University:
Rutgers University Newark
Course:
CHEM 335 | Organic Chemistry
Academic year:

2024
Views:

451

Pages:

93
Author:

Mahitab S.

CHAPTER 5 Environmental Influences and Control of Microbial Growth Copyright © 2020 W. W. Norton & Company 1 Chapter Overview  Environmental limits on growth: Temperature and Pressure  Osmolarity  Hydronium (pH) and hydroxide ion concentrations  Oxygen  Nutrient deprivation and starvation  Physical, chemical, and biological control of 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.  These differences are determined by nutrition and niche-specific physical parameters like temperature and pH. 3 5.1 Environmental Limits on Growth – 1  The “normal” growth conditions are: • Sea level • Temperature 20°C–40°C • A near-neutral pH • 0.9% salt and ample nutrients  Any ecological niche outside this window is called “extreme,” and organisms inhabiting them are called extremophiles. 4 5.1 Environmental Limits on Growth – 2  Extremophiles are microbes (bacteria, archaea, and a few eukaryotes) that are able to grow in conditions very different from those for humans. • For example: Temperature > 100°C; pH 2  According to our definition of what is “normal,” conditions on Earth when life began certainly were extreme. • Therefore, the earliest microbes likely grew in these extreme environments. 5 5.1 Environmental Limits on Growth – 3  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.  Note that multiple extremes in the environment can be met simultaneously.  Extremophiles may provide insight into the workings of extraterrestrial microbes we may one day encounter. 6 5.1 Environmental Limits on Growth – 4  Bioinformatic analysis, which uses the DNA sequence of a gene to predict the function of its protein product, allows us to study the biology of organisms that we cannot culture.  Global approaches used to study gene expression allow us to view how organisms respond to changes in their environment. • Knowing which genes and proteins are expressed in a given situation reveals how microbes grow under different conditions and defend themselves against environmental stresses. 7 5.1 Environmental Limits on Growth – 5  Microbes are commonly classified by their environmental niche. Table 5.1 Environmental parameter Classification Classification Classification Temperature Hyperthermophile-with growth above Thermophile-with growth between 50 80 degrees Celsius, considered degrees Celsius and 80 degrees extremophiles Celsius, considered extremophiles Classification Mesophile-growth between 15 degrees Celsius and 45 degrees Celsius Psychrophile-with growth below 15 degrees Celsius, considered extremophiles pH Alkaliphile (growth above pH 9) considered extremophiles Acidophile (growth below pH 3) considered extremophile Empty cell Osmolarity Halophile* (growth in high salt, Empty cell greater than 2 molar upper N-a upper C-l) considered extremophiles Empty cell Empty cell Oxygen Strict aerobe (growth only in upper O 2) Facultative microbe (growth with or without upper O 2)) Microaerophile (growth only in small amounts of upper O 2)) Strict anaerobe (growth only without upper O 2)) Pressure Barophile* (growth at high pressure, greater than 380 atmospheres) considered extremophiles Empty cell Barotolerant (growth between 10 and 500 atmospheres) Empty cell Neutralophile (growth between p H 5 and p H 8) 8 Temperature Effects on Physiology  Bacterial cell temperature matches that of its immediate environment.  Changes in temperature impact every aspect of microbial physiology.  Each organism has an “optimum” temperature, as well as minimum and maximum temperatures that define its growth limits.  A species grows most quickly at temperatures where all of the cell’s proteins work most efficiently; growth stops when rising temperatures cause critical proteins or cell structures to fail. 9 Growth Rate and Temperature  Microbes that grow at higher temperatures typically can achieve higher rates of growth.  Microbial growth rates roughly double for every 10°C rise in temperature.  Thermodynamic principles limit a cell’s growth to a narrow temperature range. • The typical temperature growth range usually spans the organism’s optimal growth temperature by 30 to 40°C. 10 Microbial Classification by Growth Temperature – 1  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. 11 Microbial Classification by Growth Temperature – 2 12 Microbial Classification by Growth Temperature – 3 13 The Heat-Shock Response  The heat-shock response is caused by rapid temperature changes during growth that activate groups of stress response genes.  