There are billions or trillions of them.Microbes are found everywhere in the biosphere, so wherever you look around their presence has invariable affects the environment.And that effects has good and bad effects.mainly their good effects are the nutrient cycles and the cycle of elements in all living things which is carbon,hydrogen,oxygen,nitrogen,sulfur,phosphorus,potassium,iron,sodium,calcium and magnesium.Nitrogen fixation and decomposition and oxidation of the atmosphere by cyanobacterias.And the bad effects is they cause huge diseases allied with viruses bombing the humanity forever