0-General-2-Bacterial Physiology & Growth (1)

8/10/2019 0-General-2-Bacterial Physiology & Growth (1)

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BatterjeeMedical College


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Ass. Prof . Dr. Manal El Said

Head of M icrobiology Department

Bacteria Growth

and Physiology


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Define the following:

a. binary fission

b. generation time

c. geometric progression

Learning Objectives for

"Bacterial Growth"

After completing this section you should be able to perform

the following objectives.


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Bacteria reproduce by binary fission, a process by which

one parent cell divides to form two progeny cells.

Bacterial Reproduction (1)


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Bacterial Reproduction (2)

Binary Fission


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Exponential growth (logarithmic growth):

one cell gives rise to two progeny cells

The doubling (generation) time of bacteria:

It is the time it takes for a population of bacteria to double in

number.

It ranges from 20 minutes for Escher ichia col ito more than

24 hours for Mycobacter ium tubercu los is .

Bacterial Growth Curve (1)


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The growth cycle of bacteria has four major phasesThe standard growth curve can be demonstrated:

If a small number of bacteria are inoculated into a liquid nutrient medium

and the bacteria are counted at frequent intervals

1- The lag phase:

During which metabolic activity occurs but cells do not divide (few

minutes up to many hours).

2- The log (logarithmic or Exponential) phase:

- Rapid cell division occurs.

--Lactam drugs (e.g. penicillin) act during this phase because they are

effective when cells are dividing.3- The stationary phase:

Nutrient depletion or toxic products cause growth to slow until no. of

new cells balances no. of cells death resulting in a steady state.

4-The death phase:

- Decline in the number of viable bacteria.



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1. Define the following:

a. Psychrophile

b. Psychrotroph

c. Mesophile

d. Thermophilee. Obligate aerobe

f. Obligate anaerobe

g. Aerotolerant anaerobe

h. Facultative anaerobe

2. State the optimum pH range for most bacteria3. Define the following:

a. Phototroph

b. Chemotroph

c. Autotroph

d. Heterotroph

e. Fastidious

Learning Objectives for

"Factors Influencing Bacterial Growth"

After completing this section you should be able to perform the following

objectives.


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Physical Requirements

Factors Influencing Bacterial Growth

Nutritional Requirements

1. Temperature

2. Oxygen requirements3. PH

4. Osmosis

1- Energy source

2- Carbon source3- Nitrogen source

4- Minerals

- Sulfur- Phosphorus

- Potassium, magnesium & calcium- Iron

- Trace elements

5- Water

6- Growth factors


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1-Temperature

Factors Influencing Bacterial Growth:


Definition Optimum growth temperature

Psychrophiles Cold-loving bacteria Between5C and 15C.

Mesophiles Bacteria that grow

at moderate

temperatures.

Between 20C and 40C.

Most bacteria are

mesophilic & include soil

bacteria and bacteria that

live in and on the body.Thermophiles Heat-loving bacteria Between 45C and 70C.

Hyperthermophiles Bacteria that grow

at very high

temperatures

Between 70C and 110 C.

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Definition They obtain energy through

Obligate aerobes Grow only in the presence of oxygen Aerobic respiration

Microaerophiles - Require a low concentration ofoxygen (2% to 10%) for growth

- Higher concentrations are

inhibitory

Aerobic respiration

Obligate anaerobes Grow only in the absence of oxygen(inhibited or killed by its presence).

- Anaerobic respiration

-or fermentation

Aerotolerantanaerobes (obligate

fermenters )

- Cannot use oxygen to transformenergy

- Can grow in its presence.

Only by fermentation

Facultative

anaerobes

Most bacteria

- Grow with or without oxygen

- But generally better with oxygen.

-Aerobic respiration if

oxygen is present

- Fermentation or anaerobic

respiration if it is absent.

2- Oxygen requirements



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2- Oxygen requirements (2)



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3- pH

Neutrophiles Acidophiles Alkaliphiles

pH range of 5-8 ph 8.5pH 5.5

Most pathogens grow at pH 7.2=

pH of blood and body tissues



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Osmosis is the diffusion of water

across a membrane:

-Fromhigher water concentration(lower solute concentration)

-To lower water concentration(higher solute concentration)

Osmosis does not require energy.

