The Microbial World
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1-3 Microbes are often helpful, not harmful
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[Prev] | [Next]- Microbes form important mutualistic relationships with all sorts of organisms. Many of these relationships are important from a human perspective.
From the beginning of microbiology, significant resources have been spent to understand and fight disease-causing microorganisms. You may be surprised to learn that only a small fraction of microbes are involved in disease; many other microbes actually enhance our well being. The harmless microbes that live in our intestines and on our skin actually help us fight off disease. They actively antagonize other bacteria and take up space, preventing potential pathogens from gaining a foothold on our bodies. The microbial community in humans not only protects us from disease, but also provides needed vitamins, such as B12. We have entire communities of microorganisms in our digestive systems that contribute to our overall health. In fact, like all other large organisms, humans are actually consortia of different organisms - there are more non-human cells in and on our bodies than there are human cells!
Human health and nutrition also depends on healthy farm animals. Cows, sheep and other ruminant animals utilize their microbial associates to degrade plant material into useful nutrients. Figure 1-1 shows the cow, one example of a ruminant animal. Without these bacteria inside ruminants, growth on plant material would be impossible.
Figure 1-1 The cow as an example of a ruminant animal
In contrast to humans, ruminant animals have a complex system of stomachs that harbor large numbers of microorganisms. These microbes degrade the tough plant material eaten by the animal into usable nutrients. Without the assistance of the microbes, ruminant animals would not be able to digest the food they eat. (Source: Keith Weller, USDA.)
Commercial crops are also central to human prosperity, and much of agriculture depends upon the activities of microbes. For example, an entire group of plants, the legumes, forms a cooperative relationship with certain bacteria. These bacteria convert nitrogen gas to ammonia for the plant, an important nutrient that is often limiting in the environment. Figure 1-17 shows a leguminous plant and the special structures on the roots that house these helpful bacteria. Microbes also serve as small factories, producing valuable products such as cheese, yogurt, beer, wine, organic acids and many other items. In conclusion, while it is less apparent to us, the positive role of microbes in human health is at least as important as the negative impact of pathogens.
Figure 1-17 A leguminous plants
Nitrogen-fixing bacteria form special structures, called nodules, on the roots of leguminous plants. In the picture, peas are shown that have either been exposed to bacteria (left) or not (right). The small bumps on the roots on the left are the nodules and contain millions of bacteria actively fixing N2 for the plant's use. Though not obvious from this figure, the plants on the left are more robust because of that nitrogen. (Source: E. B. Fred, et al., 1921. Soil Science 11:479-491.)
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