2. MICROBES (MICRO-ORGANISMS)
A microbe, or microorganism, is a microscopic organism that
comprises either a single cell (unicellular); cell clusters; or multicellular,
relatively complex organisms.
Tiny living things that are found all around us and are too small to
be seen by the naked eye.
A subject that began with Anton van Leeuwenhoek’s discovery of
microorganisms in 1675, using a microscope of his own design.
Live in water, soil, and in the air. The human body is home to
millions of these microbes too.
The study of microorganisms is called Microbiology.
4. MICROBIAL DIVERSITIES
Account for most of the diversity of life on our planet.
More kinds of microbes than plants, vertebrates, and insects
combined.
Adapted to nearly every environment on earth and can eat just about
anything, including metals, acids, petroleum, and natural gas—all of
which are toxic to us.
Live Everywhere—even in places we used to think were
incompatible with life.
5. BACTERIA
Single celled microbes.
The cell structure is simpler than that of other organisms as there is
NO Nucleus or Membrane Bound Organelles.
Instead their control centre containing the genetic information is
contained in a single loop of DNA. Some bacteria have an extra
circle of genetic material called a Plasmid.
For Example it may contain a gene that makes the bacterium
resistant to a certain Antibiotic.
Found in every habitat on Earth: soil, rock, oceans and even arctic
snow. Some live in or on other organisms including plants and
animals including humans.
6. There are approximately 10 times as many bacterial cells as human
cells in the human body.
Some bacteria live in the soil or on dead plant matter where they
play an important role in the cycling of nutrients.
Bacteria reproduce by binary fission
Some bacteria can form endospores. These are dormant structures,
which are extremely resistant to hostile physical and chemical
conditions such as heat, UV radiation and disinfectants
7. VIRUSES
Viruses are the Smallest of all the microbes.
They are said to be so small that 500 million rhinoviruses (which
cause the common cold) could fit on to the head of a pin.
They are Unique because they are only alive and able to multiply
inside the cells of other living things. The cell they multiply in is
called the host cell.
A virus is made up of a core of genetic material, either DNA or
RNA, surrounded by a protective coat called a Capsid which is
made up of protein.
Sometimes the capsid is surrounded by an additional Spikey coat
called the Envelope.
8. Viruses only exist to make more viruses.
The virus particle attaches to the host cell before penetrating it. The
virus then uses the host cell’s machinery to replicate its own genetic
material.
Once replication has been completed the virus particles leave the
host by either budding or bursting out of the cell (lysis).
The virus particles burst out of the host cell into the extracellular
space resulting in the death of the host cell.
H3N2 Influenza
Virus Particles
9. FUNGI
Single celled or very complex multicellular organisms.
They are found in just about any habitat but most live on the land,
mainly in soil or on plant material rather than in sea or fresh water.
A group called the DECOMPOSERS grow in the soil or on dead
plant matter where they play an important role in the cycling of
carbon and other elements.
Some are PARASITES of plants causing diseases such as mildews,
rusts, scabs or canker.
In crops fungal diseases can lead to significant crops loss for the
farmer.
A very small number of fungi cause diseases in animals. In humans
these include skin diseases such as athletes’ foot, ringworm etc.
10. The three major groups of fungi are:
Multicellular filamentous moulds.
Macroscopic filamentous fungi that form large fruiting bodies.
Sometimes the group is referred to as ‘mushrooms’
Single celled microscopic yeasts.
Candida Albicans (Yeast & Hyphae)
11. PROTOZOA
Single celled organisms.
They come in many different shapes and sizes ranging from
An Amoeba which can change its shape
Paramecium with its fixed shape and complex structure.
They live in a wide variety of moist habitats including fresh water,
marine environments and the soil.
Some are parasitic, which means they live in other plants and
animals including humans, where they cause disease.
Plasmodium, for example, causes malaria.
12. Motile and can move by:
Cilia - tiny hair like structures that cover the outside of the microbe.
Flagella - long thread-like structures that extend from the cell
surface.
Amoeboid Movement - the organism moves by sending out
Pseudopodia.
Stentor (Protozoan)
13. ALGAE
Exist as single cells
Most live in fresh or sea water where they can either be free-
floating (Planktonic) or attached to the bottom.
Grow on rocks, soil or vegetation as long as there is enough
moisture.
Examples are : Chlamydomonas, or joined together in chains
like Spirogyra or made up of many cells, for
instance Rhodymenia (red seaweed).
Contain a pigment called Chlorophyll A (other types of chlorophyll
such as b, c and/or d may also be present) and they make their own
food by photosynthesis.
The chlorophyll is contained in the chloroplasts and gives many
algae their Green Appearance.
14. Appear brown, yellow or red because in addition to chlorophylls
they have other accessory pigments that camouflage the green
colour.
Diatoms, a type of algae, are found floating in the phytoplankton of
the seas. Their cell walls contain a hard substance called silica.
Batrachospermum
(Red Algae)
15. ARCHAEA
Spherical, rod, spiral, lobed, rectangular or irregular in shape.
An unusual flat, square-shaped species that lives in salty pools has
also been discovered. Some exist as single cells, others form
filaments or clusters.
Until the 1970s this group of microbes was classified as bacteria.
Archaea are a group of micro-organisms that are similar to, but
evolutionarily distinct from bacteria.
Many archaea have been found living in extreme environments.
For Example at high pressures, salt concentrations or temperatures.
These types of organisms are called Extremophiles.
16. Their cell wall differs in structure from that of bacteria and is
thought to be more stable in extreme conditions
Archaea can live in many of the most HARSH environments on
Earth.
Examples of archaea habitats are boiling hot springs and geysers
such as those found in Yellow Stone Park, USA and Ice.
22. DEVELOPMENT OF MICROBIOLOGY
The quest to solve drug resistance, identify viruses, and develop
vaccines requires sophisticated research techniques and correlated
studies that were never dreamed of in the days of Koch and Pasteur.
Bacteriology, the study of bacteria, began with van Leeuwenhoek’s
first examination of tooth scrapings.
Mycology, the study of fungi, includes medical, agricultural, and
ecological branches.
Parasitology is the study of protozoa and parasitic worms.
Immunology, the study of immunity, dates back in Western culture
to Jenner’s first vaccine in 1796. Since then, knowledge about the
immune system has accumulated steadily and expanded rapidly.
Vaccines are now available for numerous diseases
23. The study of viruses, Virology originated during the Golden Age of
Microbiology.
Recombinant DNA Technology Microorganisms can now be genetically
modified to manufacture large amounts of human hormones and other
urgently needed medical substances.
When recombinant DNA is inserted into bacteria (or other microbes), it
can be used to make large quantities of the desired protein. The technology
that developed from this technique is called Recombinant DNA
Technology
Its origins can be found in two related fields.
The first, Microbial Genetics, studies the mechanisms by which
microorganisms inherit traits.
The second, Molecular Biology, specifically studies how genetic
information is carried in molecules of DNA and how DNA directs the
synthesis of proteins.
24. Microbial Ecology, the study of the relationship between
microorganisms and their environment, originated with the work of
these scientists.
Sewage Treatment, using Microbes to recycle Water
Some bacteria can actually use pollutants as energy sources; others
produce enzymes that break down toxins into less harmful
substances. By using bacteria in these ways—a process known as
BIOREMEDIATION—toxins can be removed from underground
wells, chemical spills, toxic waste sites, and oil spills
Insect Pest Control by Microorganisms
GENE THERAPY—inserting a missing gene or replacing a
defective one in human cells. This technique uses a harmless virus
to carry the missing or new gene into certain host cells, where the
gene is picked up and inserted into the appropriate chromosome.
