Population dynamics of a bacterial consortium from a marine sediment of the Gulf of Mexico during biodegradation of the aromatic fraction of heavy crude oil.

In the marine environment, uncontained crude oil is dispersed and degraded by abiotic or biotic processes; native bacterial populations gradually adapt to integrate interspecific and intraspecific metabolic networks for efficient and dynamic utilization of xenobiotic substrates as carbon source. Aromatic compounds accumulate in marine sediments and bacterial populations at these sites play a crucial role in the mobilization of those complex molecules into the global geochemical cycles. The aim of this work was to use native bacteria from a marine sediment sample in the Gulf of Mexico to enhance the biodegradation of the aromatic fraction from a heavy crude oil, as the sole carbon source, during a 200-day microcosm experiment. This process involved the gradual increase of the aromatic fraction into the culture to promote bacterial enrichment; the increase in viable cells correlated well with a biodegradation pattern of the aromatic fraction at some points. Bacterial biodiversity, as revealed by metagenomic and microbiological approaches, indicates that bacterial groups are present at all fraction concentrations, but with changes in abundance, richness and dominance. Population dynamics revealed the presence of bacteria that modify emulsification and surface tension reduction values, which could promote the incorporation of the highly hydrophobic polyaromatic compounds into the culture aqueous phase for their biodegradation by hydrocarbonoclastic bacteria present. On the other hand, the presence of non-hydrocarbonoclastic bacteria probably is sustained by cross-feeding events involving sugars, amino acids, short carbon compounds, lipids produced by the former bacteria by co-metabolism of complex aromatic substrates, which are transformed into diverse biomolecules for biofilm development to promote a bacterial population dynamics adapted to this environment.