bs148h 27 September 2007
Read: Text ch 31
• fungi
• characteristics
• fungusfocus.com
• doctorfungus.com
• biology of antifungal agents
• new phylogeny (dang!!!)
• microsporidia
• chytrids
• zygomycota
• glomeromycota
• basidiomycota
• fun with fungi!
Fungi are the sister group of animals
and part of the eukaryotic crown group
that radiated about a billion years ago …
... a monophyletic group that shares some characters with animals
such as chitinous structures {fungi have chitinous cell walls, unlike animals}
storage of glycogen,
glycogen and mitochondrial UGA coding for tryptophan.
tryptophan
The branch uniting the fungi & animals is well-supported
from nuclear small subunit ribosomal RNA gene
{ close phylogeny makes finding safe antifungal antibiotics challenging }
They are heterotrophic:
heterotrophic export hydrolytic enzymes that break down biopolymers
{ esp cellulose & lignin in wood }, which can be absorbed for nutrition.
{fungi are aerobic; anaerobic bacteria can’t decompose lignin;
wood doesn’t decompose in anaerobic conditions, like the bottom of a lake}
Fungi live in their own food supply and simply grow into new food
food …
Should food become depleted, {sex, and then} sporulation is triggered.
triggered
Although the fungal filaments and spores are microscopic, the colony can be very large
with individuals of some species rivaling the mass of the largest animals or plants.
The Kingdom Fungi includes
some of the most important organisms,
organisms
in terms of their ecological & economic roles.
- decompose & recycle organic mattermatter-nutrients
- most vascular plants could not grow without
symbiotic fungal mycorrhizae in/on roots
- provide bacterial antibiotics – penicillin,
penicillin etc
- food:
food mushrooms, the bubbles in bread,
alcohol in champagne & beer etc
- many plant & animal diseases;
diseases
close phylogeny, genetics & biochemistry
makes fungal diseases very difficult to treat.
Phylogenetic systematics suggests that
fungi evolved from a flagellated ancestor.
While the majority of fungi lack flagella,
the chytrids do have flagella, and
the protists that share a close common ancestor
with animals and fungi also have flagella.
These three groups of eukaryotes
- the fungi, animals, their protist relatives –
are called opisthokonts: clade Opisthokonta. This
name refers to the posterior (opistho) location
of the flagellum in these organisms.
Ancestral Flagellated Eukaryote
One fungus body constructed of
tubular filaments (hyphae)
was brought to our attention
when molecular techniques
were used to show that
it was extensive
(37
37 acres and an estimated
blue whale size of 110 tons.
tons
The Michigan fungus clone
(Armillaria bulbosa)
grew in tree roots and soil.
{mycorrhizae = ‘fungus roots’}
In 2000, scientists discovered
the mycelium of one giant individual of
the fungus Armillaria ostoyae in Oregon
that is 3.4 miles in diameter and
spreads through 2,200 acres of forest,
equivalent to over 1,600 football fields.
This fungus is at least 2,400 years old
and hundreds of tons in weight,
qualifying it as one of Earth’s oldest and largest organisms.
Yeast and molds belong to a broader family of life called fungus ...
Some fungus feed off dead organisms, nature's garbage disposal,
while other, parasitic fungus, feed off live organisms.
These pathogenic fungus cause plant, animal, and human diseases such as
athlete's foot, swimmer's ear, ringworm, dandruff, Valley Fever,
fingernail and toenail infections, rosacea, and yeast infections.
Typically, fungus sprout from a spore and grow as filaments: hyphae ~ 5-10 μm dia.
(It's not that there is a main body that produces hyphae, the fungus is the hyphae.)
Hyphae from individual fungus cells interconnect with hyphae from other cells,
forming one large organism termed the mycelium.
The fuzzy mass of a bread mold is a good example.
Hyphae extend at their tips, while drawing the protoplasm forward as they grow.
Tip growth enables fungus to grow continuously into fresh zones of nutrients
and also to penetrate hard surfaces such
as plant cell walls, insect cuticle, your skin, etc.
When given the chance,
fungal hyphae can grow straight through human cells.
http://botit.botany.wisc.edu/TOMS_FUNGI/JAN99.HTML
{Glucans in fungal cell walls
are a new target of antifungal agents}
You can't just scrape off athlete's foot
because it has grown deep into the tissues ...
{not so deep: Doctor Fungus says
‘The infection is restricted to the nonliving cornified layers of epidermis
since the fungus lacks the ability to penetrate
the viable tissues of the immunocompetent host}
Both pseudohyphae and
blastoconidia (yeast cells)
from patient with candidiasis.
