Comprehensive Study Guide: Foundations of Microbiology

Introduction to Microbiology

Roles of Microbes (Other Than Causing Disease)

Microbes play essential roles in ecosystems and human health beyond causing disease.

• Decomposition: Microbes break down organic matter, recycling nutrients in the environment.

• Symbiosis: Many microbes live in mutualistic relationships with plants, animals, and humans (e.g., gut flora).

• Biotechnology: Microbes are used in food production (e.g., yogurt, cheese), pharmaceuticals, and bioremediation.

• Photosynthesis: Cyanobacteria and algae contribute significantly to global oxygen production.

Where Are Microbes Found?

• Microbes are ubiquitous, found in soil, water, air, extreme environments (hot springs, deep sea vents), and within other organisms.

Taxonomy and Classification

Binomial Nomenclature and Taxonomy

• Binomial Nomenclature: Scientific names use two parts: genus (capitalized) and species (lowercase), both italicized (e.g., Escherichia coli).

• Hierarchy: Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species (DKPCOFGS).

Three Domains of Life

• Bacteria

• Archaea

• Eukarya

Characteristics of Microbes

Major Groups

• Bacteria: Prokaryotic, unicellular, diverse metabolism.

• Archaea: Prokaryotic, often extremophiles, unique membrane lipids.

• Fungi: Eukaryotic, includes yeasts and molds.

• Viruses: Acellular, require host cells to replicate.

• Protists: Eukaryotic, diverse group including protozoa and algae.

• Multicellular Parasites: Eukaryotic, includes helminths (worms).

Disproving Spontaneous Generation

Key Experiments

• Redi's Experiment: Showed that maggots do not arise spontaneously from meat.

• Pasteur's Swan-Neck Flask: Demonstrated that microorganisms come from the environment, not spontaneous generation.

Koch’s Postulates and Their Limitations

• Set of criteria to establish a causative relationship between a microbe and a disease.

• Limitations: Some microbes cannot be cultured, ethical issues, some diseases are multifactorial.

Hand Washing in Medical Settings

• Delayed implementation due to lack of understanding of germ theory and resistance to change in medical practice.

Prokaryotes vs. Eukaryotes

• Prokaryotes: No nucleus, circular DNA, no membrane-bound organelles (e.g., bacteria, archaea).

• Eukaryotes: Nucleus, linear DNA, membrane-bound organelles (e.g., fungi, protists, animals, plants).

Bacterial Morphology and Structures

Bacterial Shape and Arrangement

• Cocci: Spherical

• Bacilli: Rod-shaped

• Spirilla: Spiral-shaped

• Arrangements: Chains (strepto-), clusters (staphylo-), pairs (diplo-)

External Structures

• Capsule/Slime Layer/Glycocalyx: Protective, aids in adherence, evasion of immune response.

• Fimbriae: Attachment to surfaces.

• Flagella: Motility; arrangements include monotrichous, lophotrichous, amphitrichous, peritrichous.

• Pili: Conjugation (sex pilus), attachment.

Bacterial Cell Envelope

• Cell Wall: Provides shape and protection; composed of peptidoglycan.

• Gram-Positive: Thick peptidoglycan, teichoic acids.

• Gram-Negative: Thin peptidoglycan, outer membrane with lipopolysaccharide (LPS), lipid A (endotoxin).

• Acid-Fast: Mycolic acids in cell wall (e.g., Mycobacterium).

• Penicillin: Inhibits peptidoglycan synthesis.

Cell Membrane

• Phospholipid bilayer; amphipathic lipids have hydrophilic heads and hydrophobic tails.

Internal Components

• Ribosomes: Protein synthesis (70S in prokaryotes).

• Chromosome: Single, circular DNA molecule.

• Plasmids: Small, extrachromosomal DNA; often carry antibiotic resistance genes.

Endospores

• Formed by genera Bacillus and Clostridium.

• Highly resistant to heat, chemicals, desiccation.

• Concern in sterilization and infection control.

Microbiome

• Community of microbes living in and on the human body.

• Functions: Digestion, immune modulation, protection against pathogens.

• Importance: Disruption linked to diseases (e.g., allergies, obesity).

Germ-Free Mice

• Used to study the role of the microbiome in health and disease.

Prebiotics and Probiotics

• Prebiotic: Non-digestible food ingredients that promote growth of beneficial microbes.

• Probiotic: Live beneficial microbes administered to confer health benefits.

Bacterial Metabolism

Basic Concepts

• Metabolism: All chemical reactions in a cell.

• Catabolism: Breakdown of molecules, releases energy (exergonic).

• Anabolism: Synthesis of molecules, requires energy (endergonic).

• ATP/ADP: Adenosine triphosphate (ATP) is the main energy currency; hydrolyzed to ADP to release energy.

Collision Theory

• Explains how chemical reactions occur and why rates differ for different reactions.

