Virtually all methane released to the biosphere (estimated to be approximately 1 billion tons per year) is produced by methanogenic archaea living in close association with other anaerobic microorganisms. We have examined the genetic and metabolic basis of this common interdependency using model systems composed of different pairings of facultative syntrophs (Desulfovibrio species) growing in syntrophic association with hydrogenotrophic methanogens. Combined genetic and physiological studies have revealed significant variability among species in the electron transfer systems supporting syntrophy, but also point to common roles of electron bifurcation and electron confurcation in energetics.
Complementary studies have also revealed the capacity for rapid adaptive improvement of nascent mutualisms over relatively short evolutionary time periods in the laboratory. Evolved communities grew two- to three-fold faster and were up to 40% more productive than ancestral community assemblies. Sequence analysis of the genomes of evolved populations has identified shared mutations in metabolic systems associated with energy transformation, suggesting common adaptive solutions. Thus, these experiments are providing mechanistic understanding of a mutualism typical of that sustaining most biogenic methane production.Back