Wednesday, December 17, 2014

Christmas Greenery - Friend Or Foe?

Biology concepts – toxin, botany, cancer chemotherapies, pregnancy, evergreen

Noche de Rábanos (Night of the Radishes) is celebrated in
Oaxaca, Mexico on December 23. The townspeople carve
radishes into shapes, characters or scenes and then they are
judged.  It began as a suggestion by a couple of monks to
bring people in to the market to buy the produce that the
farmers had raised, so it’s a Christmas plant tradition that
really has little to do with Christmas.
In the middle of Northern hemisphere’s winter we use plants to help celebrate Christmas, but the practice is much older than Christmas. Decorating houses with evergreen boughs was related to the pagan tradition of the circle of the seasons, a guarantee that life would again return to the land.

Different regions used different evergreens, based on their folklore and what was locally grown. The poinsettia (Euphorbia pulcherrima) wasn’t considered a winter flower at first. It is native to southern Mexico and Central America, where it carried no real significance in holiday traditions, but was used by the Aztecs for making red dye and for treating fevers (using just the sap).

The first US ambassador to Mexico, Joel Poinsett, brought them back to the states and distributed them to botanical gardens. In the 1950’s, the Tonight Show was one of the first shows to be broadcast in color, and growers offered them free poinsettia plants as set decoration near Christmas. This, with additional donations for magazine layouts and Bob Hope specials created a huge market for the flower, which is now the most popular potted plant in America.

No matter what plants your corner of the world has chosen to include in their winter holiday tradition, they bring joy and warmth and yes, a sense of returning spring. ….. And many of them can kill you. To be fair, science is finding ways that they can save us as well. Let’s look at the major Christmas evergreens and how they can ruin or save your holiday.

Christmas trees – Several species of pines are used in the United States and Europe as Christmas trees. While not lethal, my pet peeve is the itchy rash I get on my arms while putting the tree in its stand and decorating it.

Many types of firs, pines, and spruces are used for Christmas,
but I think the bonsai Christmas has been severely underused.
Think of the budget savings, not many presents will fit under
that tree. And if it catches on fire, it might not even set off
your smoke detector.
It’s called irritant contact dermatitis (ICD) and can come from the wood or needles. Many people have trouble with the sawdust from cutting pine trees. I know it won’t kill me, but since I have few allergies and therefore am not used to being itchy, this bugs me.

Many people tout the health benefits of drinking tea made from pine needles, but this could get you into trouble. Many evergreen tree species (Ponderosa pine, Lodgepole pine, the cypresses, junipers) have high levels of a chemical called isocupressic acid (ICA).

ICA causes spontaneous abortions in cattle, and perhaps humans. A 2002 study showed that progesterone levels were affected by ICA. Progesterone is important for maintaining a pregnancy through the third trimester, ie. stopping premature labor. Progesterone relaxes the uterine muscles to prevent contractions; giving high risk women progesterone gel has been show to reduce premature delivery by 45%. You can see why ICA might be a problem.

A very recent study showed that ICA inhibits the transcription of two enzymes called StAR and P450scc. And a 2005 study links these two enzymes progesterone production. This is compelling evidence that eating pine needles that contain ICA suppresses the body’s work to prevent early labor.

On the other hand, pine needle tea might just save your life. A 2014 study showed that extracts from the Taiwan white pine (Pinus morrisonicola) needle can affect some cancer cells, specifically glioblastoma cells (cancer of the support cells of the brain).

Not all Christmas trees are evergreens. The New Zealand
Christmas tree (Metrosideros excelsa, or pohutukawa) turns
red around Christmas. A 2010 study indicated that extracts
from this tree were lethal to tuberculosis organisms as well
as Staph. aureus….. you know, that bacteria that is becoming
resistant to so many antibiotics.
One chemical in the pine needles, chrysin, could not only kill cancer cells on its own, but also prevented and reversed the molecular events in glioblastoma cells that had become insensitive to the cancer drugs used to treat gliobastoma. And lucky for us, Taiwan white pine needles are very low in ICA , so we can use it to treat cattle that are pregnant and have brain cancer…. and people too.

