Characterization of rhamnolipid production by Burkholderia glumae

Aims: To investigate if Burkholderia glumae can produce rhamnolipids, define a culture medium for good production yields, analyse their composition and determine their tensioactive properties Methods and Results: Burkholderia glumae AU6208 produces a large spectrum of mono-and di-rhamnolipid congeners with side chains varying between C-12-C-12 and C-16-C-16, the most abundant being Rha-Rha-C-14-C-14. The effects on rhamnolipid production of the cultivation temperature, nitrogen and carbon source were investigated. With urea as the nitrogen source and canola oil as the carbon source, a production of 1000 7 mg l) 1 was reached after 6 days. These rhamnolipids display a critical micelle concentration of 25-27 mg l(-1) and decrease the interfacial tension against hexadecane from 40 to 1 8 mN m(-1). They also have excellent emulsifying properties against long chain alkanes. Conclusions: Burkholderia glumae AU6208 can produce considerable amounts of rhamnolipids. They are produced as diversified mixtures of congeners. Their side chains are longer than those normally produced by those of Pseudomonas aeruginosa. They also present excellent tensioactive properties. Significance and Impact of the Study: In contrast with the classical rhamnolipid producer Ps. aeruginosa, B. glumae is not a pathogen to humans. This work shows that the industrial production of rhamnolipids with this species could be easier than with Ps. aeruginosa.