Microbial Growth and Culture

DARLINA DAUD

Growth and Cell Division

Microbial Growth Defined:

1. Mother or parent cell doubles in size2. Divides into two daughter cells

Microbial growth is defined as the increase in the number of cells, which occurs by cell division

Cell DivisionBinary fission (equal cell division):

A cell duplicates its components and divides into two cells

Septum: A partition that grows between two daughter cells and they separate at this location

Budding (unequal cell division): A small, new cell develops from surface of exisiting cell and subsequently separates from parent cell

Binary Fission

Thin section of the bacterium Staphylococcus, undergoing binary fission

Environmental Factors Influencing Growth

1. Temperature2. O2 3. pH4. Osmotic Pressure5. Others: radiation,

atmospheric pressure

•Psychrophiles: cold-loving•Mesophiles: moderate temperature-loving•Thermophiles: heat-loving•Each has a minimum, optimum, and maximum growth temperature

Temperature

OxygenObligate aerobesFacultative anaerobes Obligate anaerobesAerotolerant Microaerophiles

pHAcidophiles

Neutrophiles

Alkalophiles

Osmotic Pressure

Phases of Growth Consider a population of

organisms introduced into a fresh, nutrient medium

Such organisms display four major phases of growth

1. The lag phase2. The logarithmic phase3. The stationary phase4. The death phase

The Lag PhaseOrganisms do not increase significantly

in number

They are metabolically active

Grow in size, synthesize enzymes, and incorporate molecules from medium

Produce large quantities of energy in the form of ATP

The Log PhaseOrganisms have adapted to a growth

medium

Growth occurs at an exponential (log) rate

The organisms divide at their most rapid rate

a regular, genetically determined interval (generation time)

Stationary Phase:1. Cell division decreases to a point that

new cells are produced at same rate as old cell die.

2. The number of live cells stays constant.

Decline (Death) Phase: 1. Condition in the medium become less

and less supportive of cell division2. Cell lose their ability to divide and thus

die3. Number of live cells decreases at a

logarithmic rate

Growth in Batch CultureGrowth is generally used to refer to the

acquisition(perolehan) of biomass leading to cell division, or reproduction

A “batch culture” is a closed system in broth medium in which no additional nutrient is added after inoculation of the broth

Growth in Continuous CultureA “continuous culture” is an open system

in which fresh media is continuously added to the culture at a constant rate, and old broth is removed at the same rate.

This method is accomplished in a device called a chemostat.

Typically, the concentration of cells will reach an equilibrium level that remains constant as long as the nutrient feed is maintained.

Standard Growth Curve