Surfactants from the sea: rhamnolipid production by marine bacteria

Biosurfactants produced from microbial sources are increasingly viewed by industry as more sustainable and less toxic alternatives to their chemically derived counterparts. One major class of biosurfactant that has the potential for commercial exploitation are the rhamnolipids. Rhamnolipids are composed of one or two rhamnose monosaccharides covalently bonded to fatty acid chains of varying molecular weights. The major microbial producer of rhamnolipid is Pseudomonas aeruginosa, however as this is a known human pathogen many industries are reluctant to utilise rhamnolipids synthesised by this bacterium. In order to avoid this problem a consortium of both academic and industrial partners have been screening marine bacteria for their ability to synthesis biosurfactants in a project called MARISURF. Here we report our findings of rhamnolipid production by two marine bacterial strains. Rhamnolipid production by these strains was first identified via the phenotypic screening of surface tension reduction. Rhamnolipid synthesis was then confirmed and characterised via HPLC-MS and NMR. Both 16S rDNA and subsequent genomic sequencing revealed these strains to be Marinobacter sp. and Pseudomonas mendocina, both species where rhamnolipid production was previously un-reported. Finally, both strains were assessed for potential pathogenicity using the Galleria mellonella model. Importantly for commercial exploitation, neither strain was shown to be harmful to G. mellonella over a 72 h infection period. Confirmed identification of rhamnolipid production in bacterial strains isolated from the marine environment highlights global oceans as an untapped resource in the ocean for the discovery of novel sources of biosurfactants.