These tiny worms are very abundant. In a typical spade full of moist soil, there may be over a million nematodes. In fact, they are the most abundant multi- celled animals in the soil. The third type is the nematode that is considered the most important. It damages roots by sucking out the fluids of cells causing destruction of tissues and allowing an avenue for other diseases and microorganisms to infect the plant.
Producers use pesticides on certain plants that are very susceptible to nematodes.
The most common microorganism however are bacteria. In fact there are so many that in one teaspoon there can be as many as 500 million bacteria. Several types of these bacteria live in what is known as symbiotic relationship with plants. This means that organisms of different types live together for mutual benefit. The most common type of symbiotic bacteria are the nitrogen fixing bacteria, Rhizobia, that live in the roots of certain plants.