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6. Microbial Nutrition and Growth. Metabolism Results in Reproduction. Result of microbial growth is discrete colony – an aggregation of cells arising from single parent cell Reproduction results in growth. Growth Requirements. - PowerPoint PPT Presentation
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MicrobiologyWith Diseases by Taxonomy
Second Edition
PowerPoint® Lecture Slides
PART A
Copyright © 2007 Pearson Education, Inc. publishing as Benjamin Cummings
6Microbial Nutrition and Growth
Copyright © 2007 Pearson Education, Inc. publishing as Benjamin Cummings
Metabolism Results in Reproduction
Result of microbial growth is discrete colony – an aggregation of cells arising from single parent cell
Reproduction results in growth
Copyright © 2007 Pearson Education, Inc. publishing as Benjamin Cummings
Growth Requirements
Organisms use a variety of nutrients for their energy needs and to build organic molecules and cellular structures
Most common nutrients – those containing necessary elements such as carbon, oxygen, nitrogen, and hydrogen
Microbes obtain nutrients from variety of sources
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Nutrients: Chemical and Energy Requirements
Sources of carbon, energy, and electronsOxygen requirementsNitrogen requirementsOther chemical requirements
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Sources of Carbon, Energy, and Electrons
Organisms are categorized into two groups based on source of carbon Those using an inorganic source of carbon (carbon
dioxide) are autotrophs Those catabolizing reduced organic molecules
(proteins, carbohydrates, amino acids, and fatty acids) are heterotrophs
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Sources of Carbon, Energy, and Electrons (continued)
Organisms categorized into two groups based on whether they use chemicals or light as source of energy Those that acquire energy from redox reactions
involving inorganic and organic chemicals are chemotrophs
Those that use light as their energy source are phototrophs
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Four Basic Groups of Organisms
Figure 6.1
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Oxygen Requirements
Oxygen is essential for obligate aerobes (final electron acceptor in ETC)
Oxygen is deadly for obligate anaerobesHow can this be true?
Neither gaseous O2 nor oxygen covalently bound in compounds is poisonous
The forms of oxygen that are toxic are excellent oxidizing agents
Resulting chain of oxidations causes irreparable damage to cells by oxidizing compounds such as proteins and lipids
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Four Toxic Forms of Oxygen
Singlet oxygen – molecular oxygen with electrons boosted to higher energy state Occurs during photosynthesis so phototropic
organisms have carotenoids that remove the excess energy of singlet oxygen
Superoxide radicals – some form during incomplete reduction of oxygen in aerobic and anaerobic respiration So reactive that aerobes produce superoxide
dismutases to detoxify them Anaerobes lack superoxide dismutase and die as a
result of oxidizing reactions of superoxide radicals formed in presence of oxygen
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Four Toxic Forms of Oxygen (continued)
Peroxide anion – formed during reactions catalyzed by superoxide dismutase and other reactions Aerobes contain either catalase or peroxidase to
detoxify peroxide anion Obligate anaerobes either lack both enzymes or have
only a small amount of each
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Four Toxic Forms of Oxygen (continued)
Hydroxyl radical – results from ionizing radiation and from incomplete reduction of hydrogen peroxide The most reactive of the four toxic forms of oxygen Not a threat to aerobes due to action of catalase and
peroxidase
Aerobes also use antioxidants such as vitamins C and E to protect against toxic oxygen products
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Classification of Organisms Based on Oxygen Requirements
Aerobes – undergo aerobic respirationAnaerobes – do not use aerobic metabolismFacultative anaerobes – can maintain life via
fermentation or anaerobic respiration or by aerobic respiration
Aerotolerant anaerobes – do not use aerobic metabolism but have some enzymes that detoxify oxygen’s poisonous forms
Microaerophiles – aerobes that require oxygen levels from 2-10% and have a limited ability to detoxify hydrogen peroxide and superoxide radicals
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Nitrogen Requirements
Anabolism often ceases due to insufficient nitrogen needed for proteins and nucleotides
Nitrogen acquired from organic and inorganic nutrients; also, all cells recycle nitrogen from amino acids and nucleotides
The reduction of nitrogen gas to ammonia (nitrogen fixation) by certain bacteria is essential to life on Earth because nitrogen is made available in a usable form
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Other Chemical Requirements
Phosphorus required for phospholipid membranes, DNA, RNA, ATP, and some proteins
Sulfur is a component of sulfur-containing amino acids, disulfide bonds critical to tertiary structure of proteins, and in vitamins (thiamin and biotin)
Trace elements – usually found in sufficient quantities in tap water
Growth factors – organic chemicals that cannot be synthesized by certain organisms (vitamins, certain amino acids, purines, pyrimidines, cholesterol, NADH, and heme)
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Physical Requirements for Growth
Temperature pHOsmolarityPressure
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Temperature
Effect of temperature on proteinsEffect of temperature on lipid-containing membranes
of cells and organelles If too low, membranes become rigid and fragile If too high, membranes become too fluid and cannot
contain the cell or organelle
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Effects of Temperature on Growth
Figure 6.4a
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Effects of Temperature on Growth
Figure 6.4b
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Catagories of Microbes Based on Temperature Range
Figure 6.5
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pH
Organisms sensitive to changes in acidity because H+ and OH- interfere with H bonding in proteins and nucleic acids