Speaking of cancer drugs, a different kind of evergreen tree is the source of one of the most powerful cancer chemotherapeutics we have. In many parts of Britain and Europe, yew trees were used as Christmas trees instead of pines or firs. Taxol itself is found in greatest quantity in bark of the slow growing Pacific Yew.

As you have probably guessed, some people like to make tea from the bark of the Pacific Yew, so it care needs to be taken here as well. Remember that cancer drugs kill cells that are reproducing. In the case of taxol, the chemical binds to parts of the cell that help line up and pull apart the chromosomes during mitosis (called microtubules).

Since normal cells use microtubules in exactly the same way as cancer cells do for cell division, taxol inhibits their function as well. This is why people lose their hair during many cancer treatments. Cancer drug therapy is balanced on a knife edge; hopefully it kills the fast dividing cancer cells just a little bit better and faster than it kills the cells that we need, like stomach lining cells, bone marrow cells, and hair follicles.

Mistletoe – prior to the advent of the Christmas tradition in Britain, kissing bunches were popular. An evergreen would be hung in a circular hoop and couple would kiss beneath it. In some traditions, the white berries of the mistletoe (Viscum album) also were used. Each time a kiss was taken, a berry had to be pulled; when the berries were gone, the kissing was over.

On the left is the older kissing hoop, or kissing bough. The
purpose of the apples eludes me, but they may be there to keep
the hot wax from dripping on your head. The right side is our
more modern mistletoe bough. It still has the white berries, but
we don’t pick them off with each kiss anymore.
The berries of mistletoe are poisonous to humans, so I hope that the young men who had to pick the berry after a kiss didn’t just pop it in their mouth in an attempt to impress the girl or make her laugh. Both the leaves and the berries contain toxins that would require a call to Poison Control if ingested.

Different species have different cocktails of toxins, but most, including phoratoxin and tyramine, will bring you (before they kill you) nausea, vomiting, blurred vision, and dangerously low blood pressure. Some companies tout European mistletoe extract as a natural antihypertensive treatment, but safe dosages have not been worked out, so I would caution against it as an herbal medicine not taken under a doctor’s supervision.

ON THE OTHER HAND, some extracts from some species of mistletoe might save your life. A chemical called viscothionin from a Korean species of mistletoe has been shown in a 2014 series of experiments to improve liver function in people that have fatty buildups in their liver tissue. Another 2014 study showed similar benefits to the liver and other tissues in rats that had low levels of estrogen, implying that it could be of benefit to post-menopausal women.

Pancreatic cancer is staged from 1 to 4, with 1 being the least
aggressive or least progressed. Notice that the survival
timess are in MONTHS, not years. No wonder we need to
find additional drugs for this cancer and why people are looking
for drugs to make people’s live easier while they suffer with
this cancer.
In a more philosophically complicated study, mistletoe extract was given to patients with advanced, terminal pancreatic cancer. Only patients who had refused further treatment were included in the study, to see if the mistletoe extract could improve their quality of life in the time they had remaining.

It did, as witnessed by increased body weight, increased appetite, less pain, better sleep, and less fatigue during the day. Great you say, but it also prolonged their life. Again you say great….. but I wonder if is this what all the patients wanted? Improved quality of life is amazing, but if they live longer, it just means living a little longer with a horribly painful cancer. A study of the ethics of this treatment should be warranted as well.

IvyHedera helix is scientific name for English ivy, used for centuries in Christmas decorations and symbols. One of the most popular Christmas carols remains, The Holy and the Ivy, but we will focus on just the ivy here.

As an evergreen, ivy was used as a symbol of everlasting life, but there was a time when Christians in England outlawed the use of ivy as a Christmas decoration. Some thought that since it grows in the shade, it could represent the sin that takes place outside of the light of day; secrecy and debauchery must have been on their minds.

English churches used to decorate the outside with 
ivy for Christmas, but only the outside. And of, 
course this during the period when they believe
that ivy was the houseplant of the devil.
I’m not sure why they would decorate with ivy, 
most of them are covered with it anyway.
In keeping with the evil associated with ivy, all parts of the plant are toxic. Cats and horses are especially susceptible to the toxins ivy contains, including facarinol. Ingestion can lead to convulsions, breathing problems, paralysis and coma. At least in humans it takes a pretty large dose to bring on big trouble.

