Bromate and Nitrate Bioreduction Coupled with Poly-β-hydroxybutyrate Production in a Methane-Based Membrane Biofilm Reactor

This work demonstrates bromate (BrO₃ ^-) reduction in a methane (CH₄)-based membrane biofilm reactor (MBfR), and it documents contrasting impacts of nitrate (NO₃ ^-) on BrO₃ ^- reduction, as well as formation of poly-β-hydroxybutyrate (PHB), an internal C- and electron-storage material. When the electron donor, CH₄, was in ample supply, NO₃ ^- enhanced BrO₃ ^- reduction by stimulating the growth of denitrifying bacteria (Meiothermus, Comamonadaceae, and Anaerolineaceae) able to reduce BrO₃ ^- and NO₃ ^- simultaneously. This was supported by increases in denitrifying enzymes (e.g., nitrate reductase, nitrite reductase, nitrous-oxide reductase, and nitric-oxide reductase) through quantitative polymerase chain reaction (qPCR) analysis and metagenomic prediction of these functional genes. When the electron donor was in limited supply, NO₃ ^- was the preferred electron acceptor over BrO₃ ^- due to competition for the common electron donor; this was supported by the significant oxidation of stored PHB when NO₃ ^- was high enough to cause electron-donor limitation. Methanotrophs (e.g., Methylocystis, Methylomonas, and genera within Comamonadaceae) were implicated as the main PHB producers in the biofilms, and their ability to oxidize PHB mitigated the impacts of competition for CH₄.