Bioaugmentation is a common bioremediation strategy for the clean up of polluted environments. It is still unknown whether the acceleration of hydrocarbon degradation rates after bioaugmentation results directly from the degradative activity of the added microbes or from positive interactions that promote the degradative activity of native community members. The application of stable isotope probing has allowed researches to link the degradation of hydrocarbons to specific marine hydrocarbonoclastic taxa. This technique therefore has potential in elucidating the contribution of bioaugmentation strains to contaminant mass removal.
In this study, RNA-stable isotope probing (RNA-SIP) was used to track the carbon from hexadecane and benzene into marine microbial communities after biostimulation and bioaugmentation regimes in laboratory microcosms. Bacteria Pseudomonas alcaliphila (naphthalene degrader)and Alteromonas addita (benzene degrader) isolated from coastal seawater were applied.
Acceleration of the degradation rates of naphthalene and benzene was observed in bioaugmented microcosms irrespective of the nutritional conditions. Analysis of the community using DGGE after RNA-SIP showed that the bioaugmentation strain P.alcaliphila dominated carbon acquisition from naphthalene in the absence of nutrients, but shared the consumption of the heavy carbon isotopes with the indigenous Ketogulonigenium vulgare under biostimulation conditions. In contrast, the bioaugmentation strain A. addita stimulated benzene degradation by indigenous bacteria (Rhodococcus opaus and Aestuaribacter halophilus), but did not derive carbon from benzene.
These results, particularly with benzene biodegradation, revealed potential microbial interactions that have not been observed before. They illustrate that bioaugmentation can have positive results from the promotion of other native populations that in conjunction are more efficient in biodegradation. This study is a major achievement that can have direct implications in the bioremediation of oil hydrocarbons in the marine environment.