The protein products of these genes include chaperones that maintain protein shape and enzymes that change membrane lipid composition.  This type of response has been documented in all living organisms examined so far. 14 Adaptation to Pressure – 1  Living creatures at Earth’s surface (sea level) are subject to a pressure of 1 atmosphere (atm), which is equal to 0.101 megapascal (Mpa), or 14 pounds per square inch (psi).  Barophiles or piezophiles are organisms adapted to grow at very high pressures. • Up to 1,000 atm (101 MPa, or 14,600 psi)  Barotolerant organisms grow well over the range of 1–50 MPa, but their growth falls off thereafter. 15 Adaptation to Pressure – 2  Note that many barophiles are also psychrophiles because the average temperature at the ocean floor is 2°C.  How bacteria survive pressures of 80–120 Mpa (11,600–17,404 psi) is still a mystery. • However, it is known that increased hydrostatic pressure and cold temperatures reduce membrane fluidity. • Therefore, specially-designed membranes and protein structures are needed. 16 Adaptation to Pressure – 3 17 5.2 Osmolarity  Water is critical to life, but environments differ in the amount of water actually available to growing organisms.  Water activity (aw) is a measure of how much water is available for use. • Typically measured as the ratio of the solution’s vapor pressure relative to that of pure water • Most bacteria require water activity levels >0.91. • Fungi can tolerate water activity levels >0.86. 18 Osmotic Stress – 1  Osmolarity is a measure of the number of solute molecules in a solution and is inversely related to water activity (aw).  Osmolarity is also important for a cell because of the cell’s semipermeable plasma membrane. • The membrane allows water to pass, but NOT all solutes. • For a cell in a hypertonic medium, water will leave the cell in an attempt to equalize osmolarity across the membrane. • In contrast, suspending a cell in a hypotonic medium will cause an influx of water. 19 Osmotic Stress – 2  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. 20 Protection against Osmotic Stress  In addition to moving water, microbes have at least two mechanisms to minimize osmotic stress: 1. In hypertonic media, bacteria protect their internal water by synthesizing or importing compatible solutes (e.g., proline, glutamic acid, or K+). 2. In hypotonic media, pressure-sensitive or mechanosensitive channels can be used to leak solutes out of the cell. • Outside their osmotic comfort range, these housekeeping strategies become ineffective at controlling internal osmolarity. 21 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.  To achieve a low internal concentration of Na+, halophilic microbes use special ion pumps to excrete sodium and replace it with other cations, such as K+. 22 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.  However, living cells tolerate a greater range in environmental concentration of H+ than of virtually any other chemical substance. 23 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. • Careful pH regulation allows some bacterial species to grow in extremely acidic or alkaline environments. • Biological membranes are relatively impermeable to protons. However, uncharged organic acids can readily cross the membrane then dissociate inside the cell, releasing a proton and disrupting internal pH. 24 Neutralophiles, Acidophiles, and Alkaliphiles – 1  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. – • Include most pathogens Are often chemoautotrophs Alkaliphiles grow at pH 9–11. – Typically found in soda lakes 25 Neutralophiles, Acidophiles, and Alkaliphiles – 2 26 Neutralophiles, Acidophiles, and Alkaliphiles – 3 27 Neutralophiles, Acidophiles, and Alkaliphiles – 4  Often, an organism that is an extremophile for one environmental factor is an extremophile with respect to others as well.  Sulfolobus acidocaldarius is a thermophile and an acidophile. 28 Neutralophiles, Acidophiles, and Alkaliphiles – 5  Salty (saline) soda lakes have high salt concentrations and pH values as high as pH 11.  These contain alkalophiles such as: • The archaeon Halobacterium salinarum • The cyanobacterium Spirulina – It produces high concentrations of carotene pigments that give it a distinct pink color. – It also is a food staple for flamingos indigenous to Africa’s soda lakes and is, in fact, the reason these birds are famously pink! o Humans also consume Spirulina as a health food supplement, but we do not turn pink because the cyanobacteria are only a small component of our diet. 29 Neutralophiles, Acidophiles, and Alkaliphiles – 6 30 Neutralophiles, Acidophiles, and Alkaliphiles – 7  The key to the survival of alkaliphiles is the cell-surface barrier that sequesters fragile cytoplasmic enzymes away from harsh extracellular pH. • Cell wall = Acidic polymers and excess of hexosamines • Cell membrane = High levels of diether lipids  Most alkaliphiles use a sodium motive force in addition to a proton motive force to do much of the work of the cell. They also rely heavily on Na+/H+ antiporters to bring protons into the cell. 31 Neutralophiles, Acidophiles, and Alkaliphiles – 8 32 pH Homeostasis and Acid Resistance – 1  When cells are placed in pH conditions below the optimum, protons can enter the cell and lower internal pH to lethal levels.  