However, many people develop a contact dermatitis reaction to ivy. Weeping blisters are common and severe itching accompany even the slightest contact. Heaven forbid the kind of itching that might accompany the eating of ivy! A 2010 review concluded that ivy should be one of the standard botanical allergens to be tested for.

ON THE OTHER HAND, ivy extracts might save your life. The same toxin that makes you sick, falcarinol, inhibits breast cancer cells from becoming resistant to cancer drugs (2014 study). Falcarinol stops the action of proteins in the cancer cell that work to pump cancer drugs back out. Called efflux pumps, cancer cells with increased pump activity keep pumping the cancer drugs out of the cell. Ivy extract stops the efflux pump from being produced so the cancer drug can do its job.

The poinsettia has undergone many hybridizations over the years
and has been selectively bred to keep its colored bracts (leaves)
for much longer. But the purpose of the blue poinsettia escapes
me. Is it supposed to look cold? My wife says it doesn’t have to
have a purpose, it’s just pretty.
According to another recent study, a toxin from ivy leaves, hederagenin, induces colon cancer cells to kill themselves (apoptosis). I think the take home message here is that Christmas evergreens are pretty and can be meaningful, but don’t add them to the holiday meal unless instructed by a doctor.

And as for poinsettia, they have a bad reputation for being poisonous, but a child would have to eat about 500 leaves for them to be in big trouble. And they taste so bad, that no kid would eat more than one. It’s strange how some have the reputation and other that are more dangerous are not thought of as toxic.

Next week, myrrh was one of the original Christmas gifts. It had many functions in ancient times, but now we know WHY it's such a great gift.

Liu, B., Zhou, J., Li, Y., Zou, X., Wu, J., Gu, J., Yuan, J., Zhao, B., Feng, L., Jia, X., & Wang, R. (2014). Hederagenin from the leaves of ivy (Hedera helix L.) induces apoptosis in human LoVo colon cells through the mitochondrial pathway BMC Complementary and Alternative Medicine, 14 (1) DOI: 10.1186/1472-6882-14-412

Tröger W, Galun D, Reif M, Schumann A, Stanković N, & Milićević M (2014). Quality of life of patients with advanced pancreatic cancer during treatment with mistletoe: a randomized controlled trial. Deutsches Arzteblatt international, 111 (29-30) PMID: 25142075

Tsui, K., Wang, J., Wu, L., & Chiu, C. (2012). Molecular Mechanism of Isocupressic Acid Supresses MA-10 Cell Steroidogenesis Evidence-Based Complementary and Alternative Medicine, 2012, 1-12 DOI: 10.1155/2012/190107

Earl, E., Altaf, M., Murikoli, R., Swift, S., & O'Toole, R. (2010). Native New Zealand plants with inhibitory activity towards Mycobacterium tuberculosis BMC Complementary and Alternative Medicine, 10 (1) DOI: 10.1186/1472-6882-10-25

Since most of this post is about how certain plants can be poisonous, I have decided not to include links for more information on how these things can kill you. If you must know, you’ll have to look them up yourself.

Wednesday, December 10, 2014

Christmas Trees Have Trouble Seeing The Light

Biology concepts – photoprotection, photosynthesis, non-photochemical quenching, reaction center, yule, evergreen, chlorophyll

Yule was/is a pagan celebration in midwinter. Krampus
was the spirit who came during Yule to punish children
who had misbehaved. Yule celebrations used evergreens
(note his headdress) and this has continued in the
modern Christmas celebration, but the Krampus became
paired with good Saint Nicholas, so they kind of went
the other way with that one.
Christmas trees are pagan holdovers from when early Christianity adopted December 25th as the date of the holiday. Pagan religions used evergreens as a reminder that the Earth would bloom with life again even in the winter when the sun was scarce. The joke is on them though – biology shows us that evergreens have to protect themselves from the life giving sun.

The Romans decorated their houses with evergreen boughs in December, and in particular, the Germanic and Norse pagans celebrated the jexla or jol (respectively) festivals in late December until early January. In English, this became Yule, or Yuletide (yule time).

