Microbiology is the science that studies organisms that are usually too small to be seen with the naked eye. 

The environment is that part of the earth’s crust in which life exists. It consists of the biosphere, aerosphere, hydrosphere and lithosphere.

 The biosphere is the region of the earth inhabited by living organisms, the plants and animals including micro-organisms.  Micro-organisms are found in the air (aerosphere) we breathe; in the water (hydrosphere) we drink and in the soil (lithosphere) where crops are grown for the food we eat.

Many microbes are beneficial but some are harmful by causing diseases, deterioration and biodegradation. Human beings and micro-organisms are the major inhabitants of the environment. For human beings to control the diseases and other hazards caused by micro-organisms and to take advantage of the beneficial effects of these micro-organisms in the environment, it is necessary to know and understand the roles of this micro -organisms in the various environments.

Indigenous and Non-Indigenous Micro-organisms

 Micro- organisms can be categorised as indigenous or non-indigenous to an environment.