Mr. Ramavatar Sharma
(Reg. no. 10-104-2012)
Prof. P.D. Chavda
College of RE & EE
Microbiology is the study of microorganisms, which are unicellular or cell-cluster
microscopic organisms. This includes eukaryotes such as fungi and protists, and
prokaryotes. Viruses, though not strictly classed as living organisms, are also studied.
Microorganisms are very tiny one-celled organisms, viruses, fungi, and bacteria, and
are found everywhere in the world. They are found in all living things, plants and
There are more microorganisms on and inside your body than there are cells that make
up your entire body. Microorganisms can live in the air, on land, and in fresh or salt
water environments. Some of them, pathogens, can be harmful and causes diseases,
but there are some microorganisms that are needed for living things to survive.
Characteristics of viruses
Virus is a Latin Word Which Means Poison and Toxin.
Kunkle in 1947 in distinguishing virus diseases from fungal diseases came
to the conclusion that viruses are most efficient pathogen.
Viruses get themselves into the cells by the finest and most efficient
hypodermic syringes known to man, that is the proboscis of insects.
Viruses escape quarantine screening very simply in masked carries hosts.
When the plant being attacked becomes immune, they mutate to produce a
more virulent strain that can successfully invade the plant.
Viruses are invisible, non microscopic except with electron microscope.
Bowden in 1964 describes viruses as ”submicroscopic” , infective entities that
multiply only intracellularly and are potentially pathogenic.
He associated viruses with three characteristics
(iii) Ability to multiply only intracellularly
Because some viruses could pass through becterial filters, they are described
as filterable virus.
They are host specific i.e. each type of virus can infect and parasitise only a
limited range of host cells called host ranges.
They identity their specific host by a lock and key system i.e. fit
between proteins and the outside of the virus specified receptor
molecules on the surface of cells.
Some virus can infect a broad host range e.g. the rabies virus can
infect rodents, dogs and humans.
Viruses that parasitise bacteria e.g. Escherichia coli are called
The phages parasitize only the bacterium E.coli. The influenza virus
only infect the lining of human upper respiratory tract ignoring other
The AIDS virus binds to specific receptor on certain type of white
blood cells passes through bacterial filters.
Chester in 1974 is described viruses as one of the most interesting,
mysterious and elusive plant pathogens. They are contagious,
transmissible and are capable of causing some of the most destructive
diseases not only on plants but also on animals and man.
Virus are non-motile but are carried by insects vectors.
Viruses lack metabolic capabilities possessed by bacteria and fungi
but depend on their hosts not only for substances but also for the
mechanism that synthesise their substances.
Tobacco mosaic virus has a helical capsid with overall shape of a rigid
Adenovirus has a polyhedral capsid with a protein spike at each
vertex. Some adenoviruses cause respiratory infections in humans.
Influenza virus has an outer viral envelope studded with glycoprotein
Viruses can either be living or non-living
They are Living particles because they have the ability to:
Multiply within appropriate cell, a process resembling reproduction
To undergo mutation.
They are non-living particles because they have no:
Ability to respond to stimuli
Can not be cultured outside the host cell i.e. they are obligate parasite.
They live in the host cells intracellularly.
Deleterious effects of viruses
Man is effected by many virus diseases, e.g. smallpox, common cold,
epidemic influenza, mumps, measles, poliomyelitis, rabies etc.
Animal are also affected by viruses e.g. foot and mouth disease of cattle,
sheep and goats. Cattle plague, rabies of cats, dogs, sheep and goats,
newcastle disease of pigeons, ducks, turkeys, fowl-pox, cow pox and
psittacosis of birds.
Domesticated honey bees are affected by fowl brood and caterpillar wilt,
fishes are said to have virus also and even bacteria are affected by virus.
As cited by Bowden in 1964, Gandy and Hollings in 1962 reported the
die-back of mushrooms.
Viruses have no protein synthesing apparatus for manufacturing of
ribosome, transfer RNA, mRNA. A virus therefore depends on its host cell
for its energy and for translating its genomes into proteins, t-RNA, mRNA a and r-RNA e.g. they infect bacteria cells to give rise to what is
known as a bacteriophage e.g. Escherichia coil and T2 even phage.
Comparison of viruses with other micro-organisms
A virus particle is not a micro-organism because:
An organism consists of one or more cells that operate by following
the instruction of their genomes. A virus on the other hand is an
independent genome enclosed in a protective covering that allows it
to survive outside the host cell and to invade functioning cells which
becomes its host.
The virus takes the form of a particle called virion each of which
consists of a nucleic acid genome encloses in a capsid. The virion
contain only one kind nucleic acid ether DNA or RNA.
Viruses reproduce solely by using the information in the one nucleic
acid while the organisms including parasites reproduce through
integrated actions of all there constituents.
