Microorganisms: Introduction and Importance

Definition and Significance

Microorganisms are living organisms that are too small to be seen unaided. They play essential roles in ecosystems, human health, and industry.

• Primary producers in the environment (e.g., photosynthetic algae and cyanobacteria).

• Decomposers recycle nutrients and waste (e.g., saprophytic fungi and bacteria).

• Production of chemicals (e.g., ethanol, acetone, cellulose, insulin).

• Impact on disease and health (e.g., pathogens, beneficial microbes in hospitals).

• Food production and preservation (e.g., fermentation, spoilage).

Types of Microorganisms

Major Groups

• Bacteria

• Viruses

• Protozoa

• Fungi (molds and yeasts)

• Algae

• Helminths (parasitic worms)

Naming and Classifying Microorganisms

Binomial Nomenclature

Developed by Carl Linnaeus, this system assigns each organism two names:

• Genus (always capitalized)

• Species (always lowercase)

Names are italicized or underlined in print. Often, names are Latinized and may honor scientists or describe features.

Examples

• Homo sapiens: Homo = human, sapiens = wise

• Staphylococcus aureus: Staphylo- = clustered, -coccus = round, aureus = golden (colony color)

• Escherichia coli: Escherichia honors Theodor Escherich, coli = colon (habitat)

Three Domains of Life

Classification

• Bacteria

• Archaea

• Eukarya (includes protists, fungi, plants, animals)

Ancestors to bacteria were the first life on Earth; first microbes observed in 1673.

Taxonomy of Microorganisms

Bacteria

• Cell type: Prokaryote (no nucleus)

• Cell structure: Peptidoglycan cell walls

• Reproduction: Asexual (binary fission)

• Metabolism: Organic/inorganic chemicals, photosynthesis, or combinations

Archaea

• Cell type: Prokaryote

• Cell structure: Polysaccharide cell walls (no peptidoglycan)

• Reproduction: Asexual (binary fission)

• Metabolism: Organic/inorganic chemicals

• Other: Extremophiles (e.g., extreme environments)

Fungi

• Cell type: Eukaryote (true nucleus), multicellular (molds) or unicellular (yeasts)

• Cell structure: Polysaccharide cell walls

• Reproduction: Sexual/asexual

• Metabolism: Organic chemicals (saprophytes)

Protozoa

• Cell type: Eukaryote

• Cell structure: No cell walls

• Reproduction: Asexual (binary fission), sexual

• Metabolism: Organic chemicals (ingestive absorption)

• Other: Motility via pseudopods, cilia, or flagella

Algae

• Cell type: Mostly eukaryotes

• Cell structure: Carbohydrate cell walls

• Reproduction: Asexual (fragmentation), sexual

• Metabolism: Photosynthesis

Viruses

• Cell type: Acellular

• Structure: Protein coat (capsid), DNA or RNA core, may have lipid envelope

• Reproduction: Intracellular parasites

• Metabolism: N/A

Multicellular Animal Parasites

• Cell type: Eukaryote

• Cell structure: No cell walls

• Reproduction: Sexual/asexual

• Metabolism: Organic chemicals (ingestive absorption)

• Other: Many are parasites (e.g., helminths, roundworms), microscopic life stages

History of Microbiology

First Observations

• Robert Hooke (1665): Observed "cells" in cork; cell theory: all living things are composed of cells.

• Rudolf Virchow (1858): Cells arise from pre-existing cells.

• Antoni van Leeuwenhoek (1673-1723): First to describe live microorganisms using a microscope.

Spontaneous Generation vs. Biogenesis

• Spontaneous Generation: Life arises from nonliving matter.

• Biogenesis: Life arises from pre-existing life.

Golden Age of Microbiology

• Louis Pasteur: Disproved spontaneous generation, developed aseptic techniques, fermentation, pasteurization.

• Germ Theory of Disease: Specific microbes cause specific diseases.

• Agostino Bassi: Fungus causes silkworm disease (1835).

• Louis Pasteur: Protozoan causes silkworm disease (1865).

• Ignaz Semmelweis: Handwashing prevents puerperal fever (1840s).

• Joseph Lister: Chemical disinfectant for surgical tools (1860s).

• Robert Koch: Koch's postulates: procedure to link specific microbes to specific diseases.

Vaccination

• Edward Jenner (1796): Used cowpox to protect against smallpox; concept of immunity.

The Modern Age

Chemotherapy

• Alexander Fleming: Discovered penicillin (antibiotic from fungus).

• Paul Ehrlich: Developed synthetic drug for syphilis (Salvarsan, 1910).

• Sulfonamides: Synthetic drugs (1930s).

Modern Developments

• Bacteriology: Study of bacteria

• Mycology: Study of fungi

• Parasitology: Study of parasites

• Immunology: Study of immune system

• Virology: Study of viruses

• Genomics: Study of genes

• Microbial ecology: Relationships between microbes and other organisms

Breakthroughs Using Microbes

• Genes encode enzymes (Beadle and Tatum, 1942)

• DNA is hereditary material (Avery, McLeod, McCarty, 1944)

• Recombinant DNA (Berg)

• mRNA role in protein synthesis (Jacob and Monod, 1961)

• Nobel Prizes for discoveries in microbiology (e.g., Koch, Fleming, Prusiner)

Biotechnology and Genetic Engineering

• Use of microbes for specific tasks (e.g., cheese, bread, vaccines, enzymes)

• Genetically modified organisms (e.g., golden rice, BT cotton/corn)

Microbes and Human Welfare

Biogeochemical Cycling

• Bacteria recycle carbon, sulfur, phosphorus, nutrients

Bioremediation

• Microbes degrade organic matter and detoxify pollutants

Food Spoilage

• Microbial control helps food last longer

Pest Control

• Some microbes are pathogenic to pests (e.g., Bacillus thuringiensis)

Normal Microbiota

• Bacteria colonize humans, providing benefits (e.g., vitamin K, protection from pathogens)

Disease

• Some microbes cause disease (pathogens)

• Emerging infectious diseases: West Nile virus, BSE, E. coli O157:H7, Ebola, SARS, COVID-19, HIV/AIDS, Cryptosporidiosis, Influenza (H5N1)

Examples of Disease Transmission and Impact

• West Nile virus: transmitted by mosquitoes, affects birds and humans

• Bovine Spongiform Encephalopathy (BSE): prion disease in cattle

• E. coli O157:H7: toxin-producing strain causing diarrhea

• Ebola virus: hemorrhagic fever

• HIV/AIDS: global pandemic

• Cryptosporidiosis: waterborne protozoan infection

Summary Table: Key Experiments in Biogenesis Debate

Additional info:

• Some content inferred and expanded for clarity and completeness.

• Tables recreated from slide images and text.