What is Microbiology?
Microbiology is the discipline of biology that studies the fundamental nature and utility of unicellular organisms, both prokaryotic and eukaryotic, that are too small to be seen with the naked eye, i.e.. Many people think of microbiology as a largely medical discipline, to the study of disease-causing bacteria, fungi, protozoa and viruses. The importance of medical microbiology cannot be disputed, and the study of animal pathogens generates a large amount of human interest; but this definition of microbiology is far too narrow. The vast majority of microorganisms do not cause animal diseases and are not of immediate medical importance.
Recent work of microbiologists who were studying the molecular phylogeny of diverse bacteria has revealed that all living organisms on Earth belong to one of three co-equal, phylogenetic Domains of life. The Domains are the Bacteria (formerly "eubacteria") the Archaea (formerly "archaebacteria"), and the Eucarya (formally eukaryotic), consisting of animals, plants, fungi, algae, and protists. The Bacteria and Archaea Domains consist of prokaryotes, cells that usually are unicellular and undifferentiated but do not possess a true nucleus surrounded by a membrane. This modern view of phylogeny and cellular structure provides an evolutionary framework for studying the unifying themes among all organisms. This view also emphasizes the extreme biodiversity found among prokaryotic and eukaryotic microorganisms.
The prokaryotic cells appeared upon the earth shortly after the solidification of the earth's crust, billions of years before the appearance of the Eucarya-type cell of plants of animals. The longevity of the prokaryotic form of life may in part explain the astonishing physiological and molecular diversity found within the microbial world. Microorganisms have colonized all conceivable environments on the earth. Prokaryotic cells have been observed growing at temperatures ranging from below freezing to well over boiling, and at extremes of salinity, pH, and pressure. They have been found living and growing in Antarctic deserts, in saturated salt brines, in deep ocean thermal vents, and even in rocks several miles beneath the earth's surface. Despite their vast numbers, only a few percent of microbial species have even been observed by scientists and an even smaller percentage of those have been cultivated in the laboratory.
A major intellectual force driving our discipline, perhaps its most important question, is that of the extent to which microorganisms play a role in sustaining life on Earth. Microorganisms are key agents in the cycling of all the major elements of life. Thus, they are of primary importance as agents of biogeochemical changes. Photosynthesis is a process invented during evolution by prokaryotic organisms that were similar to today's cyanobacteria. Modern cyanobacteria and the green plant-chloroplasts that evolved along with them, are solely responsible for the photosynthetic water-splitting reactions that produce virtually all of the oxygen in our atmosphere. Likewise, until the advent of modern chemical engineering, only prokaryotes could fix atmospheric nitrogen in a form that is usable by other organisms. We know that microbes play essential roles as catalysts in the cycling of carbon, nitrogen, phosphorus, sulfur, iron, and other minerals through the biosphere. We are not yet able to understand how communities of microorganisms living together can carry out such a multitude of reactions so efficiently and effectively. Most ecologists and geochemists take microbial processes for granted without knowing about the vast diversity underlying those reactions.
A major goal of microbial ecology is to understand those processes at the most fundamental level of organisms, the biochemistry, the genes and their regulation. Microorganisms have served for decades as model systems for basic biological research in biochemistry, molecular biology, physiology, and genetics. They have been instrumental in introducing new concepts into molecular evolution and genomics; and they have great potential for exploitation in industry, agriculture, food production and environmental restoration. Currently, there is renewed interest in the ecology and diversity of microbial life in extreme environments, and because of the hypothesis that extant microbes in extreme environments on Earth, may be used as models for life on Mars and other planets. Microorganisms also are studied for their many practical applications and economic exploitation. They are used for the preparation of food and fiber, for preservation of foods, for production of chemicals, medicines, for the bioleaching of ores, and elimination of toxic material from the environment, to name a few well established areas of applied microbiology. Though some of these uses originate from traditional processes developed in antiquity, many other applications have sprung from fundamental research on the physiology, genetics, and molecular biology of microorganisms. Restriction endonucleases and the heat-stable DNA polymerases used in the polymerase chain reaction, enzymes derived solely from prokaryotic organisms, are two examples that illustrate the recent developments and utility of this research. The vast economic potential of diverse prokaryotes remain virtually unknown and untapped. The diversity of microorganisms, most of which remains to be documented, far exceeds that of animals (including insects) and plants.
The fundamental questions outlined above constitute the broad outline of the current discipline of General Microbiology. This discipline motivates thousands of microbiologists and their students in their scholarly pursuits. It also presents major opportunities for new discoveries in basic areas of biology that cannot be ignored.