This document discusses the classification of microorganisms based on their mode of nutrition. It describes three main criteria for classification: carbon source, energy source, and electron source. Based on carbon source, microorganisms are either autotrophs, which produce their own organic carbon from inorganic carbon dioxide, or heterotrophs, which rely on other organisms for organic carbon. Based on energy source, they are either phototrophs, which use light as an energy source, or chemotrophs, which use chemical compounds. Based on electron source, they are either lithotrophs, which use inorganic electron donors, or organotrophs, which use organic electron donors. The document also lists the five main nutritional types

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Mrs. Sweta Bade Manita Lama Roll. No. 37
Shristi Basnet Roll No. 36
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2. Table of Contents
1. Introduction
2. Types of Micro-organisms on the basis of Mode of Nutrition
3. Classification on the basis of Carbon Source
4. Classificaion on the basis of Energy Source
5. Classification on the basis of Electron Source
6. Nutritional Types of Micro-organisms
7. References

3. Introduction
A microorganism is a living thing that is too small to be seen
with the naked eye.
Microorganisms are divided into seven types: bacteria, archaea,
protozoa, algae, fungi, viruses, and multicellular animal
parasites ( helminths ).
Each type has a characteristic cellular composition,
morphology, mean of locomotion, and reproduction.
 Microorganisms are found virtually everywhere, except for
environments that have been made artificially sterile by
humans.

4.  Microorganisms are beneficial in producing oxygen,
decomposing organic material, providing nutrients for plants,
and maintaining human health, but some can be pathogenic and
cause diseases in plants and humans.
 Nutrition is substance used in biosynthesis and energy
production and therefore are required for all living things.
 All microbes have a need for three things: carbon, energy, and
electrons. There are specific terms associated with the source
of each of these items, to help define organisms.

5. Types of Micro organisms on the basis of
mode of Nutrition
3 Different Criterias
1.Carbon Source
2. Energy Source
3. Electrons Source

6. 1. On the basis of Carbon Source
Organisms can be identified according to the source
of carbon they use for metabolism as well as their
energy source.
 Classified into two types: The prefixes auto-
(“self”) and hetero- (“other”) refer to the origins of
the carbon sources various organisms can use.
A. Autotrophs
B. Heterotrophs

7. A. Autotrophs
 Autotrophs are organisms that undergo autotrophic
mode of nutrition.
 They convert inorganic carbon dioxide (CO2) into
organic carbon compounds.
Examples: Usually members of the plant kingdom and
certain unicellular organisms like cyanobacteria

8. B. Heterotrophs
 Heterotrophs are organisms which cannot prepare their
own food and depend upon producers or green plants
and other animals for their food. This mode of nutrition
is known as the heterotrophic mode of nutrition.
Examples: All members of the animal kingdom

9. 2. On the basis of Energy Source
• Organisms can also be identified by the energy source
they use.
• Classified into two types: The prefixes photo- (“light”)
and chemo- (“chemical”) refer to the energy sources that
various organisms use.
A. Phototrophs
B. Chemotrophs

10. A. Phototrophs
 They use sunlight as their main source of energy to
produce their food.
They capture light energy and convert it into chemical
energy inside their cells,
E.g. green plants convert light energy into chemical
energy by photosynthesis or they are able to fix carbon
from the carbon dioxide into organic compounds.

11. Further classified into two main groups:
• Photoautotrophs: E.g. green plants and
photosynthetic bacteria.
• Photoheterotrophs: E.g. purple non-sulfur bacteria
and green non-sulfur bacteria.

12. B. Chemotrophs
They get their energy from the oxidation or breakdown
of carbon dioxide or inorganic chemical compounds by
chemosynthesis.
During this process, simple molecules with carbon like
carbon dioxide and methane are converted into organic
compounds by oxidizing hydrogen gas, hydrogen
sulphide, sulphur etc.

13. They are further classified into two:
• Chemoautotrophs: E.g. sulphur and iron bacteria.
They are usually found in hostile habitats such as deep
sea vents.
• Chemoheterotrophs: E.g. fungi, bacteria and some
sulphur bacteria, etc.

14. 3. On the basis of Electron Source
A. Lithotrophs
 Organisms that obtain its energy from inorganic
compounds (such as ammonia) via electron transfer.
They use inorganic matter as an energy source.
 Also known as “Rock Eaters” since they have been
found growing in rock formations thousands of meters
below the surface of Earth.

15. B. Organotrophs
 Organisms that obtain its energy from organic
compounds.
 They use organic molecules as an energy source .
 Known as “Organic-eater”.
 Examples: Animals, fungi, protists

16. Nutritional Types of Micro-Organisms
1. Photolithoautotrophy
2. Photo organoheterotrophy
3. Chemo lithoautotrophy Carbon+Energy+Electrons
4. Chemo lithoheterotrophy
5. Chemo organoheterotrophy

17. Nutritional
Type
Photolithoauto-
trophy
Photo
organohetero-
trophy
Chemolitho
autotrophy
Chemolitho
heterotrophy
Chemo organo
heterotrophy
Carbon Source CO2 Organic Carbon CO2 Organic Carbon
but CO2 may
also be used.
Organic Carbon
Energy Source Light Light Inorganic
Chemicals
Inorganic
Chemicals
Organic
Chemicals, often
same as Carbon
source
Electron Source Inorganic
electron donor
Organic electron
donor but CO2
may also be used.
Inorganic
electron donor
Inorganic
electron donor
Organic electron
donor, often same
as carbon source
Examples: Purple and Green
Sulfur bacteria,
Cyanobacteria
Purple non sulfur
bacteria, Green
non sulfur
bacteria
Sulfur oxidizing
bacteria,
Hydrogen
Oxidizing
bacteria,
Methanogens,
Nitrifying
Bacteria
Some sulfur
oxidizing
bacteria (eg.
Beggiatoa)
Mostly Non-
photosynthetic
bacteria including
pathogens, fungi,
many protists and
many archae

18. References
• Madigan M; Martinko J, eds. (2006). Brock Biology of
Microorganisms (13th ed.). Pearson Education. p. 1096.
• Sutton, J. (1998). Heterotrophic Nutrition. In Biology
(pp. 349-362). Palgrave, London.
• https://rsscience.com/autotrophs-vs-heterotrophs/
• https://www.sciencedirect.com/topics/immunology-and-
microbiology/microorganism