This document provides information about microbes including their types, growth, and role in the environment. It discusses that microbes are tiny organisms that can only be seen under a microscope. They are found everywhere and play vital roles such as breaking down waste, producing nutrients for plants, and maintaining healthy human microbiomes. The document also describes the different types of microbes based on oxygen needs, temperature tolerance, pH tolerance, and other characteristics. It explains the growth phases of microbes and factors that influence their growth such as nutrients, temperature, oxygen levels and pH. Finally, it discusses the important roles microbes play in environments like producing oxygen, nutrient cycling, supporting agriculture, and maintaining livable climates.

1. Microbes
Bibhabasu Mohanty
Asst. Prof. Dept. of civil Engineering
SALITER, Ahmedabad

2. Content…
Types of microbes, Growth and their role
in environment.

3. Microbes
Are invisible to the naked eye, you need a
powerful microscope to see them.
Are everywhere around us, inside us, on us, in
our food, in our homes, in the air we breathe
and the water we wash in.
Are mostly useful, but some are harmful
Are vital for life on Earth.

4. What do Microbes look like ?
Magnified 1000‘s of times and coloured using
dye, we see -

5. Microbes exist in huge numbers
In one single teaspoon of garden soil, there are
over 100,000 microbes. In 1ltr of
seawater, there are over 1bn microbes.
On your hands there are more microbes than
there are people in the world.
There are so many microbes, that scientists
have only named 0.5% of them.
Microbes outnumber all other species and
make up most of the living matter on the
planet.

6. Microbes live among us
In our food
Cleaning up our waste
Killing pests
Making medicines
In the making of such things as leather, soy
sauce, cheese and paper.
In our bodies.

7. Types of Microbes
Named based on their particular physiological
and nutritional characteristics.
Oxygen Description
Aerobe Capable of using oxygen as a
terminal electron acceptor
Anaerobe Grows in the absence of oxygen
Facultative anaerobe Can grow aerobically or
anaerobically
Microaerophile Capable of oxygen-dependent
growth but only at low oxygen levels

8. Temperature Description
Psychrophile/ Optimal temperature for growth is 15 °C or lower,
facultative maximal temperature is approximately 20 °C, and
psychrophile minimal temperature is 0 °C or lower
Psychrotroph Capable of growing at 5 °C or below, with maximal
temperature generally above 25 °C to 30 °C
Mesophile optimal temperature for growth, which is
approximately 37 °C; frequently grows in the range
from 8 °C to 10 °C and from 45 °C to 50 °C
Thermophile Grows at 50 °C or above
Hyperthermophile Grows at 90 °C or above, although optimal
temperature for growth is generally above 80 °C;
maximal growth of pure cultures occurs between
110 °C and 113 °C,

9. pH Description
Acidophile Grows at pH values less than 2
Alkalophile Grows at pH values greater than 10
Neutrophile Grows best at pH values near 7
Salinity Description
Halophile Requires salt for growth: extreme halophiles (all are archaea), 2.5
M to 5 M salt; moderate halophiles, usually low levels of NaCl as
well as 15 to 20 percent NaCl
Hydrostatic pressure Description
(100 atmospheres per
1,000-m depth)
Barophile Obligate barophiles, no growth at 1 atmosphere
of pressure; barotolerant bacteria, growth at 1
atmosphere but also at higher pressures. (0.987
atm = 1 bar = 0.1 megapascal [Mpa])

10. Nutrition Description
Autotroph Uses carbon dioxide as its sole source of carbon
Heterotroph Unable to use carbon dioxide as its sole source of
carbon and requires one or more organic
compounds
Chemoorganoheterotroph Derives energy from chemical compounds and
uses organic compounds as a source of electrons
Chemolithoautotroph Relies on chemical compounds for energy and uses
inorganic compounds as a source of electrons.
hydrogen bacteria, iron bacteria, sulfur bacteria,
ammonia oxidizers, and nitrite oxidizers.
Mixotroph Capable of growing both
chemoorganoheterotrophically and
chemolithoautotrophically
Oligotroph Can develop at first cultivation on media containing
minimal organic material (1 to 15 micrograms
carbon per liter)

11. Microbes – three types
Bacteria strep bacteria
Virus rotavirus
Fungi
mould

12. Bacteria
 Have three main shapes
spiral (boriella) little balls(-cocci) rods (-bacilli)
 Can move about on their own
 Join up together to form chains
called ‗bio-films‘. As on teeth !

13. Virus
 Come in 1000s of different shapes and sizes.
 They hang about waiting to meet a ‗host‘ which they
then invade, hijacking the host‘s cells. Beware the air
you breathe and door handles !

