Fig. 6.

A proposed conceptual model of a subsurface microbial loop for nutrient recycling at anoxic hydrocarbon- and organohalide-contaminated habitats. Hydrocarbons and organohalides serve as exogenous energy, electron, and carbon inputs, leading to primary biomass production in the absence of sunlight. Bacteria like environmental Spirochaetes use extracellular hydrolases and fermentative pathways to recycle biomass. In turn, they release usable electron donors such as hydrogen and potentially nutrients like phosphorus and nitrogen to the system. This in turn may stimulate microbial degradation processes performed by key players, e.g., sulfate-reducing bacteria and organohalide-respiring bacteria, and other community members like methanogenic archaea