Biosurfactant Production with Glucose as a Carbon Source

H. Rashedi, E. Jamshidi, M. Mazaheri Assadi and B. Bonakdarpour

Abstract
A rhamnolipid producing bacterium, P.aeruginosa MM1011, was previously over years isolated from crude oil. Isolated strain was identified by morphological, biochemical, physiological, and 16srRNA.1 The identified Pseudomonas aeruginosa was 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 to 27.5 μg of FeSO4 · 7H20 per g of glucose. A carbon-to-phosphate mass ratio, ζc/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 g l–1 of glucose, a biosurfactant mass concentration (expressed as rhamnolipids) of up to 1.1 g l–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–1.2,3

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Keywords
biosurfactant, wild type, Pseudomonas aeruginosa, sugar beet Molasses