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It’s
one thing for Dr. Fleming to have discovered pencillin by
accident.
It’s another to admit to everyone – most people
would
just say, “I meant to do that.” Fleming was great at
serendipity;
he discovered human lysozyme when some
snot
dripped from his nose when he had a cold onto a
bacteria
filled agar plate and they died.
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Serendipity plays a crucial role in doing science, and there
are myriad examples of how scientists have discovered one thing while looking
for something else. Penicillin is a good example. Alexander Fleming had an
awful time keeping extraneous organisms from growing on his bacterial agar
plates. It was his prepared mind that recognized that the mold (penicillium)
growing on one of them had cleared the bacteria away in a wide circle.
Today we have an example of serendipity in story-telling. I
set out to continue our story of undulipodia
(flagella and cilia) use in the different types of organisms. We had used the
undulipodia to talk about how hard it is to classify protists, first
animal-like protists, then plant-like organisms, and today the fungus-ish
protists.
However, in terms of undulipodia, the fungal-like protists
are pretty much all the same. They all use flagella to propel their gamete
cells. It’s interesting that some fungal cells are motile, but it’s not the
most interesting thing in their story. In looking at the three phyla of fungus-like protists, I found
that the biology of each is amazing – see if you agree.
Phylum Acraisomycota
– As unappealing as it may sound, this phylum consists of the cellular slime molds. These protists
spend much of their life as individual cells, moving around via amoeboid motion
through the soil, looking for decaying organic material and bacteria to eat. But
when hunger, they become ranchers. Yee-ha!
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When
food is scarce, the amoebas of D.
discoidium will
join
together into a grex, or sometimes called a slug. They
remain
individual cells, unlike acellular slime molds that
join
together as a single huge cell. This video is sped up considerably.
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When about 100,000 cells join together to form a grex or a slug, they all move as one to try and find food, and to produce
reproductive bodies so that their progeny will be protected, waiting as spores for better
conditions. Without the benefit of speech or sign language, the single cells
will start to take on different jobs, including building stalks that stick up
into the air with fruiting bodies on top.
Inside the fruiting bodies are the spores, the progeny cells
inside protective cellulose spore coats. They are environmentally resistant in
this form and can wait until the conditions are right to become amoeboid cells
of the next generation.
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After
forming a slug, fruiting bodies will be formed on top
of D. discoidium stalks. Remember that the
individual cells
are
organisms, but they act like a multicellular organism.
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Their 2011 paper showed that some of the dictyostelium cells were not eating all the bacteria
available; they were letting them reproduce and then storing them in their
spores. When those spores were blown or carried to new locations and
germinated, the bacteria would grow as well, becoming food for the cells. In
turn, their progeny would be gathered into the next generation of spores.
Protist ranchers are amazing enough, but there’s more. The ranchers hire cowhands to protect their herd. The spores contain not only the
food bacteria, but some other bacteria as well. These other bacteria (of the
family Burkholderia) secrete chemicals that keep the non-ranching clones of
dictyostelium from rustling the bacterial cattle. Not only are some of the protists
ranchers, they protect what they raise using armed guards! It only took us several hundred million years to catch up to them.
Phylum Myxomycota - These are the acellular slime molds. The individuals
cells don’t join together just when food is scarce, they spend most of their
lives all packed together.
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This
is P. polycephalum, or dog vomit
mold. I bet you have
seen
it before and walked FAR around it. When grown
in
high moisture and food, it is slimy, when it dries out, it
forms
a crust over the top to protect the huge
plasmodium
below.
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A good, if not so pleasantly named, example of the myxomycota
is the dog vomit mold (Physarum polycephalum). It’s named that
because it often looks like that. But the skills of this slimy mass help it to
overcome the poor name and the yellow gooeyness (gooiness?). Acellular slime molds are math
geniuses – and they are going to help you avoid your math homework by playing
on the internet.
It all started when a 2000 paper showed that dog vomit mold
can find its way through a maze. With food at the opposite end of a labyrinth, P. polycephalum will consistently find
the shortest path to the food. The
mold grows toward food in such a way as to be most efficient.
Here, efficient means using the least amount resources and
the quickest route, ie. the shortest path. It creates a redundant system as well –
more than one way to get to the target in case the primary path is disrupted by
a misplaced footstep or a carelessly discarded whoopie pie wrapper (I must be
hungry).
Finding fast, short, efficient, and redundant paths involves
high level math - very high level math. P.
polycephalum doesn’t have a calculator, or even a brain, but we're
learning a lot from this mathlete.
