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Physical conditions for cultivation of
bacteria
 Mrs. V. A. Warad
 Assistant Professor
 Pharmaceutical Microbiology
 PES, Modern College of Pharmacy, (for Ladies), Moshi, Pune
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Microbiology/ Physicalconditions for bacterial growth /VAW

Objectives
 To understand temperature , gaseous and pH requirement of bacteria
 To study effect of physical conditions on growth of microorganisms
 To understand concepts of optimum temperature and pH of growth.
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Introduction
 In addition to proper nutrients, it is necessary to know
physical environment in which organisms will grow best.
 Physical conditions required for growth are-
Temperature
Gaseous conditions
pH
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Temperature
Growth depends on biochemical reactions and hence it
is influenced by temperature.
Growth rate increases with temperature.
Each bacteria has three cardinal growth temperatures:
Minimum growth temperature - Temperature below
which bacteria will not grow
Optimum growth temperature – Temp. at which
organism grow best – highest growth rate
Maximum growth temperature - Temperature above
which organism can not grow
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Groups of bacteria depending on
temperature requirement
On the basis of temperature relationships bacteria
are divided into three groups.
1. Psychrophiles
2. Masophiles
3. Thermophiles
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Psychrophiles
They are able to grow at 0⁰c or lower.
True psychrophiles - Their optimum temperature is
15⁰c or lower.
Maximum temp. 20 ⁰c or lower
Facultative psychrophiles / psychrotroph- able to grow
at 0⁰c but maximum temp. is above 20 ⁰c
Reason: Heat instability of ribosomes, enzymes and
membrane.
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Examples of psycrophiles –
V. marinus
V. psychroerythrus
Arthrobacter sp.
Psycrobacter sp.
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Mesophiles
Grow best in middle range of temperature.
Saprophytic bacteria – optimum temperature is
between 25 – 35 ⁰c
Human pathogenic bacteria - optimum
temperature is between 35 – 45 ⁰c
Ex. – E. coli
S. aureus
Salmonella
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Thermophiles
 Optimum temperature is above 45 ⁰c.
 True or obligate thermophiles
 Facultative thermophiles
 Reason: Increased thermal stability of ribosomes, membranes and
enzymes.
 In nature found in hot water springs and deep sea hydrothermal
vents, compost
 Ex. - Themoactinomycetes vulgaris
Thermomonospora
Thermus aquaticus
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Classification of thermophiles based on
optimum temperature
1. Simple thermophiles – 50 - 64⁰C
2. Extreme thermophiles – 65 -79 ⁰C
3. Hyperthermophiles – 80 ⁰C and beyond but
not below 50 ⁰C
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Obligate thermophiles / extreme thermophiles –
can not grow in mesophillic temperature range
Facultative thermophiles / modertate thermophiles
- can thrive at high temperature but also at lower
temperature – below 50
Hyperthermophiles – optimum temperature is
above 80
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Gaseous requirement
Gases that affect bacterial growth are O2 and CO2.
On basis of O2 bacteria are divided into four
groups.
1) Aerobic bacteria – require O2 for growth and can
grow when incubated in an air atmosphere.
Ex .- B. subtilis, Mycobacterium tuberculosis,
Pseudomonas, Vibrio spp.
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Gaseous requirement
2)Anaerobic bacteria – do not use oxygen to obtain
energy. Oxygen is toxic to them.
Ex. – Clostridium tetani, Nesseria, Methanobacter
3) Facultatively anaerobic bacteria – do not require
oxygen for growth although they may use it for energy
production if available.
Ex. – E. coli, Enterobacter, Salmonella, Shigella
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Gaseous requirement
4) Microaerophillic bacteria –
Require low levels of oxygen for growth.
But can not tolerate oxygen level present in air.
Many microaerophillic bacteria require elevated
concentrations of carbon dioxide – capnophillic (10%
Campylobacter)
Ex.
Campylobacter
Helicobater
Lactobacillus spp.
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pH requirement
Most of the bacteria neutrophiles.
Optimum pH is 6.5 – 7.5.
Acidophiles - Grow at acidic pH.
Thiobacillus thiooxidance
Optimum pH – 2 - 3.5
pH range - 0.5 – 6
Basophiles - grow at alkaline pH.
V. cholerae
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When bacteria grow in medium they change pH in
medium
Shift in pH may be so great that growth of organism
may be inhibited.
Buffers are added to media to resist change in pH.
Buffers like acetic acid buffer, phosphate buffers are
used in nutrient media.
Peptone added in media also has buffering capacity.
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Osmotic pressure
Microorganisms grow well in isotonic (iso-osmotic)
environment.
Growth decreases in hypo and hyper osmotic medium.
Yeast and fungi are more osmotolerent than bacteria
Halophillic bacteria - Halobacteria - grow at high
osmotic pressure.
1. Slight halophiles – 2-5 % NaCl
2. Moderate halophiles – Up to 20%
3. Extreme halophiles – 20 -30%
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Other requirements
Light -
Required by Photobacteria
Scotobacteria – Majority of bacteria grow in
absence of light
High hydrostatic pressure –
Bacteria from deep ocean if grown in laboratory
we have to simulate conditions of deep ocean
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Physical conditions for cultivation of bacteria

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