Uptake and active efflux of polycyclic aromatic hydrocarbons by Pseudomonas fluorescens LP6a

The mechanism of transport of polycyclic aromatic hydrocarbons (PAHs) by Ps eudomonas fluorescens LP6a, a PAM-degrading bacterium, was studied by inhib iting membrane transport and measuring the resulting change in cellular upt ake. Three cultures were used: wild-type LP6a which carried a plasmid for P AH degradation, a transposon mutant lacking the first enzyme in the pathway for PAM degradation, and a cured strain without the plasmid. Washed cells were mixed with aqueous solutions of radiolabelled PAH; then the cells were removed by centrifugation, and the concentrations of PAM in the supernatan t and the cell pellet were measured. The change in the pellet and supernata nt concentrations after inhibitors of membrane transport (azide, cyanide, o r carbonyl cyanide m-chlorophenyl hydrazone) were added indicated the role of active transport. The data were consistent with the presence of two conf licting transport mechanisms: uptake by passive diffusion and an energy-dri ven efflux system to transport PAHs out of the cell. The efflux mechanism w as chromosomally encoded, Under the test conditions used, neither uptake no r efflux of phenanthrene by P, fluorescens LP6a was saturated. The efflux m echanism showed selectivity since phenanthrene, anthracene, and fluoranthen e were transported out of the cell but naphthalene was not.