Lecture Notes: Chapter 4 of Microbiology: An Evolving Science
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Course
Microbiology (BIOM122)
Institution
University Of California - Irvine
Typed lecture notes covering chapter 4 of Microbiology: An Evolving Science, the textbook used in the "General Microbiology" course (BioM122) at UCI. Aligns with lecture 4.
• Macronutrients: major elements in cell macromolecules and cations necessary for protein function.
• Micronutrients: trace elements necessary for enzyme function.
• Autotrophs: fix CO2 and assemble into organic molecules. Ex. Photoautotrophs, Chemiolithoautotrophs
• Heterotrophs: used pre-formed organic molecules and assemble them into new organic molecules. Ex. Photoheterotrophs,
Chemoheterotrophs/organotrophs
○ Receive their energy from breaking down complex organic molecules.
• Phototrophs: obtain energy from chemical rxns triggered by/that absorb light.
• Chemotrophs: obtain energy from oxidation-reduction source; does NOT absorb light.
• Lithotrophs: use inorganic molecules to donate electrons.
• Organotrophs: use organic molecules to donate electrons.
• Nitrogen fixers: possess nitrogenase, which converts N2 to ammonium ions (NH4+).
○ May be free-living in soil or water, or they may form symbiotic associations w/ plants. Ex. Rhizobium are symbionts in
leguminous plants.
• Nitrifiers: oxidize ammonia to nitrate (NO3-).
• Denitrifiers: convert nitrate to N2. Ex. Anaerobic bacteria in the lungs use nitrate as an alt e- acceptor to oxygen.
• Selectively permeability in membrane:
○ Permeases: substrate-specific carrier proteins.
○ Dedicated nutrient-binding proteins that patrol the periplasmic space.
○ Membrane-spanning protein channels/pores
• Facilitated diffusion: passive transport; molecules are moving down their conc gradient. NO energy used!
• Active transport: uses energy b/c molecules are moving against their conc gradient.
○ In symport, molecules travel in the same direction.
○ In antiport, molecules are actively transported in the opposite direction. Uses ATP.
• ABC transporters: largest family of energy-driven transport systems.
○ Uptake ABC transporters: essential for transporting nutrients.
○ Efflux ABC transporters: used as multidrug efflux pumps.
• Siderophores: specialized molecules secreted to bind ferric ion (Fe3+) and transport it into the cell. Iron is released into the
cytoplasm and reduced to the more useful ferrous form (Fe2+).
• Group translocation: uses energy to chemically alter the substance during its transport. Changes chemical composition of a
molecule so that conc gradient doesn't matter.
○ Phosphotransferase system (PTS): present in all bacteria. Uses energy from PEP to attach a phosphate to specific sugars.
• Bacteria are grown in culture media, in either:
○ Liquid/broth: useful for studying pure cultures.
○ Solid (agar gel): useful for separating mixed cultures.
• Pure colonies are isolated in 2 main techniques:
○ Dilution streaking: a loop is dragged across the surface of an agar plate. Goal is to isolate cells so that one can start a
colony.
○ Spread plate: tenfold serial dilutions are performed on a liquid culture. A small amt of each dilution is plated.
○ Absorbance measurement of optical density: shines light thru liquid culture to quantify cells present.
• Types of media:
○ Complex media: nutrient-rich but poorly defined.
○ Minimal defined media: contain solely essential growth nutrients.
• All components and concentrations known.
○ Enriched media: complex media where specific-blood components are added.
○ *Selective media: favor growth of one organism over another.
○ *Differential media: exploit differences b/w 2 species that grow equally well.
• Different microbes have specificity of conditions (ie growth factors) they need in order to grow in a laboratory media.
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