Impact of Antibiotics Pretreatment on Bioelectrochemical CH₄ Production

Methane (CH₄)-producing bioelectrochemical systems (BES) are an attractive way to store excess renewable electricity and captured CO₂. Studies have suggested that methanogenesis via direct electron uptake from a biocathode is more energetically efficient than hydrogenotrophic methanogenesis. However, mechanisms and key microorganisms involved in direct electron uptake remain unclear, primarily because of H₂ produced by bacteria or extracellular hydrogenases in the system. In an attempt to minimize biological H₂ production and enrich for methanogens that could efficiently convert electrons from the cathode surface to CH₄, cathode chambers were pretreated with antibiotics targeting bacteria. We found that antibiotics pretreatment effectively reduced the proportion of H₂-producing bacteria and H₂-utilizing methanogens associated with the biocathode biofilm, and significantly promoted growth of acetoclastic methanogens from the genera Methanosarcina and Methanosaeta, several of which are known to participate in direct interspecies electron transfer. This shift in microbial community structure corresponded with 14%–36% higher cathode capture efficiencies. These results suggest that suppression of H₂ production by antibiotics pretreatment could be a promising way to enrich for methanogens that can efficiently transform electrons from a biocathode into CH₄