? Antony van Leeuwenhoek
(1632-1723) and his
microscope.
? Louis Pasteur (1822-1895)
working in his laboratory.
? Robert
Koch
(1843-
1910)
Examining
a
specimen
in his
laboratory.
? Two fundamentally different types of cells
exist,Procaryotic cells have a much
simpler morphology than eucaryotic cells
and lack a true membrane-delimited
nucleus,All bacteria are procaryotic,In
contrast,eucaryotic have a membrane-
enclosed nucleus; they are more complex
morphologically and are usually larger
than prokaryotes,Algae,fungi,protozoa,
higher plants,and animals are eucaryotic,
Procaryotic and eucaryotic cells differ in
many other ways as well.
? Bacteria consist of only a
single cell,but don't let their
small size and seeming
simplicity fool you,They're
an amazingly complex and
fascinating group of
creatures,Bacteria have
been found that can live in
temperatures above the
boiling point and in cold that
would freeze your blood,
They "eat" everything from
sugar and starch to sunlight,
sulfur and iron,There's
even a species of
bacteria— Deinococcus
radiodurans— that can
withstand blasts of radiation
1,000 times greater than
would kill a human being,
? This is a cowpea virus,
which infects certain
bean plants including
snap peas,pinto
beans,green beans
and,of course,
cowpeas,
? This image was
created by a
computer.
? This alien-looking,single-
celled creature is a form of
algae called a diatom (die-
uh-tom),Diatoms live in
fresh or ocean water and
make their own food from
sunlight,like plants,
? Diatoms have hard shells
made up in part by silica,or
glass,When diatoms die,
these shells sink to the
bottom,They are mined and
used to make products we
use everyday,For example,
diatom shells are the grit in
your toothpaste and the
stuff that makes painted
stripes on the road shiny,
? This is protozoan
called paramecium
(pair-ah-me-see-um),
It looks hairy because
it's covered by long,
thin projections called
cilia (silly-uh),The
cilia beat in a regular,
continuous pattern,
moving the
paramecium through
its freshwater home
and sweeping food
into the mouth-like
opening you can see
on its side,
? Pick up a fistful of garden soil and you're
holding hundreds if not thousands of
different kinds of microbe in your hand,A
single teaspoon of that soil contains over
1,000,000,000 bacteria,about 120,000
fungi and 25,000 algae.
? Other heat-loving microbes live in volcanic
cracks miles under the ocean surface
where there is no light and the water is a
brew of poisonous arsenic,sulfur and
other nasty chemicals,The little blobs
shown in this photo are bacteria that live
on mussel shells around a volcanic vent
called the Galapagos Vent.
? Some scientists even believe there is the
possibility bacteria may have once lived
on Mars,This photograph taken through a
microscope shows what some scientists
believe may be the fossils of tiny bacteria
in a rock that formed on Mars about 4.5
billion years ago,The rock crash-landed
on Earth as a meteorite thousands of
years ago,
? Researchers are using bacteria
that eat methane gas to clean up
hazardous waste dumps and
landfills,These methane-
munching bacteria,or
methanotrophs,(meth-an-oh-trofs)
make an enzyme that can break
down more than 250 nasty
pollutants into harmless molecules,
By piping methane into the soil,
we can increase growth of the
methanotrophs that normally live
in the polluted soil,More
methanotrophs means faster
pollution break up.
? We're using bacteria,like those
pictured here,as one of the tools
to clean up oil spills,like the
Exxon Valdez mess,These
bacteria chow on the oil,turning it
into carbon dioxide and other
harmless by-products,
Early Bacterial Exposure May Extend Fly Life
Exposure to bacteria during the first week of adult life increased Drosophila
lifespan,but exposure late in life decreased longevity,new research reports,
All animals develop in at least partially sterile environments and are
colonized by bacteria soon after birth,In model organisms such as zebrafish,
paramecia,and various mammals,scientists have noted that
microorganisms can have a profound effect on the animal’s health,
especially on digestion,conditioning the immune system,and longevity,
Seymour Benzer from the California Institute of Technology and
colleagues investigated a possible connection between the microscopic
fauna on Drosophila and longevity by growing the fruit flies in sterile
environments,then periodically exposing them to non-sterile conditions,The
researchers report that flies grown only under sterile conditions had a 30%
decrease in mean lifespan,Further,Benzer’s team discovered a window of
time during which bacterial exposure is beneficial,exposure to bacteria
during the first 4-7 days of adult life produced the full life-extending effect,
while exposure after 7 days had no beneficial effect,Alternatively,the
researchers found that transferring adult flies from normal conditions to a
sterile environment,effectively removing bacteria late in life,showed a 10%
increase in longevity,Additional experiments with mutant fruit flies provided
evidence that microscopic fauna interact with the host on a genetic level,
Benzer and his team indicate that model organisms such as Drosophila may
give important clues to understanding longevity in humans and other
animals,
Koch’s Postulates
? The microorganism must be present in every
case of the disease but absent from healthy
organisms.
