Chapter 2: Syntrophy in Anaerobic Digestion
Syntrophy is the closely associated relationship between at least two organisms based on electron (usually in the form of H2 or formate) transfer from one to the other. Syntrophs are bacteria that decompose a variety of organic materials (usually fatty acids, alcohols and aromatic compounds) to produce acetate and H2, through thermodynamically endergonic reactions. To make this reaction energetically feasible, syntrophs, as the name suggests, depend very much on H2-consuming methanogens. The dependence on partner organisms is also characterized by their close physical proximity that allows for instantaneous interspecies H2 transfer. Anaerobic ecosystems are based on such H2-producing and H2-consuming partnerships. Syntrophs are well-known as one of the most elusive organisms to cultivate, but efforts have been made to isolate them in the presence of partner organisms. Together with physiological and biochemical analyses of cultured syntrophs, recent high-throughput sequencing technologies are revealing the complex ecosystems in which syntrophs and methanogens drive the decomposition of organic materials.
