Ch 06 Lecture Presentation

Microbial Nutrition and

Growth

Growth Requirements

• Microbial growth – Increase in a population of microbes

• Result of microbial growth is discrete colony – An aggregation of cells arising from single parent

cell• Reproduction results in growth

© 2012 Pearson Education Inc.

Growth Requirements

• Organisms use a variety of nutrients for their energy needs and to build organic molecules and cellular structures

• Most common nutrients contain necessary elements such as carbon, oxygen, nitrogen, and hydrogen

• Microbes obtain nutrients from variety of sources


Growth Requirements

• Nutrients: Chemical and Energy Requirements– Sources of carbon, energy, and electrons

– Two groups of organisms based on source of carbon– Autotrophs– Heterotrophs

– Two groups of organisms based on source of energy– Chemotrophs– Phototrophs


Figure 6.1 Four basic groups of organisms

Growth Requirements

• Nutrients: Chemical and Energy Requirements– Oxygen requirements

– Oxygen is essential for obligate aerobes – Oxygen is deadly for obligate anaerobes– How can this be true?

– Toxic forms of oxygen are highly reactive and excellent oxidizing agents

– Resulting oxidation causes irreparable damage to cells


Growth Requirements


– Four toxic forms of oxygen– Singlet oxygen– Superoxide radicals– Peroxide anion– Hydroxyl radical


Growth Requirements


– Aerobes– Anaerobes– Facultative anaerobes– Aerotolerant anaerobes– Microaerophiles


Figure 6.3 Oxygen requirements of organisms-overview

Growth Requirements

• Nutrients: Chemical and Energy Requirements– Nitrogen requirements

– Anabolism often ceases because of insufficient nitrogen

– Nitrogen acquired from organic and inorganic nutrients

– All cells recycle nitrogen from amino acids and nucleotides

– Nitrogen fixation by certain bacteria is essential to life on Earth


Growth Requirements

• Nutrients: Chemical and Energy Requirements– Other chemical requirements

– Phosphorus – Sulfur– Trace elements

– Required only in small amounts– Growth factors

– Necessary organic chemicals that cannot be synthesized by certain organisms


Growth Requirements

• Physical Requirements– Temperature

– Effect of temperature on proteins– Effect of temperature on membranes of cells and

organelles– If too low, membranes become rigid and fragile– If too high, membranes become too fluid


Figure 6.4 Microbial growth-overview

Figure 6.5 Four categories of microbes based on temperature ranges for growth

Psychrophiles

Mesophiles

Thermophiles

Hyperthermophiles

Gro

wth

rate

Temperature (°C)

Figure 6.6 An example of psychrophile-overview

Growth Requirements

• Physical Requirements– pH

– Organisms are sensitive to changes in acidity – H+ and OH– interfere with H bonding

– Neutrophiles grow best in a narrow range around neutral pH

– Acidophiles grow best in acidic habitats– Alkalinophiles live in alkaline soils and water


Growth Requirements

• Physical Requirements– Physical effects of water

– Microbes require water to dissolve enzymes and nutrients

– 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

– Two physical effects of water– Osmotic pressure– Hydrostatic pressure


Growth Requirements


– Osmotic pressure– Pressure exerted on a semipermeable membrane by

a solution containing solutes that cannot freely cross membrane

– Hypotonic solutions have lower solute concentrations– Hypertonic solutions have greater solute

concentrations– Restricts organisms to certain environments

– Obligate and facultative halophiles


Growth Requirements


– Hydrostatic pressure– Water exerts pressure in proportion to its

depth– Barophiles live under extreme pressure

– Their membranes and enzymes depend on pressure to maintain their shape


Growth Requirements

• Associations and Biofilms– Organisms live in association with different species

– Antagonistic relationships– Synergistic relationships– Symbiotic relationships


Growth Requirements

• Associations and Biofilms– Biofilms

– Complex relationships among numerous microorganisms

– Develop an extracellular matrix– Adheres cells to one another– Allows attachment to a substrate– Sequesters nutrients– May protect individuals in the biofilm

