Overview
This lecture introduces core concepts in microbiology, including cell structure, classification, metabolism, microscopy techniques, and the foundational role of microbes in ecosystems and human health.
Course Structure and Learning Outcomes
- Understand core concepts and lab skills in microbiology.
- Demonstrate hypothesis testing, experimental design, data interpretation, and communication of results.
- Analyze scientific literature related to microbiology.
- Assessment: Three lecture exams, final exam, weekly assignments, iClicker questions, lab exams, report, presentation, and notebook.
Laboratory Essentials
- Learn sterile technique, culturing, isolation, identification, DNA extraction, biochemical assays, and quantification of microbes.
- Practice food and water microbiology, phage assays, and bacterial physiology.
Microbial World: History, Classification, Roles
- Microorganisms are ancient (3.5–4 billion years old) and found everywhere life is possible.
- Major groups: Bacteria, Archaea (prokaryotic); Protozoa, Algae, Fungi, Small invertebrates (eukaryotic); Viruses and Prions.
- Microbes cycle nutrients (carbon, nitrogen), decompose material, and impact agriculture and food through fermentation.
Cell Structure and Function
- Prokaryotes: no nucleus, single cell, smaller, possess cell walls.
- Eukaryotes: nucleus, organelles (mitochondria, Golgi), larger, can be multicellular.
- All cells share cytoplasmic membrane, DNA, ribosomes, and metabolism.
- Cell morphologies: cocci (spherical), rods, spirilla, spirochetes, pleomorphic forms.
Microscopy and Staining
- Types: Bright-field, phase-contrast, dark-field, fluorescence microscopy.
- Magnification (up to ~2,000x), resolution, and contrast are key.
- Gram stain differentiates bacteria: Gram-positive (thick peptidoglycan, purple), Gram-negative (thin peptidoglycan, LPS outer layer, pink).
Cell Membranes and Walls
- Bacterial/Eukaryotic membranes: phospholipid bilayer with embedded proteins, stabilized by ions.
- Archaeal membranes: ether-linked isoprenes, sometimes monolayers, no fatty acids.
- Cell wall structure: Bacteria (peptidoglycan), Archaea (pseudomurein or S-layers).
Other Cell Surface Structures
- Capsules/slime layers: protect, aid attachment, resist desiccation.
- Fimbriae and pili: attachment, genetic exchange.
- Inclusions: storage of carbon, phosphates, sulfur, iron, gas vesicles for buoyancy.
- Endospores: dormant, resistant cells formed mainly by Gram-positive bacteria.
- Flagella: mobility; arrangement and structure differ between Bacteria and Archaea.
Metabolic Strategies
- Metabolism = all chemical reactions in a cell; divided into catabolism (energy release) and anabolism (energy use).
- Energy from redox (oxidation-reduction) reactions; electron donors (oxidized) and acceptors (reduced).
- Major energy conservation pathways: Fermentation (substrate-level phosphorylation), Respiration (oxidative phosphorylation), Photosynthesis (photophosphorylation).
- Types of metabolism: aerobic respiration (O2 as acceptor), anaerobic respiration (other acceptors), fermentation (organic molecule as acceptor).
- Microbes display metabolic diversity: chemoorganoheterotrophs, chemolithoautotrophs, phototrophs.
Microbial Photosynthesis and Carbon Fixation
- Anoxygenic photosynthesis: no O2 produced, different electron donors.
- Oxygenic: uses H2O as donor, O2 produced, two photosystems (Z scheme).
- Calvin cycle: fixes CO2 to organic carbon using RubisCO enzyme.
Nitrogen Metabolism and Syntrophy
- Nitrogen fixation: only some prokaryotes convert N2 to ammonia.
- Anaerobic respiration uses alternatives to O2 as final electron acceptor (e.g., nitrate).
- Syntrophy: microbial partnerships degrade substances together, important in carbon cycling.
Key Terms & Definitions
- Prokaryote — cell lacking nucleus and organelles (Bacteria, Archaea).
- Eukaryote — cell with nucleus and organelles (protozoa, fungi, algae).
- Gram Stain — differential stain to classify bacteria by cell wall type.
- Peptidoglycan — structural polysaccharide in bacterial cell walls.
- Endospore — highly resistant, dormant cell type in some bacteria.
- Chemotroph — organism deriving energy from chemical compounds.
- Phototroph — organism deriving energy from light.
- Autotroph — organism using CO2 as carbon source.
- Heterotroph — organism using organic carbon.
- Fermentation — energy process with internal organic electron acceptor.
- Aerobic Respiration — energy process with O2 as final electron acceptor.
- Calvin Cycle — pathway fixing CO2 into organic molecules.
Action Items / Next Steps
- Submit lecture assignment (LA 4 and 5) by 9/21.
- Review microscopy, cell structure, and metabolic diversity for next class.
- Complete group homework on microbial nutrition and photosynthesis.
- Read assigned article by Wei et al. (2023) and answer provided questions.