This document discusses the physical factors that affect bacterial growth, including nutrient concentration, temperature, pH, ions and salt concentration, gaseous concentration, and water. It explains that bacterial growth rates depend on these factors and each bacterium has optimal requirements for things like temperature, pH, and nutrients in order to grow.

1. Physical Factors
Affecting Bacterial
Growth
By:Assist.Prof.Chaitali Kalamkar.S
Arihant COP. Ahmednagar

2. Physical Factors Affecting Bacterial Growth
• Factors affecting bacterial growth are:
1. Nutrition concentration
2. Temperature
3. Gaseous concentration
4. pH
5. Ions and salt concentration
6. Water

3. Physical Factors Affecting Bacterial Growth........
1. Nutrient concentration:
• Bacterial growth is directly
proportional with the available
nutrients. If culture media is rich in
nutrients, growth of bacteria occurs
faster and vice versa.
• Nutritional requirement varies with
the bacterial species.
• Bacteria vary considerably in their
requirements for nutrients and in their
ability to synthesize for themselves
various vitamins and growth factors.

4. Physical Factors Affecting Bacterial Growth......
Nutrient concentration:
• The relationship between
substrate concentration
(nutrition) and growth rate is
shown in figure.
• With increase in concentration of
nutrients, growth rate of bacteria
increases up to certain level and
then growth rate remains
constant irrespective of nutrition
addition

5. Physical Factors Affecting Bacterial Growth....
2. Temperature:
• The lowest temperature that allows the growth
is called minimum temperature.
• The highest temperature that allows growth
is called maximum temperature.
• There is no growth below minimum and
above maximum temperature.
• Below minimum temperature cell
membrane solidifies and become stiff to
transport nutrients in to the cell, hence no
growth occurs.
• Cellular proteins and enzymes denatures at
maximum temperature, so the bacterial
growth ceases.
• The relationship between temperature and
growth rate is shown in Figure.

6. Physical Factors Affecting Bacterial Growth.....
Temperature:
• Growth rate of bacteria increases because the rate of metabolic reaction increases
with increase in temperature.
• At certain temperature the growth rate become maximum, this temperature is known
as optimal temperature.
• On further increasing the temperature above optimal, growth rate decreases
drastically and completely ceases with reaching maximum temperature.
• Thermophile organisms are heat-loving bacteria. Their optimum growth
temperature is between 45°C and 70°C and are commonly found in hot springs and
in compost heaps.
• Hyperthermophile bacteria grow at very high temperatures. Their optimum growth
temperature is between 70°C and 110°C. They are usually members of the Archaea.
• Psychrophiles are grown between −5°C to 20°C.
• Mesophiles are grown between 20°C to 45°C.

7. Physical Factors Affecting Bacterial Growth....
3. pH:
•
• pH affects the ionic properties of
bacterial cell so it affects the growth of
bacteria.
• Most of the bacteria grow at neutral
pH (6.5-7.5). However, there are
certain bacteria that grow best at acidic
or basic pH.
• The relationship between pH and
bacterial growth is given in Fig.
• Microorganisms that have medical or
pharmaceutical signifi cance have pH
growth optima of between 7.4 and 7.6
but may grow suboptimally at pH
values of 5 – 8.5

8. Physical Factors Affecting Bacterial Growth.....
pH:
• The pH of a pharmaceutical preparation may Dictate
the range of microorganisms that could potentially
cause its spoilage.
• Microorganisms can be placed in one of the following
groups based on their optimum pH requirements:
1. Neutrophiles grow best at a pH range of 5 to 8.
2. Acidophiles grow best at a pH below 5.5.
3. Alkaliphiles grow best at a pH above 8.5.

9. Physical Factors Affecting Bacterial Growth.....
4. Ions and salt:
• All bacteria requires metal ions such as K+, Ca ++, Mg++, Fe++, Zn++,
Cu++, Mn++ etc. to synthesize enzymes and proteins.
• Most bacteria do not require NaCl in media and they can tolerate very low
concentration of salt.
• Some halophilic bacteria such as Archeobacteria require high
concentration of salt in media.
• It is balanced with Osmosis process.
• Most bacteria require an isotonic environment or a hypotonic
environment for optimum growth.

10. Physical Factors Affecting Bacterial Growth...
5. Gaseous requirement:
• Oxygen and carbon-dioxide are important
gases that affect the growth of bacteria.
• Oxygen is required for aerobic respiration
and obligate aerobic bacteria must require Or
growth.
• For example: Mycobacterium, Bacillus.
• For obligate anaerobes oxygen is harmful or
sometime lethal but facultative anaerobes can
tolerate low concentration of O2.
• Carbon-dioxide is needed for capnophilic
bacteria. Such as Campylobacter,
Helicobacter pylori.

11. Physical Factors Affecting Bacterial Growth....
6. Water:
• Water is the most essential factor
for bacterial growth.
• Available water in the culture
media determines the rate of
metabolic and physiological
activities of bacteria.
• Sugar, salts and other substances
are dissolved in water and are
made available for bacteria.