Chapter 4: Bacterial Growth Requirements

Growth

involves an orderly and organized increase in the sum of all components of the organisms.

process entails the replication of all cellular structures, organelles, and components

Microbial growth

concerned with the increase in the number of cells and not an increase in the size of organism

Bacterial colony

composed of thousand of cells

Nutritional Requirements

Carbon

Nitrogen

Sulfur

Phosphorus

Inorganic Ions

Growth factors

Carbon

makes up the structural backbone or skeleton of all organic molecules

autotrophs (lithotrophs)

heterotrophs (organotrophs)

Based on their carbon source, microorganisms may be classified into

Autotrophs (lithotrophs)

microorganisms that utilize inorganic compounds & inorganic salts as their sole carbon source

Heterotrophs (organotrophs)

make use of organic substances like sugars or glucose as their carbon source

photolithorophs and photoorganothrophs

For both autotrophs and heterotrophs may be derived from either light

chemolithotrophs and chemoorganotrophs

For both autotrophs and heterotrophs or the oxidation of inorganic substances

Nitrogen and sulfur

required for synthesis of proteins

Nitrogen and phosphorus

essential for the synthesis of nucleic acid and ATP

14%

dry weight of bacterial cell is nitrogen

4%

sulfur and phosphorus

Inorganic ions

magnesium, potassium, calcium, iron and trace elements

Magnesium

stabilizes ribosomes, cell membranes and nucleic acid

serves as co-factor in the activity of many enzymes

Potassium

required for the normal functioning and integrity of ribosomes and participates in certain enzymatic activities of the cell

Calcium

important component of gram-positive bacterial cell wall

contributes to the resistance of bacterial endospores against environmental conditions

Iron

component of cytochrome

component of electron transport chain

functions as a co-factor for enzymatic activities

Trace elements

components of enzymes and functions as a co-factor

some are necessary for the maintenance of protein structure

Growth factors

to promote the growth and development of the bacterial cell.

Include vitamin B complex and amino acids

Physical Requirements

Moisture and water

Oxygen

Temperature

pH

Osmotic Conditions

Moisture and Water

serves as the medium from which bacteria acquire their nutrients

Oxygen

used by aerobic bacteria for cellular respiration and serve as a final electron acceptor.

aerobes

microorganisms that utilize molecular oxygen for energy production

require oxygen for growth

obligate anaerobes

microbes that cannot survive in the presence of oxygen

do not have enzymes that break down free radicals produced in the body

facultative organisms

can grow and survive under both aerobic and anaerobic conditions

most medically important bacteria

microaerophiles

able to grow at low oxygen tension but their rate growth is diminished

capnophiles

require the addition of carbon dioxide to enhance their growth

thermophiles

grow best at temp higher than 4O degree celsius

mesophiles

optimal temperature of 20-40 degree celsius

psychrophiles

optimum temp of 10-20 degree celsius

medically important bacteria

pH

requirement of bacteria is the extent of acidity or alkalinity of their environmental

alkalophiles

grow best in pH 8.4-9.0

neutrophiles

grow best in pH 6.5-7.5

medically important bacteria

7.0-7.2

pH of most human tissue

acidophiles

certain bacteria require a pH less than 6.0

osmotic conditions

organisms grow best under ideal conditions determined by salt concentration

halophiles

require high salt concentration for growth

osmophiles

require high osmotic pressure for optimal growth

Bacterial growth curve

illustrates the phases in the growth of the population of bacteria when they are grown in a culture of fixed volume

Lag phase

Log/Logarithmic/Exponential phase

Stationary phase

Death or Decline phase

different stages in the growth of the organism

Lag phase

period of adjustment for the bacteria

no appreciable increase in the number of microorganisms

organisms show increased metabolic activity in order to synthesize DNA

may last for 1 to 4hrs

Log/Logarithmic/Exponential phase

rapid cell division increase in the number of bacteria

exhibits high metabolic activity

generation time or doubling time of organisms is determined

duration of this phase is about 8hrs

Stationary phase

period of equilibrium

the rate of growth starts to slow down

nutrients starts to deplete

toxic wastes begin to accumulate

gram + organisms may become gram - organisms in this phase

Sporulation occurs towards the end of this phase

Death or Decline phase

number of dead cells is greater than the number of living cells

nutrients are depleted

toxic wastes accumulate

Sporulation continues at this stage

duration of this phase varies from a few hours to a few days