Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 24, 2004
Publication Date: May 1, 2005
Citation: Gunther, N.W., Nunez, A., Fett, W.F., Solaiman, D. 2005. Production of rhamnolipids by pseudomonas chlororaphis, a non-pathogenic bacterium. Applied and Environmental Microbiology. 71(5):2288-2293. Interpretive Summary: The United States of America's agricultural production of fats and oils currently exceeds the domestic demand for these commodities. In addition, increasing competition in the export market for these agricultural materials has resulted in a significant decline in the potential value of this resource. The work described in this manuscript attempts to address this problem by finding a non-pathogenic bacterium harmless to humans, animals, and plants that is capable of making a valuable biosurfactant. Future research will then focus on adapting the innocuous bacterium, with its newly discovered ability to produce biosurfactant, to using agricultural oils as its sole food source. Previous to our discovery the only known producers of this type of biosurfactant were disease causing bacteria. In addition to being non-pathogenic our bacteria produce the biosurfactant under less energy-requiring conditions compared to the pathogenic organisms. Therefore, our discovery has taken the essential initial step to making it more feasible to use agricultural oils in the production of a valuable product through microbial bioconversion, potentially adding value, through new uses, to agriculturally derived commodities.
Technical Abstract: Rhamnolipids, naturally occurring biosurfactants constructed of rhamnose sugar molecules and ß-hydroxyalkanoic acids, have a wide range of potential commercial applications. In the course of a survey of thirty different bacterial isolates, we have identified, using a phenotypic assay for rhamnolipid production, a strain of the non-pathogenic bacterial species Pseudomonas chlororaphis that is capable of producing rhamnolipids. Rhamnolipid production by P. chlororaphis was achieved by growth at room temperature in static cultures of a mineral salts medium containing 2% glucose. We obtained yields of roughly 1 g/L of rhamnolipids, an amount comparable to the production levels reported in Pseudomonas aeruginosa grown with glucose as the carbon source. The rhamnolipids produced by P. chlororaphis appear to be exclusively the mono-rhamnolipid form. The most prevalent molecular species had one monounsaturated hydroxy fatty acid of 12 carbons and one saturated hydroxy fatty acid of 10 carbons. Pseudomonas chlororaphis, a nonpathogenic saprophyte of the soil, is currently employed as a biocontrol agent against certain types of plant fungal diseases. The pathogenic nature of all bacteria previously known to produce rhamnolipids has been a major obstacle to commercial production of rhamnolipids. The use of P. chlororaphis therefore greatly simplifies this matter by removing the need for containment systems and stringent separation processes in the production of rhamnolipids.