Role of rhamnolipid biosurfactants in the uptake and mineralization of hexadecane in Pseudomonas aeruginosa

A study was undertaken to investigate the mechanisms for biosurfactant-enha nced hexadecane uptake into Pseudomonas aeruginosa. Two strains of Ps. aeru ginosa were studied, one producing rhamnolipids (PG201) and the other rhamn olipid deficient (UO299). Rhamnolipids produced by PG201 acted to increase the solubility of n-hexadecane in the culture medium (from 1.84 to 22.76 mu g l(-1)). Rates of C-14-n-hexadecane uptake and mineralization were higher in PG201 than in UO299. However, the degree of difference was lower than e xpected. Additional studies were carried out on the cell surface properties of the two strains. During growth on n-hexadecane, the cell surface hydrop hobicity of both PG201 (50.5%) and UO299 (33.7%) increased compared with th at observed in water-soluble growth substrates (7-8%). Studies mere also ca rried out to ascertain any energy requirements for the transport of n-hexad ecane into Ps. aeruginosa cells. The addition of CCCP (an inhibitor of cyto chrome oxidase which thereby blocks oxidative phosphorylation) at a range o f concentrations caused a marked decrease in n-hexadecane uptake, indicatin g that n-hexadecane uptake in Ps. aeruginosa is an energy-dependent process . These studies support the hypothesis of alkane transport into microbial c ells by direct contact with larger alkane droplets and by pseudosolubilizat ion. Also, it appears that both mechanisms occur simultaneously.