Transcript Chapter 28: Microbiology - Johnston Community College

Chapter 28: Microbiology
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Viruses
Viruses are noncellular, nonliving
particles and therefore are not included
in the classification scheme.
Comparable in size to a large protein
macromolecule, many viruses can be
purified, crystallized, and stored as
chemicals.
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Structure of Viruses
A virus has an outer capsid composed of
protein subunits, and an inner core of
nucleic acid.
An outer membranous envelope may be
acquired when the virus buds from the
cell.
It may also include enzymes for nucleic
acid replication.
Viruses are classified by type of nucleic
acid, viral shape and size, and by
presence of an outer envelope.
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Adenovirus
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Parasitic Nature
Viruses are obligate intracellular
parasites.
Viruses are very specific for the type of
cells they infect (e.g., HIV only infects
certain kinds of blood cells).
Viruses are likely derived from the very
host they infect, and therefore evolved
after cells evolved.
Some viruses, such as the flu virus, can
mutate rapidly.
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Replication of Viruses
Viruses are specific to a particular host
cell because they bind to a particular
plasma membrane receptor.
After viral nucleic acid enters the host
cell, it takes over the metabolic
machinery of the host cell so that more
viruses are produced.
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Replication of Bacteriophages
Bacteriophages are viruses that parasitize
bacteria.
Some undergo two cycles, a lytic cycle and
a lysogenic cycle.
The lytic cycle is divided into five phases:
attachment, penetration, biosynthesis,
maturation, and release.
In the lysogenic cycle, the infected
bacterium does not immediately produce
viruses but may do so sometime in the
future; the phage has a latent period and
is called a prophage during this time.
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Lytic and lysogenic cycles
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Replication of Animal Viruses
Entire animal virus penetrates host cell
by endocytosis.
Once inside, the virus is uncoated to
remove the envelope and capsid.
The viral genome, either DNA or RNA, is
now free and biosynthesis proceeds.
The assembled viruses bud from the cell
and acquire envelopes.
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Retroviruses are RNA animal viruses that
have a DNA stage.
They have an enzyme called reverse
transcriptase that carries out RNA →
cDNA transcription.
Following replication, cDNA integrates
into the host genome until viral
reproduction occurs.
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Reproduction of HIV, a retrovirus
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Viral Infections
Viruses cause infectious diseases of
plants and animals, including humans.
Some crop diseases are attributed not to
viruses but to naked strands of RNA
called viriods.
Some diseases in humans and animals
are attributed to prions which are
protein particles.
Mad cow disease (BSE) in Britain is
believed to be a prion disease.
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The Prokaryotes
The bacteria (domain Bacteria) and
archaea (domain Archaea) are
prokaryotes.
Prokaryotes lack a membrane bounded
nucleus and the chromosome is in a
nucleoid that lacks an envelope.
There are no membranous organelles but
they do have ribosomes; prokaryotes
have a cell wall that may be surrounded
by a capsule.
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Generalized structure of a
prokaryote
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Some prokaryotes move by flagella, and
some adhere to surfaces by means of
small, hairlike appendages called
fimbriae.
They reproduce by binary fission, and
some can form endospores.
Three means of genetic recombination
(but not sexual reproduction) have
been observed in bacteria: conjugation,
transformation, and transduction.
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Binary fission
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The endospore
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Most bacteria are aerobic, requiring a
constant oxygen supply for cellular
respiration.
Obligate anaerobes are unable to grow in
the presence of oxygen; facultative
anaerobes are able to grow in the
presence or absence of oxygen.
Bacteria are saprotrophs which externally
digest organic compounds and absorb
nutrients.
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Bacteria are the decomposers in
ecosystems.
Some bacteria are symbiotic and live in
association with other organisms.
The bacteria that reside in the human
intestinal tract are mutualistic;
commensalistic bacteria reside on our
skin; and parasitic bacteria cause a
wide variety of diseases.
The cyanobacteria are photosynthetic in
the same manner as plants.
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The Bacteria
Bacteria occur in three shapes: rod
(bacillus), round (coccus), or spiral
(spirillum).
Based on a dye test, bacteria are either
Gram-positive or Gram-negative: Grampositive bacteria have a thick layer of
peptidoglycan; Gram-negative bacteria
have a thin layer.
A new method to classify bacteria is to use
rRNA sequences; previously,
endospores, metabolism, growth, and
mode of nutrition were considered.
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Diversity of bacteria
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Cyanobacteria
Cyanobacteria are photosynthetic
prokaryotes that are rather large (1 µm
to 50 µm in length) and may be
unicellular, colonial, or filamentous.
Some have heterocysts where nitrogen
fixation occurs.
Cyanobacteria are sometimes symbiotic
with fungi (forming lichens) and other
organisms.
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Diversity among the
cyanobacteria
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The Archaea
The plasma membrane of archaea have
unusual lipids so they can withstand
high temperatures and extreme
conditions.
