Expression of genes involved in rhamnolipid synthesis in Pseudomonas aeruginosa PAO1 in a bioreactor cultivation.

There is a growing demand for economic bioprocesses based on sustainable resources rather than petrochemical-derived substances. Particular attention has been paid to rhamnolipids--surface-active glycolipids--that are naturally produced by Pseudomonas aeruginosa. Rhamnolipids have gained increased attention over the past years due to their versatile chemical and biological properties as well as numerous biotechnological applications. However, rhamnolipid synthesis is tightly governed by a complex growth-dependent regulatory network. Quantitative comprehension of the molecular and metabolic mechanisms during bioprocesses is key to manipulating and improving rhamnolipid production capacities in P. aeruginosa. In this study, P. aeruginosa PAO1 was grown under nitrogen limitation with sunflower oil as carbon and nitrate as nitrogen source in a batch fermentation process. Gene expression was monitored using quantitative PCR over the entire time course. Until late deceleration phase, an increase in relative gene expression of the las, rhl, and pqs quorum-sensing regulons was observed. Thereafter, expression of the rhamnolipid synthesis genes, rhlA and rhlC, as well as the las regulon was downregulated. RhlR was shown to remain upregulated at the late phase of the fermentation process.