Evergreens, as the name suggests, stay green all winter; they don’t drop the majority of their leaves (needles) and they keep chlorophyll in their leaves all year round. Chlorophyll is green, so there you have it - evergreen.

Chlorophyll is energetically costly to make and maintain, so if there isn’t enough sunlight to make photosynthesis a net gain (once you subtract the energy needed to make and maintain leaves and chlorophyll); a good strategy might be to just drop them and start over again in the spring.

So one reason for being an evergreen would be that there is enough sun and moisture in a certain location to warrant chlorophyll production and maintenance year round. But there might be a more pressing reason for keeping leaves all year round - nutrients.

When deciduous trees lose their leaves, there are letting a lot of nutrients blow away with the wind – usually into my yard. This is costly, especially if you grow in nutrient poor soil like many evergreens do. In cold climates, leaf litter doesn’t decay fast enough to allow nutrients back into the soil, so holding on to your nitrogen is a good idea. Conifer needles tend to be lower in nitrogen than deciduous leaves, so they hold on to their nutrients better.

Conifer forests are often quite bare on the ground. This is
for a few reasons. One, the ground is usually nutrient poor
and fewer things can grow there. Two, the needles cover
the ground and reduce the light for seedlings. And three,
needles are acidic and make the ground acidic, making it
even harder for other things to grow. Fewer competitors
makes it good for the conifers.
In addition, being able to grow in acidic soil or soil that has less nitrogen and phosphorous is an evolutionary strategy for the evergreens; if fewer plants can grow there, than then will have fewer competitors for what nutrients there are and for sunlight. Some evergreen litter is designed to make soil acidic, so that fewer competitors will try and put down roots.

The result of all this is that evergreens, conifer trees and some bushes, stay green year round. But they’re just fighting to stay alive, not growing year round. It turns out that evergreens spend a lot of energy to avoid sun damage caused by the very mechanisms that allow them to gather sunlight light year round. In winter: chlorophyll + sunlight = death. Just like vampires, they have to protect themselves from the suns rays, or they burn up.

The truth is, evergreen trees in cold climates do very little photosynthesis in the winter, even if there is sunshine. They'll make carbohydrates from sunlight, water, and CO2 (the three ingredients needed for photosynthesis) when they’re each available, but available is a relative term.

Air is always available, so CO2 isn’t problem. The sun is at a lower angle in the winter, but it isn’t cloudy and gray every winter day; it just seems that way. So sunshine is available at least part of the time - usually daytime.

The large diameter tubes are vessels, while the narrower
ones are tracheids. Conifers only have tracheids, no vessels.
This is good for growing in cold weather environments.
When water freezes in the vessels, the width promotes gas
bubble formation. This will lock the vessel and no water can
ever be transported again. The narrow tracheids of conifers
prevent gas bubble formation.
The problem is water. Sure it’s there, but it may be solid. If the weather is cold enough to freeze the water on and in the shallow soil, it may also be cold enough to freeze the water in the tree trunk and leaves. Any photosynthetic plant, including trees, needs to split water into hydrogen and oxygen during photosynthesis. If they don’t have a source of water, then they can’t perform that little miracle that is the source of all life on Earth.

Even temperatures near freezing can slow down water movement in plants, and since cold air holds less water (humidity), more water can be lost from leaves - even the wax covered, thick leaves of conifers. The end result is that photosynthesis is just not feasible during most points of the winter.

Yet the evergreens don’t drop their leaves and keep their chlorophyll in their chloroplasts. That means that every time the sun comes out, some of the energy of the rays are caught and transferred to the photosynthetic reaction centers, including chlorophyll. If photosynthesis can’t be completed because of a lack of available water, then what happens to all that energy? It is free to bounce around and damage plant tissues, usually in the form of reactive oxygen species (ROS, see this post). Enough damage and the plant will lose its ability to function and die.

To avoid the irony and embarrassment of becoming a dead midwinter symbol of life, evolution has provided plants with certain photoprotective mechanisms. Not just evergreen plants, but all plants. It turns out that photosynthesis pathways are saturable, only so much sunlight can be used to produce energy and then carbohydrates.

