Prokaryotic Growth Dynamics

Dynamics of Prokaryotic Growth

• A pure culture contains a single species of microorganism without contamination.
• Pure cultures are maintained in labs using agar plates (solid media) or liquid broth.
• Streak plate and pour plate techniques are used to obtain pure cultures.

Bacterial Growth and Metabolite Production

• Bacterial growth stages include Lag Phase, Log Phase, Stationary Phase, Death Phase, and Prolonged Decline.
• Cells in the log phase rapidly divide, producing primary metabolites and are most susceptible to antibiotics.
• In the stationary phase, growth slows, producing secondary metabolites, and antibiotic resistance increases.

Bacterial Fission and Exponential Growth

• Binary fission is when one cell splits into two identical daughter cells.
• Exponential growth occurs when cell numbers double at a constant rate.
• Generation time is the time it takes for a population to double.

Colony Forming Units (CFU)

• CFU represents viable cells that can divide.
• The center of a colony dies first due to nutrient depletion and waste accumulation.

Environmental Factors Affecting Growth

• Temperature affects growth as follows:
  • Psychrophiles thrive in cold.
  • Mesophiles thrive at human body temperature..
  • Thermophiles thrive in heat.
• Oxygen affects growth as follows:
  • Obligate aerobes require oxygen.
  • Facultative anaerobes can grow with or without oxygen.
  • Obligate anaerobes cannot grow with oxygen.
• pH affects growth as follows:
  • Acidophiles prefer low pH.
  • Alkaliphiles prefer high pH.
• Halophiles thrive in high salt conditions.

Microbes That Spoil Food in a Refrigerator

• Psychrotrophs and Psychrophiles can grow at low temperatures.

Q10 Rule

• A 10°C increase doubles enzyme activity and growth rate.

SOD and Catalase

• Superoxide Dismutase (SOD) converts superoxide radicals to hydrogen peroxide.
• Catalase breaks down hydrogen peroxide into water and oxygen.
• Aerobic microbes produce SOD and catalase.

Diffusion, Osmosis, & Microbial Growth

• Movement of water and solutes across membranes affects pH and nutrient uptake.
• High salt or sugar environments can cause plasmolysis.

Microbial Strategies for High/Low pH and Salt

• Acidophiles use proton pumps.
• Halophiles accumulate solutes to retain water.

Foods Preserved by Salt/Sugar

• Salt is used to preserve cured meats and pickles.
• Sugar is used to preserve jams and honey.

Nutritional Factors and Microbial Growth

• Photoautotrophs use light and CO2.
• Chemoheterotrophs use organic molecules for energy and carbon.

Growth Factors & Fastidious Organisms

• Growth factors are compounds that microbes cannot synthesize.
• Fastidious organisms require specific nutrients to grow.

Cultivating Prokaryotes

• Liquid media are good for large populations, but isolating species is difficult.
• Solid media help isolate pure colonies.
• A closed system has no new nutrients added.
• An open system has nutrients added and waste removed.

Bacterial Growth Curve

• Bacterial growth curves include Lag, Log, Stationary, Death, and Prolonged Decline phases.

Stage of Prolonged Decline

• Some cells survive by adapting and consuming dead cells.

Counting Bacterial Growth

• Direct counts (microscopy, plate count) count only live cells.
• Indirect counts (turbidity, dry weight) estimates the total number of cells.

Growth in Nature and Biofilms

• Biofilms are communities of bacteria encased in slime.
• Snotites are bacteria in caves that form biofilms to aid cave formation.
• Tissue-like biofilms have cells that specialize and communicate.

Control of Microbial Growth: Antimicrobial Procedures

• Factors include Microbe type, contamination level, environmental conditions and safety concerns..
• Microbial control is important in hospitals, food production, and laboratories.

Effects of Temperature, pH, and Debris on Death Rates

• High temperatures speed up killing.
• Extreme pH enhances microbial death.
• Debris protects microbes, making them harder to kill.

Moist and Dry Heat Methods

• Moist heat:
  • Boiling is disinfection.
  • Autoclaving is sterilization.
  • Pasteurization reduces microbes.
• Dry heat:
  • Oven sterilization
  • Incineration.

Time of Exposure & Death Rate

• 90% are killed in 5 minutes starting with 10,000 cells.
  • 5 min: 1,000 remain
  • 10 min: 100 remain
  • 15 min: 10 remain
  • 20 min: 1 remains
  • Total: 25 min for complete elimination

Sterilants & Disinfectants

• Sterilants destroy all microbes.
• High-level disinfectants kill most microbes, including viruses.
• Intermediate-level disinfectants kill fungi, bacteria, and most viruses.
• Low-level disinfectants kill some bacteria and viruses.

Germicidal Chemicals

• Alcohols disinfect surfaces.
• Aldehydes sterilize medical tools.
• Halogens are used for disinfection.
• Peroxygens are safe and degrade into water.
• Quaternary Ammonium Compounds (Quats) are found in household disinfectants.

Filtration Methods

• Depth filters trap large particles.
• Membrane filters remove bacteria.
• HEPA filters remove airborne microbes.

Radiation & Killing Mechanisms

• Ionizing radiation (X-rays, Gamma rays) damages DNA.
• UV radiation damages DNA, good for surfaces.
• Microwaves heat water to kill microbes.
• Shorter wavelengths are more effective.

