Chapter 1 - The Microbial World and You

The overall theme of this textbook is the ​ (a)   between ​ (b)   —very ​ (c)   organisms that usually require a ​ (d)   to be seen—and our lives. We’ve all heard of ​ (e)   of infectious diseases such as plague or smallpox that wiped out populations.

• relationship
• microbes
• small
• large
• microscope
• epidemics

Finally, we will discuss ​ (a)   as the cause of diseases such as ​ (b)   virus disease, ​ (c)   (bird) flu, ​ (d)   virus disease, and diarrhea, and we examine the growing public health problem of ​ (e)   -resistant bacteria.

• Zika
• avian
• Ebola
• microbes
• antibiotic
• plague
• smallpox
• MRSA

Microbes in Our Lives

For many people, the words germ and ​ (a)   bring to mind a group of tiny creatures that do not quite fit into any of the categories in that old question, “Is it animal, vegetable, or mineral?” ​ (b)   actually comes from the Latin word germen, meaning to spout from, or germinate. Think of wheat germ, the plant embryo from which the plant grows. It was first used in relation to microbes in the nineteenth century to explain the rapidly growing cells that caused disease. Microbes, also called ​ (c)   , are minute living things that individually are usually too small to be seen with the unaided eye. The group includes bacteria, ​ (d)   (yeasts and molds), protozoa, and ​ (e)   algae. It also includes viruses, those noncellular entities sometimes regarded as straddling the border between life and nonlife (Chapters 11, 12, and 13, respectively).

• microbe
• Germ
• Germen
• bacteria
• microorganisms
• macroorganisms
• fungi
• Archaea
• microscopic

We tend to associate these small organisms only with infections and inconveniences such as spoiled food. However, the majority of microorganisms actually help maintain the balance of life in our environment. Marine and freshwater microorganisms form the basis of the food chain in oceans, lakes, and rivers. Soil microbes break down wastes and incorporate nitrogen gas from the air into organic compounds, thereby recycling chemical elements among soil, water, living organisms, and air. Certain microbes play important roles in (a)   , a food- and oxygen-generating process that is critical to life on Earth.

Microorganisms also have many commercial applications. They are used in the synthesis of such chemical products as vitamins, organic acids, enzymes, alcohols, and many drugs. For example, microbes are used to produce acetone and butanol, and the vitamins B2 (riboflavin) and B12 (cobalamin) are made biochemically. The process by which microbes produce acetone and butanol was discovered in 1914 by Chaim (a)   , a Russian-born chemist working in England. With the outbreak of World War I in August of that year, the production of acetone became very important for making cordite (a smokeless form of gunpowder used in munitions). Weizmann’s discovery played a significant role in determining the outcome of the war.

The food industry also uses microbes in producing, for example, vinegar, sauerkraut, pickles, soy sauce, cheese, yogurt, bread, and alcoholic beverages. In addition, (a)   from microbes can now be manipulated to cause the microbes to produce substances they normally don’t synthesize, including cellulose, human insulin, and proteins for vaccines.

The Microbiome

An adult human is composed of about 30 trillion body cells and harbors another 40 trillion bacterial cells. Microbes that live stably in and on the human body are called the human microbiome, or microbiota. Humans and many other animals depend on these microbes to maintain good health. Bacteria in our intestines, including E. coli, aid digestion (see Exploring the Microbiome) and even synthesize some vitamins that our bodies require, including B vitamins for metabolism and vitamin K for blood clotting. They also prevent growth of (a)   (disease-causing) species that might otherwise take up residence, and they seem to have a role in training our immune system to know which foreign invaders to attack and which to leave alone. (See Chapter 14 for more details on relationships between normal microbiota and the host.)

The Microbiome

Even before birth, our bodies begin to be populated with bacteria. As newborns, we acquire viruses, fungi, and bacteria (Figure 1.1). For example, E. coli and other bacteria acquired from foods take residence in the large intestine. Many factors influence where and whether a microbe can indefinitely colonize the body as benign normal microbiota or be only a fleeting member of its community (known as transient (a)   ). Microbes can colonize only those body sites that can supply the appropriate nutrients. Temperature, pH, and the presence or absence of chemical compounds are some factors that influence what types of microbes can flourish.

True or False

Figure 1.1

Several types of bacteria found as part of the normal microbiota in an adult's intestine.

• A. True

• B. False

To determine the makeup of typical microbiota of various areas of the body, and to understand the relationship between changes in the microbiome and human diseases, is the goal of the Human Microbiome Project, which began in 2007. Likewise, the National Microbiome Initiative (NMI) launched in 2016 to expand our understanding of the role microbes play in different ecosystems, including soil, plants, aquatic (a)   , and the human body. Throughout the book, look for stories related to the human microbiome, highlighted in the Exploring the Microbiome feature boxes.