The effect of carbon, nitrogen and iron ions on mono-rhamnolipid production and rhamnolipid synthesis gene expression by Pseudomonas aeruginosa ATCC 15442

Pseudomonas spp. are the main producers of rhamnolipids. These products have applications in pharmaceuticals, cosmetics, food industry and bioremediation. The biosynthesis of rhamnolipids is influenced by nutrient composition, pH and temperature. In this study, the impact of nutrients on the expression levels of rhamnolipid synthesis genes was evaluated in P. aeruginosa ATCC 15442. Glucose and glycerol were used as carbon sources; while, NaNO 3 , NH 4 NO 3 and yeast extract/peptone were employed as nitrogen sources. The effect of different concentrations of Fe 2+ and Fe 3+ on rhamnolipid synthesis genes was also evaluated. Highest biosurfactant production was obtained in minimal medium supplemented with glucose, NaNO 3 and Fe 2+ . Two rhamnolipid synthesis genes, r hlA and rhlB , were amplified with PCR. CapLC ESI–Ion trap-MS/MS detected only mono-rhamnolipid Rha–C 10 –C 10 in the extract. Although similar induction levels were recorded in the presence of 0.05 g/L iron ions, the presence of Fe 2+ resulted in higher expression levels than Fe 3+ at concentrations equivalent to 0.025 and 0.075 g/L.