? The suspected microorganism must be isolated
and grown in a pure culture.
? The same disease must result when the isolated
microorganism is inoculated into a healthy host.
? The same microorganism must be isolated again
from the diseased host.
Molecular Koch’s Postulates
? The virulence trait under study should be
associated much more with pathogenic strains
of the species than with nonpathogenic strains.
? Inactivation of the gene or genes associated
with the suspected virulence trait should
substantially decrease pathogenicity,
? Replacement of the mutated gene with the
normal wild-type gene should fully restore
pathogenicity.
? The gene should be expressed at some point
during the infection and disease process.
? Antibodies or immune system cells directed
against the gene products should protect the
host.
The Future of Microbiology
? 1,New infectious diseases are continually arising and old diseases are
once again becoming widespread and destructive,AIDS,hemorrhagic
fevers,and tuberculosis are excellent examples of new and reemerging
infectious diseases,Microbiologists will have to respond to these threats,
many of them presently unknown.
2,Microbiologists must find ways to stop the spread of established
infectious diseases,Increase in antibiotic resistance will be a continuing
problem,particularly the spread of multiple drug resistance that can render
a pathogen impervious to current medical treatment,Microbiologists have to
create new drugs and find ways to slow or prevent the spread of drug
resistance,New vaccines must be developed to protect against diseases
such as AIDS,It will be necessary to use techniques in molecular biology an
recombinant DNA technology to solve these problems.
3,Research is needed on the association between infectious agents and
chronic diseases such as autoimmune and cardiovascular diseases,It may
be that some of these chronic afflictions partly result from infections.
? 4,We are only now beginning to understand how pathogens interact with
host cells and the ways in which diseases arise,There also is much to learn
about how the host resists pathogen invasions.
? 5,Microorganisms are increasingly important in industry and environmental
control,and we must learn how to use them in a variety of new ways,For
example,microorganisms can (a) serve as sources of high-quality food and
other practical products such as enzymes for industrial applications,(b)
degrade pollutants and toxic wastes,and (c) be used as vectors to treat
diseases and enhance agricultural productivity,There also is a continuing
need to protect food and crops from microbial damage.
? 6,Microbial diversity is another area requiring considerable research.
Indeed,it is estimated that less than 1% of the earth’s microbial population
has been cultured,We must develop new isolation techniques and an
adequate classification of microorganisms,one which includes those
microbes that cannot be cultivated in the laboratory,Much work needs to be
done on microorganisms living in extreme environments,The discovery of
new microorganisms may well lead to future advances in industrial
processes and enhanced environmental control.
? 7,Microbial communities often live in biofilms,and these biofilms are of
profound importance in both medicine and microbial ecology,Research on
biofilms is in its infancy; it will be many years before we more fully
understand their nature and are able to use our knowledge in practical ways.
In general,microbe-microbe interactions have not yet been extensively
explored.
? 8,The genomes of many microorganisms already have been sequenced,and many
more will be determined in the coming years,These sequences are ideal for learning
how the genome is related to cell structure and what the minimum associated of
genes necessary for life is,Analysis of the genome and its activity will require
continuing advances in the field of bioinformatics and the yse of computers to
investigate biological problems.
? 9,Further research on unusual microorganisms and microbial ecology will lead to a
better understanding of the interactions between microorganisms and the inanimate
world,Among other things,this understanding should enable us to more effectively
control pollution,Similarity,it has become clear that microorganisms are essential
partners knowledge of symbiotic relationships,Greater knowledge of symbiotic
relationships can help improve our appreciation of the living world,It also will lead to
improvements in the health of plants,livestock,and humans.