© Copyright 1992, SCP Communications, Inc.
Fungus ... must eat other organisms ... live in damp environments
so that the hyphae can absorb nutrients that are dissolved in water.
They ... release extracellular enzymes into their environment
to degrade complex nutrients like cellulose that they cannot absorb.
In addition to simple enzymes, such as those that break down starches into sugar,
many fungus produce toxins (called mycotoxins)
mycotoxins) and enzymes
that can disable, kill, and dissolve their food ...
Some toxins, such as gliotoxin produced by Candida and Aspergillus (among others),
inactivates important enzymes, kills cells and disrupts the immune system.
The fungus is injecting its host (you) with toxins to dissolve and
and digest you.
Even if the infection is localized, the toxic enzymes are transported throughout the body.
… the five licensed antifungal drugs …
the most important and commonly used agents
against the systemic fungal diseases are
flucytosine,
flucytosine amphotericin B & three azole drugs,
drugs
ketoconazole, itraconazole, and fluconazole.
Ergosterol,
Ergosterol the principal sterol
in the fungal cytoplasmic membrane,
is the target site of action of
amphotericin B and the azoles.
Amphotericin B … binds irreversibly to ergosterol,
resulting in disruption of membrane integrity …
The azole drugs inhibit synthesis of ergosterol
{interfere with the enzyme} necessary for
the conversion of lanosterol to ergosterol.
Terbinafine {Lamacil} inhibits ergosterol biosynthesis
… flucytosine,
flucytosine inhibits fungal DNA & RNA synthesis.
Flucytosine ... is converted to 5-fluorouracil (5-FU)
which inhibits thymidylate synthetase. Thymidine is required for DNA synthesis.
Vertebrate cells have little of the enzyme {cytosine deaminase } required to convert
{poison precursor} flucytosine to the active {poison} fluoroucil.
... more recently, the echinocandins disrupt the synthesis of glucan,
glucan,
a fungal cellcell-wall, structure not present in mammalian cells
http://www.aber.ac.uk/biology/research/skellygrp/azole.htm
The basic cell construction of fungus is different from that of bacteria, plants and animals.
Bacteria, plants, and fungus cells have a rigid cell wall;
wall
animals do not have a cell wall.
wall
A major component of fungal cell walls is chitin (also found in the exoskeleton of insects),
whereas the major component of plant cell walls is cellulose.
Chitin and cellulose are chemically similar, and the fungal cell wall also includes cellulose,
The cell wall structure is important in the discussion of treatments ...
The plasma membrane {beneath the cell wall} of fungal cells contain ergosterol,
ergosterol,
whereas animal membranes have cholesterol;
cholesterol
plants have sitosterol and other 'phytosterols'.
Due to the similarity of the cell membrane of fungus (ergosterol
(ergosterol))
and animals (cholesterol
),
(cholesterol),
there are few antifungal drugs that are safe for humans.
Unfortunately, chemicals that can poke holes in a fungus
can make your cells spill their guts as well.
Whereas there are dozens of prescription antibacterial drugs,
there are very few oral drugs
available for treatment of yeast and fungus.
... include itraconazole (Sporanox), ketoconazole (Nizoral),
fluconazole (Diflucan), flucytosine (also called 5-F),
Amphotericin B, nystatin, caspofungin (Cancidas),
terbinafine (Lamisil), plus voriconazole (Vfend).
Yeasts are unicellular.
The spheroid form of the yeast cells is only half their life story.
The other half is more sinister. Yeast can transform themselves
and grow hyphae (or very similar structures called pseudohyphae).
At 37 degrees C, which happens to be 98.6 F, body temperature,
the Candida grows hyphae
that burrow into its food source (you).
Editor's Summary
19 October 2006
The AFTOL (Assembling the Fungal Tree of Life) project ... reconstructed
the early evolution of fungi by tracking six gene regions through nearly 200 species.
News and Views: Evolutionary biology: A kingdom revised.
Tom Bruns, Nature 443, 758-761 (19 October 2006)
Before now ... phylogenetic trees of the fungi were based on sequences of
a single gene - that encoding the small-subunit (18S) ribosomal RNA.
... different genes can give different views of evolutionary history.
AFTOL ... two additional rRNA genes, and three protein-coding loci.
The results of are similar to those from the earlier 18S data ...
... the Chytridiomycota & Zygomycota are paraphyletic ... dang!!!
