Bacteria are small single-celled organisms. Bacteria are found almost everywhere on Earth and are vital to the planet's ecosystems. Some species can live under extreme conditions of temperature and pressure. The human body is full of bacteria, and in fact is estimated to contain more bacterial cells than human cells. Most bacteria in the body are harmless, and some are even helpful. A relatively small number of species cause disease

Rhizobium is a bacteria which converts nitrogen into usable form it also produce a symbiotic relationship with the plant it lives in the root nodules of leguminous plant.

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