what is bacteria

Bacteria are ubiquitous, mostly free-living organisms often consisting of a single biological cell. They constitute a large domain of prokaryotic microorganisms and are typically a few micrometers in length. Bacteria were among the first life forms to appear on Earth and are present in most of its habitats, including soil, water, and even extreme environments such as acidic hot springs and radioactive waste. While most bacteria are harmless and even beneficial, some can cause disease. The human body is full of bacteria, and in fact, it is estimated to contain more bacterial cells than human cells. Bacteria play a vital role in many ecosystems and are essential for processes such as nutrient cycling and the decomposition of dead matter