Microbes can prevent the unwanted influx of protons by exchanging extracellular K+ for intracellular H+ when the internal pH becomes too low.  Under extremely alkaline conditions, the cells can use the Na +/H+ antiporter to bring protons into the cell in exchange for expelling Na +.  Many, if not all, microbes also possess an emergency global response system referred to as acid tolerance or acid resistance. 33 pH Homeostasis and Acid Resistance – 2 34 5.4 Oxygen – 1  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. • In most cases, aerobes use molecular oxygen as a terminal electron acceptor (TEA) in an electron transport system. • This process is called aerobic respiration. 35 5.4 Oxygen – 2 36 Oxygen Has Benefits and Risks – 1  Oxygen is a benefit to aerobes, which are organisms that can use it as a TEA to extract energy from nutrients.  Oxygen is toxic to anaerobes, and to all cells that do not have enzymes capable of efficiently destroying oxygen’s breakdown products, called reactive oxygen species (ROS). • ROS examples: singlet oxygen, superoxide, hydrogen peroxide, and hydroxyl radicals • ROS seriously damage DNA, RNA, proteins, and lipids by stripping them of electrons. 37 Oxygen Has Benefits and Risks – 2 38 Oxygen Has Benefits and Risks – 3  Different species have evolved to either utilize oxygen, tolerate it, or avoid it altogether. Table 5.2 Aerobic microbes Azotobacter spp. Soil microorganisms; fix atmospheric nitrogen Neisseria spp. Causative organisms of meningitis, gonorrhea Facultative microbes Microaerophilic microbes Anaerobic microbes Actinomyces spp. Soil microorganisms; synthesize antibiotics Bacillus anthracis Cause of anthrax Campylobacter spp. One cause of gastroenteritis Escherichia coli Normal gut biota; additional pathogenic strains Helicobacter pylori Cause of gastric ulcers Azoarcus tolulyticus Degrades toluene Pseudomonas fluorescens Found in soil; degrades TNT and aromatic hydrocarbons Saccharomyces cerevisiae Yeast; used in baking Lactobacillus spp. Ferment milk to form yogurtCause of gastric ulcers Bacteroides spp. Normal gut biota Rhizobium spp. Soil microorganisms; plant symbionts Staphylococcus spp. Found on skin; cause boils Treponema pallidum Cause of syphilis Clostridium spp. Soil microorganisms; causative agents of tetanus and botulism Empty Vibrio cholerae Cause of cholera Empty Desulfovibrio spp. Reduce sulfate 39 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. • They possess both the ability for fermentative metabolism and respiration (anaerobic and aerobic). 40 Aerobes versus Anaerobes – 2 41 Culturing Anaerobes in the Laboratory – 1  Three oxygen removal techniques are used today: 1. Special reducing agents (thioglycolate) or enzyme systems (Oxyrase) eliminate dissolved oxygen from ordinary liquid culture media. 2. A palladium catalyst housed within a sealed anaerobe jar removes oxygen by causing it to react with hydrogen gas to form water. 3. A vacuum system removes all atmospheric gases from an anaerobic glove box so they can be replaced with a precise oxygen-free mixture of N2 and CO2. 42 Culturing Anaerobes in the Laboratory – 2 43 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.  The response is usually triggered by the accumulation of small signal molecules such as cAMP or guanosine tetraphosphate, which globally transform gene expression. • These highly soluble, small molecules can quickly diffuse throughout the cell, promoting a fast response. 44 Starvation Activates Survival Genes – 1  Some organisms growing on nutrient-limited agar form colonies with intricate geometrical shapes that help the population cope, in some unknown way, to food stress. 45 Starvation Activates Survival Genes – 2  When severely stressed by starvation, some members of a bacterial population appear to sacrifice themselves to save others.  