[Construction of mono/di-rhamnolipid ratios-manipulable strains and characterization of their corresponding...

Rhamnolipids (RLs) have emerged as one of the most promising classes of biosurfactants. The ratio of mono-RL to di-RL plays a significant role in determining its performance. Therefore, strains whose production of mono-RL and di-RL are manuplable, have advantage on applications in various scenarios. In this study, we developed a rhlC deletion mutant strain in Pseudomonas aeruginosa PAO1, which produced primarily mono-RL. Subsequently, we generated two complemented strains by integrating the arabinose-induced P_BAD-rhlC gene, either directly into the chromosomes or expressing it on plasmids. Our results indicate that the ratio of mono-RL to di-RL synthesized by the complemented strain gradually decreased as the concentration of arabinose (the inducer) increased. Consequently, there was a decrease in emulsification ability and an increase in surface tension and critical micelle concentration (CMC) of the corresponding rhamnolipids. The complemented strains without inducer can produce a small amount of di-rhamnolipids, which enhanced the surfactant properties. Notably, the rhamnolipids induced by 0.10% arabinose exhibited the most potent antibacterial effect.