The microbial community of sub-surface sediment of a chronically contaminated SIC

Abstract

Hydrocarbons (HC), especially high molecular weight HC, are trapped in the sediments for a long time, making the benthic system a permanent pollution source, with several effects on the biota. Sediment bacterial communities play a significant role in the degradation of contaminants, both under aerobic and anaerobic conditions. In this work we focused on the bacterial communities of sediments (5-10 cm below surface), of a Site of Community Importance, the Priolo Bay, in Central Mediterranean Sea. The bay is situated in proximity to the Augusta Harbour, affected for decades by pollution from industrial and petrochemical plants. The microbial communities of sediments from six stations on two transects of the Priolo Bay were analysed by DGGE analysis, immediately after sampling and after two-months-enrichment on crude-oil under microaerophilic conditions. The communities responded to oil supplementation with a significant reduction in biodiversity and a shift in the composition that was different for each sampling station. Random sequencing of DGGE bands after crude-oil enrichment revealed the massive presence of Gammaproteobacteria and Clostridia followed by Alphaproteobacteria. Sequences were assigned to known HC-degrading genera (Marinobacter, Pseudomonas, Halomonas), to anaerobic nitrate-reducers (Vallitalea) and sulphate-reducers (Peptoniphilus) and to other genera already described in oiled sediments. Most of the detected bacteria were also isolated in pure culture. Epsilonproteobacteria were detected only at one station and were almost exclusively represented by the genus Arcobacter (98% clones of a 16S rDNA library). Molecular detection of Archaea is in progress. The composition of microbial communities inhabiting the subsurface sediments of the Priolo Bay is similar to that of subsurface petroleum reservoirs and produced water, where a syntrophic HC metabolism has been described