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1、Introduction to MicrobiologyMicrobes have a large impact on human health(微生物對人類健康有很大的影響) Microbes cause many infectious diseases.(微生物導致許多傳染病) Vaccines, antibiotics, and many other advances have lessened the impact of infectious disease in the developed world, but infectious disease in developing cou
2、ntries is high.(疫苗、抗生素以及許多其他的進步降低了傳染病對開發中地區的衝擊，但是發生在開發中國家的傳染病仍然偏高) New illnesses caused by microorganisms continue to emerge and known pathogens are becoming resistant to treatment.(微生物所導致的新疾病持續出現，而且已知有許多病原體逐漸對醫療處理產生抗性) In 1900 in the United States the infant mortality rate was near 50%, mostly due
3、to childhood infectious disease and until about 1930, microbes were the major cause of death in humans. From todays perspective this is a horrendous(可怕的)statistic(統計量), over half of all infants did not make it to adulthood! With the advent of antibiotics, vaccines and better water sanitation, humani
4、ty has reduced the impact of pathogenic microbes in developed countries, but they will always remain an important social concern. The discipline of microbiology emerged from the study of these diseases, and most advances in treating various ailments had their roots in this relatively young science.
5、Ancient diseases continue to be a problem where nutrition and sanitation are poor, and emerging diseases such as Acquired Immunodeficiency Syndrome (AIDS) are even more dangerous for such populations. The Centers for Disease Control and Prevention (the U.S. government agency charged with protecting
6、the health and safety of people) estimates that about 9% of adults between the ages of 18-49 in Sub-Saharan Africa are infected with HIV. Yet, AIDS is only one of a number of new diseases that have emerged. Many of these diseases have no known cure. Influenza and pneumonia are leading killers of the
7、 elderly even in the U. S. and other developed nations. Even the common cold causes illness and misery for almost everyone and drains the productivity of all nations. Many of the new diseases are viral in nature, making them notoriously difficult to treat. Surprisingly, many diseases that were previ
8、ously thought to have only behavioral or genetic components have been found to involve microorganisms. The clearest case is that of ulcers, which was long thought to be caused by stress and poor diet. However the causative agent is actually a bacterium, Helicobacter pylori, and many ulcers can be cu
9、red with appropriate antibiotics. Work on other non-infectious diseases such as heart disease, stroke and some autoimmune diseases also suggest a microbial component that triggers the illness.Finally, some pathogenic microbes that had been controlled through the use of antibiotics are beginning to d
10、evelop drug resistance and therefore reemerge as serious threats in the industrialized world as well as developing nations. Tuberculosis is an illness that was on the decline until the middle 80s. It has recently become more of a problem, partly due to drug resistance and partly due to a higher popu
11、lation of immunosuppressed individuals from the AIDS epidemic. Staphylococcus aureus strains are emerging that are resistant to many of the antibiotics that were previously effective against them. These staph infections are of great concern in hospital settings around the world. Understanding both f
12、amiliar killers and new pathogens will require an understanding of their biology, and thus an understanding of the field of microbiology.Microbes are often helpful, not harmful(微生物經常是有益而非有害的) Microbes form important mutualistic relationships with all sorts of organisms. Many of these relationships a
13、re important from a human perspective(微生物與許多生物形成重要的互利關係，而自人類角度而言其中有許多是很重要的關係) Only a small faction 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 acti
14、vely antagonize other bacteria and take up space, preventing potential pathogens from gaining a foothold on our bodies. Indeed, like all large organisms, humans have entire communities of microorganisms in their digestive systems that contribute to their overall health. The microbial community in hu
15、mans not only protects us from disease, but also provides needed vitamins, such as B12. Human health and nutrition depends on healthy farm animals. Cows, sheep, horses and other ruminant animals utilize their microbial associates to degrade plant material into useful nutrients. Without these bacteri
16、a inside ruminants, growth on plant material would be impossible. 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
17、 bacteria form a mutualistic relationship within the plant: the plant provides carbon and energy, while the bacteria convert atmospheric nitrogen gas into a useful nitrogen source for the plant. Microbes also serve as small factories, producing valuable products such as cheese, yogurt, beer, wine, o
