Interactions between Nitrate-Reducing and Sulfate-Reducing Bacteria Coexisting in a Hydrogen-Fed Biofilm

摘要

To explore the relationships between denitrifying bacteria (DB) and sulfate-reducing bacteria (SRB) in H_2-fed biofilms, we used two H_2-based membrane biofilm reactors (MBfRs) with or without restrictions on H_2 availability. DB and SRB compete for H_2 and space in the biofilm, and sulfate (SO_4~(2-)) reduction should be out-competed when H_2 is limiting inside the biofilm. With H_2 availability restricted, nitrate (NO_3~-) reduction was proportional to the H_2 pressure and was complete at a H_2 pressure of 3 atm; SO_4~(2-) reduction began at H_2 ≥ 3.4 atm. Without restriction on H_2 availability, NO_3~- was the preferred electron acceptor, and SO_4~(2-) was reduced only when the NO_3~- surface loading was ≤0.13 g N/m~2-day. We assayed DB and SRB by quantitative polymerase chain reaction targeting the nitrite reductases and dissimilatory sulfite reductase, respectively. Whereas DB and SRB increased with higher H_2 pressures when H_2 availability was limiting, SRB did not decline with higher NO_3~- removal flux when H_2 availability was not limiting, even when SO_4~(2-) reduction was absent. The SRB trend reflects that the SRB's metabolic diversity allowed them to remain in the biofilm whether or not they were reducing SO_4~(2-). In all scenarios tested, the SRB were able to initiate strong SO_4~(2-) reduction only when competition for H_2 inside the biofilm was relieved by nearly complete removal of NO_3~-.