Soil microorganisms are very important because they play an active role in soil fertility and are responsible for the decomposition of organic matter. Most soil microorganisms are beneficial to plants; however, some are pathogenic, which can cause different types of plant diseases.
Bacteria are prokaryotes (no true nucleus). They have one chromosome of double-stranded DNA in a ring and reproduce by binary fission. Most bacteria lack or have very few internal membranes. Most bacteria are beneficial, and only a few are pathogens.
Bacteria are tiny microorganisms that are invisible to the naked eye. They are one of three shapes: coccus (round); bacillus (rod-shaped); or spirillum (spiral). Beneficial bacteria decompose and use up dead plant and animal matter. Certain species of bacteria that live on the roots of plants convert nitrogen to plant food and feed the plants with essential plant nutrients.
Fungi prefer moist soils. Spores (young fungi) germinate and grow into slender tubular threads called hyphae, which may or may not have cross-walls depending on the species. Many species of soil fungi have their hyphae intimately attached to the roots of forest trees. These beneficial fungi help trees absorb water and mineral nutrients. Many fungi are pathogenic and can invade and kill plants systematically. Fungi can multiply and grow up to a mile long.
Protozoa are mostly free-living and unicellular. They are microscopic, do not have cell walls, lack specializations into tissues and usually reproduce asexually by binary fission. They feed by holophytic (produce their own food), holozoic (engulfing) or saprozoic (absorb nutrients from the extracellular environment) means; some are predatory or parasitic. Amoeba, paramecium and euglena are the three types of protozoa. Some are helpful because they eat harmful bacteria and are food for fish and other animals. Protozoa prefer soil that has plenty of water.