14. Fungi
 Not just mushrooms –
 athlete‘s foot, penicillin, and yeast.
 Yeast is used in bread making,
and brewing

15. Algae are also Microbes
Algae photosynthesise – taking their energy
from the sun, and producing oxygen in the
process. Algae are thought to produce over
50% of the oxygen in the world.

16. And finally
 Without microbes, life on this planet would be entirely
different – they generate oxygen, are part of the carbon
and nitrogen cycles, and can survive the harshest
conditions.
 Without microbes, our bodies would not process the
food we eat.
 They drive the chemistry of life, breaking things down
into their parts so that life can being again.
 Microbes are small but mighty !

17. Microbial Growth
refers to the no. of cells, not the size of the
cells

18. Factors that Influence Growth
Growth vs. Tolerance
– ―Growth‖ is generally used to refer to the
acquisition of biomass leading to cell division, or
reproduction
– Many microbes can survive under conditions in
which they cannot grow

19. The suffix ―-phile‖ is often used to describe
conditions permitting growth, whereas the term
―tolerant‖ describes conditions in which the
organisms survive, but don‘t necessarily grow
For example, a ―thermophilic bacterium‖ grows
under conditions of elevated temperature, while a
―thermotolerant bacterium‖ survives elevated
temperature, but grows at a lower temperature

20. Factors that Influence Growth
Obligate (strict) vs. facultative
―Obligate‖ (or ―strict‖) means that a given condition is
required for growth
―Facultative‖ means that the organism can grow under
the condition, but doesn‘t require it
The term ―facultative‖ is often applied to sub-optimal
conditions
For example, an obligate thermophile requires
elevated temperatures for growth, while a facultative
thermophile may grow in either elevated
temperatures or lower temperatures

21. Factors that Influence Growth
Temperature
– psychrophiles (cold loving microbes )
•range 0 C - 20 C
– mesophiles (moderate temp. loving microbes)
•range 20 C - 40 C
– thermophiles (heat loving microbes)
•range 40 C - 100 C

22. Factors that Influence Growth
 pH
 Most bacteria grow between pH 6.5 - pH 7.5
 Very few can grow at below pH 4.0
many foods, such as sauerkraut, pickles, and cheeses are
preserved from spoilage by acids produced during
fermentation

23. Factors that Influence Growth
Salt concentration
Halophiles require elevated salt concentrations
to grow; often require 0.2 M ionic strength or
greater and may some may grow at 1 M or
greater; example, Halobacterium.
Osmotolerant (halotolerant) organisms grow
over a wide range of salt concentrations or ionic
strengths; for example, Staphylococcus aureus.

24. Factors that Influence Growth
Oxygen concentration
– Strict aerobes: Require oxygen for growth (~20%)
– Strict anaerobes: Grow in the absence of oxygen;
cannot grow in the presence of oxygen
– Facultative anaerobes: Grow best in the presence of
oxygen, but are able to grow (at reduced rates) in the
absence of oxygen
– Aerotolerant anaerobes: Can grow equally well in the
presence or absence of oxygen
– Microaerophiles: Require reduced concentrations of
oxygen (~2 – 10%) for growth

25. Osmotic Pressure
Microbes obtain almost all their nutrients in
solution from surrounding water
Tonicity
– isotonic
– hypertonic
– hypotonic

26. Factors that Influence Growth
Macro & Micro Elements
 C HOPKINS CaFe Mg NaCl

27. Limiting factors in the environment
Lack of food, water or nutrients
space
accumulation of metabolic wastes
lack of oxygen
changes in pH
temperature

28. Phases of Growth
4 Phases
1. Lag Phase
2. Log Phase
3. Stationary Phase
4. Death Phase

30. Lag Phase
Bacteria are first introduced into an
environment or media
Bacteria are ―checking out‖ their surroundings
cells are very active metabolically
 no of cells changes very little
1 hour to several days

31. Log Phase
Rapid cell growth (exponential growth)
population doubles every generation
microbes are sensitive to adverse conditions
– antibiotics
– anti-microbial agents

32. Stationary Phase
Death rate = rate of reproduction
cells begin to encounter environmental stress
– lack of nutrients
– lack of water
– not enough space
– metabolic wastes
– oxygen
– pH
Endospores would form now

33. Death Phase
Death rate > rate of reproduction
Due to limiting factors in the environment

34. Roles of microbes in environment
Microbes—life forms too tiny to see—play a
surprisingly large role in life on Earth.
Humans depend on microbial communities in
more ways than you can imagine.

35. Make air breathable
Keep us healthy
Provide sources of new drugs
Help us digest food
Clean up hazardous chemicals
Support and protect crops

36. Microbes keep us healthy
Partners for life
Invite a microbe to dinner
Nature‘s master chemists
New possibilities

37. Microbes keep our planet healthy
Liveable climate.
Healthy farms
Cleaning up
Productive ecosystem