They do so by undergoing what is termed programmed cell death. • The dying cells release nutrients that neighboring cells use to survive. • One of the mechanisms for programmed cell death involves so-called toxin-antitoxin (TA) systems. • For each TA pair, the toxin protein will stop growth or kill the cell, but the antitoxin (sometimes a protein, sometimes a small RNA molecule) can inactivate the toxin and allow the cell to survive. • An important toxin-antitoxin system in E. coli is the MazE (antitoxin)– MazF (toxin) module. 46 Starvation Activates Survival Genes – 3 47 Microbes Encounter Multiple Stresses in Real Life  Bacterial stress responses have traditionally been studied in terms of individual stresses.  In the world outside of the laboratory, environmental situations can be quite complex, involving multiple, not just single, stresses. • For example, an organism could simultaneously undergo carbon starvation in a high-salt, low-pH environment. 48 Humans Influence Microbial Ecosystems – 1  Human activities have striking impacts on microbial ecosystems.  Natural ecosystems are typically low in nutrients (oligotrophic), but teem with diversity so that numerous species compete for the same limiting nutrients.  Maximum diversity in an ecosystem is maintained, in part, by the different nutrient-gathering profiles of competing microbes. 49 Humans Influence Microbial Ecosystems – 2  Eutrophication is the sudden infusion of large quantities of a formerly limiting nutrient. • It can lead to a “bloom” of microbes, which can threaten the existence of competing species.  Humans have caused nutrient pollution in several ways: • Runoff from agricultural fields, urban lawns, and golf courses • Untreated or partially treated domestic sewage 50 Humans Influence Microbial Ecosystems – 3  Human-induced climate change is another process that will gradually alter microbial ecosystems. • The addition of heat-trapping CO2 to the atmosphere by burning hydrocarbons is speeding Earth’s warming. • Since 1980, the average atmospheric temperature has risen 0.6°C (1.2°F). 51 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 • Disinfection: killing or removal of pathogens from inanimate objects; does not necessarily result in sterilization • Antisepsis: killing or removal of pathogens from the surface of living tissues • Sanitation: reducing the microbial population to safe levels 52 Cells Treated with Antimicrobials Die at a Logarithmic Rate  Microbes die according to a negative exponential curve, where cell numbers are reduced in equal fractions at constant intervals.  Decimal reduction time (Dvalue) is the length of time it takes an agent or a condition to kill 90% of the population. 53 Physical Agents That Kill Microbes – 1  High temperature • Moist heat is more effective than dry heat. • Boiling water (100°C) kills most cells. • Killing spores and thermophiles usually requires a combination of high pressure and temperature. • At high pressure, the boiling point of water rises to a temperature rarely experienced by microbes. – Even endospores quickly die under these conditions. 54 Physical Agents That Kill Microbes – 2  Steam autoclave • 121°C (250°F) at 15 psi for 20 minutes • Similar conditions are produced in pressure cookers when canning vegetables! 55 Physical Agents That Kill Microbes – 3  Pasteurization • Three time and temperature combinations are approved by the U.S. government for milk pasteurization. – LTLT (low temperature/long time): 63°C for 30 minutes – HTST (high temperature/short time): 72°C for 15 seconds – UHT (ultra-high temperature): 134°C for 1 to 2 seconds – All three methods kill Coxiella burnetii, the causative agent of Q fever and the most heat-resistant non-spore-forming pathogen known. UHT yields nearly sterile milk with a 6-month shelf life. 56 Physical Agents That Kill Microbes – 4  Cold • Low temperatures slow growth and preserve strains. • Refrigeration temperatures (4 to 8°C) are used for food preservation. • For long-term storage of cultures, bacteria are either (a) suspended in a glycerol solution and stored at or below -70°C, or (b) lyophilized (freeze-dried). 57 Physical Agents That Kill Microbes – 5  Filtration • Micropore filters with pore sizes of 0.2 m can remove microbial cells, but not viruses, from liquid solutions. • Samples from 1 ml to several liters can be drawn through a membrane filter by vacuum or can be forced through it using a syringe. 58 Physical Agents That Kill Microbes – 6  Air can also be sterilized by filtration. • Laminar flow biological safety cabinets force air through HEPA filters, which remove >99.9% of airborne particulate material 0.3 μm in size or larger. • Biosafety cabinets are critical to protect individuals working with highly pathogenic material. • Newer technologies embed antimicrobial agents or enzymes directly into the fibers of the HEPA filter. 