The sun is unwilling to play the game; once the saturation limit is reached, it just keeps on shining. On bright summer days, just about any plant is susceptible to damage from excess energy absorption in chloroplasts. Some plants have elaborate mechanisms to change the angle of their leaves so that they receive less sunlight.

Some plants, like this Oxalis triagularis can quickly change the
angle of their leaves so that low levels of sun can be maximized
or that high levels of sun can be avoided. Evergreens can’t do t
his, so they need more mechanisms of photoprotection
Evergreens, especially conifers, can’t regulate the amount of light that shines on them, so they need additional photoprotective mechanisms. Plants of the genus Taxus, like English yew, move their chloroplasts (discussed in this post) instead of their needles.

According to a 2007 study from Japan, yew cell chloroplasts congregate in the center of the cell volume in response to low temperatures, whereas in summer they can be found along the edges closest to where the light comes in. In this way, many chloroplasts can be shielded from sunlight in the winter, so less energy will be harvested. Pretty smart.

For many evergreen plants, their chlorophyll is doomed to harvest sunlight all winter without being able to use it for photosynthesis, so what can they do with it - other than just let it damage them until they die?

It is important that the plant dissipates the light energy before it reaches the reaction center. Chlorophyll isn’t the molecule that changes sun energy to chemicoelectrical energy. Chlorophyll is the pigment that absorbs the energy. That energy can be transferred to an adjacent chlorophyll molecule and so on until it reaches the reaction center. Here, the accumulated the energy is used to split a water molecule and two electrons move into the electron transport chain. It's the reaction center that actually transduces (changes) the energy from light to chemical form.

The photosystem is made up of the reactions center and the
surrounding light harvesting complex (LHC). The LHC is made
up of many chlorophyll molecules that gather light energy and
bounce it around toward the reaction center. The reaction center
has many proteins that work together to transduce the light
energy into chemical energy by splitting water.
If the electrons are generated by the combined work of the protein complexes of the reaction center, then damage can be done because they can’t go on to fix CO2 and turn it into carbohydrate. Those electrons are free to attack any nearby proteins or lipids and break them down. In particular, they can attach themselves to oxygen and create ROS. These molecules are just itching to react with something, anything, and this leads to damage to many structures of the cell.

Plants can try to stop this by producing more antioxidants, which can absorb the electrons from ROS molecules. They might be destroyed in the process, but at least they aren’t allowing the ROS to damage something important. Evergreens ramp up antioxidant molecule production (especially glutathione and alpha-tocopherol) in the winter to prevent ROS damage.

Notice that we said above that the reaction center splits a water to generate the free electrons. Didn’t we also say that in winter, freezing conditions wouldn't allow for available water? This true, but damage to the reaction center and/or chlorophyll is possible BEFORE the point where water would be split. This energy has to be dealt with as well.

To dissipate the energy before it damages the chlorophyll or the reaction center, plants use a technique called non-photochemical quenching (NPQ). Demonstrated in a classic 1987 study, the physical positions of proteins in the photosystem (chlorophylls + reaction center) can be shifted during NPQ so that they create energy traps. In these traps, different pigments, called carotenoids (see this post for plant pigments), can accept the energy of the light.

When the energy hits a carotenoid pigment called violaxanthin, it converts it to another pigment, zeaxanthin. Zeaxanthin can’t passed energy along to the reaction center, but is good at giving it up as heat. When sunlight can be used for photosynthesis, zeaxanthin is turned back to violaxanthin and the photosystem redistributes itself so that light energy can be focused to the reaction center. This is called the xanthophyll cycle.

Cadmium is used in batteries, paint pigments, metal plating
and in the production of other metals, like copper and zinc.
Long-term exposure can lead to kidney damage, but a new
study shows the problem may be worse than that. The
experiments showed that cadmium can interrupt non-
photochemical quenching in barley. This can lead to damage
and reduced barley harvests. Barley is used in making beer –
something must be done!
The zeaxanthin NPQ mechanism (truthfully, it's much more detailed than we have talked about here) is best for quick changes in sunlight level, However, the cycle can be disconnected in winter so that zeaxanthin is maintained for a long time. In addition, a 1995 study showed that some evergreens will prevent damage by inactivated or down-regulating (making less of) proteins of the reaction center, so that the high energy electrons won’t be generated.

