micrb lec 4
What’s the point of the “composition of a cell” slide?
Cells are mostly macromolecules + elements, so growth depends on getting the right elements + nutrients.
Define macronutrients (microbio context).
Nutrients required in large amounts that play major roles in cell structure + metabolism (ex: C, H, O)
: Define micronutrients/trace elements.
Needed in small amounts; mainly for enzyme function + maintaining protein structure (ex: Mn, Zn, Ni).
What are growth factors/vitamins (why needed)?
Organic compounds some microbes can’t synthesize, so they must be supplied for growth.
Why is iron a special case nutrient?
Often scarce/insoluble → microbes use siderophores to capture it.
What are the 3 cardinal temperatures and what do they mean?
Minimum (slow growth; membranes/enzymes sluggish), optimum (enzymes best), maximum (can’t grow)
Why does growth rise with temperature until the optimum?
Chemical reactions/metabolism speed up as temp increases.
Why does growth drop sharply after the optimum?
Proteins denature, membranes destabilize → loss of function/lysis risk.
What matters more on the temperature curves: exact numbers or shape?
Shape/relationship matters more than memorizing exact temperatures.
Match each class to the idea: psychrophile, mesophile, thermophile, hyperthermophile.
Cold-lover / human-ish optimum / heat-lover / extreme-heat lover.
“Pink snow” is caused by what type of organism?
Psychrophiles (example slide: snow algae).
Where do hyperthermophiles commonly live?
Hydrothermal vents/geysers (very hot environments).
How can bacteria adapt proteins to high temperatures (example from slides)?
Ca²⁺ can stabilize proteins/enzymes so they stay active at high temps.
Define osmolarity vs tonicity.
Osmolarity = total solute concentration; tonicity = concentration of permeable solutes (effective osmotic pressure).
Hypotonic / isotonic / hypertonic: what’s the key idea?
Direction of water movement depends on solute differences across the membrane.
What does osmotolerant mean (with example)?
Can grow well in high-solute conditions (example: yeast).
What is a halophile vs halotolerant (concept)?
Halophile requires salt; halotolerant survives salt but doesn’t require it.
How do halophiles avoid water loss in salty environments?
They adjust internal osmolarity using compatible solutes that aren’t membrane-permeable.
What’s the point of “compatible solutes”?
Raise internal solute to match outside without disrupting proteins.
What’s the big idea of pH optima for microbes?
Different microbes have different pH ranges where enzymes/membranes work best.
Know the 3 pH classes and what they prefer.
Acidophiles (low pH), neutrophiles (~neutral), alkaliphiles (high pH).
Oxygen requirement isn’t just about metabolism—also about what?
Handling toxic oxygen species (ROS).
List the 3 key ROS
Superoxide (O₂⁻), hydrogen peroxide (H₂O₂), hydroxyl radical (•OH).
What enzymes protect aerobes from ROS (name them)? (3)
Superoxide dismutase, catalase, peroxidase.
What does the oxygen test tube diagram represent conceptually?
Where different microbes grow along an O₂ gradient (top = oxic, bottom = anoxic), reflecting oxygen tolerance.
What’s the key link between oxygen growth patterns and metabolism?
O₂ availability relates to ETC usage and the terminal electron acceptor.
Catalase test—what’s the “positive” sign?
Bubbling from O₂ release when H₂O₂ is broken down (concept shown).
What is hydrostatic pressure relevance for microbes?
Deep-sea environments have high pressure that affects membranes/proteins.
Barotolerant vs barophilic
barotolerant: affected but can tolerate; barophilic: requires pressure due to adaptations (esp. membranes)
What does a spectrophotometer OD reading actually measure here?
Light scattering (turbidity)—OD is not true absorbance in this context.
Why does OD become unreliable at high cell numbers?
O D vs cell density isn’t perfectly linear (especially at higher densities).
Why can’t OD distinguish living vs dead cells?
Dead cells can still scatter light → OD counts “stuff,” not viability.
When is membrane filtration useful vs OD?
When cells are too dilute for OD or you want specific organisms (common for aquatic samples).
What’s the key principle of membrane filtration counting?
Filter traps bacteria (pores too small for bacteria), then incubate membrane on nutrient source → colonies form.
What’s a major advantage and limitation of membrane filtration?
advantage: counts viable culturable cells; limitation: only counts what grows on your media and takes longer.
What are fecal coliforms (why used in water testing)?
Indicator bacteria originating in intestines of warm-blooded animals.
Defined vs complex media (core difference + example).
defined: exact chemicals known (ex: sucrose + specific salts).
Complex: exact composition unknown (ex: tryptone, yeast extract).
Selective vs differential media
Selective favors some organisms/inhibits others (antibiotics, high salt). Differential makes visible differences among growers (pH indicator, blood).
Why do serial dilutions before plating?