59 Physical Agents That Kill Microbes – 7 60 Physical Agents That Kill Microbes – 8  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 heat-sensitive items 61 Physical Agents That Kill Microbes – 9  Some bacteria are highly resistant to irradiation  Example: Deinococcus radiodurans • Has the greatest ability to survive radiation of any known organism • Has exceptional capabilities for repairing DNA damaged by radiation • Was genetically engineered for use in bioremediation 62 Chemical Agents – 1  A number of factors influence the efficacy of a given chemical agent, including: • The presence of organic matter • The kinds of organisms present • Corrosiveness • Stability, odor, and surface tension 63 Chemical Agents – 2  The phenol coefficient test uses the high potency of phenol as the benchmark against which all other disinfectants are measured.  Phenol is a toxic liquid, and as such is no longer used as a routine disinfectant. 64 Commercial Disinfectants – 1  These include: • Ethanol • Iodine (Wescodyne and Betadine) • Chlorine • Ethylene oxide (a gas sterilant)  These damage proteins, lipids, and/or DNA. • Are used to reduce or eliminate microbial content from objects 65 Commercial Disinfectants – 2 Table Phenolics Alcohols Aldehydes Quaternary ammonium compounds The 2 dimensional structure of phenol. An alcohol group is attached to one The 2 dimensional structure of ethanol. The carbon of a methyl groupis of the carbons on a benzene ring. bonded to another carbon, which is also bonded to two hydrogens and an alcohol group. The 2 dimensional structures for formaldehyde. A carbon atom is double bonded to an oxygen atom and single bonded to two hydrogen atoms. The 2 dimensional structures for cetylpyridinium chloride. The cetylpyridinium ion has a ring of 5 carbon atoms and 1 nitrogen atom. Every other bond in this ring is a double bond, totaling to 3 double bonds in the ring. The nitrogen atom is also bonded to a left parenthesis upper C upper H 2 right parenthesis 15 upper C upper H 3 group. This ion has a positive 1 charge. The chloride ion has a negative 1 charge. The 2 dimensional structure of hexachlorophene. There are two benzene rings connected by an additional carbon atom. The carbon atom is also bonded to 2 hydrogens. The structure is symmetric with the plane of symmetry at the connecting carbon atom. The top carbon of each benzene ring is connected to an alcohol group. Three of the other fourcarbons not attached to groups are bonded to chlorine atoms. The 2 dimensional structures for glutaraldehyde. Thereis a 5 carbon chain. The three carbon atoms in the middle are each bonded to 2 hydrogens. The carbon atoms on the end are double bonded to an oxygen and single bonded to a hydrogen. The left end carbon atomhas the oxygenbonded above the hydrogen and the right end carbon atom has the oxygen bonded below the hydrogen. The 2 dimensional structures for benzalconium chloride or also known as mixture. This is an ionic complex whose cation has the following structure. A benzene ring on the left is attached to a carbon atom thatis also bonded to two hydrogen atoms. This carbon atom is bonded to the right by a nitrogen atom. This nitrogen atom is bonded from the top and bottom by methyl groups and to the right by an R group. Below the structure, R equals an alkyl that is upper C 8 upper H 17 to upper C 18 to upper H 37. Theanion for this compound is the chloride ion. The 2 dimensional structure of isopropanol or also known as rubbing alcohol. There is a chain of three carbons. The central carbon is bonded above by a hydrogen and below by an alcohol group. Theother two carbons are a part of methyl groups. Gases The 2 dimensional structures for ethylene oxide. The geometry for this structure is trigonal planar between the carbon atoms of two methyl groups and an oxygen atom. The 2 dimensional structures forbetapropiolactone. There is a rectangular structure between the carbon atoms of two methyl groups, an oxygen atom, and another carbon atom. The carbon atom is also double bonded to another oxygen atom. 66 Bacteria Can Develop Resistance to Disinfectants  This has been achieved via several mechanisms: • Altering the fatty acid synthesis protein normally targeted by triclosan • Producing membrane-spanning, multidrug efflux pumps • Forming multispecies biofilms, which offer collaborative protection 67 Antibiotics Selectively Control Bacterial Growth – 1  Antibiotics are chemical compounds synthesized by one microbe to either kill (bactericidal) or stop the growth of (bacteriostatic) other competing microbial species.  Isolation, purification, and administration of these therapeutic chemicals to patients suffering from an infectious disease can rid patients of the microbial causative agents.  