Laso-Pérez et al.3 propose a pathway for the anaerobic breakdown of butane in a microbial consortium formed between Candidatus Syntrophoarchaeum archaeal microbes and HotSeep-1 bacteria. Although the overall reaction in Candidatus Syntrophoarchaeum is thermodynamically unfavourable, the reaction proceeds by coupling to a thermodynamically favourable reaction in HotSeep-1 bacteria. The initial butane cleavage, a step known as hydrocarbon activation, creates a butane derivative bound to coenzyme M (butyl–CoM). The authors propose that butane activation is catalysed by an enzyme similar to methyl coenzyme M reductase (MCR). Through unknown steps, the intermediate butyl–CoM is converted to butyryl–CoA, which then undergoes four steps of fatty-acid oxidation to form acetyl–CoA. Wood–Ljungdahl pathway7 enzymes convert acetyl–CoA to carbon dioxide and a methyl group bound to the coenzyme tetrahydromethanopterin (H4MPT). This methyltetrahydromethanopterin derivative is then converted by Wolfe-cycle8 enzymes to CO2 in a process related to the methane degradation pathway known as reverse methanogenesis1. In the microbial butane-degradation pathway, the Wood–Ljungdahl pathway enzymes and Wolfe-cycle enzymes act to degrade, rather than synthesize, their normal products. These enzyme reversals occur when these reactions are coupled to the thermodynamically favourable reduction of sulfate to hydrogen sulfide, which occurs through interspecies electron transfer to HotSeep-1 bacteria.