Thursday, May 19, 2016

Antimicrobial antenna bacteria of bee-hunting wasps

For many people, including myself, a mention of the word wasp brings to mind a particular yellow and black annoyance found hovering around garbage cans in the summertime. However, as is usually the case with the natural world, wasps are far more interesting than our common experiences with them let on. To start, there are thousands upon thousands of species, not just the yellow jackets we try to avoid being stung by as we eat at a picnic table out in the park. Wasps are close cousins of bees and ants. Some live in groups, but most are loners (solitary wasps). Many wasps, as adults, feed upon sugary liquids (be they nectar, rotting fallen apples, or unfinished cans of soda). It's a whole other ballgame when it comes to their young though. Solitary wasps have a tendency to lay their eggs inside other living things, including oak trees and various insects. The larvae then feed upon their living surroundings. As many of the insects consumed by wasp larvae themselves consume plants we like to eat, look at, or make things from, wasps are a big help to us.

Beewolves refer to several genera of bee-hunting solitary wasps. In addition to having an awesome name, they are involved in a neat mutually-beneficial symbiosis. Females dig underground nests in which to lay their eggs. They then go out and capture bees by injecting them with a paralytic venom, bringing them back to the nest as fresh food for their offspring. After devouring the immobilized bees, the wasp larvae encase themselves in cocoons and undergo metamorphosis. Adults emerge the following summer.

Beewolf emerging from its underground nest (Source)

Now, the soil surrounding a beewolf nest is typically filled with a diverse collection of bacteria and fungi, some of which are capable of infecting and killing the larvae as they hang out in their cocoons. This is particularly likely since it's fairly warm and humid inside the nest, ideal growth conditions for many microbes. To minimize the chances of infection, beewolf mothers douse their nests with a white liquid they release from glands within their antennae. These glands happen to house an antibiotic-producing bacterium belonging to the genus Streptomyces. The bacterium is taken up by the larvae as they construct their cocoons, providing protection against bacteria and fungi seeking to get inside and chow down on the immature wasps. Imaging of the outside of the cocoons has revealed they are thoroughly coated with protective antibiotics. The beewolf Streptomyces produces at least nine different antibiotics, making it difficult for disease-causing microbes to develop resistance to their collective lethal effects.

That a species of Streptomyces should be producing antibiotics is of no surprise. This genus is responsible for many of the antibacterial and antifungal drugs we use to treat our infections. We isolated them from the soil in which they lived and uncovered the killer compounds they were pumping out. While we've only gained access to their antimicrobial weapons in the last hundred years, beewolves have been using Streptomyces to ward off infections for tens or millions of years now!


Kaltenpoth M et al. 2014. Partner choice and fidelity stabilize coevolution in a Cretaceous-age defensive symbiosis. PNAS 111(17):6359-6364. [Full text]

Seipke RF, Kaltenpoth M, Hutchings MI. 2012. Streptomyces as symbionts: An emerging and widespread theme? FEMS Microbiology Reviews 36(4):862-876. [Full text]

Wednesday, May 18, 2016

Why antibiotics in ointments differ from those in pills

There are many ways to get a drug into a person. Two common approaches are to swallow a small soluble solid or inject a liquid into a vein, causing it to be transported throughout the body to wherever it is needed.

Topical medications are those applied to a body surface, be it skin, eyeballs, or the insides of your lungs. This is usually done to deliver the drug to the particular place requiring repair (e.g. eye drops for an eye infection) while minimizing the amount of drug ending up in other parts of the body where it can cause unwanted (side) effects. Alternatively, a drug may be administered topically but in such a way to ensure it ends up all over (e.g. fentanyl transdermal patches applied to the skin to alleviate severe pain by slowing releasing the drug into the body).

In the case of antibacterial ointments, the gooey greases applied to cuts and scrapes to prevent infection, the drugs they contain differ from those typically given as pills or injections. Ointments such Neosporin or the classic Triple Antibiotic Ointment tend to contain three drugs: neomycin, polymyxin B, and bacitracin. All three were originally isolated from bacteria (bacitracin has a particularly interesting origin story) and act in different ways to harm particular groups of bacteria. Together they form a potent team of bacteria killers.

Triple Antibiotic Ointment still life (Source)

However, none of three drugs are commonly used to fight internal infections. There are two major reasons for this. First of all, they aren't particularly adept at making their way into your bloodstream if you ingest them. In other words, they are poorly absorbed from the gastrointestinal tract. Neomycin has instead been fed to people in order to selectively target and kill off a bunch of the bacteria growing inside their guts, essentially an external internal body surface (and so still a sort of topical application).