In an amazing 2010 study, pieces of food were placed on an
agar plate in the relative locations of Japanese towns around Tokyo. A small
amount of P. polycephalum was placed
where Tokyo would be, and it was allowed to grow toward the food. The result – the
mold recapitulated the Tokyo rail system map!!! Five dollars worth of agar and
48 hours achieved the same design result as years of time and hundreds of
millions of Japanese yen – maybe just a bit embarrassing?
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The
networks formed by dog vomit mold become well
defined
as they are reinforced. The fronts are looking for
food,
and many are resorbed to reveal only the most efficient
pathways
once food is found (watch the left side).
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Graphics programs use slime mold math to build geometric
shapes which become smooth and realistic surfaces and moving objects in your
video game. Dog vomit mold can even be used to model the movements of
characters within the games. Who knew that Assassin’s Creed involved so much math?
Phylum Oomycota - These are the water molds or downy
mildews. We have talked about them before in terms of their presence in your bathtub and shower, but they have more stories to tell. For instance, they were
responsible for the number of Irish Catholic priests in America.
One of the most amazing things about this phylum is that you
pronounce both of the first two O’s – say “Oh! Oh! Mycota” real fast. The name
means “egg fungi,” and as with the two other phyla, they used to be mistaken
for fungi. However, these molds grow in long filaments, not as slime molds.
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This is
what happens to potatoes contaminated with the P.
infestans parasitic oomycete. The
potatoes rot in the ground,
so
when you finish growing them all summer, you have
nothing
to harvest. It isn’t the plague, but it still killed a
million
people.
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You can directly relate the number of Irish priests in America to an oomycota
called Phytophthora infestans. The
land in Ireland in the 1700-1800’s was particularly fertile; they were the
breadbasket of the UK. This meant that they grew a lot of potatoes. True, the
English land owners took most of the crop, but the Irish that worked the land
benefited as well by having more food than most other people in their
sociopolitical group could manage.
Because they
had more food, they had better overall health. Better health led to, amongst
other things, more children. The population growth in Ireland was much higher
than in other parts of the UK. Then a ship arrived with P. infestans in 1845 and the Great Famine followed in its wake.
P. infestans wasn’t a problem for the potatoes growing the Americas because
the parasite and the potato had co-evolved, every mutation
that made the protist more dangerous to the potato was countered by a potato
mutation to increase their defense. This was possible because, as we have discussed before, the potato is one of the crops native only to the Americas.
Historically,
a ship from South America Andes has been blamed for bringing the ill-fated
protozoan to Ireland, but 2014 research on genetics shows that the particular P. infestans that went to Ireland
probably developed in central Mexico.
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The
French wine industry was almost wiped out by another
oomycete
from the Americas. P. viticol was
introduced to
Europe
in the 1870’s by some American grape vines that
were
brought to France to try and breed a more aphid
resistant
vine.
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With
their new land, the Irish adopted a new attitude. So many children had been
lost to the potato blight that they began to rethink the idea of large
families. They looked to the teachings of economist Thomas Malthus for ways to
have fewer children and still remain true to their Catholic beliefs.
Malthus said
that people could reduce their population growth by marrying later, by going
into public service, or by joining the clergy. So many Irish boys became
priests or policemen. By the 1870’s, over 80% of priests ordained in America
were from Irish families. A protozoan parasite led directly to Barry Fitzgerald's and Bing Crosby's characters in Going My Way.
Do you agree that
those are some amazing stories? If you didn’t already love biology, I bet you
do now. Let’s bring Christmas into this lovefest next week. Your evergreen
Christmas tree actually fights off the Sun in winter time; it could die otherwise.
Goss, E., Tabima, J., Cooke, D., Restrepo, S., Fry, W., Forbes, G., Fieland, V., Cardenas, M., & Grunwald, N. (2014). The Irish potato famine pathogen Phytophthora infestans originated in central Mexico rather than the Andes Proceedings of the National Academy of Sciences, 111 (24), 8791-8796 DOI: 10.1073/pnas.1401884111
Tero, A., Takagi, S., Saigusa, T., Ito, K., Bebber, D., Fricker, M., Yumiki, K., Kobayashi, R., & Nakagaki, T. (2010). Rules for Biologically Inspired Adaptive Network Design Science, 327 (5964), 439-442 DOI: 10.1126/science.1177894
For
more information or classroom activities, see:
Serendipity
in science –
Slime
molds –
Potato
famine –
