lecture 4 - bacteria nutrition, metabolism and growth

8/14/2019 Lecture 4 - Bacteria Nutrition, Metabolism and Growth

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Bacteria nutrition, metabolism

and growth.

Dr. Edet E. Udo PhD

Department of MicrobiologyFaculty of Medicine, Kuwait University.


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1. Gram- positive bacteria contain a thick layer of peptidoglycan (T/F)

2. The periplasmic space is present in both Gram-positive and Gram-negative bacteria ( T/F)

3. Bacterial LPS has both antigenic and virulent properties (T/F)

4. Staphylococcus is Gram-positive cocci in clusters (T/F)

5. A bacterial spore germinates into two daughter cells ( T/ F).

Match the following

1. Gram- positive cell wall contains____________ 2. Gram positive cocci in chains __________________

3. Has no cell wall ________________

4. A primary pathogen __________________________

5. An opportunistic pathogen _________________________

E.coli, Klebsiella spp, Streptococcus, Haemophilus influenzae,Teichoic acid, Vibro cholerae, Mycoplasma,


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Bacteria nutrition, metabolism and growth.

Objectives Define nutrition, explain the nutritional

requirements of bacteria.

Define bacterial growth.

Discuss the phases of microbial growth andtheir relationship to generation time

Define metabolism and the fundamental

differences between anabolism and catabolism Describe cultivation of bacteria in the

laboratory


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Bacterial nutrition

Definition: Nutrition

Nutrition is a process by which organisms acquire

chemical substances (Nutrients) used in cellularactivities such as metabolism and growth.

Organisms differ in the use of particular elements,their source and chemical form.

Microbial growth

Microbial growth refers to both the increase in cellsize and number of cells in a population


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Metabolismincludes all the biochemical reactions that

occur in the cell.It consists of anabolic and catabolic reactions.

Categories of essential nutrients

Macronutrients: required in relatively large

quantities e.g. proteins, carbohydrates Micronutrients or trace elements: required

in smaller amounts.

E.g. zinc, manganese.

Are involved in enzyme functions andmaintenance of protein structure.


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Bacterial growth

Cell division:binary or transverse

division.

During binary fission,

the parent cell enlarges,duplicates its

chromosomes and forms a

central transverse septum

that divides the cell into

two daughter cells.


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Cell division

Generation or doubling time:The average generation time forbacteria is 30-60 minutes underoptimum conditions.

Most pathogens such as Staphylococcusaureus and Escherichiacoli double in 20 30 minutes.

The longest generation time requiresdays. E.g. Mycobacterium leprae thatcauses leprosy doubles in 20 to 30days.


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Planes of division


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The growth curve


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The growth curve The growth curve is a graphic representation of

closed population of bacteria overtime This occurs in four phases, lag, log, stationary and

decline phases.

1.The lag phase, Cells adjust to new environment. There is no change in the number of cells but

metabolic activity is high leading to increase incellular components.

2. The log or exponential phase, Bacteria multiply at the fastest rate possible under

the conditions provided. Are susceptible to cell wall active antibiotics Form metabolic end products


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3. The stationary phase

there is an equilibrium between cell divisionand cell death caused by : decrease in nutrient,

increase in cell population and accumulation of

metabolic waste / end products e.g antibiotics. Sporulating cells initiate spore formation

4. Death or Decline phase

The number of death cells exceeds the number

of new cells formed due to lack of nutrientsand accumulation of toxic waste


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Factors affecting bacterial

growth Nutritional requirements Chemical: water, carbon source, nitrogen, minerals, oxygen,growth factors

Carbon Source: All bacteria require carbon for growth.

Bacteria can been classified on the basis of theircarbon source. Autotrophs: use carbon dioxide as the sole

source of carbon Heterotrophs: use more complex organic

compounds such as carbohydrates and aminoacids as source of carbon Photoautotroph- energy need is supplied by

light Chemoautotroph - energy is extracted from

inorganic substances


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Inorganic nutrients (ions):

Contain no carbon and hydrogen atoms :

phosphates, potassium, magnesium, nitrogen,sulfur, iron and numerous trace metals.

Organic nutrients:

contain carbon and hydrogen atoms. Includecarbohydrates, lipids amino acids, Nucleic acids etc.

Carbohydrates:

are used as the initial carbon source for manybiosynthetic pathways and as electron donors(energy source) by many bacteria.

Amino acids are important source of carbon and nitrogen. The

nitrogen is converted to ammonia.


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Nutritional factors Phosphorus is present as phosphates salts.

They function in energy metabolism and asconstituents of nucleic acids, phospholipids,

teichoic acids, ATP, etc Minerals:

K, Mg, Ca, Fe are required in relatively highlevels.

Function as cofactors in enzyme reactions and ascations they act as buffers within the cells

Vitamins,

purines and pyrimidines ( accessory growth

factors) function as coenzymes


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Physical factors

Oxygen requirement:

Bacteria can be divided into five groups on thebasis of their oxygen requirements

1. Obligate or strict aerobes:

The growth of bacteria is inhibited by absenceof oxygen An example of a strict or obligateaerobe is Pseudomonas aeruginosa

2. Obligate anaerobes:

Growth is inhibited by the presence of oxygen. Examples of obligate anaerobe are Clostridium spp

and Bacteriodes spp.


