Primary and secondary endosymbionts aphid

Symbiosis is a condition in which organisms of two different species coexist for an extended length of time. The organisms which are involved in symbiosis are called symbionts. When a microorganism is involved in the symbiosis it is called microbial symbiosis and there are different types. If both the organisms are mutually benefited, then it is called mutualism; if one organism is benefited and another organism is neither harmed nor benefited, it is then called commensalism; when one organism is benefited and another organism is harmed it is known as parasitism, but parasitism is not considered as a symbiosis between the microbes and the host. Microbial symbiosis is widespread in various animals which are regarded as nonpathogenic and many microbes are adapted to colonize and survive in an animal system.