Abstract:Rhamnolipid is an important family of biosurfactant synthesized by many natural or engineered bacteria. Due to its excellent chemo-physical properties and environmental friendliness, it has been extensively used in many application scenarios (e.g., microbial enhanced oil recovery (MEOR), bioremediation), in place of its chemically synthesized counterparts. In commercial production, rhamnolipid is mainly produced by Pseudomonas aeruginosa, a natural producer with pathogenicity. Its genetic context also limits further enhancement of production using fermentation optimization approach. As a solution, genetic engineering approach can improve the bio-safety, yield, and product performance of rhamnolipid production, which has attracted increasing attention. However, few review articles systematically discussed this topic. Herein, we summarized recent advances in rhamnolipid production using genetically engineered microorganisms, particularly focusing on engineering strategies applied (e.g., heterogeneous production, pathway engineering, gene expression engineering, protein engineering, chassis engineering). Other than high yields, tailor-made rhamnolipid production (producing rhamnolipid mixture of specific composition) was also discussed. Finally, we proposed several potential strategies which may benefit rhamnolipid production:(1) using CRISPR-based tools for genome engineering; (2) gene expression optimization using synthetic promoter library and T7 polymerases; (3) synthetic protein scaffold for enzyme colocalization; (4) learning from polyhydroxyalkanoates (PHA) bioengineering; (5) development of in vivo directed evolution platform and rhamnolipid biosensor; (6) analysis of genome resequencing data.
