ABSTRACT
Pseudomonas aeruginosa produces glycolipidic surface-active molecules [rhamnolipids] which have potential biotechnological applications. A previously identified biosurfactants-producing environmental isolate Pseudomonas aeruginosa strain 6 [Ps. 6] was selected. Comparing the kinetics of cell growth and biosurfactants production by Ps. 6 in bioreactor with that of shake flask, the bioreactor was characterized by about 35% higher cell density than that of shake flask. However, the production of rhamnolipids was higher in shake flask culture than in bioreactor culture, where their minimum surface tension values obtained were 12 mN/m and 13.9 mN/m, respectively
The biosurfactants solution produced by Ps. 6 was stable to all tested temperatures and pH range 2-14. However, the surface tension of the biosurfactants solution increased with increasing salinity. Moreover, its emulsiflcation indexes EI24 varied from 33.3% to 58%. It was also demonstrated that this biosurfactants solution form water in oil emulsion. Furthermore, the biosurfactants had greater antimicrobial activity against Bacillus spp. than S. aureus and M. flavus with undetectable activity against Gram negative bacteria and an experiment was done to know whether rhamnolipids act on the lipid part of cell membrane or the outer protein. On testing the efficiency of the biosurfactant solution as preservative using challenge test, it was found that <0.3 g% of the crude biosurfactants solution was not sufficient for preservation up to I month. Finally, the anti-biofllm activity of the produced biosurfactants reduced the biofilm formation ofS. aureus ATCC 6538p by more than 2 log units