Antibiotics are classified according to their modes of action. • Some antibiotics target cell wall synthesis, while others attack protein synthesis, DNA replication, or cell membrane structure. • All must target a unique structure or function in bacteria. 68 Antibiotics Selectively Control Bacterial Growth – 2  Penicillin is bactericidal because actively growing cells lyse without the support of the cell wall. • Produced naturally by Penicillium notatum • Mimics a part of the cell wall • Prevents peptidoglycan synthesis and prevents cell wall formation 69 Biological Control of Microbes  Biocontrol is the use of one microbe to control the growth of another. • Probiotics contain certain microbes that, when ingested, aim to restore balance to intestinal flora. – Lactobacillus and Bifidobacterium • Phage therapy aims to treat infectious diseases with a virus targeted to the pathogen. – Bacteriophages are a possible alternative to antibiotics in the face of rising antibiotic resistance. – Commercial phage products are now available to target a few foodborne pathogens. 70 Chapter Summary – 1  Microbes inhabit various niches based on their tolerance to the physical and chemical conditions.  Microbes are classified by growth temperature: • Psychrophiles, mesophiles, and thermophiles  Barophiles can grow at very high pressures.  Halophiles require high salt concentrations.  Microbes are classified by pH range: • Acidophiles, neutralophiles, and alkaliphiles  Microbes are classified by their O2 requirements: • Aerobes, facultative, microaerophiles, and anaerobes 71 Chapter Summary – 2  Cells treated with antimicrobials die at a logarithmic rate.  Physical agents used to control microbes include: • Autoclaving, pasteurization, refrigeration, filtration, and irradiation  Chemical agents used to control microbes include: • Antiseptics and disinfectants  Antibiotics selectively control microbial growth.  Biological control of microbes include: • Probiotics and phage therapy 72 Concept Check 5.1 – 1 Which of the following environments is MOST likely to harbor a microbe that could function as a human pathogen? a) Glacier on Mount Everest b) Seafloor vent at the bottom of the Pacific Ocean c) Human colon (large intestine) d) Soil beneath the Bonneville Salt Flats e) Table top in a school cafeteria 73 Concept Check 5.1 – 1 – Answer Which of the following environments is MOST likely to harbor a microbe that could function as a human pathogen? a) Glacier on Mount Everest b) Seafloor vent at the bottom of the Pacific Ocean c) Human colon (large intestine) d) Soil beneath the Bonneville Salt Flats e) Table top in a school cafeteria 74 Concept Check 5.1 – 2 Which of the following statements about microbes and temperature is FALSE? a) Within a specific range, the microbial growth rate roughly doubles for every 10°C rise in temperature. b) Changes in temperature affect membrane fluidity, and thus influence nutrient transport. c) Thermophiles are microbes that grow at temperatures between 40°C and 80°C d) Microbes have mechanisms to control their temperature. 75 Concept Check 5.1 – 2 – Answer Which of the following statements about microbes and temperature is FALSE? a) Within a specific range, the microbial growth rate roughly doubles for every 10°C rise in temperature. b) Changes in temperature affect membrane fluidity, and thus influence nutrient transport. c) Thermophiles are microbes that grow at temperatures between 40°C and 80°C d) Microbes have mechanisms to control their temperature. 76 Concept Check 5.1 – 3 What are microbes that grow at very high pressures called? a) Osmophiles b) Mesophiles c) Xerophiles d) Halophiles e) Piezophiles 77 Concept Check 5.1 – 3 – Answer What are microbes that grow at very high pressures called? a) Osmophiles b) Mesophiles c) Xerophiles d) Halophiles e) Piezophiles 78 Concept Check 5.2 – 1 Most fungi require water activity levels higher than _______, whereas bacteria typically require water activity levels of at least _______. a) 0.65; 0.75 b) 0.75; 0.85 c) 0.86; 0.91 d) 0.91; 0.95 e) 0.95; 0.99 79 Concept Check 5.2 – 1 – Answer Most fungi require water activity levels higher than _______, whereas bacteria typically require water activity levels of at least _______. a) 0.65; 0.75 b) 0.75; 0.85 c) 0.86; 0.91 d) 0.91; 0.95 e) 0.95; 0.99 80 Concept Check 5.2 – 2 Why can’t bacteria grow in solutions with very high concentrations of sugar? a) Bacteria cannot digest pure sugar. b) Sugar raises the solution’s osmolarity. c) Sugar lowers the solution’s osmolarity. d) Sugar raises the solution’s pH. e) Sugar lowers the