Their cell walls lack peptidoglycan typical
of bacteria.
Some archaea are methanogens,
halophiles, or thermoacidophiles.
None are photosynthetic nor do they
cause infectious disease.
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Habitat and structure of
thermoacidophiles
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Relationships of the Domains
Archaea have different rRNA sequences
from bacteria.
Because archaea and some bacteria are
both found in extreme environments,
they may have diverged from a
common ancestor relatively soon after
life began.
The eukaryotes appear to have diverged
from archaea; thus, eukarya are
believed to be more closely related to
the archaea than to the bacteria.
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The Protists
Protists are eukaryotes of the kingdom
Protista that are usually unicellular; if
multicellular they lack tissue
differentiation.
Protists are grouped according to mode
of nutrition, among other traits.
Three life cycles are seen among
protists: haplontic cycle, alternation of
generations, and diplontic cycle.
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Haplontic cycle
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Alternation of generations
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Diplontic cycle
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Algae
Algae are aquatic autotrophs but they do
not need to protect the zygote from
drying out.
They produce food for oceanic and fresh
water communities.
Algae are grouped according to their
color and biochemical differences,
such as the chemistry of the cell wall
and the way they store reserve food.
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Green Algae
Like plants, green algae have a cell wall of
cellulose, have both chlorophylls a and
b, and store reserve food as starch.
Unicellular green algae include
Chlamydomonas which has two whip-like
flagella, a chloroplast, a starch-storing
pyrenoid, and a haplontic life cycle.
When conditions are favorable, asexual
reproduction occurs, otherwise sexual
reproduction occurs; gametes from two
different strains form a zygote that
overwinters.
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Chlamydomonas, a flagellated
green alga
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Colonial green algae include Volvox, in
which thousands of flagellated cells
are arranged in a single layer
surrounding a watery interior.
Cells that are specialized for
reproduction divide asexually to form
a new daughter colony.
Sexual reproduction involves
heterogametes (gametes that are not
identical)—a large nonmotile egg and
small flagellated sperm.
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Volvox, a colonial green alga
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Filamentous green algae include
Spirogyra with long chains of cells that
have spiral chloroplasts.
During conjugation, cell contents of one
filament move across to cells of other
filament, forming diploid zygotes that
survive the winter.
The zygotes undergo meiosis to produce
new haploid adult filaments.
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Spirogyra, a filamentous green alga
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Multicellular green algae include Ulva, a
“sea lettuce” that is multicellular with a
leafy appearance.
The thallus is two cells thick and can be a
meter long.
Ulva has the alternation of generations
life cycle but both generations look
alike and there are isogametes.
Spores are flagellated.
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Ulva, a multicellular green alga
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Brown and Golden Brown Algae
Brown algae and golden brown algae
both have chlorophylls a and c plus
fucoxanthin, a carotenoid pigment that
gives them their color.
Some brown algae are familiar seaweeds
such as Fucus, which has a diplontic
life cycle.
Diatoms are golden brown algae with
silica valves that are significant
producers in the ocean.
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Diversification among the brown
algae
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Diatoms
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Dinoflagellates
Dinoflagellates are bounded by protective
cellulose plates and have two flagella;
one is in a transverse groove causes the
organism to spin like a top.
They are the cause of “red tides” that kill
fish because they contain poisons.
But dinoflagellates are an important
source of food and also live
symbiotically with corals.
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Dinoflagellates
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Euglenoids
One-third of euglenoids have
chloroplasts and in the absence of
sunlight, they become heterotrophic.
They have two flagella, one usually much
longer than the other.
A flexible pellicle allows euglenoids to
assume different shapes.
Reproduction is by longitudinal cell
division.
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Euglena
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Red Algae
Red algae are multicellular algae of
economic importance.
Seaweeds occur inwarm water that is
either shallow or deep.
Filaments may be simple or have a
branched or feathery appearance.
Coralline algae are red algae that have
walls of calcium carbonate and add to
the growth of coral reef.
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Red alga
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Protozoans
Protozoans are typically heterotrophic,
motile, unicellular organisms.
They have food vacuoles, contractile
vacuoles, and many reproduce sexually
during part of their life cycle.
Protozoa are not animals because they
do not undergo embryonic
development.
They are classified according to means
of locomotion.
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Amoeboids
Amoeboids are protists that move by
pseudopods, and eat by phagocytosis.
Amoeba proteus lives in fresh water.
Entamoeba histolytica causes amoebic
dysentery.
Foraminifera are amoeboids that have a
calcium carbonate shell and are largely
marine.
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Amoeboid protozoans
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Ciliates
Ciliates move by numerous cilia that beat
in a coordinated rhythm.
Cilia of Paramecium extend through a
semi-rigid pellicle.
Food moves down a gullet, food vacuoles
form, and wastes exit at an anal pore.
Trichocysts under the pellicle discharge
long, barbed threads for defense or to
capture prey.
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Ciliates have two types of nuclei: a large
macronucleus and one or more small
micronuclei.
