Rice based distillers dried grains with solubles as a low cost substrate for the production of a novel rhamnolipid biosurfactant having anti-biofilm activity against Candida tropicalis.

In this study, rhamnolipid (RL) production by Pseudomonas aeruginosa SS14 utilizing rice based Distillers Dried Grains with Solubles (rDDGS) as the sole carbon source was evaluated and the production parameters were optimized using response surface methodology. Highest RL (RL-rDDGS) yield was 14.87 g/L in a culture medium containing 12% (w/v) rDDGS and 11% (v/v) inoculum concentration after 48 h of fermentation at 35 °C. RL-rDDGS was produced as a mixture of mono and di-RL congeners with four novel homologues Rha-C18:2, Rha-C19, Rha-C9, and Rha-Rha-C19. The RL reduced the surface tension of water to 34.8 mN/m at a critical micelle concentration (CMC) value of 100 mg/L, exhibited high stability at a wide range of pH (6-12), heating time (0-120 min), and salinity (2-12% NaCl). Furthermore, RL-rDDGS demonstrated appreciable biofilm disruptive property against Candida tropicalis. This is the first report on the usage of rDDGS for sustainable and low cost production of RL.