4- Osmosis (1)



Batterjee Medical College


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4- Osmosis (2)

Both the water andsolute concentration are

the same inside and

outside the cell

Water goes into & out of

the cell at an equal rate.

(Most bacteria)

The water concentration

is greater inside the cell &

the solute concentration

is higher outside .Water goes out of the cell.

The water concentration

is greater outside the cell

&the solute concentration

is higher inside.Water goes into the cell.



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4- Osmosis (3)

Osmotolerant Organisms :can grow at high salt concentration (up to 10%).Halophiles: require high salt concentrations for growth, (up to20% or higher ).



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They use the oxidation&

reductionof chemical

compounds

1- Energy Source

They use sunlight to

convert CO2 & water into

organic materials


Nutritional Requirements (1)

Phototrophs Chemotrophs

Photosynthesis Respiration Fermentation



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Respiration:1- Aerobic Respiration

It is glucose catabolism under aerobic condition.This results in the production of energy in the form of 38 ATP

molecules.Aerobic respiration involves :

1- Glycolysis

The end product of glycolysis are:

- 2 molecules of pyruvic acid

- 2 ATP molecules.

2-The Krebs cycle

The substrate are the 2 molecules of pyruvic acidGenerating 2 ATP molecules.

3- Oxidative phosphorylation(Electron transport chain)

It result in the formation of 34 ATP molecules.

The final electron acceptor is molecular O2



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Respiration:2- Anaerobic Respiration

It occurs in the absenceof oxygen.

The final electron acceptor is an organic molecule such as

nitrate, sulfate orCO2

There is also:- Glycolysis,

- Krebs cycle

- Oxidative phosphorylation

Because nitrate, sulfate or CO2 are not good electronacceptor as oxygen, the net yield of ATP molecules is less

than it is with aerobic respiration.



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3- Fermentation

It is the process of extracting energy from the oxidation of

organic compounds, such as carbohydrates,and using an

endogenous electron acceptor, which is usually an organic

compound.

The sugarbreakdown to pyruvic acidand then, to lactic acid

or ethanol. It is the process by which facultativebacteria generate ATP

in the absence of oxygen.

There is no oxidative phosphorylation.



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Require organic forms

of carbon.

It cannot synthesize

organic moleculesfrom

inorganic nutrients.



2- Carbon Source

HeterotrophsAutotrophs

Require only carbon

dioxide as a carbon

source.

It can synthesizeorganic molecules from

inorganic nutrients.



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3- Nitrogen Source

- Amino acids

- DNA

- RNA

- ATP

Nitrogen is needed for the synthesis of :

- Nitrogen

- Nitrates

- Ammonia

- Organic nitrogen compounds

Nitrogen sources are:



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It is needed to synthesizes sulfur-containing amino acids

and certain vitamins.

Sulfur source :- Sulfates

- Hydrogen sulfide

- Sulfur-containing amino acids



4- Minerals1. Sulfur

It is needed to synthesize phospholipids, DNA, RNA & ATP.

Phosphate ionsare the primary source of phosphorus.

2. Phosphorus

3. Potassium Magnesium and Calcium

These are required for certain enzymes.



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4- Minerals

They are required in very minute amounts and function as

cofactors(electron donors or acceptors)in enzyme reactions.

They include sodium, zinc, copper, molybdenum,

manganese and cobalt ions.

4. Iron

-It is component of cytochromesand other enzymes.

-Bacteria produce iron-binding compounds (siderophores)which capture iron by chelating it, attach to specific

receptors & actively transported into the cell.

5. Trace Elements



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5- Water & 6- Growth factors Growth factors are organic compounds such as:

- Amino acids

- Purines

- Pyrimidines

- Vitamins

Cell must have them for growth but cannot synthesize itself.

They having complex nutritional requirements & needing

many growth factors

FastidiousOrganisms

0-General-2-Bacterial Physiology & Growth (1)

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