The second reason for the restricted use of these drugs is their toxicity. All three are toxic to the kidneys if they end up in the bloodstream. Neomycin also tends to cause ear damage and allergic reactions in form of contact dermatitis. Bacitracin also likes to cause allergic reactions (it's up there with penicillin as far as common drug allergies go). Funnily enough, neomycin is pretty good at killing the Gram-negative bacteria usually responsible for kidney-damaging urinary tract infections. It just happens to be a bit overzealous and can hurt the organ it should be helping to protect.

Polymyxin B doesn't like the kidneys or nervous system. However, it looks as though its toxicity might not actually be too severe, so the drug has found some use as a non-topical antibacterial agent in cases where people-infecting bacteria have developed resistance to other drugs.


Leyden JJ, Bartelt NM. 1987. Comparison of topical antibiotic ointments, a wound protectant, and antiseptics for the treatment of human blister wounds contaminated with Staphylococcus aureus. Journal of Family Practice 24(6):601-604.

Powell LW, Hooker JW. 1956. Neomycin nephropathy. Journal of the American Medical Association 160(7):557-560. [First page]

Weinberg ED. 1967. Bacitracin. In: Antibiotics (Eds. Gottlieb D, Shaw PD). Pages 90-101. Springer. [First two pages]

Zavascki AP, Goldani LZ, Li J, Nation RL. 2007. Polymyxin B for the treatment of multidrug-resistant pathogens: A critical review. Journal of Antimicrobial Chemotherapy 60(6):1206-1215. [Full text]

Thursday, April 28, 2016

Breathing Bordeaux is entirely different from drinking it!

It was the summer of 1882, and grape farmers in the Médoc region of southwest France (north of Bordeaux, on the Atlantic coast) had a problem.

Schoolchildren (or university students, or just anyone travelling the roads along which the grapevines grew, depending on what source you're reading) were pilfering their grapes. To try and ward them off, some farmers decided to dissolve some slaked lime and copper sulfate in water and spray it on their grapevines closest to the roads. The idea was the bright blue-green colour and unpleasant taste of the mixture would make the grapes less appetizing to thieves.

Grapevines sprayed with Bordeaux mixture (Source)

While it's not clear how successful this approach was, it enabled a professor of botany from the nearby University of Bordeaux to make a really useful observation: the blue-green mixture was great at preventing the growth of downy mildew (Plasmopara viticola), a fungus-like organism (oomycete) with an appetite for grapevines. Vines sprayed with the mixture (which came to be known as Bordeaux mixture) were not affected by the mildew, which was pretty rad if you were trying to grow grapes for a living!

Bordeaux mixture came to be used worldwide to prevent the growth of crop-eating fungi and oomycetes. Lots of produce was spared from microbial attack and so made it into the kitchens of the world thanks to the blue-green liquid.

The benefit of spraying pear trees with Bordeaux mixture (Source)

Unfortunately, there's a dark side to the use of Bordeaux mixture.

First of all, since copper is a metal and so doesn't break down in the environment, each time you spray a field of crops with Bordeaux mixture you end up with more copper in the soil. Although copper is an essential nutrient, you don't need a whole lot of it. At higher doses it becomes toxic. Lots of copper in a soil means everything hanging out in that soil doesn't do as well. It's bad news.

Another issue with Bordeaux mixture is the need to have someone spray it onto crops. If they're not using proper protective equipment, whoever does the spraying usually ends up breathing in lots of spray. Turns out inhaling a bunch of copper isn't great for your lungs. As the use of Bordeaux mixture continued and spread around the world, people employed to spray it on crops began complaining of lung problems. Their symptoms were consistently misdiagnosed, usually as tuberculosis, until the late 1960s. At this time, medical researchers in Portugal (Portuguese winegrowers had decided to stick with Bordeaux mixture instead of replacing it with newer fungi-killing pesticides) decided to take a look at the situation. Looking at grapevine sprayers who had recently died, they realized most of them didn't actually have tuberculosis even though their lungs were heavily damaged. The damage was comparable to the black lung disease seen in coal miners, only the lungs of sprayers were stained blue by the copper they had inhaled instead of being blackened by coal dust.

