Foundations of Microbiology: Study Notes from Lectures 1–6

Microbiology: The Study of Microbes

Definition and Scope

Microbiology is the scientific study of microorganisms, which include bacteria, archaea, some eukaryotes (fungi, protists, helminths), and viruses. Microorganisms are found in all domains of life and play essential roles in ecosystems, health, and disease.

• Microorganisms: All organisms in the domains Bacteria and Archaea, some Eukarya (Fungi, Protists, Helminths), and viruses.

• Viruses: Nonliving biological entities, often considered microbes.

Major Categories of Microbes

• Bacteria and Archaea: Unicellular, lack a nucleus, DNA not enclosed in a membrane.

• Fungi: Unicellular (yeasts) or multicellular (molds), eukaryotic.

• Protozoa: Unicellular eukaryotes, often motile.

• Algae: Photosynthetic eukaryotes, major oxygen producers.

• Helminths: Multicellular parasitic worms, included due to their life cycle involving microscopic stages.

• Viruses: Acellular, require host cells for replication.

Humans and Microbes

• Microbes were first observed in the 17th century by Anton van Leeuwenhoek.

• Microbes are ubiquitous and essential for life.

Cellular Nature of Microbes

• All living things are made of cells (Cell Theory).

• Cells arise from pre-existing cells (biogenesis).

Branches of Microbiology

• Basic: Study of microbial physiology, genetics, ecology.

• Applied: Medical, industrial, environmental microbiology.

Domains of Life

• Three domains: Bacteria, Archaea, Eukarya.

• Microbes are found in all domains.

The Chemistry of Microbiology

Water and Life

Water is essential for life, making up the majority of living organisms. Its unique properties arise from polar covalent bonds and hydrogen bonding.

• Universal solvent: Dissolves many substances, facilitating biochemical reactions.

• Hydrogen bonds: Weak bonds between water molecules and other polar molecules.

Acids, Bases, and Buffers

• Acids: Release H+ ions (pH < 7).

• Bases: Accept H+ ions (pH > 7).

• Buffers: Maintain pH stability in biological systems.

Functional Groups

• Common groups: Hydroxyl, carbonyl, carboxyl, amino, sulfhydryl, methyl, phosphate.

• Determine molecular interactions and reactivity.

Macromolecules

• Carbohydrates: Monosaccharides linked by glycosidic bonds.

• Proteins: Amino acids linked by peptide bonds.

• Nucleic acids: Nucleotides linked by phosphodiester bonds.

• Lipids: Not true polymers; composed of fatty acids and glycerol.

Polymerization and Hydrolysis

• Dehydration synthesis: Forms polymers by removing water.

• Hydrolysis: Breaks polymers into monomers by adding water.

Summary Table: Macromolecules

Polymer	Monomer	Bond	Role
Carbohydrates	Monosaccharide	Glycosidic	Energy, structure
Lipids	Fatty acids, glycerol	—	Membranes, energy storage
Nucleic Acids	Nucleotide	Phosphodiester	Genetic information
Proteins	Amino acid	Peptide	Enzymes, structure

Cell Structure and Function

Cell Theory

• All living organisms are composed of cells.

• Cells are the basic unit of structure and function.

• All cells arise from pre-existing cells.

Domains and Classification

• Bacteria and Archaea: Prokaryotes, lack a nucleus.

• Eukarya: Eukaryotes, have a nucleus and organelles.

Taxonomy and Nomenclature

• Taxonomy: Science of naming and classifying organisms.

• Nomenclature: Assigning names using binomial system (Genus species).

• Classification: Domain > Kingdom > Phylum > Class > Order > Family > Genus > Species.

Microbial Communities and Biofilms

• Microbes often exist in complex communities, not as isolated cells.

• Biofilms: Structured communities of microbes attached to surfaces, embedded in a self-produced matrix.

• Biofilms provide protection, facilitate communication, and can increase resistance to antimicrobials.

Biofilm Formation Stages

Stage	Description
Attachment	Cells adhere to surface
Colonization	Cells divide, produce matrix
Development	Biofilm matures, complex structure forms
Active Dispersal	Cells leave to colonize new locations

Biofilms and Quorum Sensing

Quorum Sensing

• Bacterial communication system that detects cell density via signaling molecules.

• Regulates gene expression, including biofilm formation and virulence.

• High concentrations of signals trigger coordinated behaviors.

Microbial Ecology and Symbiosis

• Microbes interact with each other and with hosts in various relationships:

  • Mutualism: Both benefit.

  • Commensalism: One benefits, other unaffected.

  • Parasitism: One benefits at the expense of the other.

• Human microbiome: Diverse microbial community living on and in the human body.

Roles of the Human Microbiome

• Protects against pathogens.

• Helps digest food and synthesize vitamins.

• Modulates immune system.

• Can be disrupted by antibiotics, leading to disease.

Cell Structure: Bacteria and Archaea

Bacterial Cell Morphology

• Common shapes: Cocci (spherical), Bacilli (rod-shaped).

• Arrangements: Single, pairs, chains, clusters.

Cell Envelope Organization

• Cell wall: Provides shape, protection; made of peptidoglycan in bacteria.

• Gram-positive: Thick peptidoglycan, teichoic acids.

• Gram-negative: Thin peptidoglycan, outer membrane with lipopolysaccharide (LPS).

Special Structures

• Capsule and Slime Layer: Glycocalyx for attachment and protection.

• Flagella: Motility structures.

• Pili and Fimbriae: Attachment, conjugation.

• Cell Inclusions: Storage of nutrients and minerals.

• Endospores: Dormant, resistant structures for survival.

Bacterial Membrane

• Lipid bilayer with embedded proteins.

• Selective permeability, transport, energy generation.

Transport Mechanisms

Process	Description
Passive Diffusion	Movement down concentration gradient, no energy required
Facilitated Diffusion	Uses transport proteins, no energy required
Active Transport	Requires energy (ATP), moves substances against gradient
Group Translocation	Substance is chemically modified during transport

Bacteria vs. Archaea

Feature	Bacteria	Archaea
Cell Wall	Peptidoglycan	Pseudomurein or S-layer
Membrane Lipids	Ester-linked	Ether-linked
Flagella	Flagellin-based	Archaellum (different structure)
Habitat	Ubiquitous	Often extreme environments

Archaeal Cell Structures

• Unique membrane lipids (ether bonds, branched chains).

• Cell walls lack peptidoglycan; may have S-layer or pseudomurein.

• Archaella (archaeal flagella) for motility.

• Hami: Unique grappling hook-like structures for attachment.

Summary

• Microbiology encompasses the study of diverse microorganisms and their roles in health, disease, and the environment.

• Understanding cell structure, function, and interactions is foundational for further study in microbiology.

• Biofilms, quorum sensing, and the human microbiome are key concepts in modern microbiology.