Microbial Activity in Marine Sediments Exposed to Hexadecane: A Laboratory Study

Bacteria have developed metabolic pathways that allow them to use hydrocarbons as the source of carbon and energy, so that they now play a key role throughout the degradation of petroleum in natural environments. However, knowledge regarding the degradation of petroleum by microorganisms is far larger in soils than in marine environments. Hexadecane (HXD) is one of the most representative alkanes present in petroleum, and one of the most frequently used in laboratory trials to evaluate the degradation of hydrocarbons by microorganisms. In this study, the capacity for HXD degradation by microorganisms present in marine sediments collected at 15 and 200 m depth is determined experimentally. For 42 days, kinetics studies are carried out to measure the consumption of HXD. Every 7 days the number of colony forming units (CFU) and HXD concentration are determined. Additionally, a biomass sample for pyrosequencing is collected at the beginning of the experiment (t(0)), the time of maximum bacterial growth (t(7) or t(21)) and at the end of the experiment (t(42)). A higher HXD consumption rate is observed in sediments from 15 m with respect to sediments from 200 m depth. The major HXD consumption occurs within the first 7 days for the sediments from 15 m and within 21 days for the sediments from 200 m depth; the biomass concentration CFU follows the same profile. The non-metric multidimensional scaling analysis of the non-cultivable bacteria indicates differences between bacteria species composition at different depths, which is confirmed by bacterial identification by pyrosequencing.