bacterium, P.aeruginosa MM1011 was previously isolated from crude oil over years. Isolated strain was identified by morphological, biochemical, physiological and 16srRNA (1). The identified Pseudomonas aeruginosa confirmed by Persian Type Culture Collection (PTCC idendification confirmation report No.1011). Glycolipid production by isolated bacterium using sugar beet molasses as a carbon and energy source was investigated.MM1011, was used for the development of a continuous process for biosurfactant production. The active compounds were identified as rhamnolipids. A final medium for production was designed in continuous culture by means of medium shifts, since the formation of surface-active compounds was decisively influenced by the composition and concentration of the medium components. In the presence of yeast extract, biosurfactant production was poor. For the nitrogen-source nitrate, which was superior to ammonium, an optimum carbon-to-nitrogen ratio of ca. 18 existed. The iron concentration needed to be minimized to27.5μg of FeSO4.7H20 per g of glucose. A carbon-to-phosphate ratio,Şc/p= 20, obtained the maximum production of rhamnolipids. The final productivity dilution rate diagram indicated that biosurfactant production was correlated to low growth rates (dilution rate below 0.18 h−1). With a medium containing 24.2 gr of glucose γl-1, a biosurfactant concentration (expressed as rhamnolipids) of up to 1.1 gr γl-1 was obtained in the cell-free culture liquid. The rhamnolipid mass concentration was 7.5 mg ml-1 and surface tension was reduced to 20 mN m-1