Viral genomes do not contain an apparatus for generating energy.
Viruses do not grow as cells do by enlarging and dividing nor do
they reproduces as organisms do. Either asexually or sexually.
Instead virus infected cells synthesise new virions in much the same
way a factory manufactures products.
Transitory and persistent viruses
Viruses can be transitory if:
It does not persist in its vector i.e. the infectivity decreases with
It has a short retention period
It lacks a demonstrable latent period in the vector
Infectivity is lost after the insect molts.
Viruses can be non-transitory if:
It persists in its vector.
It has a long retention period.
It has latent period vector.
It does not loose infectivity after insect molting.
Characteristics of bacteria
Bacteria are prokaryotic unicellular organisms.
Bacteria are larger organisms then virus ranging from 0.5-1.5um in
diameter they can be seen with the aid of alight microscope i.e. they
They are either gram negative or gram positive .
They have all the characteristics common to other organisms . they
are cellular, posses comparable metabolism and are microscopic
specially with the oil immersion (x 100) objective .
Some bacteria cells are flagellated. The flagella vary from one to many
which may be positioned on any part of the bacterial cell. The location of
the flagella could be group characteristics.
Bacteria are micro-organisms without a true nucleus or plastics and packing
any sexual reproduction process .
Bacteria reproduces asexually by binary fission .
Bacteria are saprophytes , parasites or autotrophs.
Bacteria can be cocci, rod-like, spiral. Bacteria can also be single cells or in
Some Bactria are naked i.e. without cell wall.
CHARACTERISTICS OF FUNGI
Fungi are plants with thread like non-photosynthetic threads called hypha.
These were initially classified among the Thallophyta (Lowson,1962) a
class under the non-flowering, non-seed producing but spore bearing
plants. However by 1969, the fungi was raised to the level of a kingdom
(Campbell, 1996). The non-photosynthetic thread (hyphae) are either
septate with cross-walls (non-coenocytic) or without crosswalls (coenocytic)
A collection of these hyphae are referred to as mycelium. Fungal hyphae are
bounded by a cell wall made up of glucans and chitin. The eukaryote contains a
nucleus with a nuclear membrane enclosing the chromosomes. Also present are
mitochondria and endoplasmic reticulum. These characteristics differentiate fungi
The fungal kingdom is divided into two division. The Myxomycota (false
fungi) and the Eucomycota (true fungi).
The Eucomycota is divided into five sub-divisions based on their reproductive
These are Hemiascomycota, Mastigomycota, Zygomycota, Ascomycota,
Basidiomycota and Deuteromycota. These five sub-divisions vary from being
unicellular as in saccharomyces to multicellular as in the advanced fungi e.g.
Ascomycota, Basidiomycota and Deuteromycota these are fungi with the
septate hyphae and heterothallic method of reproduction. The primitive fungi
are the coenocytic non-septate fungi including the Mastigomycota and
They are chlorophyll less, eukaryotic unicellular or multicellular plant.
They are heterotrophs, acquiring their nutrients by absorption , consisting
of sabrobic decomposers, parasitic species and mutualistic forms
The body or vegetative structure of a fungus is called a thallus varying in
complexity and size ranging from the unicellular yeast to multicellular
They reproduce asexually by dispersing different types of spores and sexual
reproduction can be homothallic, heterothallic or by conjugation.
They have a tremendous ecological impact as molds, yeasts, lichens,
saprophytes mycorrhizas and parasites.
Without fungi and bacteria as decomposers, biological communities
would be deprived of the essential recycling of chemical elements.
They are impotent decomposer of wood, food and other useful
Cause diseases in plants (parasitic) and animals (dermatophytic).
Characteristics of algae
Algae were formally member of the class thallophyta of the old plant
They are of various colors ranging from green, blue-green, red,
brown or golden.
They are the eukaryotic-with distinct nucleus.
They could be heterrotropsh, photoautotrophic except the prokaryotic
cyanobacteria(blue-green algae in a symbiotic reltions).
Some are flagellated while other are not.
They are aquatic either fresh water or as marine phytoplankton.
Algae from the bases of aquatic food webs that support enormous
abundance and diversity of life.
All algae posses’ chlophyll, the primary pigments that trap
wavelength of length to which chlorophyll is not as sensitive.
The mixture of pigments chloroplasts lend characteristic color related
to these algae.
Algae from the bases of aquatic food webs that support enormous
abundance and diversity of life.
All algae posses’ chlophyll, the primary pigments that trap wavelength of
length to which chlorophyll is not as sensitive.
The mixture of pigments chloroplasts lend characteristic color related to
They are filamentous, thread like, photosynthetic plants ranging from
unicellular as in Chlamydomonas sp.