? 10,Because of their relative simplicity,microorganisms are excellent subjects for the
study of a variety of fundamental questions in biology,For example,how do complex
cellular structures develop and how do cells communicate with one another and
respond to the environment?
? 11,Finally,microbiologists will be challenged to carefully assess the implications of
new discoveries and technological developments,They will need to communicate a
balanced view of both the positive and negative long-term impacts of these events on
society.
(a) A modern compound light microscope,Various key parts of the
microscope are labeled,(b) Path of light through a compound light
microscope,Besides 10X,eyepieces (oculars) are available in 15-30X.
Photomicrographs of the same field of cells of
the baker’s yeast,saccharomyces cerevisiae,
taken by different types of light microscopy,(a)
Bright-field,(b) Phase contrast,(c) Dark-field.
Photomicrographs of various
microorganisms as visualized by
fluorescence microscopy.
Staining cells for microscopic
observation,
The Gram stain
A modern electron microscope,This instrument
encompasses both transmission and scanning
electron microscope functions.
Electron micrographs of bacterial cells taken with (a)
transmission and (b) scanning electron microscopes.
Representative cell shapes
(morphology) in prokaryotes,Next to
each drawing is a phase
photomicrograph showing an example
of that morphology,Organisms are
coccus,Thiocapsa roseopersicina
(diameter of a single cell =1.5um); rod,
Desulfuromonas acetoxidans
(diameter =1um); spirillum,
Rhodospirillum rubrum (diameter
=1um); spirochete,spirochaeta
stenostrepta (diameter =0.25um);
budding and appendaged,
Rhodomicrobium vannielii (diameter
=1.2um); filamentous,chloroflexus
aurantiacus (diameter=0.8um).
Spherical and rod-shaped
bacteria,which associate in
characteristically different ways
as viewed by scanning electron
microscopy,
(a) streptococcus,a chain-
forming organism that divides
only in one plane,
(b) staphylococcus,a coccus
that divides only in one plane,
Cells of both organisms are
about 1um in diameter.
(c) Chains of the rod-shaped
bacterium Bacillus,Cells are
about 0.8 um in diameter.
Fundamental structure of a phospholipids bilayer.
Use of ion separation
in the proton motive
force,in this case the
separation of protons
from hydroxyl ions
across the membrane,
to transport inorganic
ions by specific
transport proteins,
Note that there is a
separation both of
protons and of
electrical charge.
Cell walls
of
Bacteria
High magnification thin section of the cell envelope of
Escherichia coli showing the periplasmic gel bounded by the
outer membrane and the cytoplasmic membrane,The large,
dark particles in the cytoplasm are ribosomes.The thickness
of the cytoplasmic membrane is 7.5nm
Cell wall synthesis
in gram-positive
Bacteria.
The bacterial nucleoid,(a) Transmission electron
micrograph of a thin section of Escherichia coli.
(b) Same as (a),but with the nucleoid colored.
Light photomicrograph of cells of Escherichia coli
treated in such a way as to make the nucleoid visible.
The bacterial chromosome,(a) Open circular form,
(b) Supercoiled form,Note that in either case the DNA is
present in a covalently closed form typical of most prokaryotes.
The double-stranded DNA in the chromosome of the bacterium
Escherichia coli contains over 50 supercoiled domains,each of
which is stabilized by binding to specific proteins.
Electron micrograph of a
dividing cell of salmonella
typhi,showing flagella and
fimbriae,A single cell is
about 0.9 um in diameter
Fimbriae are considerably shorter
than flagella and are more numerous
but,like flagella,consist of protein,
The functions of fimbriae are not
known for certain in all cases,but
there is some evidence that they
enable organisms to stick to surfaces
including animal tissues in the case
of some pathogenic bacteria or to
form pellicles or scums on the
surfaces of liquids.
The presence of pili on an E,coli cell is revealed by the use of viruses
that specifically adhere to the pilus,The cell is about 0.8 μm in diameter.
Pili are similar structurally to fimbriae but are generally longer,and only
one or a few pili are present on the surface,There is strong evidence that
pili are involved in the process of conjugation in prokaryotes.
