microbial nutrition and growth

MicrobiologyWith Diseases by Taxonomy

Second Edition

PowerPoint® Lecture Slides

PART A

6Microbial 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

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

Nutrients: Chemical and Energy Requirements

Sources of carbon, energy, and electronsOxygen requirementsNitrogen requirementsOther chemical requirements

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

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

Four Basic Groups of Organisms

Figure 6.1

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

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

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

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

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

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

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)

Physical Requirements for Growth

Temperature pHOsmolarityPressure

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

Effects of Temperature on Growth

Figure 6.4a

Effects of Temperature on Growth

Figure 6.4b

Catagories of Microbes Based on Temperature Range

Figure 6.5

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

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

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

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

Hydrostatic Pressure

Water exerts pressure in proportion to its depth For every addition of depth, water pressure increases

Organisms that live under extreme pressure are barophiles Their membranes and enzymes depend on this pressure

to maintain their three-dimensional, functional shape

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

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

Clinical Sampling

Table 6.3

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

Streak Plate Method

Figure 6.8a

Streak Plate Method

Figure 6.8b

Pour Plate Method

Figure 6.9a

Pour Plate Method

Figure 6.9b

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

Special Media Techniques

Techniques developed for culturing microorganisms Animal and cell culture Low-oxygen culture Enrichment culture

Preserving Cultures

RefrigerationDeep-freezingLyophilization

Growth of Microbial Populations

Figure 6.17a

Growth of Microbial Populations

Figure 6.17b

Arithmetic Versus Logarithmic Growth

Figure 6.18a-b

Phases of Microbial Growth

Figure 6.20

Measuring Microbial Growth

Direct methods Viable plate counts Membrane filtration Microscopic counts Electronic counters Most probable number

Viable Plate Counts

Figure 6.21

Membrane Filtration

Figure 6.22a

Microscopic Counts

Figure 6.23

Most Probable Number

Figure 6.24

Measuring Microbial Growth

Indirect Methods Metabolic activity Dry weight Turbidity

Turbidity and Spectrophotometric Measurement

Figure 6.25a

Turbidity and Spectrophotometric Measurement

Figure 6.25c

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

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

Simple Stains

Figure 4.16b

Gram Stain

Figure 4.17.1

Gram Stain

Figure 4.17.2

Gram Stain

Figure 4.17.3

Gram Stain

Figure 4.17.4

Acid-Fast Stain

Figure 4.18

Endospore Stain

Figure 4.19

Negative (Capsule) Stain

Figure 4.20

Flagellar Stain

Figure 4.21

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