Prokaryotic cells.
Highly diverse metabolism, cell envelopes and ecological roles.
Side 64
Microbiology
A study of microscopic life and infectious agents. Microbiology connects cellular structure, metabolism, growth, genetic exchange, microbial communities and host interaction across organisms too small to understand by naked-eye observation alone.
cell→metabolism→growth→interaction→ecology / pathogenesis
06microbial lenses
05growth controls
05interaction modes
64Side
“Microbe” describes scale more than one lineage.
Bacteria, archaea, microscopic eukaryotes and viruses differ fundamentally in structure and replication.
Distinct prokaryotic lineage.
Share some cellular features with bacteria but differ deeply in membranes and molecular machinery.
Eukaryotic microbes.
Yeasts and molds obtain nutrients by absorption and can be decomposers, symbionts or pathogens.
Diverse unicellular eukaryotes.
Many are motile and occupy aquatic, soil or host-associated habitats.
Photosynthetic microbial eukaryotes.
Important primary producers in aquatic systems.
Replicating genetic entities dependent on host cells.
Viruses lack independent cellular metabolism and reproduce through host machinery.
Microbes exploit extraordinary chemical possibilities.
Energy source, electron donor and carbon source can vary independently, producing many metabolic strategies.
Where does biomass carbon come from?
CO₂ or organic compounds?
Autotrophs fix inorganic carbon; heterotrophs use organic carbon.
Light or chemical reactions?
Phototroph or chemotroph.
Energy acquisition can be decoupled from carbon source.
What supplies reducing power?
Organic or inorganic donors.
Electron donors drive redox metabolism.
Where do electrons end?
O₂, nitrate, sulfate, other?
Different terminal acceptors support different respiratory strategies.
What is released?
CO₂, acids, gases, reduced compounds?
Microbial by-products reshape environments and host systems.
Microbial growth is population growth.
Cell division responds to nutrients, temperature, pH, oxygen and accumulated waste.
Lag
Adapt before rapid division.
Cells adjust gene expression and metabolism to new conditions.
Exponential
Population doubles repeatedly.
Under favorable conditions, abundance grows geometrically.
Stationary
Net growth slows.
Nutrient limitation and waste accumulation balance division with death.
Death
Viable cells decline.
Environmental stress can exceed maintenance capacity.
Biofilm
Surface-associated community state.
Biofilms alter diffusion, gene expression and resistance to environmental stress.
Microbes exchange genes as well as inherit them.
Mutation and horizontal gene transfer can spread new traits rapidly through microbial populations.
Create new sequence variants.
Large populations generate many mutations even when per-cell rates are low.
Take up free DNA.
Some microbes can incorporate DNA from the environment.
Viruses move bacterial DNA.
Bacteriophages can transfer genes between cells.
Direct cell-to-cell DNA transfer.
Plasmids can spread metabolic or resistance traits.
DNA can move within genomes.
Transposons and related elements restructure genetic context.
Environment filters variants.
Antibiotics, nutrients and host conditions can rapidly change population composition.
Most microbes live in communities, not isolation.
Competition, metabolic exchange and signaling create collective behavior.
| Interaction | Mechanism | Community effect |
|---|---|---|
| Competition | Shared resource limitation | Exclusion or niche separation |
| Cross-feeding | One species consumes another’s product | Metabolic interdependence |
| Quorum signaling | Population-density-dependent molecules | Coordinated gene expression |
| Biofilm formation | Attachment + extracellular matrix | Spatial structure and protection |
| Phage interaction | Viral infection of microbes | Population control and gene transfer |
Pathogenesis is an interaction between microbe and host.
Disease depends on entry, replication, tissue interaction, immune response and transmission—not microbe presence alone.
Entry
Reach a suitable host site through an exposure route.
Adhere
Attach or colonize despite physical clearance mechanisms.
Acquire
Obtain nutrients and conditions needed for replication.
Evade
Avoid or manipulate host defenses long enough to persist.
Damage
Direct microbial effects and host inflammation can both injure tissue.
Transmit
Exit one host and reach another, completing the ecological cycle.
Brock Biology of Microorganismsmicrobiology foundation
Prescott’s Microbiologymicrobial diversity and metabolism
Medical Microbiologyhost–microbe interaction
Microbial Ecologycommunities and environmental microbiology