Pathogenic microbes, though relatively few in number, have had and continue to have considerable impact on humans. Thus one of the most active and important fields in microbiology is medical microbiology, which deals with diseases of humans and animals. Medical microbiologists identify the agents causing infectious diseases and help plan measures for their control and elimination. Frequently they are involved in tracking down new, unidentified pathogens such as those causing variant Creutzfeldt-Jakob disease (the human version of “mad cow disease”), hantavirus pulmonary syndrome, and West Nile encephalitis. These microbiologists also study the ways microorganisms cause disease.
our understanding of the role of microbes in disease began to crystallize when we were able to isolate them in pure culture. Today, clinical laboratory scientists, the microbiologists who work in hospital and other clinical laboratories, use a variety of techniques to provide information needed by physicians to diagnose infectious disease. Increasingly, molecular genetic techniques are also being used.
Public health microbiology
Major epidemics have regularly affected human history. The 1918 influenza pandemic is of particular note; it killed more than 50 million people in about a year. Public health microbiology is concerned with the control and spread of such communicable diseases. Public health microbiologists and epidemiologists monitor the amount of disease in populations. Based on their observations, they can detect outbreaks and developing epidemics, and implement appropriate control measures. They also conduct surveillance for new diseases as well as bioterrorism events. Public health microbiologists working for local governments monitor community food establishments and water supplies to ensure they are safe and free from pathogens.
To understand, treat, and control infectious disease, it is important to understand how the immune system protects the body from pathogens; this question is the concern of immunology. Immunology is one of the fastest growing areas in science. Much of the growth began with the discovery of the human immunodeficiency virus (HIV), which specifically targets cells of the immune system. Immunology also deals with the nature and treatment of allergies and autoimmune diseases such as rheumatoid arthritis.
Microbial ecology is another important field in microbiology. Microbial ecology developed when early microbiologists such as Winogradsky and Beijerinck chose to investigate the ecological role of microorganisms rather than their role in disease. Today, a variety of approaches, including non-culture-based techniques, are used to describe the vast diversity of microbes in terms of their morphology, physiology, and relationships with organisms and the components of their habitats. The importance of microbes in global and local cycling of carbon, nitrogen, and sulfur is well documented; however, many questions are still unanswered. Of particular interest is the role of microbes in both the production and removal of greenhouse gases such as carbon dioxide and methane. Microbial ecologists also are employing microorganisms in bioremediation to reduce pollution. A new frontier in microbial ecology is the study of the microbes normally associated with the human body-so-called human microbiota. Scientists are currently trying to identify all members of the human microbiota using molecular techniques that grew out of Woese’s pioneering work to establish the phylogeny of microbes.
Agricultural microbiology is a field related to both medical microbiology and microbial ecology. Agricultural microbiology is concerned with the impact of microorganisms on agriculture. Microbes such as nitrogen-fixing bacteria play critical roles in the nitrogen cycle and affect soil fertility. Other microbes live in the digestive tracts of ruminants such as cattle and break down the plant materials these animals ingest. There are also plant and animal pathogens that have significant economic impact if not controlled. Furthermore, some pathogens of domestic animals also can cause human disease. Agricultural microbiologists work on methods to increase soil fertility and crop yields, study rumen microorganisms in order to increase meat and milk production, and try to combat plant and animal diseases. Currently many agricultural microbiologists are studying the use of bacterial and viral insect pathogens as substitutes for chemical pesticides.
Another important advance in industrial microbiology occurred in 1929 when Alexander Fleming discovered that the fungus Penicillium sp. produced what he called penicillin, the first antibiotic that could successfully control bacterial infections. Although it took World War II for scientists to learn how to mass-produce penicillin, scientists soon found other microorganisms capable of producing additional antibiotics. Today industrial microbiologists also use microorganisms to make products such as vaccines, steroids, alcohols and other solvents, vitamins, amino acids, and enzymes. Microbes are also being used to produce biofuels such as ethanol. These alternative fuels are renewable and may help decrease pollution associated with burning fossil fuels.
Industrial microbiologists identify or genetically engineer microbes of use to industrial processes, medicine, agriculture, and other commercial enterprises. They also utilize techniques to improve production by microbes and devise systems for culturing them and isolating the products they make.
The advances in medical microbiology, agricultural microbiology, food and dairy microbiology, and industrial microbiology are in many ways outgrowths of the labor of many microbiologists doing basic research in areas such as microbial physiology, microbial genetics, molecular biology, and bioinformatics. Microbes are metabolically diverse and can employ a wide variety of energy sources, including organic matter, inorganic molecules (e.g., H2 and NH3), and sunlight. Microbial physiologists study many aspects of the biology of microorganisms, including their metabolic capabilities. They also study the synthesis of antibiotics and toxins, the ways in which microorganisms survive harsh environmental conditions, and the effects of chemical and physical agents on microbial growth and survival. Microbial geneticists, molecular biologists, and bioinformaticists study the nature of genetic information and how it regulates the development and function of cells and organisms. The bacteria E. coli and Bacillus subtilis, the yeast Saccharomyces cerevisiae (baker’s yeast), and bacterial viruses such as T4 and lambda continue to be important model organisms used to understand biological phenomena.
Clearly, the future of microbiology is bright. Genomics in particular is revolutionizing microbiology, as scientists are now beginning to understand organisms in toto, rather than in a reductionist, piecemeal manner. How the genomes of microbes evolve, the nature of host-pathogen interactions, the minimum set of genes required for an organism to survive, and many more topics are aggressively being examined by molecular and genomic analyses. This is an exciting time to be a microbiologist. Enjoy the journey.