The Microbial World and You

Microorganisms

Microorganisms, or microbes, are living entities too small to be seen with the unaided eye. They play diverse roles in nature and human society, ranging from beneficial to harmful.

• Helpful roles: Decomposition, recycling nutrients, food production, and synthesis of chemicals and useful products.

• Harmful roles: Cause diseases and spoilage.

• Environmentally important: Essential for ecosystem functioning.

• Types of microbes: Bacteria, Fungi, Protozoa, Microscopic algae, Viruses, and Prions.

Example: Bacillus thuringiensis is used in agriculture for pest control.

Normal Microbiota

Normal microbiota are microorganisms that reside on or within a healthy human, contributing to health and immunity.

• Functions: Maintain health, prevent pathogen growth, and train the immune system.

• Transient microbiota: Microbes present temporarily, differing from normal microbiota which are consistently present.

Example: Lactobacillus species in the gut help digest food and inhibit pathogens.

Scientific Names

The scientific naming system, established by Carolus Linnaeus in 1735, provides a universal method for identifying organisms.

• Format: Genus (capitalized) + specific epithet (lowercase), both italicized.

• Example: Escherichia coli (shortened as E. coli).

Major Types of Microorganisms

Microorganisms are classified based on cellular structure, reproduction, and other features.

• Bacteria: Prokaryotic, unicellular, cell wall with peptidoglycan, reproduce by binary fission.

• Archaea: Prokaryotic, lack peptidoglycan, often inhabit extreme environments.

• Fungi: Eukaryotic, cell wall with chitin, yeasts (unicellular), molds (multicellular).

• Protozoa: Eukaryotic, free-living or parasitic, motility via pseudopods, cilia, or flagella.

• Algae: Eukaryotic, photosynthetic, cell wall with cellulose.

• Viruses: Acellular, contain DNA or RNA, protein coat, require host cell for replication.

• Multicellular Animal Parasites: Eukaryotic, multicellular, include helminths (flatworms and roundworms), some life stages are microscopic.

• Prions: Infectious proteins, cause neurodegenerative diseases.

Key distinguishing features:

• Bacteria: Peptidoglycan

• Archaea: No peptidoglycan

• Fungi: Chitin

• Algae: Cellulose

• Viruses: Acellular, host required

Three Domains of Life

Carl Woese (1978) classified all life into three domains based on genetic and biochemical differences.

• Bacteria: Prokaryotic microorganisms.

• Archaea: Prokaryotic, distinct from bacteria, often extremophiles.

• Eukarya: Eukaryotic organisms, including protists, fungi, plants, and animals.

Early Microbiology

Early discoveries laid the foundation for microbiology as a science.

• Robert Hooke (1665): Observed "cells" in cork, beginning cell theory.

• Anton van Leeuwenhoek (1673–1723): First detailed observations of microorganisms, termed "animalcules."

Key association: Hooke = cells; Leeuwenhoek = microbes.

Spontaneous Generation vs. Biogenesis

Debate over the origin of life led to key experiments and the development of biogenesis theory.

• Spontaneous generation: Life arises from nonliving matter.

• Biogenesis: Life arises from preexisting living cells.

Important experiments:

• Francesco Redi (1668): Covered meat jars; no maggots appeared, supporting biogenesis.

• John Needham (1745): Boiled broth, covered flask; microbial growth occurred, interpreted as spontaneous generation.

• Lazzaro Spallanzani (1765): Boiled broth in sealed flasks; no growth, supporting biogenesis.

• Rudolf Virchow (1858): Proposed living cells arise from preexisting cells.

• Louis Pasteur (1861): Used S-shaped flasks; broth remained sterile, disproving spontaneous generation.

Scientist sequence: Redi → Needham → Spallanzani → Virchow → Pasteur

First Golden Age of Microbiology (1857–1914)

This period saw major advances in understanding microbes, disease, and laboratory techniques.

• Linking microbes to disease

• Immunity studies

• Improved microscopes

• Culturing microorganisms

• First vaccines

• Aseptic techniques

• First chemotherapeutic drugs

• Studies of microbial chemical activities

Fermentation & Pasteurization

Microbes are responsible for fermentation and pasteurization, both important in food and beverage industries.

• Fermentation: Microbes convert sugars to alcohol in the absence of air.

