Q.What is meant by the ubiquitous occurrence of micro-organisms?

Microbiology is the branch of biology devoted to the study of micro-organisms - living things too small to be seen with the unaided eye, including bacteria, which are found in essentially every habitat on Earth, from soil and water to the bodies of other organisms, an occurrence described as ubiquitous. The importance of microbiology as a field lies in exactly this ubiquity: because micro-organisms are involved in almost every natural process, from decomposition and nutrient cycling to disease and digestion, understanding them is essential to agriculture, medicine, industry and biotechnology alike.

Bacteria themselves are best understood as both friends and foes of man, and it is a misconception to think of them only as causes of disease. On the beneficial side, bacteria such as Escherichia coli - the intestinal bacterium widely used as a host organism in biotechnology - are used to manufacture useful products by genetic engineering; decomposer bacteria recycle nutrients from dead organic matter back into the environment; nitrogen-fixing bacteria such as Rhizobium enrich agricultural soils; and bacteria living naturally in the human gut assist with digestion. On the harmful side, a comparatively smaller number of bacterial species are pathogenic and cause disease. Because the beneficial roles of bacteria - in agriculture, industry, biotechnology and the natural recycling of nutrients - vastly outweigh their role as disease agents, describing bacteria only as 'germs' gives a misleadingly narrow and negative picture of their true importance.