Enzymes

• Biological catalysts that speed up reactions by lowering activation energy.

Phosphorylation

• Attachment of a phosphate group to a molecule.

• Three types: substrate-level, oxidative, photophosphorylation.

Cellular Respiration

• Aerobic: Uses oxygen as terminal electron acceptor.

• Anaerobic: Uses other molecules (e.g., nitrate, sulfate).

Pathways

• Glycolysis: Glucose to pyruvate, produces ATP and NADH.

• Pentose-Phosphate Pathway: Generates NADPH and pentoses.

• Entner-Doudoroff Pathway: Alternative to glycolysis in some bacteria.

Electron Carriers

• NAD+, FAD, and others shuttle electrons during metabolism.

The Citric Acid Cycle

• Completes oxidation of organic molecules, produces NADH, FADH2, and ATP.

Electron Transport Chain (ETC)

• Series of proteins in membrane; electrons transferred to terminal acceptor, generating proton gradient and ATP.

• In bacteria, ETC occurs in the cell membrane.

• Aerobic ETC uses O2; anaerobic uses other acceptors.

Fermentation

• Occurs when no terminal electron acceptor is available; regenerates NAD+ from NADH.

Evolution in Microbes

• Genes and Alleles: Genes are DNA segments coding for traits; alleles are variants.

• Mutations: Changes in DNA sequence; source of genetic variation.

• Selective Pressure: Environmental factors favoring certain traits.

• Evolution: Change in allele frequencies in a population over time.

Microbial Growth

Binary Fission

• Primary method of bacterial reproduction; one cell divides into two.

Growth Curve and Phases

• Lag Phase: Adaptation, no division.

• Log Phase: Exponential growth.

• Stationary Phase: Nutrient depletion, waste accumulation, growth rate = death rate.

• Death Phase: Decline in viable cells.

• Long-Term Stationary: Population dynamics fluctuate due to adaptation and resource recycling.

Factors Impacting Growth

• Oxygen Utilization: Obligate aerobes, obligate anaerobes, facultative anaerobes, microaerophiles, aerotolerant anaerobes.

• Temperature: Psychrophiles, mesophiles, thermophiles, hyperthermophiles.

• pH: Acidophiles, neutrophiles, alkaliphiles; microbes have mechanisms to maintain internal pH.

• Exploiting these factors helps control microbial growth (e.g., refrigeration, pickling).

Growth in Lab vs. Environment

• Lab cultures are controlled; environmental conditions are variable.

• Eutrophic: Nutrient-rich.

• Oligotrophic: Nutrient-poor.

• Persisters: Dormant cells tolerant to antibiotics.

Biofilms

• Biofilm: Community of microbes attached to a surface, embedded in extracellular matrix.

• Emergent Properties: New traits arise from group behavior (e.g., increased resistance).

• Biofilms impact health by causing persistent infections and increasing resistance to treatment.

• Quorum Sensing: Cell-to-cell communication regulating gene expression in response to population density.

• Control methods: Physical removal, antibiotics, quorum sensing inhibitors; physical removal is often most effective.

Bacterial Genetics

DNA vs. RNA

• DNA: Double-stranded, deoxyribose sugar, thymine.

• RNA: Single-stranded, ribose sugar, uracil.

Central Dogma

• Replication: DNA copied by DNA polymerase.

• Transcription: DNA to RNA by RNA polymerase; sigma factor initiates in prokaryotes.

• Translation: RNA to protein; coupled in prokaryotes.

Gene Transfer

• Vertical: Parent to offspring; increases diversity via mutation (DNA pol IV and V).

• Horizontal: Between cells; includes conjugation (F plasmid, relaxasome, transferasome), transformation (competency, used in medicine/industry), and transduction (bacteriophage, lysogenic conversion).

• Both contribute to antibiotic resistance.

Mechanisms of Antibiotic Resistance

• Biofilm formation, impermeability, target modification, inactivating enzymes, efflux pumps, R factors (resistance plasmids).

Ames Test

• Assesses mutagenic potential of compounds using bacteria.

Viruses

Structure

• Genetic material (DNA or RNA), protein coat (capsid), sometimes envelope with spike proteins.

Life Cycles

• Bacteriophage: Lytic and lysogenic cycles.

• Animal Viruses: Attachment, entry, uncoating, replication, assembly, release.

Influenza Virus

• Flu shot changes due to antigenic drift (small mutations) and antigenic shift (reassortment of genome segments).

• Spike proteins (e.g., hemagglutinin, neuraminidase) are targets for immune response and vaccine design.

Feature	Prokaryotes	Eukaryotes
Nucleus	No	Yes
DNA Shape	Circular	Linear
Organelles	No	Yes
Cell Wall	Peptidoglycan (Bacteria)	Cellulose (plants), chitin (fungi), none (animals)

Additional info: This guide expands on outline points with academic context, definitions, and examples for clarity and exam preparation.