Micro Organisms in Air and Water – Bacteria, Viruses, algae, Protozoa, fungi
Micro-organisms are very tiny living organisms are also known as microbes.
Human immunodeficiency virus (HIV) is the cause of acquired immunodeficiency syndrome (AIDS). By infecting CD4 T-lymphocytes, a type of white blood cell, HIV weakens the immune system and leaves the infected individual open to deadly infections. The viruses gain access to a T-lymphocyte by attaching to CD4 proteins on the outer surface of the cell membrane.


Anthony Van Leeuwenhoek (1632 – 1733) was the first scientist to discover microbes with his newly invented microscope.

Micro-organisms are dreaded as disease causing agents (germs). However, many microbes are of great benefits to man e.g. saprophytic microbes that bring about decay of organic matter. Those microbes that affect man negatively are mainly the parasitic ones which are called pathogem.

Micro-organisms are found everywhere – in the air, water, soil, in our food, on our food, on surfaces of objects, and on and inside living organisms, on our bodies, inside of our bodies and on our clothes in shut, anywhere everywhere.

1. Groups of Micro-organisms

Microbes are very many and are grouped as follows:

(i) Bacteria

(ii) Viruses

(iii) Some algae

(iv) Protozoa

(v) Some fungi

Most microbes are unicellular but some fungi and algae are multi-cellular. Several microbes survive adverse conditions of temperature or humidity by forming spaces the within the cell. On the return of favourable condition of the spores are released carried in the air and on landing on suitable substrate grow and produce more spores.


Types of Bacteria

3. Based on Gram’s staining technique

• Gram positive bacteria: retains the purple/violet stain in its peptidoglycan (a large structural molecule found in the bacteria cell wall)
• Gram negative bacteria: loses or do not retain the purple stain in the cells
Bacteria can be the cause of a number of plant and animal diseases.
(a) Plant diseases caused by bacteria e.g. web blight in cowpeas, black arm in cotton, etc.
(b) Animal diseases caused by bacteria e.g. leprosy, lockjaw, cholera, etc.

Picture: Anatomy of simple bacterium

2. Viruses

They are unicellular in nature, without nucleus, cytoplasm and cell membrane. Smaller than bacteria and can only be seen under electron microscope. Virus lack life. Thus it cannot respire nor carry out metabolism. They can only survive inside living cells.

Types of Viruses

Viruses can be grouped based on:

  1. Type of nucleic acid (DNA/RNA)
  2. Nature of Protein coat

1. Based on type nucleic acid

  • Adenovirus, Herpesvirus (DNA)
  • Picornavirus, Togavirus, Orthomyxovirus, Paramyxovirus, Coronavirus (RNA)

2. Based on nature of protein coat

  • Adenovirus, Herpesvirus, Picornavirus, Togavirus (icosahedral in nature – i.e a polygon with 20 faces and 12 corners)
  • Orthomyxovirus, Paramyxovirus, Coronavirus (helical in nature)

3. Algae

They are mainly free-living microscopic plants. They survive in a wide range of habits such as wet soil, fresh water, sea etc. they have chlorophyll to a number of other pigments giving rise to green algae, brown algae, blue/green algae etc. examples of algae are: Sprirogyra, volvox, chlamy domonas,nostoc, Diatoms etc.

4. Protozoa

These are unicellular microscopic animals. They are found in damp soil and water. Some of them are parasitic while others live freely in their habit. Examples of parasitic protozoa are: Trypanosome, plasmodium etc. examples of free-living Protozoa are: Amoeba, Paramecium etc. parasitic protozoans are pathogens that cause disease like Malaria, sleeping sickness, Bilharziasis etc.

5. Fungi

These are non-green simple plants. They feed Saprophytically or parasitically. Saprophytic fungi such as mucor, yeast, penicilium are useful to man. Parasitic fungi do cause diseases which are unpleasant to man. Example of animal diseases caused by fungi is: Ringworm, Athelet’s foot, mouth thrush, candidiases etc. Plant diseases caused by parasitic fungi are: mildews, spots, wild, blights and Rots.

The Concept of Culturing

Culturing is a technique of growing micro-organisms in the laboratory for the studying the microbes.

The process has to do with:

  1. Preparing a sterile medium
  2. Inoculating
  3. Incubating
  4. Examining micro-organism in the medium.

While bacteria, fungi and algae can be grown in test tubes and Petri dishes in culture media, viruses cannot be grown. They can only grow and multiple inside living cells of an organism.

Through Tissue culture, living tissues and cells of multi-cellular organism are cultured in appropriate media and studied. To carry out studies involving viruses, viruses are cultured in the laboratory by injecting the virus into the fertilized bird’s egg e.g. egg of duck.

On the culture medium, micro-organisms occur as colonies. Colonies of micro-organism do clump together in large number of organism of the same kind. Colour, appearance other characteristics of the colonies enable the investigator to identify and differentiate microbes in a culture medium.


1 (a) What are Micro-organism?

(b) List the important groups, giving examples of each group.

2 (a) Expalin the concept of culturing.

(b) What steps will you take in preparing a culture solution and state precautions in preparing it.

(c) Identify sources of samples for culturing.

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