Reconstructing the early evolution of Fungi using a sixsix-gene phylogeny.
T.Y. James et al. 2006. Nature 443, 818-822 Full Text
Fungi,
Fungi Viridiplantae and Animalia
descended from unicellular, flagellated, aquatic forms
that radiated extensively on land.
Key adaptations to the terrestrial habit in the fungi include
the evolution of a filamentous growth form
and the development of aerially dispersed spores.
The sister kingdom to the Fungi (Animalia)
evolved diverse body plans
capable of feeding by ingestion,
whereas the fungal branch developed
a myriad of unicellular and filamentous
forms optimized for absorptive nutrition.
Traditional fungal phylogenies indicate that
fungi with flagellated cells (Chytridiomycota)
are the sister group of the remaining
non-flagellated fungi
Zygomycota,
{bread molds}
Glomeromycota, {endomycorrhizae}
Ascomycota & {yeasts & morels}
Basidiomycota ... {mushrooms}
However ... continued
continued
continuing James et al.
The combined gene phylogeny supported monophyly of
the Ascomycota,
Ascomycota Basidiomycota & Glomeromycota.
Glomeromycota
The Ascomycota & Basidiomycota formed a clade 'dikarya'
... also supported a clade uniting dikarya & Glomeromycota,
in agreement with previous 18S rRNA phylogenies.
The opisthokont clade
(Fungi, Metazoa and Choanoflagellida)
Choanoflagellida)
was also recovered ...
Microsporidia are
obligately endoparasitic,
protist-like organisms
Two unexpected results were
the placements of the ... chytrids ... is polyphyletic
and {the “chytrid”} R. allomycis grouped with the microsporidia
as the earliest diverging branch of the Fungi.
Microsporidia – unicellular parasites of animals & protists,
characterized by the production of {tiny} resistant spores.
Unlike most eukaryotes, they lack conventional mitochondria.
... microsporidia are not primitive eukaryotes, but rather
highly derived {obligate intracellular parasites}
They are often used in the biological control of insect pests.
Chytrids are primitive, aquatic flagellated fungi.
{Fig 31.11: Chytrids ar ‘paraphyletic’}
The microsporidium, Thelohania solenopsae,
causes the slow demise of a fire ant colony.
... the most common pathogens of fire ants in S. Am.
Origin of the amphibian chytrid fungus.
Weldon et al. Emerg Infect Dis [serial on the Internet]. 2004 Dec.
Available from http://www.cdc.gov/ncidod/EID/vol10no12/03-0804.htm
A defining characteristic is the mechanism by which
the spore contents are injected into the host's cytoplasm
through a tube.
The sudden appearance of chytridiomycosis,
chytridiomycosis the cause of amphibian deaths
and population declines in several continents, suggests that
its etiologic agent, the amphibian chytrid Batrachochytrium dendrobatidis,
dendrobatidis
was introduced into the affected regions.
However, the origin of this virulent pathogen is unknown.
A survey was conducted of 697 archived specimens of 3 species of Xenopus collected
from 1879 to 1999 in southern Africa ...
The earliest case of chytridiomycosis found was in a Xenopus laevis frog in 1938,
Chytridiomycosis was a stable endemic infection in southern Africa for 23 years ...
We propose that Africa is the origin of the amphibian chytrid and that the international
trade in X. laevis that began in the mid-1930s was the means of dissemination.
Microsporidiosis:
Microsporidiosis: current status.
Didier ES, Weiss LM. Curr Opin Infect Dis. 2006 19:485-92.
Microsporidiosis is an emerging and opportunistic infection
associated with a wide range of clinical syndromes in humans.
Effective commercial therapies
for Enterocytozoon bieneusi,
the most common microsporidian species
identified in humans, are still lacking ...
Zygomycota
– molds
paraphyletic
Glomeromycota - arbuscular, {endo}micorrhizal
micorrhizal fungi
Complementary mating types:
different genotypes;
signal with pheromones.
A common zygomycete
is black bread mold:
asexual repro
‘Safe
Safe Sex:
Sex
the barrier method’
mycelium is aseptate,
except to wall off area
where haploid nuclei
are combining - keep
“parasitic” DNA out!
http://www.pacificcoast.net/%7Emycolog/CHAP3b.htm
…a petri dish containing nutritive agar medium.
Two sexually compatible strains
of Phycomyces blakesleeanus were inoculated
on opposite sides of the plate.
The mycelia spread across the surface.
Where they met, a line of zygosporangia
with spiny appendages formed.