Looking at the living, Portuguese researchers found sprayers often had lung fibrosis (scarring of the lung tissue due to long-term inflammation, making it difficult to breathe), which worsened with time and eventually resulted in advanced lung disease. Lung fibrosis is also seen in coal miners and those working with silica. In the end, you can't breathe well enough on your own to get enough oxygen and can die from respiratory failure. It's a horrific illness, particularly since it's so often preventable. To top it all off, sprayers of Bordeaux mixture were found to be more likely to develop lung cancer.

The lung disease came to be known as "vineyard sprayer’s lung" and was found to be common among career sprayers. They only sprayed for a couple of months every year, but this was enough to inflict lasting and eventually fatal damage to their lungs. Copper also made its way to their livers, where it caused fibrosis and other types of damage.

Banana trees in Mexico City (Source)

Decades before Portuguese researchers decided to take a closer look at the copper-coated lungs of vineyard sprayers, employees on banana plantations were being exposed to even greater amounts of Bordeaux mixture. In the mid-1930s, a fungus by the name of Mycosphaerella musicola made the jump from the South Pacific to the Caribbean and Central America. M. musicola is responsible for a disease of banana plants called yellow sigatoka, named for the Sigatoka Valley in Fiji where it caused major destruction earlier in the century. It damages the leaves of the banana plant, diminishing its ability to carry out photosynthesis, which in turn reduces how many bananas the plant produces and causes the fruit to mature early.

In response to a growing yellow sigatoka epidemic, the United Fruit Company set up an incredibly intense spraying operation to deliver, every two weeks for the entire year, 250 gallons of Bordeaux mixture to every acre of banana plants. Central facilities pumped the mixture through miles of metal pipes to which workers attached hoses to spray it on the plants.

Unlike the vineyard sprayers in Portugal, banana sprayers worked year-round. Furthermore, because banana plants grow up to forty feet in height, and it was necessary to treat both sides of each giant leaf, workers (who lacked any sort of effective protective equipment) spent a lot of time looking up while spraying the plants. This meant they inhaled, and ingested, and absorbed through their skin, a hell of a lot of Bordeaux mixture. It accumulated on their faces, arms, legs, and clothing, staining them a blue-green that persisted even after scrubbing with soap and water. Sprayers were nicknamed pericos (parakeets) after the colouration they shared with these birds. Bordeaux mixture permeated their bodies to such an extent that ex-workers reportedly produced slightly blue-green sweat for months after leaving the job!

It's very likely many of the thousands of people employed as pericos ended up with serious lung damage, probably misdiagnosed as tuberculosis. The intensive Bordeaux mixture spraying approach continued until the early 1960s, well before researchers in Portugal realized just how dangerous Bordeaux mixture was. It's a tragedy no one connected the dots prior and did something to protect the workers.


Aggrawal A. 2006. Agrochemical poisoning. In: Forensic Pathology Reviews, Volume 4. Humana Press. [First two pages]

Marquardt S. 2002. Pesticides, parakeets, and unions in the Costa Rican banana industry, 1938-1962. Latin American Research Review 37(2):3-36. [First page]

Pimentel JC, Marques F. 1969. 'Vineyard sprayer's lung': A new occupational disease. Thorax 24(6): 678-688. [Full text]

Wednesday, April 20, 2016

Almost lichens: Green algae growing on mushrooms

Mushrooms come in many shapes and colours. In the case of green ones, which I've written about previously, a subset owe their colour not to any particular pigment they themselves produce, but rather to algae living on top of them.

These algae-bearing fungi are usually polypores, otherwise known as bracket or shelf fungi. They tend to live inside dead trees, although they also be found in soil living in association with tree roots. After eating their fill of delicious wood, polypores produce shelf-like fruiting bodies with numerous pores (thus the name polypore) on their underbellies. Some of these fruiting bodies, or conks as they are also known, take on the character of the wood from which they grow. Their resilience means they can be spotted during the winter when other mushrooms have long since decayed away.

The polypore Trametes gibbosa covered with green algae (Source)

Polypores upon which algae have been spotted include species of the genera Trametes and Trichaptum, as well as Cerrena unicolor, Fomes fomentarius, Stereum subtomentosum, and Lenzites betulina (a polypore with gills instead of pores, since nature likes to defy neat categories).

Now, the coexistence of fungi and algae is nothing new. Lichens are essentially algae (or cyanobacteria) living inside a fungus. This fungus is usually a member of the ascomycetes, one of the two major groups of mushroom-producing fungi. Polypores are members of the second group, the basidiomycetes.