18、rganic 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.Microbes have profound effects on the environment (微生物對環境有深遠的影響作用) Microbes make up the major portion of the b
19、iomass present on the Earth. Therefore, the nutrients they eat and the products they form greatly influence the environment.(微生物是現存地球上生物質量的主要組成份子，因此，它們所吃掉的養分以及它們所形成的產物對環境有巨大的影響) Cyanobacteria and algae in the oceans are responsible for most photosynthesis and are a major sink for carbon dioxide, a g
20、reenhouse gas.(存在海水中的藍綠菌和藻類是大部份光合作用的來源，也是主要的溫室效應氣體-二氧化碳的收集處) Microbes release nutrients from dead organisms, making them available to the rest of the ecosystem.(微生物將養分自死亡的生物體釋放出來，提供給生態系中其餘生物所利用) Some microbes play a role in the production of energy, while other microbes interfere with energy product
21、ion.(部份微生物在能量的產生中扮演一角，其餘的微生物則妨礙能量的產生) Whether measured by the number of organisms or by total mass, the vast majority of life on this planet is microscopic. These teaming multitudes profoundly influence the make-up and character of the environment in which we live . Presently, we know very little ab
22、out the microbes that live in the world around us because less than 2 % of them can be grown in the laboratory. Understanding which microbes are in each ecological niche and what they are doing there is critical for our understanding of the world. Microbes are the major actors in the synthesis and d
23、egradation of all sorts of important molecules in environments. Cyanobacteria and algae in the oceans are responsible for the majority of photosynthesis on Earth. They are the ultimate source of food for most ocean creatures (including whales) and replenish the worlds oxygen supply. Cyanobacteria al
24、so use carbon dioxide to synthesize all of their biological molecules and thus remove it from the atmosphere. Since carbon dioxide is a major greenhouse gas, its removal by cyanobacteria affects the global carbon dioxide balance and may be an important mitigating factor in global warming. In all hab
25、itats, microorganisms make nutrients available for the future growth of other living things by degrading dead organisms. Microbes are also essential in treating the large volume of sewage and wastewater produced by metropolitan areas, recycling it into clean water that can be safely discharged into
26、the environment. Less helpfully (from the view of most humans), termites contain microorganisms in their guts that assist in the digestion of wood, allowing the termites to extract nutrients from what would otherwise be indigestible. Understanding of these systems helps us to manage them responsibly
27、 and as we learn more we will become ever more effective stewards.Energy is essential for our industrial society and microbes are important players in its production. A significant portion of natural gas comes from the past action of methanogens (methane-producing bacteria). Numerous bacteria are al
28、so capable of rapidly degrading oil in the presence of air and special precautions have to be taken during the drilling, transport and storage of oil to minimize their impact. In the future, microbes may find utility in the direct production of energy. For example, many landfills and sewage treatmen
29、t plants capture the methane produced by methanogens to power turbines that produce electricity. Excess grain, crop waste and animal waste can be used as nutrients for microbes that ferment this biomass into methanol or ethanol. These biofuels are presently added to gasoline and thus decreasing poll
30、ution. They may one-day power fuel cells in our cars, causing little pollution and having water as their only emission.Finally, We are increasingly taking advantage of the versatile appetite of bacteria to clean up environments that we have contaminated with crude oil, polycholorinated biphenvyls (P
31、CBs) and many other industrial wastes. This process is termed bioremediation and is a cheap and increasingly effective way of cleaning up pollution.Studying microbes helps us to understand the world around us(研究微生物協助我們瞭解在我們周遭的世界) Microbes are useful tools in research because of their rapid life cycl
32、e, their simple growth requirements, and their small size.(由於快速的生活史、簡單的生長需求與渺小的體型，微生物是有用的研究工具) Due to this simplicity, microbes have been essential in understanding core questions in biology.(由於它簡單的結構，微生物一直是生物學中瞭解核心問題所不可缺的) Attempts to classify microorganisms have lead to a classification system tha
33、t divides all organisms into three domains of life, Archaea, Bacteria, and Eukarya(試圖分類微生物也導致生物分類系統的形成，將所有生物分為原生菌、細菌、真核生物三大領域) Microbes provide tools for use in molecular biology. These tools have allowed scientists to make rapid progress in investigating many types of microorgansims.(微生物提供分子生物學所使用的