Most bacteria and protozoa grow best in a narrow range around neutral pH (6.5-7.5) – these organisms are called neutrophiles
Other bacteria and fungi are acidophiles – grow best in acidic habitats Acidic waste products can help preserve foods by
preventing further microbial growth
Alkalinophiles live in alkaline soils and water up to pH 11.5
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Physical Effects of Water
Microbes require water to dissolve enzymes and nutrients required in metabolism
Water is important reactant in many metabolic reactions
Most cells die in absence of water Some have cell walls that retain water Endospores and cysts cease most metabolic activity in
a dry environment for years
Two physical effects of water Osmotic pressure Hydrostatic pressure
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Osmotic Pressure
Is the pressure exerted on a semipermeable membrane by a solution containing solutes that cannot freely cross membrane; related to concentration of dissolved molecules and ions in a solution
Hypotonic solutions have lower solute concentrations; cells placed in these solutions will swell and burst
Copyright © 2007 Pearson Education, Inc. publishing as Benjamin Cummings
Osmotic Pressure
Hypertonic solutions have greater solute concentrations; cells placed in these solutions will undergo crenation (shriveling of cytoplasm) This effect helps preserve some foods
Restricts organisms to certain environments Obligate halophiles – grow in up to 30% salt Facultative halophiles – can tolerate high salt
concentrations
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Hydrostatic Pressure
Water exerts pressure in proportion to its depth For every addition of depth, water pressure increases
1 atm
Organisms that live under extreme pressure are barophiles Their membranes and enzymes depend on this pressure
to maintain their three-dimensional, functional shape
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Ecological Associations
Organisms live in association with different species Antagonistic relationships Synergistic relationships Symbiotic relationships
Biofilms Complex relationships among numerous individuals Form on surfaces often as a result of quorum sensing
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Culturing Microorganisms
Inoculum introduced into medium (broth or solid) Environmental specimens Clinical specimens Stored specimens
Culture – refers to act of cultivating microorganisms or the microorganisms that are cultivated
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Clinical Sampling
Table 6.3
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Obtaining Pure Cultures
Cultures composed of cells arising from a single progenitor Progenitor is termed a CFU
Aseptic technique is used to prevent contamination of sterile substances or objects
Two common isolation techniques Streak plates Pour plates
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Streak Plate Method
Figure 6.8a
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Streak Plate Method
Figure 6.8b
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Pour Plate Method
Figure 6.9a
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Pour Plate Method
Figure 6.9b
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Culture Media
Majority of prokaryotes have never been grown in culture medium
Six types of general culture media Defined media Complex media Selective media Differential media Anaerobic media Transport media
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Special Media Techniques
Techniques developed for culturing microorganisms Animal and cell culture Low-oxygen culture Enrichment culture
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Preserving Cultures
RefrigerationDeep-freezingLyophilization
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Growth of Microbial Populations
Figure 6.17a
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Growth of Microbial Populations
Figure 6.17b
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Arithmetic Versus Logarithmic Growth
Figure 6.18a-b
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Phases of Microbial Growth
Figure 6.20
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Measuring Microbial Growth
Direct methods Viable plate counts Membrane filtration Microscopic counts Electronic counters Most probable number
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Viable Plate Counts
Figure 6.21
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Membrane Filtration
Figure 6.22a
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Microscopic Counts
Figure 6.23
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Most Probable Number
Figure 6.24
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Measuring Microbial Growth
Indirect Methods Metabolic activity Dry weight Turbidity
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Turbidity and Spectrophotometric Measurement
Figure 6.25a
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Turbidity and Spectrophotometric Measurement
Figure 6.25c
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Staining
Increases contrast and resolution by coloring specimens with stains/dyes
Smear of microorganisms (thin film) air dried to slide and then fixed to surface by heat or chemical fixation
Microbiological stains are usually salts composed of cation and anion and one is colored (chromophore)
Acidic dyes stain alkaline structures; basic dyes stain acidic structures and are used more commonly
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Staining
Simple stains Differential stains
Gram stain Acid-fast stain Endospore stain
Special stains Negative (capsule) stain Flagellar stain Fluorescent stains
Staining for electron microscopy
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Simple Stains
Figure 4.16b
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Gram Stain
Figure 4.17.1
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Gram Stain
Figure 4.17.2
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Gram Stain
Figure 4.17.3
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Gram Stain
Figure 4.17.4
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Acid-Fast Stain
Figure 4.18
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Endospore Stain
Figure 4.19
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Negative (Capsule) Stain
Figure 4.20
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Flagellar Stain
Figure 4.21