Environmental Influences and Control of Microbial Growth PDF

CHAPTER 5 (5.1-5.6) Environmental Influences and Control of Microbial Growth Copyright © 2024 by W. W. Norton & Company, Inc. Learning Objectives 1. Know the basic classifications used to describe microbes based on their growth under various laboratory-controlled conditions and how that relates to t...

CHAPTER 5 (5.1-5.6) Environmental Influences and Control of Microbial Growth Copyright © 2024 by W. W. Norton & Company, Inc. Learning Objectives 1. Know the basic classifications used to describe microbes based on their growth under various laboratory-controlled conditions and how that relates to their environment 2. Explain how microbes adapt to variations or extremes in temperature, pressure, pH, levels of oxygen and osmotic stress 3. Highlight some of different ways humans use stress to control or eliminate microbes 2 Introduction § Microbes have both the fastest and the slowest growth rates of any known organisms. Some hot-springs bacteria can double in as little as 10 minutes, whereas deep-sea-sediment microbes may take as long as 100 years. What are some differences that could be impacting this? 3 Introduction § These differences are determined by nutrition and niche-specific physical parameters like temperature and pH. 4 5.1 Environmental Limits on Growth § The “normal” growth conditions are: Sea level Temperature 20°C–40°C (68°F - 104°F) A near-neutral pH (~7) 0.9% salt and ample nutrients § These are essentially the conditions for comfortable human living 5 5.1 Environmental Limits on Growth § Extremophiles are any microbes (bacteria, archaea, and a few eukaryotes) that can grow in conditions very different from those for humans. What can studying extremophiles tell us? 6 5.1 Environmental Limits on Growth § The environmental habitat that a species inhabits is based on the tolerance of that organism’s proteins and other macromolecular structures to the physical conditions within that niche. 7 Temperature Effects on Physiology § Bacterial cell temperature matches that of its immediate environment. § Bacteria cannot regulate their cell temperature! 25°C 37°C 8 Temperature Effects on Physiology § Bacterial cell temperature matches that of its immediate environment. § Each organism has an “optimum” temperature, as well as minimum and maximum temperatures that define its growth limits. 25°C 37°C 9 Temperature Effects on Physiology § Changes in temperature impact every aspect of microbial physiology. § Enzymatic activity, membrane fluidity § A species grows most quickly at temperatures where the cell’s proteins work most efficiently. § Proteins are required for most cellular activity 10 Microbial Classification by Growth Temperature § Microorganisms can be classified by their growth temperature: Psychrophiles: ~0°C–20°C 11 Microbial Classification by Growth Temperature § Microorganisms can be classified by their growth temperature: Psychrophiles: ~0°C–20°C Mesophiles: ~15°C–45°C 12 Microbial Classification by Growth Temperature § Microorganisms can be classified by their growth temperature: Psychrophiles: ~0°C–20°C Mesophiles: ~15°C–45°C Thermophiles: ~40°C–80°C 13 Microbial Classification by Growth Temperature § Microorganisms can be classified by their growth temperature: Psychrophiles: ~0°C–20°C Mesophiles: ~15°C–45°C Thermophiles: ~40°C–80°C Hyperthermophiles: ~65°C–121°C 14 Microbial Classification by Growth Temperature § Microorganisms can be classified by their growth temperature: Psychrophiles: ~0°C–20°C Mesophiles: ~15°C–45°C Thermophiles: ~40°C–80°C Hyperthermophiles: ~65°C–121°C § All of these organisms have membranes and proteins best suited for their temperatures. 15 5.2 Osmolarity § Water is critical to life, but environments differ in the amount of water available to growing organisms. § Water activity is a measure of how much water is available for use. § Osmolarity is a measure of the number of solute molecules in a solution and is inversely related to water activity. 16 Osmotic Stress § Osmolarity is also important for a cell because of the cell’s semipermeable plasma membrane. 