The physical factors that affect the growth of Microorganisms

1. By
S.Abilash
Ist M.Sc Microbiology

2. INTRODUCTION
 All bacterial and archael cells are haploid. Most
reproduce by “binary fission”
 Binary fission is a relatively simple type of cell division
 The cell elongates, replicates its chromosome and
separates the newly formed DNA molecules
 Finally septum is formed at the middle of cell dividing
the parent cell into two progeny cells.

3. FACTORS AFFECTING
MICROBIAL GROWTH
 Microbes are uptake the nutrients and reproduce, but
in some conditions the microbial growth get
disturbed.
 Microorganisms are able to respond to variations in
nutrient levels.
 Microorganisms are greatly affected by the chemical
and physical nature of their surroundings.

4. FACTORS
Physical factors Chemical Factors

5. Physical Factors
 Radiation
 Pulsed electric field (PEF)
 Pulsed magnetic field (PMF)
 High power ultrasound
 Temperature
 High osmotic gradients
 High pressure

6. RADIATION
•Radiation behaves as if it were in water
•The wave length of EMW decreases
with increase in energy
•Sunlight the major source of radiation
•Photosynthatic organisms depend on
this
•Sun ray has 60% infra red rays, 3% UV
rays

7. Cont.....
 Different types of UV rays( A,B&C)ranges from longest
to shortest
 Sea level UV Wavelength is about 290nm
 Below this level it is absorbed by the ozone layer
 Two types of radiations they are
1 Ionising radiation
2Non-ionising radiation

8. Ionizing Radiation
 Very short Wavelength and high energy which causes
atoms to lose electrons
 X-rays and gamma rays
 Low level radiation may cause Mutation
 High level cause Lethal effect ,i.e. breaks hydrogen
bonds, destroys ring structure and polymerizes some
molecules
 Microorganisms are resistant to ionizing radiation e.g.
Deinococcus radiodurans which extermely resistant to
high ionizing radiation

9. UV radiation
 Kills microorganisms due to short wavelength (10-400nm)
 Most lethal wavelength is 290nm absorbed by DNA and
damages it
 However excessive exposure to UV outstrips organisms
ability to repair damage


11. UV Resistant Microorgnaisms

12. Visible Light
 Even visible light at high intensity can kill microbes
 Pigments called “photosensitizers” & oxygen are
involved
 Photosensitizers absorb light energy and become
excited then transfers its energy to oxygen generating
singlet oxygen
 P P(activated)
P(activated)+oxygen P +Oxygen
 Carotenoids convert singlet oxygen into the unexcited
state

13. PULSED ELECTRIC FIELDS (PEF)
 Strong electric field pulses applied to cells cause their
membranes to develop pores electroporation
increasing membrane permeability with a consequent
and for the undesirable migration of chemicals.
 Pulses of low intensity may result in the increased
production of secondary metabolites and a build up
of resistance

14. PULSED MAGNETIC FIELDS (PMF)
 A 2004 study found that E.coli is susceptible to
pulsed magnetic fields with a survivability figure
of 1 in 10000
 Enzymes such as lactoperoxidase, lipase and
catalase are readily inactived

15. HIGH POWER ULTRA SOUND
 Ultrasound generates cavitation bubbles within
a liquid or slurry by causing the liquid molecules
to vibrate.
 The process is used for destroying E.coli,
Salmonella, Ascaris, Cyanobacterium & polio virus
 It is also capable of breaking down organic
pesticides

16. HIGH POWER ULTRA SOUND

17. HIGH PRESSURE
 Organisms that spend their lives on land or the surface
of water are always subjected to a pressure of 1 atm
and are never affected significantly by pressure.
 High hydrostatic pressures affect membrane fluidity
and membrane associated function.
 Many microbes found at great ocean depths are
“barotolerant” increased pressure adversely affects
them but not as much as it does non tolerant
microbes.

18. PIEZOPHILIC MICROBES
 They grow more rapidly at high pressure
 A piezophile is defined as an organism that has a
maximal growth rate at pressures greater than 1atm
but less than about 590atm
 An important adaptation observed in piezophiles is
that they change their membrane lipids in response to
increasing pressure.
 Eg:Photobacterium, Shewanella

19. Temperature

20. Temperature

21. Temperature
 Microorganisms are particularly susceptible to external
temperatures because they cannot regulate their
internal temperature.
 High temperature denature enzymes, transport
carriers and other proteins.
 Temperature also has a significant effect on microbial
membranes.
 Low - membrane solidify
 High - the lipid bilayer simply melts & disintegrates

22. Based on the temperature range microbes are classified
into
 Psycrophiles
 Psycrotolarent
 Mesophiles
 Thermophiles
 Hyperthermophiles
 Extermethermophiles

23. Psycrophiles
It grow well at 0°C and have an optimum
growth temperatures of 15°C ; the maximum
is around 20°C.
Eg: Pseudomonas, Vibrio, Bacillus,
Shewanella etc.
Many psychrophiles begin to leak cellular
constituents at temperature higher than
20°C because of cell membrane disruption
Psycrophiles

24. Cold active enzyme
 It is a holoenzyme with high amount of Alpha helix
and low amount of beta sheets
 Has greater polar ends and lesser hydrophobic end
 The cytoplasm of psycrophiles have high amount of
unsaturated fattty acid
 E.g. Psychroflexus sp has fatty acids with 4-5 double
bond molecules