Algae-covered fungi on a rotting log (Source)

As is the case for lichens, the algae on top of a polypore arrangement appears to benefit both partners. The algae (usually single-celled ball-shaped green algae), being filled with green photosynthetic pigments, use sunlight to make sugars out of carbon dioxide gas. Some of these leak out and are absorbed and consumed by the fungi as an extra source of energy-rich organic carbon. The fungus, in turn, provides a solid platform upon which the algae can set up shop and grow into dense green communities.

Polypore-based algae don't appear to be committed to this particular lifestyle, as they are also found in lichens (e.g. Trebouxia) or growing on plants or other sunlit surfaces.


Mukhin VA, Patova EN, Kiseleva IS, Neustroeva NV, Novakovskaya IV. 2016. Mycetobiont symbiotic algae of wood-decomposing fungi. Russian Journal of Ecology 47(2):133-137. [First two pages]

Zavada MS, Dimichele L, Toth CR. 2004. The demi-lichenization of Trametes versicolor (L.: Fries) Pilat (Polyporaceae): The transfer of fixed 14CO2 from epiphytic algae to T. versicolor. Northeastern Naturalist 11(1):33-40.

Tuesday, April 12, 2016

Return of the wild: How nature breaks down what we build up

When I was a teenager, I read Stephen King's book The Stand. It begins with the near-obliteration of humankind by a lethal virus. This was weirdly alluring stuff for a angsty teenage daydreamer. What would you do if the world ended? What would be your fate? I figured I'd make it a couple of months on canned food before succumbing to some sort of brutal antibiotic-resistant bacterial infection.

These days, I find one of the most interesting aspects of post-apocalyptic fiction is it requires an apocalypse. This often means a horrific scenario inspired by science: astronomy (impact event, e.g. Lucifer's Hammer), microbiology (pandemic, e.g. Oryx and Crake / blight, e.g. Interstellar), cybernetics (people-hating intelligent machines, e.g. The Matrix), climate science (climate change, e.g. Cat's Cradle), physics (fallout/nuclear winter from nuclear war, e.g. Fallout), and the list goes on. Evidently it's easy for artists to get caught up with taking what we know about the world around us and twisting it to envision destruction.

For today's post, I'd like to explore the science of a particular end of the world scenario in which (1) people are selectively wiped out or at least made an endangered species, (2) there is minimal damage to the planet during the wiping, and (3) all other organisms survive unscathed. So basically The Stand, but from the perspective of nature. The question I'm interested in is: how would the numerous organisms we share the world with set about breaking down the infrastructure we've constructed for ourselves? How would the Earth undo our great works?

Let's start with wood. Many organisms are good at making holes in trees in order to digest them for food and/or construct homes in which they can hide out and reproduce. This is a transferable skill, as tree-damaging organisms also break down human-built wooden structures: fence posts, utility poles, railroad ties, buildings (frames, flooring, stairs, roofing), playgrounds, etc.

Take the wood poles used to distribute phone and power lines, for example. They can be damaged by fungi, insects (e.g. termites and certain ants and beetles), woodpeckers, and, for poles stuck in the ocean, wood-boring animals (e.g. shipworms). As a pole is hollowed out, its structural integrity decreases until it falls over. Since utility poles are connected in series via the lines they carry, the collapse of a single pole can bring down many of its neighbours.

I've heard there are sections of power lines where they've had to replace all of the wood poles with ones made out of a composite material since woodpeckers were continually pecking holes in them. Woodpeckers tend to drill way more holes than they need for roosting or nesting, and these holes facilitate further damage. Utility poles are often treated with poisons (e.g. creosote or chromated copper arsenate) intended to prevent wood-eating organisms from doing their thing, but this usually only covers the surface of the pole. If a woodpecker makes a hole (preservatives don't seem to repel them), other organisms can use it to bypass the poison and cause decay.

Pileated woodpecker hanging out in a hydro pole (Source)

Many fungi are capable of damaging the wooden parts of buildings. They'll grow wherever there's wood (food), water, oxygen, and a favourable temperature (at least above freezing). Two of the most destructive are the brown-rot (cellulose-eating) fungi Meruliporia incrassata and Serpula lacrymans. They pump out hydrogen peroxide, which soaks through wood and weakens it substantially, causing it to crumble and ultimately fail to support whatever it was holding up. M. incrassata and S. lacrymans are particularly problematic (or successful, depending on how you're looking at it) because they can transport water and nutrients over long distances. This means they can do annoying things like grow throughout a connected wooden structure even if only one part of it is damp, or invade homes by growing through mortar and concrete.