34、工具，這些工具使科學家在調查多種型態的微生物時能夠達成快速的進步) Microorganisms used in research have many useful properties. They will grow on simple, cheap medium and will often rise to large populations in a matter of 24 hours. It is easy to isolate their genomic material, manipulate it in the test tube and then place it back
35、into the microbe. Due to their large populations it is possible to identify rare events and then with the use of powerful selective techniques isolate interesting bacterial cells and study them. These advantages have made it possible to test hypothesis rapidly . Using microbes scientists have expand
36、ed our knowledge about life. Below are a few examples. In scientific research, microorganisms have been indispensable instruments for unlocking the secrets of life. The molecular basis of heredity and how this is expressed as proteins was described through work on microorganisms . For an in-depth di
37、scussion on the molecular basis of heredity see DNA is the hereditary material in Molecular Biology Essentials. Due to the similarity of life at the molecular level, this understanding has helped us to learn about all organisms, including ourselves.Some prokaryotes are capable of growing under unima
38、ginably harsh conditions and define the extreme limits of where life can exist. Some species have been found growing at near100 C in hot springs and well above that temperature near deep-sea ocean vents. Others make their living at near 0 C in freshwater lakes that are buried under the ice of Antarc
39、tica. The ability of microbes to live under such extreme conditions is forcing scientists to rethink the requirements necessary to support life. Many now believe it is entirely possible that Jupiters moon Europa may harbor living communities in waters deep below its icy crust. What may the rest of t
40、he universe hold? Until recently, while we could study specific types of bacteria, we lacked a cohesive classification system, so that we could not readily predict the properties of one species based on the known properties of others. Visual appearance, which is the basis for classification of large
41、 organisms, simply does not work with many microbes because there are few distinguishing characteristics for comparison between species even under the microscope. However, analysis of their genetic material in the past 20 years has allowed such classification and spawned a revolution in our thinking
42、 about the evolution of bacteria and all other species. The emergence of a new system organizing life on Earth into three domains is attributable to this pioneering work with microorganisms.The fruits of this basic research have been used by scientists to understand microbial activity and therefore
43、to shape our modern world. Human proteins, especially hormones like insulin and human growth factor, are now produced in bacteria using in vitro.)genetic engineering. Our understanding of the immune system was developed using microbes as tools. Microorganisms also play a role in treating disease and
44、 keeping people healthy. Many of the drugs available to treat infectious disease originate from bacteria and fungi.One last recent role of microbes in informing us about our world has been the tools they provide for molecular biology. Enzymes purified from bacterial strains are useful as tools to pe
45、rform many types of analyses. Such analyses allow us to determine the complete genome sequence of almost any organism and manipulate that DNA in useful ways. We now know the entire sequence of the human genome, with the exception of regions of repetitive DNA, and this will hopefully lead to medical
46、practices and treatments that improve health. We also know the entire genome sequence of many important pathogens. Analysis of this data will eventually lead to an understanding of the function of critical enzymes in these microbes and the development of tailor-made drugs to stop them. The tools of
47、molecular biology will also affect agriculture. For example, we now know the complete genome sequence of the plant Arabidopsis (a close relative of broccoli and cauliflower). This opens a new avenue to a better understanding of all plants and hopefully improvements in important crops.Microbes have a
48、 profound impact on every facet of human life and everything around us. Pathogens harm us, yet other microbes protect us. Some microbes are pivotal in the growth of food crops, but others can kill the plants or spoil the produce. Bacteria and fungi eliminate the wastes produced in the environment, b
49、ut also degrade things we would rather preserve. Clearly they effect many things we find important as humans. In the remainder of this chapter we take a look at how scientists came to be interested in microbes and follow a few important developments in the history of microbiology.The history of microbiology is a web of discoveries(微生物學的歷史是一堆錯綜複雜的發現) Science is interdependent and new discoveries depend upon earlier contrib