Introduction to Microbiology: Microbes and Their Building Blocks

Introduction to Microbiology

Microbes: Tiny but Mighty

Microbiology is the study of organisms too small to be seen without magnification. These microorganisms include bacteria, archaea, protozoa, fungi, helminths, algae, viruses, and prions. They play essential roles in Earth's ecosystems and human health.

• Bacteria: Single-celled prokaryotes, found everywhere.

• Archaea: Single-celled prokaryotes, distinct from bacteria.

• Protozoa: Single-celled eukaryotes, often motile.

• Fungi: Eukaryotes, can be single-celled (yeasts) or multicellular (molds).

• Helminths: Multicellular parasitic worms.

• Algae: Photosynthetic eukaryotes.

• Viruses: Acellular infectious agents, require host cells to replicate.

• Prions: Infectious proteins, even simpler than viruses.

Relative Sizes of Microorganisms

Microorganisms vary greatly in size, from prions (10 nm) to eukaryotic cells (10,000 nm).

• Acellular: Prions and viruses are much smaller than cells.

• Cellular: Bacteria and archaea are smaller than eukaryotes.

Microbes and the Planet

Microbes' Role in Earth's Development

Microbes have shaped Earth's habitat for billions of years. Single-celled organisms appeared about 3.8 billion years ago, evolving into three main cell types:

• Eukaryotes: "True nucleus"

• Bacteria: No true nucleus

• Archaea: No true nucleus, distinct from bacteria

Relatedness of Organisms

The three domains of life—Bacteria, Archaea, and Eukarya—share a last common ancestor and have diversified into many lineages.

Evolutionary Timeline

The timeline of life shows the origin of Earth, the emergence of bacteria and archaea, the evolution of eukaryotes, and the appearance of multicellular organisms and humans.

Microbes Are Ubiquitous

Microbes are found everywhere: deep in the earth's crust, polar ice caps, oceans, inside plants and animals, and throughout the landscape. They are essential to life.

Theories of Evolution and Science

Theory of Evolution

The theory of evolution describes the accumulation of changes in organisms as they adapt to their environments. It is a well-tested, well-established scientific concept, not a random guess.

• Natural selection: Favors changes that enhance survival and reproduction.

• Phylogeny: Represents the natural relatedness between groups of living beings.

Microbes and Energy Flow

Microbes in Ecosystems

Microbes drive energy and nutrient flow in ecosystems. Bacteria evolved photosynthesis before plants, producing oxygen and shaping the atmosphere.

Photosynthesis

• Anoxygenic photosynthesis: Occurred in bacteria, did not produce oxygen.

• Oxygenic photosynthesis: Evolved later, more efficient, responsible for most of Earth's photosynthesis.

Microbes and Humans

Historical Uses of Microbes

Humans have used microbes for bread, alcohol, cheese production, wound treatment, mining, and bioremediation.

Biotechnology

• Genetic engineering: Manipulates genetics for new products and GMOs.

• Recombinant DNA technology: Transfers genetic material between organisms.

• Bioremediation: Uses microbes to clean up pollutants.

Microbes Harming Humans

Most microbes are harmless or beneficial, but pathogens cause disease. Over 2,000 microbes cause disease, leading to billions of infections annually.

Top Causes of Death in the U.S.

Infectious diseases are significant causes of death worldwide, though in the U.S., most top causes are noninfectious. COVID-19 is a notable exception.

Cause	2020 Deaths per 100,000	2021 Deaths per 100,000
Heart disease	168.2	173.8
Cancer	144.1	146.6
COVID-19	85.0	104.1
Unintentional injuries	57.6	64.7
Stroke	38.8	41.1
Chronic lower respiratory diseases	36.4	34.7
Alzheimer's disease	32.4	31.0
Diabetes	24.8	25.4
Chronic liver disease and cirrhosis	13.3	14.5
Kidney disease	12.7	13.6

Cellular Organization

Eukaryotes vs. Bacteria and Archaea

• Eukaryotes: Have organelles (e.g., nucleus, mitochondria, chloroplasts), can be single-celled or multicellular.

• Bacteria and Archaea: Lack organelles, all are microorganisms, ten times smaller than eukaryotes.

Viruses and Prions

• Viruses: Not independently living, composed of DNA or RNA and a protein coat.

• Prions: Infectious proteins, no nucleic acid.

Biochemical Building Blocks

Macromolecules

Cells are built from four main families of biochemicals:

• Carbohydrates: Energy and structural support.

• Lipids: Energy storage, membrane structure.

• Proteins: Enzymes, structural components.

• Nucleic acids: Genetic information (DNA, RNA).

Taxonomy and Classification

Taxonomic Categories

Taxonomy is the science of classifying living things. The hierarchy includes:

• Domain

• Kingdom

• Phylum

• Class

• Order

• Family

• Genus

• Species

Woese-Fox System

Based on ribosomal RNA sequences, this system divides life into three domains: Bacteria, Archaea, and Eukarya.

Summary Table: Types of Microorganisms

Type	Cellular/Acellular	Example	Size
Bacteria	Cellular	E. coli	~1,000 nm
Archaea	Cellular	Halobacteria	~1,000 nm
Protozoa	Cellular	Vorticella	~10,000 nm
Fungi	Cellular	Mucor	~10,000 nm
Helminths	Cellular	Taenia solium	~10,000 nm
Viruses	Acellular	Herpes simplex	~100 nm
Prions	Acellular	Prion	~10 nm

Key Images for Study

• : Visualizes the size differences among prions, viruses, bacteria/archaea, and eukaryotes.

• : Shows the phylogenetic tree of Bacteria, Archaea, and Eukarya.

• : Illustrates the timeline of life's evolution on Earth.

• : Demonstrates microbial photosynthesis and its impact on Earth's atmosphere.

• : Provides data on infectious and noninfectious causes of death.

• : Micrographs of helminth, fungus, protozoa, bacterium, virus, and prion.