– Form on surfaces often as a result of quorum sensing

– Many microorganisms more harmful as part of a biofilm


Figure 6.7 Plaque (biofilm) on a human tooth

Culturing Microorganisms

• Inoculum introduced into medium– Environmental specimens– Clinical specimens– Stored specimens

• Culture – Act of cultivating microorganisms or the

microorganisms that are cultivated


Figure 6.8 Characteristics of bacterial colonies-overview


• Obtaining Pure Cultures– Cultures composed of cells arising from a single

progenitor– Progenitor is termed a CFU

– Aseptic technique prevents contamination of sterile substances or objects

– Two common isolation techniques– Streak plates– Pour plates


Figure 6.9 Streak plate method of isolation-overview

Figure 6.10 Pour plate method of isolation-overview


• Culture Media– Majority of prokaryotes have not been grown

in culture medium– Six types of general culture media

– Defined media– Complex media– Selective media– Differential media– Anaerobic media– Transport media


Figure 6.11 Slant tube containing solid media

Slant

Butt

Figure 6.12 An example of the use of a selective medium

Fungal coloniesBacterial colonies

pH 7.3 pH 5.6

Figure 6.13 The use of blood agar as a differential medium

Beta-hemolysisAlpha-hemolysis

No hemolysis(gamme-hemolysis)

Figure 6.14 The use of carbohydrate utilization tubes as differential media

No fermentation Acid fermentationwith gas

Durham tube(inverted tubeto trap gas)

Figure 6.15 Use of MacConkey agar as a selective and differential medium-overview

Figure 6.16 An anaerobic culture system

Clamp

Chamber

Petri plates

Airtight lid

Envelopecontainingchemicals torelease CO2and H2

Palladium pelletsto catalyze reactionremoving O2

Methylene blue(anaerobicindicator)


• Special Culture Techniques– Techniques developed for culturing

microorganisms– Animal and cell culture– Low-oxygen culture– Enrichment culture



• Preserving Cultures– Refrigeration

– Stores for short periods of time – Deep-freezing

– Stores for years – Lyophilization

– Stores for decades


Growth of Microbial Populations

ANIMATION Bacterial Growth: Overview




ANIMATION Binary Fission

Figure 6.17 Binary fission events-overview

Figure 6.18 Comparison of arithmetic and logarithmic growth-overview


• Generation Time– Time required for a bacterial cell to grow

and divide– Dependent on chemical and physical

conditions


Figure 6.19 Two growth curves of logarithmic growth-overview

Figure 6.20 Typical microbial growth curve

Stationary phase

Death(decline)phaseLog

(exponential)phase

Lag phase

Time

Num

ber o

f liv

e ce

lls (l

og)



ANIMATION Bacterial Growth Curve

Figure 6.21 Schematic of chemostat

Fresh medium witha limiting amountof a nutrient

Sterile airof othergas

Culture

Culturevessel

Flow-rateregulator

Overflowtube


• Measuring Microbial Reproduction– Direct methods

– Serial dilution and viable plate counts– Membrane filtration– Most probable number– Microscopic counts– Electronic counters


Figure 6.22 Estimating microbial population size-overview

Figure 6.23 Use of membrane filtration to estimate microbial population-overview

Figure 6.24 The most probable number (MPN) method for estimating microbial numbers

1.0 ml 1.0 ml

1:1001:10Undiluted

Inoculate 1.0 ml intoeach of 5 tubes

Phenol red, pHcolor indicator,added

Incubate

Results

4 tubes positive 2 tubes positive 1 tube positive

Figure 6.25 The use of a cell counter for estimating microbial numbers-overview


• Measuring Microbial Growth– Indirect methods

– Metabolic activity– Dry weight– Turbidity


Figure 6.26 Spectrophotometry-overview


• Measuring Microbial Reproduction– Genetic methods

– Isolate DNA sequences of unculturable prokaryotes

– Used to estimate the number of these microbes


Ch 06 Lecture Presentation

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