25. Psycrotolarent
 Can grow at 0C but it has optimal temperature of 25c
and maxima at 35c
 E.g. Psychrophilic algae
 Which produce characteristic colour due to the
presence of pigment e.g. Chlamydomonas nivalis
 It has red colour pigment production
 It multiplies when the ice starts melting

26. Mesophiles
 These are microorganisms that grow in moderate
temperatures. They have growth optima around 20 –
45 °C and often have a temperature minimum of 15 –
20 °C and a maximum of about 45°C
 They are common flora which infection to the humans
 E.g. E.coli

27. Mesophiles

28. Thermophiles
Grow at temperatures between 55 and 85°C.Their
growth minimum is around 45°C
Eg:Thermoplasma acidophilum

29. Hyperthermophiles
It have growth optima between 85°C & about 113°C. They
usually do not grow below 55°C.
Eg:Pyrococcous abyssi
Hot springs
(150-500c)
Hydrothermal vents 350c

30. SOLUTE AND WATER ACTIVITY
 Because a selectively permeable plasma membrane
separates microorganisms from their environment,
they can be affected by changes in osmotic
concentration of their surroundings
 If a microorganism is placed in hypotonic solution
(lower osmotic concentration) water will enter the
cell and cause it to burst.
 If it is placed in a hypertonic solution (higher
osmotic concentration) water will flow out of the
cell.

31. Cont....
 In microbes that have cell walls the membrane
shrinks away from the cellwall a process called
“plasmolysis”.
 Dehydration of the cell in hypertonic
environments may damage the cell membrane
cause the cell to become metabolically inactive.
 Microbes be able to respond to changes in the
osmotic concentrations of their environment.

32. HALOPHILES
 It require the presence of Nacl or other salts at the
concentration above about 0.2M.
 “extreme halophiles” have adapted so completely to
hypertonic saline conditions that they require high
levels of Nacl to grow.
 Eg:Halobacterium
 It can be accumulate enormous quantities of
potassium and chloride ions

33. Types of Halophiles
 Mild Halophiles(1-6% NaCl)
 Moderate Halophiles(7-15% NaCl)
 Exterme Halophiles(15-30%)

34. OXYGEN CONCENTRATION

35. Oxygen requirement
Group Relationship Type of
metabolism
Example Habitat
Aerobes
Obligate Required Aerobic
respiration
Micrococcus
luctes
Skin,dust
Facultative Not required
but growth
better with
oxygen
Aerobic
&Anaerobic
E.coli Large intestine
Microarophiles Required lower
than
atmospheric
Aerobic Spirillum
volutus
Lake water
Anaerobe
Aerotolarent Not required
but no better
growth with
oxygen
Fermentation Streptococcus
pyogens
Upper
respiratory tract
Obligate Harmful or Methanobacteri Anoxic lake

36.  An organism able to grow in the presence of
atmospheric oxygen is an aerobe; where as one that
grow in its absence is an anaerobe.
 Almost all multicellular organisms are completely
dependent on atmospheric O2 for growth that is they
are obligate aerobes.
 Microaerphiles such as Campylobacter are damaged
by the normal atmospheric level of O2 (20%) they
require only (2 – 10%) for growth.

37.  Facultative anaerobes do not require O2 for growth but
grow better in its presence.
 Aerotolerant anaerobes such as Enterococcus faecalis
grow equally well whether O2 is present or not.
 Obligate anaerobes are usually killed in the presence of
O2.
Eg:Methanococcus, Clostridium pasteurianum

38.  A microbial group may show more than one type
of relationship to O2.
 The different relationships with O2 are due to
several factors including the “inactivation of
proteins and the effect of toxic O2 derivatives”
 Enzymes can be inactivated when sensitive groups
are oxidized.
 Eg: The nitrogen fixation enzyme nitrogenase
which is very oxygen sensitive

39. Prevention from oxygen attack
 Oxygen present in the environment sometime s may
lyse the bacterial cell
 Catalase
H2O2+H2O2 2H2O+O2
Peroxidase
H2O2+NADH+H 2H2O+NAD
Superoxide dimutase
O2+O2+2H H2O2+O2

40. Cont...
 Superoxide dimutase/Catalase incombination
4O2+4h 2H2O+3O2
Superoxide reductase
O2+2H+Cyt C H2O2+Cyt C

41. PH

42. PH
 PH is a measure of the relative acidity of a solution and
is defined as the negative logarithm of the hydrogen
ion concentration.
 Each species has a definite PH growth range and PH
growth optimum.
 Acidophiles – optimum PH 0 and 5.5
 Neutrophiles – optimum PH 5.5 and 8.0
 Alkaliphiles - optimum PH 8.0 and 11.5

43. ACIDOPHILES
 E.g. Acidithiobacillus sp, sulfolobus sp, Thermoplasma
sp, Feroplasma sp
 Ph raised cytoplasm destroyed indicating that high
concentration of H ions needed for membrane
stability

44. Alkaliphiles
 Alkali loving, need high concentration of alkali and
high carbonate solution
 Some species of this range have board range
 E.g Bacillus flemus has a range between 7.5-11

45. Neutrophiles
 Lives at ambient ph around 7
 Most of the beneficial and harmful bacteria live at this
ph
 Hence is the reason for so many microbial infection in
the human health
 E.g E.coli

46. Chemical factors
 Nutrition type
 Nutrition needed

47. OPEN SESSION
?

48. Thank
You