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3. Facultative anaerobes are able to grow in the presence or absence

of molecular oxygen. E.g. includestaphylococci, streptococci, Enteococci, etc. 4. Microaerophilic bacteria: grow best under increased carbon dioxide

tension. Examples include Neisseria

gonorrhoeae, Haemophilus influenzae 5.Aerotolerant bacteria: can survive (but not grow) for a short period

of time in the presence of atmosphericoxygen

Tolerance to oxygen is related to the abilityof the bacterium to detoxify superoxide andhydrogen peroxide produced as bye productsof aerobic respiration.


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1. Superoxide dismutase,

which converts superoxide ( a toxic metabolite)

into hydrogen peroxide is present in aerobic andaerotolerant bacteria but not in obligate anaerobes.

2. Catalase,

which converts hydrogen peroxide into water and

oxygen is also present in all aerobic bacteria but islacking in aerotolerant organisms. Strict anaerobeslack both enzymes.

O2

- + O2

- -superoxide dismutase H2

O2

(Hydrogen

peroxide) + O2-

H2O2 + H2O2 Catalase-------2H2O +O2


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Temperature: There are three critical temperature ranges for

growth:

(a) Minimum temperature- (b). Maximum temperature: . Optimum temperature: Psychrophiles: Has optimum temperature below 15 C but

capable of growth at 0 C Mesophiles:

grow at a range of 20 40 C. Include mostbacterial pathogens with optimum temp. at 37C

Thermophiles: microbes that has optimum temperature above

45 C with a general range of 45-80 C Most thermophiles form spores e.g. Bacillus

steareothermophilus


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pH:

Optimum pH for most bacteria is near pH 7.0(pH 6.5- pH 7.5)

Bacteria can be classified as alkalinophiles,neutrophiles or acidophiles according to theirdegree of tolerance to pH changes


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Osmotic pressure:

When a microbial cell is in ahypertonic solution cellular watermoves out of the cell through the cellmembrane to the hypertonic solution.

This osmotic loss of water causesshrinkage of the cell PLASMOLYSIS

In a hypotonic solution such as indistilled water, water will enter thecell and the cell may be lysed by suchtreatment (PLASMOPTYSIS).

Halophiles

require high salt concentrations for

growth. Some bacteria can tolerate15% salt. E.g. S. aureus


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Bacterial metabolism

Metabolism consists of catabolic and anabolicreactions.

Anabolic reactions are energy-requiring subset ofmetabolic reactions, which synthesize largemolecules from smaller ones.

Catabolic reactions are the energy releasingsubset of metabolic reactions, which degrade orbreakdown large molecules into smaller ones.

Metabolism is best considered in three stages

1. Energy metabolism 2. Respiratory metabolism

3. Biosynthetic pathways


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1. Energy metabolism

Energy used by bacteria is primarily produced by

fermentative and/ or respiratory metabolic pathways. Metabolic reactions are catalyzed by enzymes

Anaerobic metabolism (fermentative metabolism

A. Glycolytic ( Embden-Meyerhof ) pathway

The major glucose utilization pathway.

Glycolysis- the metabolism of glucose to yield pyruvicacid and 2 ATP molecules

B. Entner-Doudoroff pathway

Aerobic metabolism ( respiration)

The Krebs cycle

Involves the the metabolism of 2-carbon groups to carbondioxide and water and the production of ATP.


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Biosynthetic pathways Used to build small molecules with nitrogen,

sulphur and other minerals into aminoacids, purines, pyrimidines, polysaccharidesand lipids


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Bacterial metabolism

Uses of energy

For biosynthetic activities e.g. cell wall synthesis,protein synthesis, nucleic acid synthesis etc

Membrane transport and movement e.g active

transportation. Uses of metabolic products in the laboratory

Metabolic end products e.g. pyruvic acid, lactic acid,mixed gases, alcohols, are used for bacterialidentification. (Biochemical tests) e.g. oxidase tests,

catalase tests.


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Cultivation of bacteria in the

laboratory Culture media: Any material prepared for the

growth of bacteria in thelaboratory.

They can be broth (liquid) or solid media ( contains a gelling

substance such as agar)

Microbes that grow on a culturemedium are known as a culture.

When grown on solid media, thegrowth is calledcolony .

Growth in a liquid medium isdemonstrated by turbidity.


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Types of Culture media:

Defined synthetic medium: contains known quantities of specific nutrients

contain nutrients of reasonably well-

Complex medium:

known composition that varies from batch tobatch

Enrichment medium: (liquid medium)

is used to encourage the growth of aparticular organism in a mixed culture

Enriched media: (Solid medium,)

contain additional nutrients to support thegrowth of fastidious organisms. E.g bloodagar and chocolate agar


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Chocolate agar contains lysed blood.

The lysis releases intracellular nutrients such as haemin (X factor) and

the coenzyme nicotinamide adenine dinucleotide (NAD or V factor)into the agar for use by fastidious microorganisms such as

Haemophilus species andNeisseria gonorrhoeae.

Selective media:

contains salts, dyes or other chemicals that inhibit the growth

unwanted microorganisms.

Differential media:

contain chemicals that allow the distinction between different types of

organisms e.g. Lactose in MacConkey agar.

Preservation of bacterial cultures:

By refrigeration,, lyophilization, storage in liquid nitrogen


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Culture media

lecture 4 - bacteria nutrition, metabolism and growth

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