17 How can solute concentration impact cells? Hypertonic Solution Isotonic Solution Hypotonic Solution How can solute concentration impact cells? Hypertonic Solution Isotonic Solution Hypotonic Solution How can solute concentration impact cells? Hypertonic Solution Isotonic Solution Hypotonic Solution How can solute concentration impact cells? Hypertonic Solution Isotonic Solution Hypotonic Solution Aquaporins § Aquaporins are membrane-channel proteins that allow water to traverse the membrane much faster than by diffusion. These proteins help protect the cell from osmotic stress. 22 Protection against Osmotic Stress § In addition to moving water, microbes have at least two mechanisms to minimize osmotic stress: In hypertonic media, bacteria protect their internal water by synthesizing or importing solutes. 23 Protection against Osmotic Stress § In addition to moving water, microbes have at least two mechanisms to minimize osmotic stress: In hypotonic media, pressure-sensitive or mechanosensitive channels can be used to leak solutes out of the cell. 24 Halophiles Require High Salt § Halophiles require high salt concentrations. Environments from 2 to 4 M NaCl (10%–20% NaCl) – For comparison, seawater is ~3.5% NaCl. 25 5.3 Hydronium (pH) and Hydroxide Ion Concentrations § The concentration of hydrogen ions (H+) [actually, hydronium ions (H3O+)] also has a direct effect on the cell’s macromolecular structures. Extreme concentrations of either hydronium or hydroxide ions (OH−) in a solution will limit growth. 26 pH Optima, Minima, and Maxima § All enzyme activities exhibit optima, minima, and maxima with regard to pH. § Bacteria regulate internal pH to keep their enzymes functioning optimally. Organic acids H+ Intact membranes 27 Neutralophiles, Acidophiles, and Alkaliphiles § Three classes of bacteria are differentiated by the pH range at which the cells grow optimally: Neutralophiles grow at pH 5–8. Acidophiles grow at pH 0–5. Alkaliphiles grow at pH 9–11. 28 pH Homeostasis and Acid Resistance 29 5.4 Oxygen § Unlike humans, many microorganisms can grow in the absence of molecular oxygen (O2). We call these microbes anaerobes. § Other microorganisms resemble humans in their dependence on molecular oxygen. We call these microbes aerobes. Aerobic Anaerobic 30 Aerobes versus Anaerobes – 1 § Strict aerobes can only grow in oxygen. § Microaerophiles grow only at lower O2 levels. § Strict anaerobes die in the least bit of oxygen. § Aerotolerant anaerobes grow in oxygen while retaining a fermentation-based metabolism. § Facultative anaerobes can live with or without oxygen. 31 5.5 Nutrient Deprivation and Starvation § Starvation is a stress that can elicit a “starvation response” in many microbes. Enzymes are produced to increase the efficiency of nutrient gathering and to protect cell macromolecules from damage. Some microbes can go dormant until nutrients return. 32 5.6 Physical, Chemical, and Biological Control of Microbes § A variety of terms are used to describe antimicrobial control measures: Sterilization: killing of all living cells, spores, and viruses 33 5.6 Physical, Chemical, and Biological Control of Microbes § A variety of terms are used to describe antimicrobial control measures: Disinfection: killing or removal of pathogens from inanimate objects; does not necessarily result in sterilization 34 5.6 Physical, Chemical, and Biological Control of Microbes § A variety of terms are used to describe antimicrobial control measures: Antisepsis: killing or removal of pathogens from the surface of living tissues 35 5.6 Physical, Chemical, and Biological Control of Microbes § A variety of terms are used to describe antimicrobial control measures: Sanitation: reducing the microbial population to safe levels 36 Physical Agents That Kill Microbes § High temperature Moist heat is more effective than dry heat. Boiling water kills most cells. Killing spores and thermophiles usually requires a combination of high pressure and temperature. 37 Physical Agents That Kill Microbes § Cold Low temperatures slow growth and preserve strains. Refrigeration temperatures (4 to 8°C) are used for food preservation. 38 Physical Agents That Kill Microbes § Filtration Pore size 39 Physical Agents That Kill Microbes § Irradiation Ultraviolet (UV) light – Has poor penetrating power – Used only for surface sterilization Gamma rays, electron beams, and X-rays – Have high penetrating power – Used to irradiate foods and other heatsensitive items 40 Commercial Disinfectants § These include: Ethanol Iodine Chlorine § These damage proteins, lipids, and/or DNA. Are used to reduce or eliminate microbial content from objects 41