Microbes Essay ⋆ Environment Essay Examples ⋆ EssayEmpire

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Microbes are a large, diverse group of organisms that exist as single cells or as colonies (clusters of cells of the same species) that are able to grow, generate energy, and reproduce independently of other cells. Microbes may be eukaryotic or prokaryotic. The eukaryotic microbes include algae, fungi, slime molds, and protozoa, and the prokaryotic microbes are the bacteria, archaebacteria, and cyanobacteria. (Because viruses cannot metabolize and reproduce without hijacking the metabolic processes of a host cell, viruses are not true cells. Thus, debate exists about whether viruses are living organisms and thus technically “microbes.”)

Microbes colonize virtually all terrestrial and aquatic habitats on Earth, from polar glaciers to deep-ocean hydrothermal vents. Microbes contain the greatest species diversity of any group of organisms on Earth. Bacteria have particularly high species diversity, and their tremendous metabolic flexibility allows them to inhabit the extremely unfavorable environments of deep sea hydrothermal vents, polar ice, and deep buried sediments.

The first organisms to evolve on Earth, microbes have played a key role in altering the gaseous makeup of the Earth’s atmosphere, and in the evolution of higher life forms. For example, early in the history of life, enormous colonies of aquatic cyanobacteria grew as pincushion-shaped organisms termed stromatolites. Over hundreds of millions of years, oxygen emitted by stromatolites as a by-product of their prolific photosynthesis progressively oxygenated the atmosphere. Scientists believe that the cyanobacteria-mediated oxygenation of the atmosphere facilitated the evolution of new organisms that rely upon oxygen. Soil fungi may have also facilitated the evolution of higher life forms. Root imprints of the earliest land plants fossilized in sedimentary rock show evidence of fungal symbionts present in root cortical cells. This suggests that the movement of plants onto land was aided by a mutualism with mycorrhizal fungi, specialized fungal microbes that today colonize the roots of most terrestrial vascular plants to aid in nutrient uptake.

People most commonly associate microbes (“germs”) with human illness, and indeed microbes act as pathogens or parasites on a great number of humans and other animals. The effects of microbial colonization of animal tissue, however, may be positive, negative, or neutral. Hair follicles are inhabited by an array of bacteria, yeasts, and filamentous fungi. Various pathogenic bacteria cause diseases such as Stapholococcus and Streptococcus infections, diphtheria, Legionnaires’ disease, tuberculosis, and sexually-transmitted diseases. The bacterium Yersinia pestis, transmitted to humans through bites from fleas that have fed on infected rodents, caused the bubonic plague, which killed 25 million people around the world over five years during the Middle Ages. Protozoan diseases such as leishmaniasis, African sleeping sickness, malaria, and amoebic dysentery cause serious illness and death to millions of people worldwide each year. The same bacteria that can cause illness when present in the mammalian stomach, however, are essential for nutrient transformation and uptake in the large intestine.

Ecological communities are also strongly affected by microbes. Pathogenic organisms, especially fungi, can have such broad-ranging effects that the composition of entire ecosystems can be changed indefinitely. For example, an Asian fungal pathogen Cryphonectria parasitica caused a widespread chestnut blight that virtually eliminated the stately American chestnut tree (Castenea dentata) from eastern deciduous forests in the mid-1900s. Other microbial plant pathogens cause significant plant and crop damage every year, and scientists are continually studying ways to mitigate damage to desirable plant species.

By no means are all microbes pathogenic. Microbes also have enormous positive impacts on agriculture, ecology, human welfare, and global economics. The discovery of the antibiotic properties of the soil fungus Penicillium was one of the most important microbial contributions to human health in recent history. Enzymes produced by microbial processes are used commercially to produce sweeteners such as glucose and fructose, and microbial enzymes and secondary metabolites are used industrially to produce various antibiotics and other pharmaceutical products. Chemical food additives such as amino acids, riboflavin, B12, and ascorbic acid (vitamin C) are also produced industrially from microbial by-products. Selected species of the single-celled yeast fungus, Saccharomyces, are used as baker’s yeast for raising bread and for beer and wine manufacturing. Beneficial mutualisms between microbes and plants, animals, and other microbes are common in nature. And, in all natural and agricultural ecosystems, soil bacteria and fungi decompose and mineralize soil organic matter, which recycles carbon, nutrients, and minerals through the biosphere.

Recent biotechnological developments have expanded the possibilities-and risks-of the industrial use of microbes. Genetic engineering of microbial cells is used to modify antibiotic-producing microbes, to produce vaccines against deadly viruses, and to isolate and produce mammalian proteins for medical research. Microbes that degrade pollutants are used in bioremediation of polluted soil and water. Scientists in the field of gene therapy who treat genetic diseases are currently experimenting with microbes that can control the expression of particular deleterious genes. Microbial transgenes inserted into whole plants and animals may also increase agricultural productivity and the nutritional value of food. It is important to note, however, that although genetic engineering holds promise for improving the quality of life for many people, the field is still highly controversial because many possible negative consequences remain unknown. Risks of genetic engineering include the escape of crop transgenes into wild weedy relatives, and risks to human health of ingesting transgenes from allergenic organisms. Long-term research will shed light on both the opportunities for and risks of using microbes in genetic engineering.

Bibliography:

T.D. Brock, T. Madigan, J.M. Martinko, and J. Parker, Biology of Microorganisms (Prentice Hall Publishers, 1994);
D. Dyer, A Field Guide to Bacteria 2003 (Cornell University Press, 2003).