Because different plants need different relative amounts of fungi, bacteria, protozoa, and nematodes, the exact concentration and balance of bacteria, fungi, protozoa, or nematodes in the compost, extracts, or teas should reflect what needs to be added to the soil to bring the balance of the microorganisms to the levels that the plant requires.
There are beneficial and non-beneficial bacteria. Bacteria are fed directly by the plants and from organic material added to soil and hydroponic systems. Bacteria do not release the nutrients they take up from organic matter all by themselves. Instead they retain nutrients (N, P, S, Ca, Fe, etc.) in their biomass. Protozoa and nematodes are needed to complete the nutrient cycling process. Without all biological components in the plant medium, nutrient cycling will not occur.
Aerobic filamentous fungi generally grow as long threads of various diameters. These threads can branch or remain as one single thread. Fungi do not bend at sharp angles, unless branching. Fungal hyphae are of uniform diameter along their entire length, although the branch may be of a slightly different diameter than the main length of the hypha. Fungal hyphae do not tear, fray, tatter, or disintegrate. If a material is doing any of these things, then it is not a fungal hypha.
Photos of Protozoa
Protozoa are unicellular. Protozoa are motil; they produce flagella (flagellates) or cilia (ciliates) or cause their cytoplasm to stream (amoebae). All protozoa consume bacteria. Some amoebae can use enzymes to drill through fungal cell walls and consume fungal cytoplasm. Most flagellates and amoebae cannot tolerate reduced-oxygen conditions and either die (if change in conditions occurs rapidly) or become dormant, if they have time to go through the phsiological change before conditions become too bad.
Nematodes are round worms. They move like snakes. Nematodes need a layer of water in which to live and so can be restricted to soil with adequate water films. In soil, they live on the films surrounding soil particles and organic matter. Beneficial nematodes are strict aerobes and cannot tolerate reduced-oxygen conditions, whereas root-feeding nematodes seems to have no such restriction.
Microarthropods and Earthworms
Smaller organisms in soil usually hitch a ride on a local taxicabs such as a microarthropods. Microarthropods, many just barely visible to the naked eye, move all sorts of other organisms around in soil, compost, or leaf material. The fastest of these taxicabs can motor up to well over a meter a day.
Earthworms are major decomposers of dead and decomposting organic matter and derive their nutrition from the bacteria and fungi that grow upon these materials. They fragment organic matter and recycle the nutrients it contains.