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20 Φεβ 2013 (πριν από 4 χρόνια και 7 μήνες)

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“The role of the infinitely small in
nature is infinitely large”



Louis Pasteur, 1822
-
1895

Blooms of purple bacteria

Eukaryotic parasites

Giardia trophozoite

Fungi

viruses

Microorganisms

I
-

Introduction to Microbiology



Microbiology is the study of microorganisms: large and diverse group of
microscopic organisms that exist as single cells or cell clusters, and viruses,
which are not cellular.



1
-

What is microbiology ?




a
-

It is about cells, especially the bacteria, and how they work



b
-

about diversity and evolution; microorganisms existed on earth


billions of years before plants and animals appeared.



-

thus their evolutionary diversity has far outpaced that of higher


organisms.



c
-

about what microorganisms do in the world; microorganisms affect


all other life forms on Earth.




Ex:
Cyanobacteria oxygenated the atmosphere allowing other life


forms to evolve


2
-

Importance of microorganisms





a
-

In their absence higher life forms would never have arisen and


could not be sustained.



-

The oxygen we breathe is the result of past microbial activity



-

human plants and animals depend on microorganisms for




recycling key nutrients and degrading organic matter.




b
-

provided our understanding of the chemical and physical basis of


life



-

grow to high densities, amenable to biochemical and genetic




studies




c
-

tied with the fields of medicine, agriculture and industry.

3
-

Microorganisms as cells
:



-

Compartmentalization is a prerequisite for life
-




a
-

Cell Chemistry and Key structures




-

Cells are made up of large molecules called
macromolecules


(proteins, lipids, nucleic acids and polysaccharides).




-

key structures:
Cytoplasmic membrane
,
cytoplasm
, the
nucleus



or
nucleoid

(bacteria) and
ribosomes
.

The hallmarks of cellular life

For a bacterial cell to
reproduce it requires:


1
-

Energy


2
-

Replication of its
genetic material (DNA)


3
-

Gene expression to
form proper amounts of
necessary proteins and
macromolecules

4
-

Microorganisms and their Natural environments





-

Populations
: in nature cells live with other cells in assemblages


called populations. Cells in a population are derived from a single


parental cell




-

Habitat
: the location in the environment where a microbial




population lives



-

Microbial

communities
: different populations living together in a


habitat




-

Microbial

Ecology
: study of microorganisms in their natural




habitats.

Examples of microbial communities

lake

sewage

(light microscopy)

(Fluorescence microscopy)

Effect of organisms on each other and on their habitats


-

Populations in microbial communities interact in various ways, both harmful
(competition) and beneficial (waste products of the metabolic activities of
some cells can be nutrients for others)



-

Organisms in a habitat also interact with their physical and chemical
environment . Living organisms together with the physical and chemical
constituents of their environment form an
Ecosystem
.



Ecosystems


-

Major microbial ecosystems include
aquatic

(oceans, ponds, lakes,


streams springs),
terrestrial

(soil, deep subsurface), and
higher


organisms
, both plant and animal.



-

Ecosystems are controlled to significant extent by microbial




activities.


-

prokaryotic cells, small as they are, constitute the major portion of the
biomass on earth and are key reservoirs for essential nutrients for life

Ex:
amount of carbon present in bacteria equals that of all plants on


earth!

Microorganisms affect our
lives in many aspects

Note:
Few microorganisms
actually cause disease

5
-

Impact of Microorganisms on humans



a
-

Microorganisms as disease agents



-

Infectious diseases are caused by
pathogens
.



-

Today infectious diseases are of much less importance in




developed countries (mortality rates are sinking)



Reasons
: better understanding of the disease process, improved


sanitary conditions, use of antimicrobial agents



Exceptions
: infections with HIV or multi
-
drug
-
resistant pathogens



-

However many microorganisms can still be a threat to human




health in developing countries causing million of deaths (Ex:




malaria, tuberculosis, cholera, African sleeping sickness.




