Carbon source effects on the mono/dirhamnolipid ratio produced by Pseudomonas aeruginosa L05, a new human respiratory isolate

Pseudomonas strains produce rhamnolipid mixtures (RLs) that generally consist of one or two molecules of rhamnose linked to one or two molecules of 3-hydroxyalkanoic acid. This study evaluates carbon source effects (glycerol, glucose, myristic acid, and Brassica carinata oil) on the synthesis of monorhamnolipids (mono-RLs) versus dirhamnolipids (di-RLs) in a human isolate of Pseudomonas aeruginosa PAL05. Spectrophotometry, an emulsifying index (E24) test, and an orcinol assay confirmed the production of RLs by PAL05. Purified RLs were characterized by 1H NMR analysis. PAL05 primarily produces mono-RLs when provided carbon sources containing long chain fatty acids (FAs) (myristic acid and B. carinata oil) and di-RLs when provided glycerol or glucose. qRT-PCR analysis showed that delayed expression of rhlC occurred when B. carinata oil was used, but not glycerol, glucose, or myristic acid. Our data show that the carbon source influenced the transcriptional expression of the rhlC gene and, consequently, the predominance of mono-RLs or di-RLs in PAL05 cultures.