Production of rhamnolipids by semi-solid-state fermentation with Pseudomonas aeruginosa RG18 for heavy metal desorption

Foaming problem and cost of substrate limit the commercial application of rhamnolipids, a potential biosurfactant produced by Pseudomonas aeruginosa. We explored the production of rhamnolipids by a semi-solid-state (SSS) fermentation strategy with glycerol as carbon source and rapeseed/wheat bran as matrix, along with the capacity of the produced rhamnolipids to solubilize lead and cadmium in aqueous solution. Structural analysis by MALDI-TOF MS indicated the increased proportion of mono-rhamnolipids from SSS fermentation. E24 results showed the stronger emulsification capacity and reduced water tension of the SSS fermentation product. Rhamnolipids from SSS fermentation can desorb lead/cadmium from contaminated soil effectively and heavy metals in exchangeable and carbonate forms were easily removed. Our findings suggest that SSS fermentation is an alternative for the economical production of rhamnolipids and the product can be used to solubilize heavy metals from soils.