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Background  Rhamnolipids are surface active molecules composed of rhamnose and β-hydroxydecanoic acid. These biosurfactants are produced mainly by  Pseudomonas aeruginosa  and have been thoroughly investigated since their early discovery. Recently, they have attracted renewed attention because of their involvement in various multicellular behaviors. Despite this high interest, only very few studies have focused on the production of rhamnolipids by  Burkholderia  species.    Results  Orthologs of  rhlA ,  rhlB  and  rhlC , which are responsible for the biosynthesis of rhamnolipids in  P. aeruginosa , have been found in the non-infectious  Burkholderia thailandensis , as well as in the genetically similar important pathogen  B. pseudomallei . In contrast to  P. aeruginosa , both  Burkholderia  species contain these three genes necessary for rhamnolipid production within a single gene cluster. Furthermore, two identical, paralogous copies of this gene cluster are found on the second chromosome of these bacteria. Both  Burkholderia  spp. produce rhamnolipids containing 3-hydroxy fatty acid moieties with longer side chains than those described for  P. aeruginosa . Additionally, the rhamnolipids produced by  B. thailandensis  contain a much larger proportion of dirhamnolipids versus monorhamnolipids when compared to  P. aeruginosa . The rhamnolipids produced by  B. thailandensis  reduce the surface tension of water to 42 mN/m while displaying a critical micelle concentration value of 225 mg/L. Separate mutations in both  rhlA  alleles, which are responsible for the synthesis of the rhamnolipid precursor 3-(3-hydroxyalkanoyloxy)alkanoic acid, prove that both copies of the  rhl  gene cluster are functional, but one contributes more to the total production than the other. Finally, a double Δ rhlA  mutant that is completely devoid of rhamnolipid production is incapable of swarming motility, showing that both gene clusters contribute to this phenotype.    Conclusions  Collectively, these results add another  Burkholderia  species to the list of bacteria able to produce rhamnolipids and this, by the means of two identical functional gene clusters. Our results also demonstrate the very impressive tensio-active properties these long-chain rhamnolipids possess in comparison to the well-studied short-chain ones from  P. aeruginosa .

Burkholderia thailandensis harbors two identical rhl gene clusters responsible for the biosynthesis of rhamnolipids