Microbiology Quiz on Organisms and Spoilage

Agar

• Agar is not a nutrient
• Robert Koch developed methods for pure culture
• Agar is ideal for solidifying media due to chemical and physical properties that make it neutral and remain solid at room temperature.

Bacterial Reproduction

• Bacterial reproduction is known as binary fission.

Biofilms

• Most microbes live in poly saccharide-encased communities termed biofilms.
• Biofilms may enhance bioremediation efforts and protect organisms against harmful chemicals.

Pure Culture and Colony

• Pure culture: All bacterial cells that result from the replication of a single original bacteria species/organism.
• Colony: A visible cluster of microorganisms that originate from a single parent cell on growth medium.
• Streak-plate method : A method for isolating bacteria.

Bacterial Culture Storage

• Agar slant in refrigerator.
• Frozen in glycerol solution.
• Freeze-dried.

Bacterial Growth Curve

• Lag Phase: Introduction to sterile medium, cells are maturing but not dividing, and begin synthesizing enzymes required for growth.
• Exponential/Log Phase: Bacteria are rapidly increasing in number, and most susceptible to antibiotics.
• Stationary Phase: Nutrient level is low to sustain growth, and the total number of cells remains constant.
• Death Phase: Total number of viable cells declines. Some cells survive and adapt to tolerate worsened conditions.
• Bacteria can become more resistant to drugs during the death phase.

Bacterial Growth Considerations

• During which phase of growth are bacteria most susceptible to antibiotics? Exponential phase
• In which phase does the bacterial population rapidly multiply and cell numbers increase? Exponential phase

Bacterial Groups Based on Temperature, pH and Oxygen Preference

• Temperature:

  • Psychrophiles: -5 to 15 degrees Celsius, found in arctic regions.
  • Psychrotrophs: 20 to 30 degrees Celsius, associated with food spoilage.
  • Mesophiles: 25 to 45 degrees Celsius, includes pathogens (35 to 40 degrees Celsius).
  • Thermophiles: 45 degrees to 70 degrees Celsius (hot springs).
  • Hyperthermophiles: 70 to 110 degrees Celsius, members are Archaea, found in hydrothermal vents.
  • Limiting growth of fast-growing mesophiles; Psychrophiles and trophs still grow but slowly; Freezing preserves but does not kill microbes; Temperature and disease: Hansen's disease/leprosy (coolest regions - ears, hands, feet and fingers) due to preference of MYCOBACTERIU M LEPRAE.

• Oxygen:

  • Obligate aerobe: Grows only when oxygen is available; requires oxygen for respiration; produces superoxide dismutase and catalase.
  • Facultative anaerobe: Grows best when oxygen is available but can grow without it; uses O2 for respiration if available, produces superoxide dismutase.
  • Obligate anaerobe: Cannot grow when oxygen is present; does not use O2; does not produce superoxide dismutase and catalase.
  • Microaerophile: Grows only if small amounts of oxygen are available; requires O2 for respiration; produces some superoxide dismutase and catalase.
  • Aerotolerant anaerobe: Grows equally well with or without oxygen; does not use oxygen; produces superoxide dismutase but not catalase.
  • Shake tube growth demonstrates organisms' oxygen requirements.

pH

• Most microbes are neutrophils (range of pH 5 to 8, optimum near pH 7).
• Acidophiles are optimally at pH below 5.5.
• Alkaliphiles are optimally at pH above 8.5.

Proteins in Thermophiles

• Resist denaturing; PCR = polymerase chain reaction

Human Pathogens

• Human pathogens prefer which temperature range? 35 to 40 degrees Celsius (human body = 37).
• Optimum pH for most bacteria is near pH 7.
• Enzymes deal with toxic oxygen-containing molecules (superoxide dismutase and catalase deal with ROS (o2 in cells)).

### Food Preservation

• Dissolved salts and sugars make water unavailable to cells, which helps preserve food.

Metabolism

• Anabolism: Building up molecules, forming bonds between molecules, dehydration synthesis, monomer + monomer = polymer
• Catabolism: Breaking down molecules, exergonic reactions, energy released.

Energy

• Potential energy: at rest
• Kinetic energy: movement
• Exergonic vs. endergonic reaction.
• Oxidation vs. reduction.
  • Oxidation = Atom loses an electron, exergonic, supply of oxygen and removal of electron
  • Reduction = Atom gains an electron, reduced due to negative charge, endergonic

ATP Production

• REDOX = couple to make ATP, Electron acceptor = oxygen. Presence of Hydrogen = reduced, no hydrogen = oxidized

Enzymes

• Enzymes speed up conversions of substrates into products by lowering activation energy; structure and function.
• Factors influencing enzyme activity include activation energy and regulation (allosteric, competitive, non-competitive).

Inhibition

• Competitive inhibition: Inhibitor binds to active site (mimics structure of substrate)
• Non-competitive inhibition: Inhibitor binds to a different site than active site.
• Example: Sulfa drugs blocking folic acid synthesis (mimics PABA, needed for folate -> amino acid required for growth) and reversible.
• What is Feedback Inhibition? Show it schematically; Regulating the amount of product produced and often involves the use of allosteric enzymes; end-product inhibits enzyme 1.

Cofactors

• Cofactors assist enzymes.

Electron Carriers

• What are electron carriers? Give two examples; NAD, FAD, and NADP.
• Coenzymes are organic factors: FAD, NAD, and NADP.

Metabolic Pathway

• Which central metabolic pathway generates most of the reducing power? Krebs cycle (or TCA cycle).

Fermentation

• In anaerobic fermentation, carbon atoms stay in lactate or ethanol + CO2; End = no more carbon.

Electron Transport Chain

• Requires a membrane and generates a concentration gradient of protons; oxygen serves as the terminal electron acceptor.
• ATP synthase.
• Hydrogen flow down concentration gradient

Energy Production

• Ready to use energy:
  1. Substrate level phosphorylation
  2. Oxidative phosphorylation
  3. Photophosphorylation (light energy donation)
• Proton Motive force: Flow of protons, drives ATP synthase
• Chemiosmosis

Respiration

• Catabolism of proteins, lipids, and polysaccharides if oxygen is not available. Aerobic vs. anaerobic respiration; Fermentation as an alternative to cellular respiration.