Sediments of Ancona harbor: impact of pollution on bacterial diversity and enrichment of oil-degrading bacterial assemblages"

The Mediterranean Sea is one of the hottest oil spill spots in the world due to the intense oil tanker traffic and the high number of extractive platforms, pipelines and refineries settled around the basin coastlines. In addition, several coastal sites are threatened by the strong impact of the anthropogenic activities contributing to the occurrence of a high risk for the marine ecosystems healthiness. The Adriatic Sea, a semi-enclosed basin in the Mediterranean Sea, hosts different vulnerable and contaminated environments, including the Ancona harbor which sediments have been investigated in the present study by cultivation dependent and independent approaches. The analysis of bacterial diversity by DNA-based fingerprinting methods unveiled a different composition of the bacterial communities colonizing contaminated and not contaminated sediments in the Ancona harbor. A distance-based multivariate analysis for a linear model was used to investigate possible links between bacterial diversity and heavy metal concentrations. Results suggest that different pollutants may play distinct roles in controlling bacterial assemblages in sediment layers. Several slurry microcosms with sediments of the Ancona harbor were set up with oil hydrocarbons as the sole carbon source. The aim was to select and identify hydrocarbon degrading bacterial consortia from the autochthonous microbiome of the polluted sediments. Denaturing Gradient Gel Electrophoresis (DGGE) applied on the 16S rRNA bacterial gene revealed that both the site of sediment collection and the supplemented pollutants are involved in the selection of peculiar bacterial communities. Although different bacterial genera were identified by DGGE analysis, isolation efforts led to the obtainment of pure cultures belonging exclusively to the genus Alcanivorax. Additional tests were performed to identify the best conditions for hydrocarbons biodegradation. Overall, the results indicated the polluted sediments of the Ancona harbor as a promising environmental niche for the selection of valuable bacterial resources to be exploited for marine bioremediation. The results demonstrated, moreover, the need of innovative cultivation approaches aimed to obtain in pure culture marine species that showed to be enriched by the presence of pollutants, but were not cultivated in standard laboratory conditions.