T o reach a dilution where colonies are countable, then back-calculate original concentration.
What’s the key math idea in serial dilutions?
Each step is often 10-fold; final CFU/mL = colonies ÷ (volume plated × dilution).
Why aren’t microorganisms killed instantly?
Death typically occurs exponentially across a population.
Define decimal reduction time (D-value).
Time required to kill 90% of organisms (1-log reduction).
What are persister/VBNC cells and why do they matter?
Viable but nonculturable cells can survive treatment and later recover → can cause infection again.
Define bacteriostatic vs bactericidal vs bacteriolytic using the slide’s logic.
Bacteriostatic stops growth (reversible). Bactericidal kills without lysis (total count may stay). Bacteriolytic kills + lyses cells.
If you remove the agent, which effect can “resume growth”?
Bacteriostatic can resume; bactericidal/bacteriolytic do not.
Sterilization vs disinfection
Sterilization removes/destroys all viable organisms. Disinfection removes/kills pathogens but typically not endospores.
Sanitization vs antisepsis.
Sanitization lowers microbes to “safe” levels. Antisepsis prevents infection on living tissue using chemical agents.
What is “chemotherapy” in this context?
Antibiotics used to kill/inhibit microbes inside the body.
High moist heat (autoclaving): what does it do and what category is it?
Sterilization method; destroys viruses, fungi, bacteria including endospores.
Pasteurization (low moist heat): what’s the goal?
Doesn’t sterilize; kills pathogens and reduces microbial load to slow spoilage (milk/beer/etc).
How does temperature affect D-value conceptually?
Higher temperature → shorter D-value (kills faster).
UV radiation: why is ~260 nm most bactericidal and what’s the damage?
DNA absorbs strongly → forms thymine dimers blocking replication/transcription.
What’s the main limitation of UV sterilization?
Poor penetration (blocked by glass, films, water, dirt) → mostly surface sterilization.
Gamma radiation: what’s the key advantage + what damage does it cause?
Penetrates deeply; causes DNA double-strand breaks, ROS, membrane damage; can kill endospores.
Membrane filtration for liquids: what pore size is used on the slide?
About 0.2 µm filters (for removing microbes from liquids).
: HEPA filtration is used for what type of sample?
Air/gaseous samples—to create sterile airflow/workspace (not for sterilizing “a liquid sample”).
Phenolics—mechanism + what they kill + major limitation.
Denature proteins + disrupt membranes; kill bacteria incl. M. tuberculosis, fungi, enveloped viruses; not spores; effective with organic material but can irritate skin/odor.
Alcohols—what they kill, what they don’t, and the concentrationa
Bactericidal/fungicidal, kills enveloped viruses; not sporicidal; works by protein denaturation + lipid dissolution; concentration matters (too high can dehydrate and reduce effectiveness; ~50–70% is good
Halogens vs aldehydes vs quats vs hydrogen peroxide
halogens: oxidize/iodinate; antiseptics; may kill spores at high conc but irritation/staining.
Aldehydes: crosslink proteins; can kill spores (strong disinfectants).
Quats: detergent-like; kill most bacteria but not M. tuberculosis or endospores; inactivated by hard water/soap.
H₂O₂: oxidizes proteins/lipids/sugars; kills many bacteria/viruses/fungi; works on skin + surfaces.
Macronutrient vs micronutrient
Macronutrients are required in larger quantities than micronutrients.
Can thermophiles grow at 80°C
No—at that temperature their proteins denature
Compared to mesophiles, what membrane feature helps psychrophiles in cold temps?q
More unsaturated fatty acids → keeps membrane more fluid.
High salt outside the cell = what tonicity, and which way does water move?
Hypertonic outside → water moves out of the cell (net).
In the “high salt solution” multiple-choice, which option is correct and why?
The option saying water moves out because the solution is hypertonic (their note: “super salty outside so water comes out”).
What do halophiles do internally to handle high external salt (key phrase)?
Increase internal osmolarity using compatible solutes.
Best use of a spectrophotometer (OD) from the options?
Quantify intact cells in a pure culture
Why is OD not best for “live/viable” counts in natural samples (lake/ocean/food)?
OD can’t distinguish live vs dead vs debris, and dilute/dirty samples are a problem.
Membrane filtration is best for what scenario type?
Counting viable cells in a liquid sample (requires growth on the filter/media).
Growth curve question (bactericidal antibiotic mid-exponential) measured by OD—what’s the key idea?
Bactericidal kills but doesn’t lyse, so OD may look nearly unchanged—OD can’t separate bacteriostatic vs bactericidal well.
UV radiation kills bacteria mainly by what DNA damage?
Thymine dimers
Gamma radiation kills bacteria by
double-strand breaks + ROS + membrane disruption
Cleaning a bathroom counter suspected with C. difficile (endospores): what matters most?
Use a chemical that is sporicidal (kills endospores)