Taxonomic and functional diversity of the microbiome in a a jet fuel contaminated site as revealed by combined application of in situ microcosms with metagenomic analysis. Replan Plume Study

Natural attenuation represents all processes that govern contaminant mass removal, which mainly occurs via microbial degradation in the environment. Although this process is intrinsic its rate and efficiency depend on multiple factors. This study aimed to characterize the microbial taxonomic and functional diversity in different aquifer sediments collected in the saturated zone and in-situ microcosms (BACTRAPs) amended with hydrocarbons (13C-labeled and 12C-labeled benzene, toluene and naphthalene) using 16S rRNA gene and “shotgun” Illumina high throughput sequencing at jet-fuel contaminated site. The BACTRAPs were installed to assess metabolism by assimilation of hydrocarbons by native bacteria. Results indicated that Proteobacteria, Actinobacteria and Firmicutes were the most dominant phyla (~98%) in the aquifer sendiments samples. Meanwhile, in the benzene- and toluene-amended BACTRAPs the phyla Firmicutes and Proteobacteria accounted for about 90% of total community. In the naphthalene-amended BACTRAP, members of the SR-FBR-L83 family (Order Ignavibacteriales) accounted for almost 80% of bacterial community. Functional annotation of metagenomes showed that only sediment sample located at the source-zone border and with the lowest BTEX concentration, has metabolic potential to degrade hydrocarbons aerobically. On the other hand, in-situ BACTRAPs allowed enrichment of hydrocarbon-degrading bacteria Metagenomic data suggested that the fumarate addition is the main mechanism for hydrocarbon activation in toluene. Also, evidences of methylation, hydroxylation and carboxylation as activation mechanisms for benzene anaerobic conversion were found. After 120 days of exposure in the contaminated groundwater, the isotopic analysis of fatty acids extracted from BACTRAPs have demonstrated the assimilation of isotopic labeled compounds in the cells of microbes expressed by strong isotopic enrichment. We propose that the microbiota in this site, contaminated by jet-fuel, has metabolic potential to degrade benzene and toluene by a syntrophic process, between members of the families Geobacteraceae and Peptococcaceae (genus Pelotomaculum), coupled to nitrate, iron and/or sulfate reduction.