P14: Rhamnolipids production by Pseudomonas aeruginosa rpoS mutant

Pseudomonas aeruginosa strains have a complex gene regulatory network involved in rhamnolipids production, which is an important problem for the construction of strains with increased production of biosurfactants. Despite the advantages presented by biosurfactants, such as low toxicity, biodegradability and high stability, they are not widely used because of the high cost of production. Hence the importance of understanding the genes involved in regulating this metabolite. Therefore the aim of present study was to evaluate the relationship of the ropS gene with rhamnolipid production. The microorganisms used were P. aeruginosa PAO1 rpoS mutant and the wild strain. The experiments were conducted in 13 L bioreactor (Infors HT) with a nominal capacity of 5 L. For rhamnolipid production was used calcium-free mineral medium supplemented with sunflower oil and sodium nitrate as carbon and nitrogen source, respectively. Physicochemical parameters were: aeration – 2.0 L / min, temperature - 37 °C, pH - 6.8 ± 0.1, the stirring speed increased from 400 to 800 rpm adjusted to maintain pO₂ above 10%, the foam was controlled by antifoam Contraspum A4050. Maximum biomasses were 12.2 g/L to the unmodified bacterium and 7.6 g/L to the mutant. The rhamnolipids concentrations achieved were 22.6 and 16.3 g/ L, for the control and modified strain, respectively. Despite biosurfactant production of the mutant have been smaller, it was observed that the  induction period to begin rhamnolipids synthesis is much smaller in rpoS mutant, which starts the production from 18 hours while the wild strain only after 70 hours of fermentation.