Ecological and Evolutionary Interactions in Syntrophic Methanogenic Consortia

Abstract

In natural and engineered ecosystems, diverse species of microbes coexist and interact, resulting in the emergence of community functions. Since microbes have evolved under such circumstances, it is reasonable to deduce that they have acquired strategies for specific interspecies interactions in complex microbial communities. In this review, we discuss the ecological and evolutionary interactions in syntrophic methanogenic consortia comprised of organic acid-oxidizing bacteria and methanogenic archaea. These microbes are known to exhibit mutual interactions (syntrophy), although the molecular mechanisms underlying these sophisticated partnerships have only just been discovered. In addition, recent genomic studies have provided insights into evolutionary interactions among members of methanogenic consortia, from which a novel concept termed "niche-associated evolution" has been proposed for interpreting how specialists evolve in a biological community. We suggest that microbial interspecies interactions are much more complex and sophisticated than hitherto realized and pivotal to the development and functioning of microbial communities.

Microbial interspecies electron transfer via electric currents through conductive minerals

“…In anaerobic biota, electrons are transferred between different species of microbes [interspecies electron transfer (IET)], establishing a basis of cooperative behaviors and community functions (17)(18)(19). IET mechanisms described so far are based on diffusion of redox chemical species (20) and/or direct contact in cell aggregates (21).…”

Role and Potential of Direct Interspecies Electron Transfer in Anaerobic Digestion

“…Energies 2018, 11, 107 5 of 17 considered the rate-limiting step of the overall AD process [33]. Therefore, under high organic loading conditions, fast growth of acidogenic bacteria can lead to excessive accumulation of VFAs and hydrogen to levels that cannot be effectively handled by slow-growing methanogens and VFA degraders.…”

“…Given that there are different types of iron oxide particles with different conductivities, such as insulative (ferrihydrite), semiconductive (hematite and goethite), and conductive (magnetite), they are suitable for use in experiments to test whether the DIET mechanism is stimulated by conductive materials. Kato and Watanabe [33] first explored the use of this characteristic (i.e., different conductivities of different types of iron oxides) to observe interactions in soil bacteria, and they found that nanosized iron oxide particles can facilitate the respiratory mechanism of soil microbial cultures. Kato et al [10] further confirmed that the conductivity of iron oxides can determine the methanogenesis rate from enriched microbial communities from rice paddy soils.…”

“…The results suggest that the Geobacter used (semi)conductive iron oxides as electron conduits towards Methanosarcina, making them candidates for syntrophic partnership (Figure 4). Since Kato and Watanabe's [33] study, magnetite has attracted much attention as a promoter for DIET. It is the main component of iron ores on Earth, and it has conductive and ferrimagnetic characteristics.…”

“…They used nanosized (30 nm) magnetite particles to accelerate the methane production rate in the whole subculture enrichment. The addition of anthraquinone-2-sulfonate (AQS), which acted as an electron shuttle outside the cells, did not facilitate methane production, and the stimulatory effect of magnetite disappeared completely when Since Kato and Watanabe's [33] study, magnetite has attracted much attention as a promoter for DIET. It is the main component of iron ores on Earth, and it has conductive and ferrimagnetic characteristics.…”