The macronucleus controls cell
metabolism; during sexual reproduction,
micronuclei are exchanged.
During asexual reproduction, ciliates
divide by transverse binary fission.
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Ciliated protozoans
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Zooflagellates
Zooflagellates move by flagella, enter
many symbiotic relationships, and can
cause disease.
Trichonympha collaris lives in gut of
termites.
Giardia lamblia causes severe diarrhea.
Trichomonas vaginalis infects vagina and
urethra of women, prostate, seminal
vesicles and urethra of men.
A trypanosome, Trypanosoma brucei,
causes African sleeping sickness.
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Zooflagellates
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Sporozoans
Sporozoans are nonmotile parasites of
animals that form spores at some point
in their life cycle.
Plasmodium vivax causes one type of
malaria, a major killer in humans.
Pneumocystis carinii causes the type of
pneumonia seen in AIDS patients.
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Life cycle of Plasmodium vivax
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Slime Molds and Water Molds
Slime molds and water molds have some
characteristics of fungi, and form spores
like fungi.
They differ from fungi in that the vegetative
state, a plasmodium, is amoeboid and
they are heterotrophic by ingestion, not
by absorption like fungi.
Cellular slime molds exist as individual
amoeboid cells and only aggregate when
food runs out.
They have a diplontic life cycle.
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Yellow slime mold
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The Fungi
Fungi include eukaryotic multicellular
organisms that are heterotrophic by
absorption.
The body is a mycelium, a network of
filaments called hyphae.
Fungi lack chloroplasts and have cell
walls that contain chitin.
Fungi produce nonflagellated wind-blown
spores during both sexual and asexual
reproduction.
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Zygospore Fungi
In zygospore fungi, like the black bread
mold, Rhizopus stolonifer, a zygospore
forms after hyphae of opposite mating
types merge.
Upon germination of the zygospore,
sporangiophores develop and many
spores are produced by meiosis.
Zygospore fungi use the haplontic life
cycle.
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Black bread mold
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Sac Fungi
Sac fungi include red bread molds and
cup fungi.
In red bread mold Neurospora and in cup
fungi, an ascus develops after hyphae
from two mating strains merge.
An ascus produces eight ascospores.
In cup fungi the asci are located in a
fruiting body that has the shape of a
cup.
During asexual reproduction, sac fungi
produce conidiospores.
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Sac fungi
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Yeasts
Yeasts are unicellular sac fungi and
usually reproduce asexually by mitosis
or by budding.
When yeasts ferment, they produce
ethanol and carbon dioxide.
Yeasts are critical in making wine and
beer and making bread to rise.
Researchers use them in culture to study
genetic engineering for eukaryotes.
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Club Fungi
Club fungi include shelf or bracket fungi
on dead trees along with mushrooms
and puffballs.
Club fungi usually reproduce sexually.
In mushrooms, basidia are fruiting
bodies that develop after hyphae from
two mating strains merge.
Each basidium produces windblown
spores that germinate to produce
haploid mycelia.
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Club fungi
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Imperfect Fungi
“Imperfect” in the imperfect fungi refers
to the fact that no sexual stage has yet
been observed.
They always produce conidiospores
during asexual reproduction.
Penicillium (source of penicillin) and
Candida albicans (causes yeast-like
infection in women) are imperfect fungi.
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Conidiospores
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Fungal Relationships
Lichens are symbiotic relationships
between a fungus and a
cyanobacterium or a green alga.
Recent experiments show the alga grows
with no difficulty but the fungus grows
poorly when separate from the lichen;
therefore the fungus is a parasite on
the alga.
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Lichens are important soil formers.
Mycorrhizae (fungus roots) are symbiotic
relationships between soil fungi and
roots of most plants.
The fungus provides plants with
inorganic nutrients and plant provides
fungus with organic nutrients.
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Lichen morphology
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Chapter Summary
Viruses are noncellular and arose after
cellular organisms.
Viruses cause diseases of plants and
animals because they reproduce inside
host cells.
Viriods are naked strand of DNA that
cause crop diseases and prions are
strange proteins that are infectious and
seek to lack any DNA/RNA.
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Prokaryotes are small in size but very
metabolically diverse, reproduce by
binary fission, and some can form
endospores.
Most bacteria are heterotrophic by
absorption and many are symbiotic; the
cyanobacteria are important
photosynthesizers.
Archaea are unique prokaryotes that are
methanogens, halophiles, or
thermoacidophiles.
It is likely that eukaryotes arose from the
archaea.
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Protists include eukaryotic unicellular
organisms and some related multicellular
forms.
Among protists, algae are the plantlike
protists; protozoa are the animal-like
protists; slime molds and water molds
are the funguslike protists.
Fungi are multicellular eukaryotes with a
filamentous body.
Fungi are the most complex organisms to
rely on saprophytic nutrition; lichens and
mycorrhizae are important symbiotic
relationships.
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