Q What are the major ecological roles of bacteria?

Bacteria are responsible for the decomposition process at the end of food webs and chains in this process they also liberate utile gases and nutrients for other living beings. Bacteria that live in the digestive tube of ruminants and of some insects digest cellulose for these animals. Some bacteria also participate in the nitrogen cycle, making fixation of nitrogen, nitrification and denitrification, almost forever in mutualist ecological interaction with plants. Bacteria present within living beings, for instance, some that live inside the bowels, compete with other pathogenic bacteria so controlling the population of noxious agents. There are also bacteria used in the production of medical drugs and bacteria that cause diseases.

Excessive mass or proliferation destruction of bacteria can impact entire ecosystems. For example, when a river is polluted by organic material the population of aerobic bacteria increases since the organic material is food for them the great number of bacteria then exhausts the oxygen dissolved in water and other aerobic beings like fishes undergo mass death.