Assessment of the petroleum hydrocarbon biodegradation potential of the sediment microbial community from an urban fringing tidal marsh of Northern New England.

We assessed the impact of dodecane, n-hexane and gasoline on the microbial diversity of chronically polluted fringing tidal marsh sediment from the Great Bay Estuary of New Hampshire. Dilution cultures containing saturated alkane concentrations were sampled at zero, one and 10 days, and alkB and cyp153A1 alkane hydroxylase gene libraries and 16S rRNA sequences were analyzed. The initial sediment had the most diverse alkane hydroxylase sequences and phylogenetic composition whereas treated sediments became less functionally and phylogenetically diverse with alkane substrates apparently enriching a few dominant taxa. All 1- and 10-day samples were dominated by Pseudomonas -type alkane hydroxylase sequences except in dodecane treatments where primarily Rhodococcus -type alkane hydroxylases were detected. 16S rRNA profiling revealed that the Gammaproteobacteria, particularly Pseudomonas , dominated all one day samples, especially the n-hexane and gasoline treatments (63.2 and 47.2% respectively) and the 10-day n-hexane treatment (which contained 60.8% Pseudomonas and 18.6% Marinobacter ). In contrast, the 10 days of dodecane treatment enriched for Actinobacteria (26.2% Rhodococcus and 32.4% Mycobacterium ) and gasoline treatment enriched for Firmicutes (29.7%; mainly Bacillus , Lysinibacillus and Rumelibacillus ). Our data indicate that fringing tidal marshes contain microbial communities with alkane-degrading abilities similar to larger meadow marshes, and support the hypothesis that alkane exposure reduces the functional and phylogenetic diversity of microbial communities in an alkane-specific manner. Further research to evaluate the ability of such fringing marsh communities to rebound to pre-pollutant diversity levels should be conducted to better assess the threat of petroleum to these habitats.