Electrochemical communication in anaerobic digestion

Anaerobic microbial consortia oxidise or reduce a target organics (including nutrients) in order to share (i.e. extract and utilise) thermodynamic enthalpy energy (i.e. ATP with thermal energy) in anaerobic digestion or fermentation. Herein, the oxidation and reduction (i.e. electrochemical reaction) is a type of biochemical reaction that involves a transfer of electrons or hydrogens between two species and or taxa. The review discusses an electrochemical communication in the communal society leading to a 'bacterial cartel' which can be a type of struggling for life (to obtain the biochemical energy constantly). Interestingly, syntrophic bacteria (mostly acetogenic bacteria) flocculate the AD bacterial consortia and build two-layer biofilms or bioflocs to obtain the energy while producing a characteristic profile of fatty acids. The hydrolytic fermentative bacteria also dissociate with acidogenic bacteria for an association with the syntrophic bacteria when Δψ ranges in between −200 and −250 mV. Three examples (single-methanogenesis, long-chain fatty acid (LCFA) degradation and acid-fermentation process) were explained in the electrochemical origin. This concept remains quite controversial, but if true, may have major implications in broad areas of environmental and biological processes.