Impacts of bioremediation schemes on bacterial population in naphthalene-contaminated marine sediments

Microcosm experiments were conduced in which the surface of marine sediment was contaminated with naphthalene and subjected to either of three different bioremediation schemes, i.e., biostimulation (BS) by supplementing with slow-release nitrogen and phosphorus fertilizers, bioaugmentation (BA) by inoculating with Cycloclasticus sp. E2, an aromatics-degrading bacterium identified to play an important role for aromatic-hydrocarbon degradation in marine environments and combination (CB) of BS and BA. These three schemes were found to be similarly effective for removing naphthalene, while naphthalene disappearance in sediment without any treatment (WT) was slower than those in the treated sediments. Shifts in bacterial populations during and after bioremediation were analyzed by denaturing gradient gel electrophoresis (DGGE) of PCR-amplified 16S rRNA gene fragments. It was found that the Cycloclasticus rRNA type occurred as the strongest bands in the course of naphthalene degradation. Clustering analysis of DGGE profiles showed that bacterial populations in the WT, BS and CB sediments differed consistently from those in the uncontaminated control, while the profile for the BA sediment was finally included in the cluster for uncontaminated control sediments after a 150-day treatment. The results suggest that bioaugmentation with ecologically competent pollutant-degrading bacteria is an ecologically promising bioremediation scheme.