solution’s pH. 81 Concept Check 5.2 – 2 – Answer Why can’t bacteria grow in solutions with very high concentrations of sugar? a) Bacteria cannot digest pure sugar. b) Sugar raises the solution’s osmolarity. c) Sugar lowers the solution’s osmolarity. d) Sugar raises the solution’s pH. e) Sugar lowers the solution’s pH. 82 Concept Check 5.3 Jerky recipes typically include a vinegar-based marinade, copious quantities of salt, and dehydration in a food smoker. The finished product is stored at cool temperatures. Which of the following physical parameters for growth is NOT addressed by this recipe? a) Barometric pressure b) Temperature c) Osmolarity d) Hydronium ion concentration (pH) 83 Concept Check 5.3 – Answer Jerky recipes typically include a vinegar-based marinade, copious quantities of salt, and dehydration in a food smoker. The finished product is stored at cool temperatures. Which of the following physical parameters for growth is NOT addressed by this recipe? a) Barometric pressure b) Temperature c) Osmolarity d) Hydronium ion concentration (pH) 84 Concept Check 5.4 Clostridium perfringens, the causative agent of gas gangrene, is a strict anaerobe that performs both anaerobic respiration and fermentation. Which of the following changes would allow it to become an aerotolerant or facultative anaerobe? a) Remove its ability to perform anaerobic respiration b) Improve its water-pumping efficiency for regulating osmolarity c) Enhance its fermentation capabilities d) Edit its genome to include genes for superoxide dismutase and catalase 85 Concept Check 5.4 – Answer Clostridium perfringens, the causative agent of gas gangrene, is a strict anaerobe that performs both anaerobic respiration and fermentation. Which of the following changes would allow it to become an aerotolerant or facultative anaerobe? a) Remove its ability to perform anaerobic respiration b) Improve its water-pumping efficiency for regulating osmolarity c) Enhance its fermentation capabilities d) Edit its genome to include genes for superoxide dismutase and catalase 86 Concept Check 5.5 During the starvation response, most organisms can do all of the following EXCEPT: a) Undergo programmed cell death b) Form metabolically inactive endospores c) Protect against reactive oxygen species d) Protect against temperature extremes e) Protect against pH extremes 87 Concept Check 5.5 – Answer During the starvation response, most organisms can do all of the following EXCEPT: a) Undergo programmed cell death b) Form metabolically inactive endospores c) Protect against reactive oxygen species d) Protect against temperature extremes e) Protect against pH extremes 88 Concept Check 5.6 – 1 Your colleague develops a new alcohol-based disinfectant for the health care industry. He boasts that the disinfectant has a D-value of 15 seconds. When you try it out in your microbiology lab, it reduces a starting culture of 1 x 109 cells to 1 x 106 cells in 1 minute. Did your colleague’s disinfectant live up to its advertised capabilities? a) Yes. The disinfectant killed as many cells as expected. b) No. The disinfectant killed fewer cells than expected. c) There’s not enough information provided. Additional studies are needed. 89 Concept Check 5.6 – 1 – Answer Your colleague develops a new alcohol-based disinfectant for the health care industry. He boasts that the disinfectant has a D-value of 15 seconds. When you try it out in your microbiology lab, it reduces a starting culture of 1 x 109 cells to 1 x 106 cells in 1 minute. Did your colleague’s disinfectant live up to its advertised capabilities? a) Yes. The disinfectant killed as many cells as expected. b) No. The disinfectant killed fewer cells than expected. c) There’s not enough information provided. Additional studies are needed. 90 Concept Check 5.6 – 2 You work for an engineering firm attempting to improve upon the sterilization capabilities of a standard autoclave. Which one of the following design changes is the MOST promising area to research? a) Using dry heat instead of steam b) Increasing the chamber pressure c) Decreasing the treatment time d) Decreasing the treatment temperature 91 Concept Check 5.6 – 2 – Answer You work for an engineering firm attempting to improve upon the sterilization capabilities of a standard autoclave. Which one of the following design changes is the MOST promising area to research? a) Using dry heat instead of steam b) Increasing the chamber pressure c) Decreasing the treatment time d) Decreasing the treatment temperature 92 Credits This concludes the Lecture PowerPoint presentation for Chapter 5. For more resources, please visit https://stg-iig.wwnorton.com/microb5/demo 93