We isolated transposon Tn5-GM-induced mutants of Pseudomonas aeruginosa
PG201 that were unable to grow in minimal media containing
hexadecane as a
carbon source. Some of these mutants lacked extracellular rhamnolipids, as shown by measuring the surface and interfacial tensions of the cell culture supernatants. Furthermore, the concentrated
culture media of the mutant strains were tested for the presence of rhamnolipids by thin-layer chromatography and for
rhamnolipid activities, including
hemolysis and growth inhibition of Bacillus subtilis. Mutant 65E12 was unable to produce extracellular rhamnolipids under any of the conditions tested, lacked the capacity to take up 14C-labeled
hexadecane, and did not grow in media containing individual
alkanes with chain lengths ranging from C12 to C19. However, growth on these
alkanes and uptake of [14C]
hexadecane were restored when small amounts of purified rhamnolipids were added to the cultures. Mutant 59C7 was unable to grow in media containing
hexadecane, nor was it able to take up [14C]
hexadecane. The addition of small amounts of rhamnolipids restored growth on
alkanes and [14C]
hexadecane uptake. In
glucose-containing media, however, mutant 59C7 produced rhamnolipids at levels about twice as high as those of the wild-type strain. These results show that rhamnolipids play a major role in
hexadecane uptake and utilization by P. aeruginosa.