INVOLVEMENT OF A RHAMNOLIPID-PRODUCING STRAIN OF PSEUDOMONAS-AERUGINOSA IN THE DEGRADATION OF POLYCYCLIC AROMATIC-HYDROCARBONS BY A BACTERIAL COMMUNITY

A rhamnolipid-producing strain of Pseudomonas aeruginosa GL1 was isola ted from a bacterial community growing on a mixture of polycyclic arom atic hydrocarbons (PAH) as sole carbon source. Strain GL1 did not grow on PAH but grew on known degradation metabolites of phenanthrene (o-p hthalic acid) and of naphthalene (salicylic acid). In co-culture with a phenanthrene-degrading strain, Ps. aeruginosa GL1 accelerated the de gradation of phenanthrene. Strain GLI was resistant to toxic amphiphil ic compounds such as cationic and anionic detergents. Rhamnolipid prod uction took place in a late stage growth in cultures of strain GL1 on glycerol or n-hexadecane. It coincided with a substantial decrease in cell hydrophobicity and with morphological changes of the outer membra ne as observed by transmission electronic microscopy. The rhamnolipids produced inhibited the growth of bacteria such as Rhodococcus erythro polis, Bacillus cereus and Ps. fluorescens. The overall results sugges ted an outer membrane origin for the rhamnolipids. They also indicate that the utilization of PAH metabolites by strain GLI is important for the stability of the PAM-degrading community.