Involvement of a rhamnolipid-producing strain of Pseudomonas aeruginosa in the degradation of polycyclic aromatic hydrocarbons by a bacterial community

Abstract

A rhamnolipid-producing strain of Pseudomonas aeruginosa GL1 was isolated from a bacterial community growing on a mixture of polycyclic aromatic hydrocarbons (PAH) as sole carbon source. Strain GL1 did not grow on PAH but grew on known degradation metabolites of phenanthrene (o-phthalic acid) and of naphthalene (salicylic acid). In co-culture with a phenanthrene- degrading strain, Ps. aeruginosa GL1 accelerated the degradation of phenanthrene. Strain GL1 was resistant to toxic amphiphilic compounds such as cationic and anionic detergents. Rhamnolipid production took place in a late stage growth in cultures of strain GL1 on glycerol or hexadecane. It coincided with a substantial decrease in cell hydrophobicity and with morphological changes of the outer membrane as observed by transmission electronic microscopy. The rhamnolipids produced inhibited the growth of bacteria such as Rhodococcus erythropolis, Bacillus cereus and Ps. fluorescens. The overall results suggested an outer membrane origin for the rhamnolipids. They also indicate that the utilization of PAH metabolites by strain GL1 is important for the stability of the PAH-degrading community.