Rhamnolipids: Production in bacteria other than Pseudomonas aeruginosa

Rhamnolipids produced by Pseudomonas aeruginosa are the most studied biosurfactants due to their potential applications in a wide variety of industries and the high levels of their production. However, even though these biosurfactants are already produced at an industrial scale, the fact that P. aeruginosa is an opportunistic pathogen impose a restriction for its large scale production due to the intrinsic health hazard of the process. Other bacterial species that have been reported to be rhamnolipid producers are the pathogens Burkholderia mallet and B. pseudomallei, and recently the non-pathogenic B. thailandensis. This short review presents information on rhamnolipid production by bacteria different from P. aeruginosa, as well as some approaches that have been taken to produce rhamnolipids using non-pathogenic bacteria by genetic engineering of different bacteria. The low frequency of occurrence of rhamnolipid production among natural isolates that are not P. aeruginosa or Burkholderia, as well as the absence of orthologs of the genes involved in rhamnolipid synthesis (rhl genes) among the hundreds of sequenced bacterial genomes, suggest that the rare reported cases of these type of rhamnolipid-producing bacteria have acquired this trait through horizontal gene transfer either from P. aeruginosa or from a member of Burkholderia.