Relationship between microbial community composition, population densities and methyl tert-butyl ether (MTBE) bioremediation in ex situ columns and a field scale bioreactor

While bioreactors have been investigated as a treatment option for Methyl tert-butyl ether (MTBE), little is known about their microbial communities and particularly about attached bacteria in immobilized bioreactors. Our objectives were to test the potential of uninoculated, field-scale granulated activated carbon (GAC) bioreactors for MTBE degradation and to characterize the MTBE-degrading communities. Two test systems in a North Hollywood, CA, aquifer were studied: a field-scale bioreactor treating an MTBE plume and field columns fed oxygenated groundwater and a range of MTBE concentrations (0.050 to 14 mg/L). Quantitative PCR (Q-PCR) was used to enumerate total bacteria and native sequences similar to the MTBE-degrading bacterium---Methylibium petroleiphilum PM1. Bacterial fingerprints and phylogenetic compositions were compared using Denaturing Gel Gradient Electrophoresis (DGGE).; Both systems were rapidly colonized by native bacteria. MTBE and TBA removal efficiencies were >99% in the bioreactor and a maximum 100% and 98% respectively in the columns. Most bacteria (>99%) were attached rather aqueous and the GAC effectively retained high biomass. While attached total bacteria did not increase above initial densities, attached PM1-like bacteria increased on GAC surfaces by several log orders and comprised up to 30% to 40% of all bacteria in the bioreactor and columns respectively. Attached PM1-like, but not total bacteria, in columns were positively correlated to MTBE loading and removal rates. Attached communities were more similar to one other with lower species richness than aqueous communities. In the field columns, the attached microbial community in the high MTBE concentration columns differed from that of the low concentration columns. Attached communities in high concentration columns became dominated by three bands identified as M. petroleiphilum PM1 (100%), M. petroleiphilum PM1 (99%), and Rubrivivax gelatinosus (99%).; This study demonstrates that GAC bioreactors can sustain high densities of MTBE-degrading bacteria that can rapidly degrade MTBE and TBA and inoculation by ex situ bacteria may be unnecessary where native degraders are present. These experiments provide compelling evidence of the importance of native PM1-like bacteria as a member of the microbial community in immobilized MTBE treatment systems.