Effects of 2-Bromoethanesulfonic Acid and 2- Chloroethanesulfonic Acid on Acetate Utilization in a Continuous-Flow Methanogenic Fixed-Film Column

2-Bromoethanesulfonic acid (BESA) and 2-chloroethanesulfonic acid (CESA) have been reported to be potent inhibitors of methane formation during methanogenic decomposition in batch cultures. However, in a laboratory-scale continuous-flow methanogenic fixed-film column containing a predominance of acetate-decarboxylating methanogens, BESA at 6 × 10⁻⁴ M produced only a 41% inhibition of acetate utilization, and CESA at 5.4 × 10⁻⁴ M produced a 37% inhibition of acetate utilization. BESA and CESA concentrations were not monitored in the effluent, so their fate is unknown. The organisms in the column were capable of degrading trace halogenated aliphatic compounds (~30 μg/liter) with acetate (100 mg/liter) as the primary substrate. Previous exposure of the cells to halogenated organic compounds may have conferred resistance to BESA and CESA. Degradation of the inhibitor compounds is another possible explanation for the observed effects.