Chapter 7: Microbial Nutrition, Ecology, and Growth

Symbiotic (required relationship):
- Mutualism: Both benefit, essential.
- Commensalism: One benefits, other unaffected.
- Parasitism: One benefits (parasite), other harmed (host).
- Syntrophy: Partners cooperate, share nutrients.
- Antagonism: One hinders/destroys another.
Nonsymbiotic: Free-living, not essential.

Biofilms: Surface-attached communities, held by extracellular matrix; allow communication.
Quorum sensing: Microbe communication system to coordinate behavior (e.g., biofilm formation).

Human body hosts normal microorganisms (microbiota).
Antibiotics alter microbiota; debate on their use versus immune system handling infections to protect natural flora.

Carbon Sources:
- Heterotroph: Organic carbon from other organisms.
- Autotroph: Inorganic carbon (CO_2), self-sufficient.
Energy Sources:
- Chemotroph: Energy from chemical compounds.
  - Chemoorganotrophs: Organic chemicals.
  - Chemolithotrophs: Inorganic chemicals.
- Phototroph: Energy from light (photosynthesis).
Most heterotrophs are chemoheterotrophs (carbon & energy from organic compounds).
Saprobes: Decomposers, feed on dead organic matter.
Parasites: Live on/in host, get nutrients; obligate parasites require host.
Opportunistic pathogens: Cause disease under right conditions.
Growth Factors: Essential organic nutrients organisms can't synthesize (e.g., vitamins, amino acids).

Passive Transport (No energy, high \to low concentration):
- Diffusion: Small, uncharged molecules move directly.
- Osmosis: Water movement across membrane to higher solute concentration.
- Facilitated Diffusion: Uses carrier protein for specific polar/charged molecules.
Active Transport (Energy needed, low \to high concentration):
- Carrier-Mediated Active Transport: Uses carrier proteins (permeases) & energy (e.g., ATP) for ions, small organics.
- Group Translocation: Molecule chemically altered during transport; links transport to metabolism.
Bulk Transport (Energy needed for large substances via vesicles):
- Endocytosis: Bringing into cell.
  - Phagocytosis: "Cell eating" (solids).
  - Pinocytosis: "Cell drinking" (liquids).
Osmosis Example: Cell with 60% glucose in 15% glucose water \implies water moves into cell (hypotonic solution outside).

Niche: Organism's adaptation to living conditions.
Key factors: Temperature, Oxygen, pH, Osmotic pressure, Barometric pressure.

Cardinal Temperatures: Minimum (lowest for growth), Maximum (highest for growth), Optimum (fastest growth/metabolism).
Temperature Groups:
- Psychrophiles: Grow below 15 ext{°C}, can grow at 0 ext{°C}.
- Mesophiles: Grow between 20 ext{–}40 ext{°C} (most human pathogens).
- Thermophiles: Grow above 45 ext{°C}.

Oxygen use generates harmful reactive oxygen species (e.g., O_2^- ext{ and } H_2O_2).
Microbes with oxygen-detoxifying enzymes (superoxide dismutase, catalase) can use oxygen.
Categories:
- Aerobe: Uses oxygen, has detox enzymes.
  - Obligate Aerobe: Requires oxygen.
  - Facultative Anaerobe: Can use oxygen, but can grow without it (flexible).
- Microaerophilic: Needs small amount of oxygen; too much is harmful.
- Anaerobe: Does not use oxygen.
  - Obligate Anaerobe: Cannot survive with oxygen (lacks enzymes).
  - Aerotolerant Anaerobe: Does not use oxygen, but can tolerate its presence.

Barophiles (Piezophiles): Survive under high pressure; rupture at normal pressure.

Generation (Doubling) Time: Time for population to double.
Exponential Growth: N_t = N_0 \cdot 2^n
- N_0 = initial cells, N_t = cells after time t, n = generations (n = t/g).
Bacterial Growth Curve Stages:
1. Lag Phase: Adjustment, little growth.
2. Exponential (Log) Phase: Rapid, consistent growth.
3. Stationary Phase: Growth rate = death rate (nutrient depletion, waste build-up).
4. Death Phase: Cells die exponentially.