Today infectious diseases are of much less importance in
terms of mortality in developed countries



b
-

Microorganisms and Agriculture (relationship can be beneficial or harmful)




Beneficial


-

legumes associate closely with bacteria that form structures called


nodules on their roots. Bacteria in nodules convert N2 to fixed




nitrogen (NH3) that is used by plants for growth.



-

bacteria in soil convert C, N and S into forms that are readily




accessible to plants.



-

bacteria in the digestive vessel of cattle and sheep, called the




rumen
, digest cellulose




Harmful


-

microorganisms can be harmful to agriculture; diseases of animals


(mad cow disease) and plants have major economic impacts on




agricultural industry.






c
-

Microorganisms and food



-

microorganisms can cause food spoilage which results in huge




economic losses each year. Foods are frozen, dried or canned to


avoid spoilage


-

however microbial activity is beneficial for certain foods
Ex:
:




cheese, yogurt, buttermilk. Baked goods and alcoholic beverages


are based on fermentative activities of yeast.


d
-

Microorganisms, Energy and the Environment



-

phototrophic microorg harvest light energy to produce biomass,


energy stored in living organisms


-

convert waste material to biofuels like methane and ethanol.


-

help clean up pollution, process called
bioremediation
; various


microorg are used to consume spilled oil, solvents, pesticides and


other toxic pollutants.




e
-

Microorganisms and biotechnology

The discovery of microorganisms was linked to
the invention of the microscope

Microscope used by
Robert Hooke, 1664

The bluish
-
colored mold growing on surface of
leather, as drawn by Robert Hooke, 1655

Antony Van Leeuwenhoek drawing of bacteria,
1684

Antony Van Leeuwenhoek was
the first to see bacteria in 1676

In the mid
-
19
th

century two major questions
prevaded biology and medicine by that time:



1
-

spontaneous generation of germs


(Louis Pasteur)



2
-

the nature of infectious disease
(Robert Koch)

Pasteur’s experiment with swan
-
necked flask

-

Pasteur found that putrefied food is not due to microorganisms that arose
spontaneously from non
-
living material, but that dropped on the food from
the air

“I am afraid that the experiments you quote, M. Pasteur, will turn
against you. The world into which you wish to take us is really too
fantastic."




La Presse, 1860



“Will you have some microbe? There is some everywhere.
Microbiolatry is the fashion, it reigns undisputed; it is a doctrine
which must not even be discussed, especially when its Pontiff, the
learned Monsieur Pasteur, has pronounced the sacramental words,
"I have spoken". The microbe alone is and shall be the
characteristic of a disease; that is understood and settled;…..the
Microbe alone is true, and Pasteur is its prophet
.“


Rossignol, written in 1881


The germ theory of disease
(the cause and effect in
infectious diseases)

Koch and pure bacterial cultures



-

he was the first to grow bacteria on solid culture media. He


first used potato slice then devised more uniform nutrient


solution solidified with gelatine and later agar.



-

he found that a single colony is a pure form that originates


from a single cell



-

his greatest accomplishment in medical bacteriology was


the discovery of the causative agent of tuberculosis. He also


cultured the bacteria in pure form on coagulated blood




serum then on agar.


M. tuberculosis
in tissues and laboratory culture as
drawn by Koch


lung

sputum

culture in glass plates

pure colony from plates


Two major disciplines distinguish the modern era of
Microbiology


a
-

Applied Microbiology
under which we can distinguish:


-

medical microbiology


-

agricultural microbiology (study of microbial processes in the soil)


-

industrial microbiology (use of microorganisms to produce




commercial products)


-

aquatic microbiology (treating sewage and providing safe water for


humans)


-

marine microbiology



b
-

Basic Microbiology
under which we can distinguish:


-

microbial physiology (nutrients that microorganisms require and the


products they make)


-

microbial biochemistry (microbial enzymes and the reactions they


catalyze)


-

bacterial genetics (heredity and variation in bacteria)


Landmarks in Microbiology