Characterisation of rhamnolipid production in a previously un-investigated, non-pathogenic marine Pseudomonad.

This study identifies, for the first time a significantly high level of synthesis of short chain di-rhamnolipids by a non-pathogenic marine Pseudomonas species. Pseudomonas sp. MCTG214(3b1) was isolated from a phytoplankton bloom of the coast of Florida, phylogenetically identified using 16S rDNA and gyrB sequencing, however was found to be unrelated to P. aeruginosa. Cell-free supernatant samples obtained from this strain showed significant reductions in surface tension signifying potential biosurfactant synthesis. HPLC-MS and NMR analysis of these samples indicated the presence of five different rhamnolipid congeners. Di-rhamnolipid synthesis accounted for 87% relative abundance and all congeners possessed fatty acid moieties consisting of 8-12 carbons. PCR screening of this strain revealed homologues to the P. aeruginosa RL synthesis genes rhlA and rhlB, however no rhlC homologue was identified. Using the Galleria mellonella larvae model, the strain was demonstrated to be far less pathogenic than P. aeruginosa. We postulate that RL synthesis in Pseudomonas sp. MCTG214(3b1) is carried out by enzymes expressed from rhlA/B homologues similar to those of P. aeruginosa, however a lack of rhlC potentially indicates the presence of an alternative yet unknown novel rhamnosyltransferase responsible for the production of the di-rhamnolipid congeners identified by HPLC-MS.