... an ecologically significant group.
All glomeromycetes form
a distinct type of endomycorrhizae {inside-fungus-root}
called arbuscular mycorrhizae.
The tips of the hyphae that push into plant root cells
branch into tiny treelike structures
known as arbuscules.
About 90% of all plants
have such symbiotic partnerships
with glomeromycetes.
glomeromycetes.
Mycorrhizal Root Dip Gel
13 different species of beneficial
Endomycorrhizae & Ectomycorhizae.
Increases Fruit/Vegetable yields.
Promotes Fast Growth.
News Feature
Fungal roles in soil ecology:
Underground networking
John Whitfield Nature 449, 136-138
(13 September 2007)
about 95% of plants
have mycorrhizal symbionts
Mycorrhizal symbioses: two types are recognized:
1. Endomycorrhizae enter into the root cells
- are the most common type {Arbuscular Glomeromycota}.
Glomeromycota
Usually produces single spores in the soil for reproduction,
not large fruiting bodies {not
not mushrooms}.
mushrooms
2. In ectomycorrhizae the hyphal threads coat the tips of tree roots.
roots
{ectomycorriza is a convergent life form, not a phylogenetic clade,
includes Basidiomycota, Ascomycota, or Zygomycota }
Many large forest fungi form ectomycorrhizal partnerships,
both truffles with underground fruiting bodies and
fungi w/ the umbrella-shaped fruiting bodies: mushrooms.
mushrooms
Ascomycota - sac fungi
Asexual ‘naked’ spores (= conidia) formed at ends of hyphae;
produce Sexual spores in saclike asci
Sacchromyces cervisiae , an ascomycete
is most important domestic fungus
Bakers & brewer’s yeast are different domestic strains:
anaerobic fermentation of sugars to alcohol and CO2.
http://www.perspective.com/nature/fungi/ascomycota.html
http://daphne.palomar.edu/wayne/ww0504.htm#soil
The beautiful, red, fly agaric mushroom
(Amanita muscaria) is unmistakable with
its bright red cap covered with white scales.
It contains the toxic alkaloid, muscimole;
http://www.pacificcoast.net/~mycolog/chapter17.htmmycelial strands (lower)
seedlings of Douglas fir of Amanita muscaria
with and without
on Pinus strobus
ectomycorrhizal partners.
http://tolweb.org/tree?group=Ascomycota&contgroup=Fungi
... the comparison of nucleic acid sequences ...
has permitted the integration of asexual fungi
such as the yeast Candida albicans into the Ascomycota.
Ascomycota
Truffles & morels - ectomycorrhizal with tree roots
Penicillium (Penicillin)
≈ half the 60k species live as lichen partners
Basidiomycota:
Basidiomycota Club fungi w/ long-lived dikaryotic (n+n) mycelia
and transient diploid (2n) stage = Basidium
= mushroom
vaginal yeast infections are caused by Candida albicans,
albicans,
which, along with a few types of bacteria,
are normally present in small numbers in your crotch.
Sometimes the yeast multiply rapidly and take over,
causing a full-fledged yeast infection,
antibiotics are probably the leading cause of vaginal yeast infections …
say you take an antibiotic to cure your sinus infection.
the antibiotic kills the unwanted bacteria in your sinuses,
but can also kill the "good" bacteria in your crotch,
upsetting the balance of your vaginal ecosystem,
allowing the yeast to take over. {we’ll study ecosystems later}
http://www.perspective.com/nature/fungi/agaricus.html
The Agaricus family
includes the best known mushroom in the US:
The white buttons sold generically as "mushrooms"
are a cultivated variety of Agaricus
The "wild" Crimini and Portabella mushrooms
are also cultivars of this species.
Some of the fungi that attack food crops are toxic to humans.
For example, some species of the mold Aspergillus
contaminate improperly stored grain and peanuts
by secreting compounds called aflatoxins,
aflatoxins
which are carcinogenic.
One type of ascomycete, Claviceps purpurea,
forms purple structures called ergots on rye.
If diseased rye is inadvertently milled into flour and consumed,
poisons from the ergots cause gangrene, nervous spasms,
burning sensations, hallucinations, and temporary insanity.
insanity
One of the hallucinogens that has been isolated from ergots
is lysergic acid, the raw material
from which LSD is made.
http://www.plant.uga.edu/labrat/ergot.htm
LSD, an ergot derivative
strongly interferes with the neurotransmitter serotonin.
... enhance another neurotransmitter, dopamine.