They perform many functions in the ecosystem, most importantly in enzymatic transformations. They are able to oxidize or reduce many chemical elements in the soil. For example, nitrogen is tansformed from ammonium to nitrite and nitrate by two different species. Fixation of nitrogen from atmospheric N 2 into organic forms is also performed by bacteria, either in symbiotic associations with plants or independently. The net-negative electrical charge on bacteria and organic materials produced by them are important in the formation of soil aggregates and soil structure.
Actinomycetes are a special type of bacteria.
They have important roles in the decomposition of organic matter, release of plant nutrients, and in some cases form symbiotic relationships with plants including nitrogen fixation. Streptomyces spp. are responsible for the typical odor of a plowed field. Fungi are very important in the soil ecosystem. The decomposition of organic matter releases plant nutrients into the ecosystem for other organisms to use. Fungal hyphae also play a role in the developement of soil structure.