00:01
Hello and welcome to Fungi. We're going to
delve into this topic in a little more detail
and I want to start with some general principles.
And after this lecture, I hope that you'll
be able to distinguish the two general types
of fungi. You should know the different types
of human fungal diseases and their origins,
and you should be familiar with the drugs
that are used to treat fungal infections.
00:29
There are two kinds of fungi morphologically.
Most of the fungi that we know of, are called
filamentous fungi, and these are diagrammed
here. They can be made up of very extensive
networks of filaments. These are composed
of hyphae and mycelia. So mycelium is the
name for the entire filamentous growth and
it's made up of smaller segments called hyphae.
01:00
So these constitute most of the fungi that we
know of in nature. These reproduce by dividing.
01:05
They also produce spores, you can see a structure
on this mycelium that produces spores and
of course the spores disperse in nature on
animals and in the wind and they seed new
growth, so the fungi elsewhere. So these are
filamentous fungi. Mushrooms are fungi. They
are produced by filamentous fungi. The filamentous
part of the mycelium of course grows on or
in the ground, you don't see it very easily.
It’s microscopic. But periodically the mycelia
are simply rearranged and grouped together
to form a mushroom. The mushroom comes out
of the ground and its sole purpose is to produce
spores, which drop out of the cap of the mushroom,
they drop on the ground, they are dispersed
and they initiate the growth of a new fungus.
01:51
Now I say the sole purpose is to make spores,
but of course humans like to eat mushrooms,
some of them are very good to eat, some and
of course are poisonous, but not everyone
likes to eat them and those are the mushroom
kickers as I said before, and the rest are
mushroom pickers. So you have a large mycelial
growth, periodically mushrooms coming up to
make new spores. The other kind of fungus
are the yeasts, and these are the unicellular
fungi. A famous one is Saccharomyces cerevisiae
or Baker's yeast if you like bread or beer,
you have the yeasts to thank for it, because
they carry out the fermentation that make
the gases that make those products possible.
So yeasts are unicellular, you can see a diagram
of yeasts on the left part of the cell and
an actual photograph of a living yeast on
the right. They divide by budding, you have
a single yeast cell and a small new one starts
to form as a bud from the side. It starts
out smaller and smaller, it gets bigger and
bigger and then it pinches off and becomes
a new yeast cell, and you can learn more about
this process in our basic discussion of fungi.
03:06
So those are the two major types, we have
filamentous and yeasts among the fungi. All
of these organisms, all these fungi are what
we call heterotrophs. They can't make their
own precursors, the molecules they need to
build themselves. There are other organisms,
other microorganisms that are called autotrophs,
they can take minimal organic compounds and
use them to build the precursors that they
need, fungi cannot do that, they have to absorb
what they need premade from the environment,
so we call that heterotrophy and typically
fungi grow outside in the soil or on rotting
wood, many fungi secrete enzymes that then
digest the material around them and then the
fungi absorb it. So plants as you know, a
major component of plants is cellulose and
fungi can secrete enzymes that will digest
the cellulose and then they can take the components
from the digestion, absorb it and use it to
make more molecules. And so that's how fungi
grow. The mycelium can get bigger and bigger
by absorbing these molecules; they are used
to build precursors, like amino acids and
lipids, which then get made into larger structures
as well. So fungi are what we call heterotrophs.
04:24
Another important property of fungi is that
almost all of them are strict aerobes, that
is they require air and more specifically
oxygen in which to grow. If you take the oxygen
away, most fungi will not grow. Now in contrast,
there are many other microbes that can grow
in the absence of oxygen, we call those anaerobes,
but this is not the case for fungi, most of
them are strict aerobes, of course there are
exceptions to this and that's why we say almost
all fungi are strict aerobes.
04:59
The cell wall of a fungus is very different
from that of plants or bacteria or even other
eukaryotic organisms. And the cell wall is diagrammed
on the right. There is a cell membrane surrounding
the cytosol of the fungus and that's a phospholipid
bilayer, very much like the cell membrane
of other eukaryotic organisms, it has proteins
embedded in it. But where a eukaryotic membrane
would stop there, the fungal cell wall has
other layers on top of it. And just above the
lipid bilayer is a layer of chitin, and chitin
is a polymer of the sugar N-acetylglucosamine
and that is shown on the left-hand part of
the slide, in pink is the glucosamine six
carbon sugar molecule and the N-acetyl group
is shown in green. So long chain polymers
of this sugar is chitin, that's right on top
of the cell membrane and then above that is
a structure made of beta glucans, this is
another carbohydrate molecule, the carbohydrates
are polymerized in a specific way. And then
on top of the beta glucans we have mannoproteins,
these are glycoproteins, which means sugars
conjugated to proteins and they are called
mannoproteins because the largest sugar here
is mannose, or I should say the most prevalent
sugar in the mannoprotein is mannose.
06:33
Now fungi can grow in many places where other
microbes cannot, in particular they can grow
without water as long as they're in a damp
environment. So for example, your bathroom
wall may have fungi growing on it, there may
be little dark spots between the tiles or
even on the tiles and there isn't necessarily
water on them, but it gets damp when you take
a shower and the fungi can grow there, they
can require very few nutrients in order to
grow, but they will grow without overt water.
So it can grow in damp environments and of
course the soil in the forest is also damp
as well. And as I mentioned earlier, many fungi
produce spores for dispersal. This is predominantly
the filamentous fungi, where they can make
structures that aid in spore dispersal. We
talked about the different ways spores are
made in our previous discussion of fungi in
an ascus or a basidium, depending on how they
are presented, and of course the mushroom
is a structure designed simply to produce
spores for dispersal. Now spores have a role
for the fungus to produce more fungal growth.
07:46
For humans, it can cause allergies, as we inhale
spores on a regular basis. There have been
some interesting studies done of air in various
locations in cities or in the country, and
spores are a large component of the air. And even
now as I speak with you, it's likely that
there are some spores in the air and I'm inhaling
them. So we inhale them on a regular basis
and for some of us they have no consequence
whatsoever. I know that I've been in very
moldy places and inhaled lots of spores and
it had no allergic reactions, no long-term
consequences, but for other individuals who
are allergic, it can cause problems like sneezing
and other lung problems. So spores are good
for the fungi but not good for all humans.