This would presumably create more oxygen radicals from the chlorophyll since the energy can’t be transferred to the reaction center, but since zeaxanthin is being kept all winter, that energy is dissipated too. It sounds like a lot of work, but it requires much less energy than dropping leaves in the Fall and then re-growing them in Spring. You wonder why all plants aren’t evergreens – because then we wouldn’t have a special symbol to cram presents during the holidays.

So instead of being a vampire that has to stay out of the sun, the evergreen is more like a superhero that can overcome the power of the sun – his power of photoprotection saves Christmas for us. But maybe not - next week we’ll talk about how many different ways your Christmas evergreens can kill you.

Lysenko EA, Klaus AA, Pshybytko NL, & Kusnetsov VV (2014). Cadmium accumulation in chloroplasts and its impact on chloroplastic processes in barley and maize. Photosynthesis research PMID: 25315190

Demmig, B., Winter, K., Kruger, A., & Czygan, F. (1987). Photoinhibition and Zeaxanthin Formation in Intact Leaves : A Possible Role of the Xanthophyll Cycle in the Dissipation of Excess Light Energy PLANT PHYSIOLOGY, 84 (2), 218-224 DOI: 10.1104/pp.84.2.218

Ottander C, Campbell D, Öquist G (1995). Seasonal changes in photosystem II organization and pigment composition in Pinus sylvestris. Planta, 197, 176-183.

Wednesday, December 3, 2014

How Slime Molds Our World

Biology concepts – Protista, fungus-like protists, penicillin, undulipodia, serendipity, potato famine, networks, co-evolution, slime mold

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.
Have you ever had the fortunate experience of looking for one thing and finding something better? Your find wasn’t what your were looking for, or even meaning to find, but there it is. Now you’ve got something you can really use. And you didn’t even know it was out there. I think they call it serendipity.

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!

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.
When food is scarce, acraisomycota cells join together, both emotionally and physically. Dictyostelium discoideum is a cellular slime mold that has been used in research labs for years and is a well-studied example of the slime mold development.

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.

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.
Now it gets interesting. Some researchers noticed (serendipity?) that some of the fruiting body spores contained bacteria, but only some of them. Were they a contaminant? When the scientists killed off the bacteria nothing bad happened, but they noticed that the spores of the progeny that had contained bacteria also sported some bacteria in their newly formed spores.

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.

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.
With acellular slime molds, the individuals actually merge together as one cell, not one multicellular organism. This plasmodium is a single cell with thousands of nuclei, reaching sizes of 0.3 meters (1 ft. or more), so these are called the plasmodial slime molds.

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?

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).
All this math is important because many of the things you care about use this slime mold derived math to build virtual ….stuff. For example, the internet gets you pages of information by bouncing the information around networks. The more efficient that bouncing is, the faster your page loads.

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.

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.
The oomycota were originally mistaken for fungi because many feed on decaying material, but some other species are parasitic. They cause damage to crops and fisheries. One species attacks potatoes.

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.

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.
Regardless of where it came from, the European potato cultivars had not been pressured to develop defenses against P. infestans, and they rotted in the ground in a disease called late blight of potato. More than one million people died in 1847. To survive, millions left Ireland. Many came to America.

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
Toshiyuki Nakagaki, Hiroyasu Yamada & Ágota Tóth (2000). Intelligence: Maze-solving by an amoeboid organism Nature, 407 (470)

Brock, D., Read, S., Bozhchenko, A., Queller, D., & Strassmann, J. (2013). Social amoeba farmers carry defensive symbionts to protect and privatize their crops Nature Communications, 4 DOI: 10.1038/ncomms3385

Brock, D., Douglas, T., Queller, D., & Strassmann, J. (2011). Primitive agriculture in a social amoeba Nature, 469 (7330), 393-396 DOI: 10.1038/nature09668

For more information or classroom activities, see:

Serendipity in science –

Slime molds –

Potato famine –