title: Nitrate shaped the selenate-reducing microbial community in a hydrogen-based biofilm reactor.
abstract: To study the effect of nitrate (NO3(-)) on selenate (SeO4(2-)) reduction, we tested a H2-based biofilm with a range of influent NO3(-) loadings. When SeO4(2-) was the only electron acceptor (stage 1), 40% of the influent SeO4(2-) was reduced to insoluble elemental selenium (Se(0)). SeO4(2-) reduction was dramatically inhibited when NO3(-) was added at a surface loading larger than 1.14 g of N m(-2) day(-1), when H2 delivery became limiting and only 80% of the input NO3(-) was reduced (stage 2). In stage 3, when NO3(-) was again removed from the influent, SeO4(2-) reduction was re-established and increased to 60% conversion to Se(0). SeO4(2-) reduction remained stable at 60% in stages 4 and 5, when the NO3(-) surface loading was re-introduced at ≤ 0.53 g of N m(-2) day(-1), allowing for complete NO3(-) reduction. The selenate-reducing microbial community was significantly reshaped by the high NO3(-) surface loading in stage 2, and it remained stable through stages 3-5. In particular, the abundance of α-Proteobacteria decreased from 30% in stage 1 to less than 10% of total bacteria in stage 2. β-Proteobacteria, which represented about 55% of total bacteria in the biofilm in stage 1, increased to more than 90% of phylotypes in stage 2. Hydrogenophaga, an autotrophic denitrifier, was positively correlated with NO3(-) flux. Thus, introducing a NO3(-) loading high enough to cause H2 limitation and suppress SeO4(2-) reduction had a long-lasting effect on the microbial community structure, which was confirmed by principal coordinate analysis, although SeO4(2-) reduction remained intact.
authors.affiliation: Ministry of Education, Key Laboratory of Environmental Remediation and Ecosystem Health, College of Environmental and Resource Science, Zhejiang University , Hangzhou 310029, People's Republic of China.
authors.forename: Chun-Yu
authors.initials: CY
authors.lastname: Lai
authors.forename: Xiaoe
authors.initials: X
authors.lastname: Yang
authors.forename: Youneng
authors.initials: Y
authors.lastname: Tang
authors.forename: Bruce E
authors.initials: BE
authors.lastname: Rittmann
authors.forename: He-Ping
authors.initials: HP
authors.lastname: Zhao
mesh_terms: D018441:Biofilms; D019149:Bioreactors / Q000382:microbiology*; D006859:Hydrogen / Q000378:metabolism; D059013:Microbial Consortia; D009566:Nitrates / Q000378:metabolism*; D020560:Proteobacteria / Q000378:metabolism; D064586:Selenic Acid / Q000378:metabolism*
chemical_list: D009566:Nitrates; D006859:Hydrogen; D064586:Selenic Acid