Implementation of an adaptive laboratory evolution strategy for improved production of valuable microbial secondary...

Microbial surface-active agents, such as rhamnolipids, represent an attractive substitute for synthetic surfactants. However, current production bioprocesses are generally inefficient. Adaptive laboratory evolution strategies could offer a promising avenue to improve secondary metabolites production. In the bacterium Burkholderia thailandensis, the social behaviour called swarming motility relies on biosynthesis of rhamnolipids. Since experimental swarming requires lower agar concentrations, we hypothesized that augmenting the agar concentration would constrain the cells to produce more rhamnolipids. Consecutive rounds of B. thailandensis cultivation on swarming media performed with increasing agar concentrations enhanced rhamnolipid production by the evolved populations, with a correlation between rhamnolipid production and agar concentrations. Whole-genome sequencing of superior producing evoluants revealed inactivating mutations in qsmR, which codes for a transcriptional regulator not known to influence rhamnolipid production. Results indicate that QsmR represses rhamnolipid biosynthetic genes transcription. The developed directed evolution strategy could be used to improve biosurfactant yields with other producing bacteria.