Electron micrographs of gas vesicles purified from the bacterium
Microcyclus aquaticus and examined in negatively stained
preparations,A single gas vesicle is about 100nm in diameter.
A number of prokaryotic organisms that live a floating existence in
lakes and the sea produce gas vesicles,which confer buoyancy
on the cells.
Gas vesicles of the cyanobacteria
Anabaena and microcystis
(a) Anabaena flos-aquae,The cell in
the center (a heterocyst) lacks gas
vesicle,In the other cells,the vesicles
group together as phase-bright objects
that scatter light,
(b) Transmission electron micrograph
of the cyanobacterium Microcystis,
Gas vesicles are arranged in bundles,
here observable in both longitudinal
and cross section.
The rigidity of the gas vesicle
membrane is essential for the structure
to resist the pressures exerted on it
from without; it is probably for this
reason that it is composed of a protein
able to form a rigid membrane rather
than of lipid,which would form a fluid,
highly mobile membrane.
The bacterial endospore,Phase contrast photomicrographs
illustrating several types of endospore morphologies and
intracellular locations,(a) Terminal,(b)Subterminal,(c) Central.
Certain species of Bacteria produce special structures called
endospores within their cells,Endospores are differentiated cells
that are very resistant to heat and cannot be destroyed easily,even
by harsh chemicals,Endospore-forming bacteria are found most
commonly in the soil,and virtually any sample of soil has some
endospores present.
? The cell is the fundamental unit of all living matter,A single cell is an
entity,isolated from other cells by a cell membrane (and perhaps a
cell wall) and containing within it a variety of chemical materials and
subcellular structures,The cell membrane is barrier that separates the
inside of the cell from the outside,Inside the cell membrane are the
various structures and chemicals that make it possible for the cell to
function,Key structures are the nucleus or nucleoid,where the
information needed to make more cells is stored,and the cytoplasm,
where the machinery for cell growth and function is present.
? All cells contain certain types of complex chemical components,
proteins,nucleic acids,lipids,and polysaccharides,Collectively,these
are called macromolecules,Because these chemical components are
common throughout the living world,it is thought that all cells have
descended from a single common ancestor,the universal ancestor,
Through billions of years of evolution,the tremendous diversity of
cell types that exist today has arisen.
? Several evolutionary branches occur within the Bacteria,including all disease-
causing (pathogenic) prokaryotes and most of the bacteria commonly found in soil,
water,animal digestive tracts,and many other environments,Some of these
organisms contain pigments that allow them to use light as an energy source in a
process called phototrophy,others rely on organic chemicals as energy source,and
some can even use inorganic chemicals as fuel to drive cellular processes,Most of
the prokaryotes encountered in everyday life are phylogenetically Bacteria,and some
have evolved special structures such as spores for aiding survival,Oxic
environments (those containing O2) as well as various anoxic habitats are inhabited
by various species of Bacteria.
? With the prokaryotes called Archaea,in contrast,we see a much different picture,
Most Archaea are anaerobes,cells incapable of living in air,Many also thrive under
unusual growth conditions,inhabiting what humans would consider extreme
environments,hot springs (to temperatures above the boiling point of water),
extremely salty bodies of water,and highly acidic or alkaline soils and water,Indeed,
certain species of Archaea currently define the limits of biological tolerance to
physiochemical extremes,Certain Archaea also show unusual biochemical features,
such as the methanogens,which are prokaryotes that produce methane (natural gas)
as an integral part of their energy metabolism.
? Among the Eukarya that are microorganisms are the algae,fungi,and protozoa,
Algae contain chlorophyll,agree pigment that serves as a light-gathering molecule,
making it possible for them to carry out phototrophy,Algae are common in aquatic
habitats and can also be found in soil,Fungi-molds,yeasts,and mushrooms-lack
chlorophyll and obtain their energy from organic compounds in soil and water,Fungi
are thought to play a major role in the breakdown of dead organic matter in these are
other environments,Protozoa are colorless,motile Eukarya that obtain food by
ingesting other organisms or organic particles,Protozoa lack the cell walls of algae
and fungi and in this respect resemble animal cells,Many protozoa are free-living
microorganisms,but several cause disease in human and other animals.
