We studied the microbial functional and structural interactions between nitrate (NO(3)(-)) and perchlorate (ClO(4)(-)) reductions in the hydrogen (H(2))-based membrane biofilm reactor (MBfR). When H(2) was not limiting, ClO(4)(-) and NO(3)(-) reductions were complete, and the MBfR's biofilm was composed mainly of bacteria from the ε- and β-proteobacteria classes, with autotrophic genera Sulfuricurvum, Hydrogenophaga, and Dechloromonas dominating the biofilm. Based on functional-gene and pyrosequencing assays, Dechloromonas played the most important role in ClO(4)(-) reduction, while Sulfuricurvum and Hydrogenophaga were responsible for NO(3)(-) reduction. When H(2) delivery was insufficient to completely reduce both electron acceptors, NO(3)(-) reduction out-competed ClO(4)(-) reduction for electrons from H(2), and mixotrophs become important in the MBfR biofilm. β-Proteobacteria became the dominant class, and Azonexus replaced Sulfuricurvum as a main genus. The changes suggest that facultative, NO(3)(-)-reducing bacteria had advantages over strict autotrophs when H(2) was limiting, because organic microbial products became important electron donors when H(2) was severely limiting.
For the first time, we demonstrate chromate (Cr(VI)) bioreduction using methane (CH4) as the sole electron donor in a membrane biofilm reactor (MBfR). The experiments were divided into five stages lasting a total of 90 days, and each stage achieved a steady state for at least 15 days. Due to continued acclimation of the microbial community, the Cr(VI)-reducing capacity of the biofilm kept increasing. Cr(VI) removal at the end of the 90-day test reached 95% at an influent Cr(VI) concentration of 3 mg Cr/L and a surface loading of 0.37g of Cr m(-2) day(-1). Meiothermus (Deinococci), a potential Cr(VI)-reducing bacterium, was negligible in the inoculum but dominated the MBfR biofilm after Cr(VI) was added to the reactor, while Methylosinus, a type II methanotrophs, represented 11%-21% of the total bacterial DNA in the biofilm. Synergy within a microbial consortia likely was responsible for Cr(VI) reduction based on CH4 oxidation. In the synergy, methanotrophs fermented CH4 to produce metabolic intermediates that were used by the Cr(VI)-reducing bacteria as electron donors. Solid Cr(III) was the main product, accounting for more than 88% of the reduced Cr in most cases. Transmission electron microscope (TEM) and energy dispersive X-ray (EDS) analysis showed that Cr(III) accumulated inside and outside of some bacterial cells, implying that different Cr(VI)-reducing mechanisms were involved.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.