Lecture 8_7Feb2025_before class

Lecture 08: Microbial Growth, part 2

• BIOL 2221: Foundations of Microbiology

• Date: February 7, 2025

Page 2: Today's Topics

• Environmental Limits on Microbial Growth

  • Temperature

  • Salt

  • pH

• Living with Oxygen: Aerobe vs. Anaerobe

• Microbial Communities and Cell Differentiation

• Syphilis

• Due next 2

Page 4: Learning Objectives

• Identify different microbial classes based on preferred environmental niches (pH, temperature, salt).

• Describe biological properties allowing microbes to grow in extreme environments.

Page 5: Introduction to Microbial Growth Rates

• Microbes display a wide range of growth rates.

  • Fastest growth: Hot-springs bacteria can double every 10 minutes.

  • Slowest growth: Deep-sea microbes may take 100 years to double.

• Growth rates influenced by nutrition and environmental parameters (temperature, pH).

Page 6 & 10: Environmental Limits on Microbial Growth

• Bacteria: The most metabolically diverse organisms.

• Key growth considerations:

  • Temperature and pressure

  • Osmotic balance

  • pH level

  • Oxygen (O₂) levels

• Normal conditions: sea-level pressure, temperatures 20–40ºC, neutral pH, 0.9% salt, ample nutrients.

• Extreme niches: Conditions outside these limits, inhabited by extremophiles.

Page 7: Temperature Preferences

• Organisms have optimal temperature ranges for cell membranes and proteins.

Page 8 & 9: Living at Extreme Temperatures

• Thermophiles & extreme hyperthermophiles: Survive in thermal springs.

• Psychrophiles: Adapted to icy environments.

• Adaptation mechanisms:

  • Thermophiles: Saturated fatty acids in membranes for stability.

  • Psychrophiles: Unsaturated fatty acids provide membrane fluidity.

Page 11: Osmotic Pressure Adaptations

• Halophiles (extreme) : Thrive in high salt concentrations (10–20% NaCl).

• Maintain low internal Na+ levels; excrete excess with ion pumps.

• High salt/sugar media can cause cell dehydration, halting growth.

Page 12 & 13: pH and Microbial Growth

• pH levels crucial for microbial survival.

  • Bacteria regulate internal pH, with weak acids disrupting homeostasis (used in food preservation).

• All enzymatic activity depends on pH; protein structure affected by H+ concentration.

Page 14: Mechanisms for pH Homeostasis

• Microbial strategies to maintain pH:

  • Acidic (pH 2): Amino acid decarboxylases pump out protons.

  • Alkaline (pH 9): Na+/H antiport systems scavenge protons.

  • Slightly acidic (pH 5): K+/H antiport systems expel internal protons.

    

Page 16: Learning Objectives on Oxygen

• Differentiate between anaerobes and aerobes.

• Describe groups based on oxygen requirements.

Page 17: Oxygen-Related Growth Zones

• Growth varies with oxygen levels:

  • Aerobic: High O₂

  • Facultative: Can use O₂ or alternate pathways

  • Microaerophilic: Prefer low O₂

  • Anaerobic: No O₂ usage.

    

Page 19: Oxygen for Energy Metabolism

• Many microbes utilize oxygen as a terminal electron acceptor (aerobic respiration).

• Processes involved:

  1. Removal of high energy electrons from glucose.

  2. Electron transport chains extract energy and pump H+ ions.

  3. Water is formed as byproduct from oxygen.

Page 21: Comparison of Fermentation and Aerobic Respiration

• Aerobic respiration yields higher energy (ATP) compared to fermentation.

Page 26: Types of Aerobes and Anaerobes

• Strict Aerobes: Require oxygen and can detoxify ROS.

• Strict Anaerobes: Do not use oxygen; typically sensitive to ROS.

• Microaerophiles: Prefer low oxygen but can neutralize some ROS.

• Facultative Anaerobes: Function in both oxygen-rich and oxygen-poor environments, can neutralize ROS.

• Aerotolerant Anaerobes: Do not mind oxygen but do not use it for metabolism.

Page 29: Learning Objectives on Biofilms and Endospores

• Understand biofilm structure and significance in infections.

• Understand properties of endospores.

Page 30: Case History - Death by Biofilm

• Cystic fibrosis leads to microbial infections like Pseudomonas aeruginosa, linked to severe respiratory diseases.

• Issues with treatments in biofilm-associated infections.

Page 31: Understanding Biofilms

• Most bacterial growth occurs in biofilms, multi-species surface-attached communities (e.g., dental plaque).

Page 33: Properties of Biofilms

• Communication via quorum sensing.

• Increased resistance to antibiotics.

• Major contributors to implant-associated infections.

Page 35: Endospores

• Certain Gram-positive bacteria produce endospores for survival under adverse conditions.

• Examples: Bacillus anthracis, Clostridium species.

Page 37: Properties of Endospores

• High resistance to environmental stressors due to protective layers.

• Dormancy lasts for decades, requires no nutrition.

Page 38: Summary of Microbial Survival Strategies

• Microbes can thrive in extreme conditions and have developed unique adaptations.

Page 40-49: Syphilis Overview

• Syphilis: Caused by Treponema pallidum, manifests in stages: primary (chancre), secondary (rash), tertiary (organ involvement).

• Congenital syphilis involves serious complications in newborns, including neurosyphilis.

• Prevention focuses on safe sex and regular screening, while treatment often involves penicillin.