• Pasteurization: High heat for a short time kills harmful bacteria in beverages.

Example: Pasteur showed microbes cause fermentation (1857).

Germ Theory of Disease

The germ theory established that microbes cause specific diseases.

• Agostino Bassi (1835): Silkworm disease caused by fungus.

• Louis Pasteur (1865): Silkworm disease caused by protozoan.

• Ignaz Semmelweis (1840s): Promoted handwashing to prevent disease transmission.

• Joseph Lister (1860s): Used phenol as antiseptic.

• Robert Koch (1876): Identified anthrax bacterium; developed Koch's postulates.

Koch's postulates: Criteria to prove a specific microbe causes a specific disease.

Key associations: Semmelweis = handwashing; Lister = antiseptic; Koch = anthrax + postulates.

Vaccination

Vaccination is the process of inducing immunity against disease using biological agents.

• Edward Jenner (1796): Used cowpox to protect against smallpox.

• Immunity: Protection against disease.

• Origin: "Vaccination" from "vacca" (cow).

Antimicrobial Drugs

Antimicrobial drugs are used to treat infectious diseases, including antibiotics and synthetic agents.

• Paul Ehrlich (1910): Developed Salvarsan for syphilis; "magic bullet" concept.

• Sulfonamides (1930s): First synthetic antimicrobial drugs.

• Alexander Fleming (1928): Discovered penicillin from Penicillium fungus.

• Antibiotics: Chemicals produced by microbes to inhibit or kill other microbes.

• Chemotherapy: Treatment of disease with chemicals.

Antimicrobial Resistance

Microbes can develop resistance to antimicrobial drugs, complicating treatment.

• Example: Vancomycin-resistant Staphylococcus aureus.

Fields of Microbiology

Microbiology encompasses several specialized fields.

• Rebecca Lancefield: Discovered differences in cell wall polysaccharides.

• Dmitri Iwanowski & Wendell Stanley: Identified viruses as cause of tobacco mosaic disease.

• Electron microscopes: Enabled detailed study of viruses.

Genetics & Molecular Biology

Microbial genetics and molecular biology explore inheritance and molecular mechanisms in microbes.

• Microbial genetics: Study of how microbes inherit traits.

• Molecular biology: Study of genetic information carried in DNA.

• Key discoveries:

  • 1941: Beadle & Tatum — Genes encode enzymes.

  • 1944: Avery, MacLeod & McCarty — DNA is hereditary material.

  • 1953: Watson & Crick — DNA structure model.

  • 1961: Jacob & Monod — Role of mRNA in protein synthesis.

Genomics

Genomics is the study of an organism's complete set of genes, with applications in discovery, classification, and disease understanding.

• Uses: Discover, detect, classify microorganisms; study microbiomes; understand disease.

• Recombinant DNA: DNA from two different sources.

• Paul Berg (1960): Inserted animal DNA into bacterial DNA; bacteria produced animal protein.

• Third Golden Age: Began in late 1980s, driven by genomics and molecular biology advances.

Microbes & the Environment

Microbial ecology studies the interactions between microbes and their environment, including recycling and bioremediation.

• Microbes recycle: Carbon, oxygen, nitrogen, sulfur, phosphorus.

• Sewage treatment: Microbes degrade organic matter in sewage.

• Bioremediation: Use of microbes to clean up pollutants (e.g., oil, mercury).

• Insect pest control: Bacillus thuringiensis produces toxins fatal to insects; toxin gene inserted into plants for resistance.

Biofilms

Biofilms are communities of microorganisms attached to surfaces, often resistant to antibiotics.

• Locations: Teeth, pipes, rocks, medical implants.

• Significance: Can harbor antibiotic-resistant bacteria.

Biotechnology & Emerging Infectious Diseases

Biotechnology uses microbes for practical applications, including recombinant DNA technology. Emerging infectious diseases are new or increasing in incidence.

• Biotechnology: Use of microbes for practical purposes.

• Recombinant DNA technology: Enables production of useful proteins in microbes.

• Emerging infectious diseases (EIDs): New or increasing diseases, often due to evolutionary changes, transportation, or increased exposure.

• Examples: COVID-19 (SARS-CoV-2), SARS (2002), MERS (2012).

Additional info: Factors contributing to EIDs include genetic evolution, global travel, and environmental changes.