Food Preservation Methods

• Refrigeration and freezing slow or stop growth.
• Drying removes water.
• Salting/Sugaring draws water out via osmosis.
• Canning kills microbes.
• Pasteurization kills pathogens while maintaining food quality.

Catabolism and Anabolism

• Catabolism breaks down complex molecules into simpler ones, releasing energy.
• Anabolism builds complex molecules from simpler ones, requiring energy.
• Exergonic reactions fuel endergonic reactions.

Oxidation and Reduction

• Oxidation is the loss of electrons.
• Reduction is the gain of electrons.
• NAD+, FAD, NADP+ accept electrons in metabolic pathways, becoming NADH, FADH2, and NADPH.
• NADH and FADH2 donate electrons to the electron transport chain (ETC), generating ATP through oxidative phosphorylation.

Overview of Metabolic Pathways

• Glycolysis:
  • Starts with glucose.
  • Ends with pyruvate.
  • Yields 2 ATP (net).
  • Reducing power: 2 NADH.
• Transition step:
  • Starts with pyruvate.
  • Ends with Acetyl-CoA, CO2.
  • Yields 0 ATP.
  • Reducing power: 2 NADH.
• TCA Cycle:
  • Starts with Acetyl-CoA.
  • Ends with CO2.
  • Yields 2 ATP (GTP).
  • Reducing power: 6 NADH, 2 FADH2.
• Electron Transport Chain:
  • Starts with NADH, FADH2, O2.
  • Ends with H2O, ATP.
  • Yields 34 ATP.
• Pentose Phosphate Pathway:
  • Starts with Glucose-6P.
  • Ends with Ribose-5P, CO2.
  • Yields 0 ATP.
  • Reducing power: NADPH.
• Entner-Doudoroff Pathway:
  • Starts with Glucose.
  • Ends with Pyruvate.
  • Yields 1 ATP.
  • Reducing power: NADH, NADPH.

Energy from Glucose Through Cellular Respiration

• Glycolysis produces 2 ATP and 2 NADH (in cytoplasm).
• Transition Step produces 2 NADH.
• TCA Cycle produces 2 ATP (GTP), 6 NADH, and 2 FADH2.
• ETC produces 34 ATP via oxidative phosphorylation.
• The total ATP yield for aerobic respiration is approximately 38 ATP per glucose molecule.

Differences in ATP Production Mechanisms

• Substrate-level phosphorylation involves direct transfer of a phosphate group to ADP.
• Oxidative phosphorylation produces ATP via a proton gradient in the ETC.
• Photophosphorylation produces ATP using light energy.

Oxygen in Aerobic Cellular Respiration

• Oxygen is the final electron acceptor in the ETC, forming water.
• Without oxygen, the ETC stops, halting ATP production.

Energy Acquisition Efficiency

• Fermentation:
  • Yields 2 ATP (glycolysis only).
  • Uses organic molecules as electron acceptors.
• Aerobic Respiration:
  • Yields ~38 ATP.
  • Uses oxygen as the electron acceptor.
• Anaerobic Respiration:
  • Yields less than 38 ATP.
  • Uses nitrate, sulfate, or CO2 as electron acceptors.

Hydrogen Ions and ATP Synthase in ATP Production

• H+ (protons) pumped across the membrane by the ETC create a proton motive force.
• Protons flow back through ATP synthase, driving ATP production.

Anaerobic Respiration

• Uses a final electron acceptor other than oxygen (e.g., nitrate, sulfate, CO2).
• Produces less ATP than aerobic respiration.

Fermentation vs. Glycolysis

• Fermentation does not use the ETC.
• Glycolysis produces pyruvate, which is converted to organic end products.
• Only substrate-level phosphorylation is used.

Types of Fermentation

• Lactic Acid Fermentation:
  • Uses pyruvate as the electron acceptor.
  • Produces lactic acid.
• Alcohol Fermentation:
  • Uses acetaldehyde as the electron acceptor.
  • Produces ethanol and CO2.
• Mixed Acid Fermentation:
  • Uses various organic compounds as electron acceptors.
  • Produces acetic acid, succinic acid, CO2, and H2.

Enzymes in Macromolecule Breakdown

• Lipids are broken down by lipases into glycerol and fatty acids.
• Proteins are broken down by proteases into amino acids.
• Polysaccharides are broken down by amylases and cellulases into simple sugars.

Biosynthesis: Photosynthesis

• Light-dependent reactions:
  • Use light and H2O as inputs.
  • Produce O2, ATP, and NADPH as outputs.
  • Function: produce energy and reducing power
• Light-independent reactions (Calvin cycle):
  • Use CO2, ATP, and NADPH as inputs.
  • Produce glucose as output.
  • Function: fix carbon

Cyclic vs. Noncyclic Electron Flow

• Cyclic electron flow produces ATP only.
• Noncyclic electron flow produces ATP, NADPH, and O2.

Oxygenic Photosynthesis vs. Other Types

• Oxygenic photosynthesis uses H2O as an electron donor, releasing O2.
• Anoxygenic photosynthesis uses H2S or other compounds, producing sulfur or other byproducts instead of O2.