Enhanced rhamnolipid production of Pseudomonas aeruginosa SG by increasing copy number of rhlAB genes with modified promoter

Rhamnolipid is a potent natural biosurfactant for industrial and environmental applications such as enhanced oil recovery, bioremediation, and biodegradation. The complex regulation network of key genes involved in the biosynthesis of rhamnolipid in Pseudomonas aeruginosa represents a challenge to the industrial production of rhamnolipid. In this study, rhlAB genes with native promoter were cloned from P. aeruginosa SG and inserted into plasmid pBBR1MCS-5 to construct recombinant plasmid pBBRPrhlAB. And rhlAB genes fused with the strong promoter of oprL gene from P. aeruginosa SG were used to construct recombinant plasmid pBBRPoprAB. Two recombinant plasmids were transformed to strain SG to construct the engineered strains PrhlAB and PoprAB. Both strains PrhlAB and PoprAB have higher yield of rhamnolipid than wild strain SG under both aerobic and anaerobic conditions. Increasing the copy number of rhlAB genes with indigenous strong promoter of oprL gene, engineered strain PoprAB has the highest yield of rhamnolipid (1.83-fold of strain SG and 1.19-fold of strain PrhlAB) under aerobic conditions. It is more efficient, economic and commercially feasible to use the engineered strain PoprAB for rhamnolipid production. Using the promoter of oprL gene to enhance production of other desirable product in P. aeruginosa may also be feasible.