Microbes in Our Lives

Introduction to Microorganisms

Microorganisms, or microbes, are organisms that are too small to be seen with the unaided eye. They play essential roles in the environment, industry, and human health.

• Microorganisms include bacteria, fungi, protozoa, microscopic algae, viruses, and prions.

• Most microbes are harmless or beneficial, but a few are pathogenic (disease-producing).

Roles of Microbes

Microbes have both destructive and beneficial effects on human life and the environment.

• Pathogenic microbes cause diseases in humans, animals, and plants.

• Some microbes cause food spoilage.

• They form the basis of the food chain in aquatic environments.

• Microbes decompose organic waste, recycling nutrients back into the ecosystem.

• They incorporate nitrogen gas from the air into organic compounds (nitrogen fixation).

• Microbes generate oxygen through photosynthesis (e.g., cyanobacteria, algae).

• They produce chemical products such as ethanol, acetone, and vitamins.

• Microbes are used to produce fermented foods (e.g., vinegar, cheese, yogurt, alcoholic beverages, bread).

• They are involved in manufacturing (e.g., cellulose) and disease treatment (e.g., production of insulin).

Example: Lactobacillus species are used in yogurt production, while Escherichia coli is used in biotechnology to produce insulin.

The Microbiome

Definition and Importance

The microbiome (also called microbiota) refers to the community of microorganisms that live stably on or in the human body. These microbes are essential for maintaining health and preventing disease.

• An adult human is composed of approximately 30 trillion body cells and harbors about 40 trillion bacterial cells.

• The microbiome helps maintain good health, prevents the growth of pathogenic microbes, and may help train the immune system to distinguish threats.

Normal and Transient Microbiota

Normal microbiota are the collection of acquired microorganisms on or in a healthy human being. They begin to be acquired before birth and may colonize the body indefinitely or only temporarily (as transient microbiota).

• Colonization occurs only at body sites that provide nutrients and the right environment for microbes to flourish.

• Normal microbiota can prevent colonization by pathogens through competitive exclusion and production of inhibitory substances.

Example: Staphylococcus epidermidis is a common normal microbiota on the skin, while Lactobacillus species are found in the gut and vagina.

Major Microbiome Research Initiatives

• The Human Microbiome Project (2007–2016): Aimed to determine the makeup of typical microbiota in various areas of the body and understand the relationship between changes in the microbiome and human disease.

• The National Microbiome Initiative (NMI) (begun in 2016): Explores the role microbes play in different ecosystems, including environmental and human-associated microbiomes.

Key Terms

• Microbiome: The total collection of microbes and their genetic material in a particular environment, such as the human body.

• Normal microbiota: Microorganisms that colonize a host without causing disease under normal conditions.

• Transient microbiota: Microorganisms that are present in or on the body for a short time without causing disease.

Summary Table: Types of Microbiota

Check Your Understanding

• Describe some of the destructive and beneficial actions of microbes.

• Define microbiome, normal microbiota, and transient microbiota.