Geobacter-based syntrophy drives biogenic element cycling in anoxic soils: a review.

Microbial syntrophy is a central organizing principle in anoxic soils, where the degradation of organic matter and the cycling of nitrogen, sulfur, and iron are constrained by electron availability and thermodynamics. Among soil anaerobes, Geobacter species occupy a distinctive ecological anoxic niche in which they form syntrophy relationship with partner cells to exchange electrons for anaerobic carbon mineralization, methane production, nitrate reduction, sulfur and Fe(III) reduction. Here, we review how Geobacter-based syntrophy contributes to C/N/S/Fe cycling in anoxic soils. We first summarize the mechanisms of Geobacter-based syntrophy through interspecies electron transfer (IET), then detailedly evaluate how Geobacter-based syntrophy regulates C/N/S/Fe cycling respectively in soils with specific metabolic pathways, enzymes, and ecological outputs. We propose that Geobacter-based syntrophy should be viewed as a redox-partitioning mechanism that determines whether electrons from organic carbon are routed toward methane, ammonium, gaseous nitrogen, minerals, or microbial biomass.