Brown-rot fungus growing beneath someone's floor (Source)

Mushrooms, the sometimes-delicious spore-releasing structures made by certain fungi, can punch holes in roads and other asphalt surfaces. Presumably, this action would leave behind holes (as the mushrooms die back, being the ephemeral structures they are) through which plants could grow and further break apart the asphalt. Fungi known to send up their mushrooms through asphalt include Agaricus bitorquis (the appropriately named pavement mushroom) Amanita muscaria (fly agaric), Phallus impudicus (common stinkhorn), Pisolithus tinctorius ([1], [2], [3]) and Podaxis pistallaris (false shaggy mane).

Mushrooms punching through pavement (Source)

Tree roots can slowly yet surely damage pretty much anything we place in their path. Sewer pipes, storm water drains, buried water and gas lines, building foundations, sidewalks, patios, streets, parking lots, walls, and swimming pools can be cracked, broken, heaved upwards, and/or shifted about by a growing root. There are two mechanisms by which this damage occurs. First, as roots grow outwards and increase in size, they lift things up or push them to the side. Second, as roots beneath a building pull moisture out of the soil, the soil shrinks and the building settles.

Driveway damaged by tree roots beneath it (Source)

Rodents, insects, and birds are known to chew on power and communications cables buried in the ground, suspended in the air, or running along the sides of buildings. Underwater telecommunications cables, of which there are millions of kilometers worth crisscrossing the world's oceans, are occasionally bitten by sharks.

In Australia, underground cables can be severed by the guillotine-like roots of a parasitic plant. The Western Australian Christmas tree (Nuytsia floribunda) grows in Western Australia and tends to bloom around Christmas (which is in the summer down under). Like mistletoe, N. floribunda is a hemiparasite. This means while it can do a bit of photosynthesis, it obtains water and nutrients by hooking its roots up to those of nearby plants and withdrawing what it needs. When it encounters a nice juicy root beneath the ground, N. floribunda uses its specialized roots (haustoria) to grow a collar around it (Figure 3A). Two folds of tissue extend around opposite sides of the host root and fuse together to completely encircle it. This collar contains a sickle-like cutting device (Figure 3D) which is sharp enough to cut tissue paper. The collar thickens and constricts the host root until the cutting device cuts right through it (Figure 3E). After severing the root, N. floribunda constructs a disc of tissue to sit up against the cut and plug into it in order to drain water and nutrients. It seeks out roots to feast on by detecting certain plant-produced compounds such as ethylene gas. These same compounds can be given off by plastic-covered cables, causing the plant to attack and damage them in search of a meal.

Nuytsia floribunda, nemesis of Australian telephone companies (Source)

If you leave a non-living surface, be it stone, glass, or metal, exposed to the great outdoors for long enough, chances are a lichen will show up. If there's a bit of soil to be had in a crack or hole somewhere, a plant may appear. Plants and lichens damage buildings and monuments made of stone, brick, or concrete by producing corrosive organic acids (e.g. oxalic acid) and punching (and then expanding) holes with their roots/thalli. Materials containing calcium carbonate, such as limestone, are particularly susceptible to acid damage.

Corrosive acids are also produced by certain bacteria living on stones/bricks/concrete. Ammonia-oxidizing bacteria bring about the production of nitric acid using ammonia from lichens, algae, or bird crap. Sulfur-oxidizing bacteria produce sulfuric acid from hydrogen sulfide and other partially reduced forms of sulfur. This acid will convert hard marble into soft and crumbly calcium sulfate. Sulfur-oxidizing bacteria are a major cause of concrete deterioration in sewers systems and sewage treatment plants, as there's lots of poop and thus sulfur for the bacteria to convert to sulfuric acid. Hydrogen sulfide, produced by sulfur-reducing bacteria, can also contribute to corrosion.

Chunks of concrete after spending time in a sewer (Source)

Bacteria also corrode pipes and storage tanks made out of metal. These are found in water distribution systems, oil pipelines, and most industrial facilities (e.g. pulp and paper, food processing, oil refining, etc.). As they grow on the insides of metal pipes and tanks, bacteria can alter the local environment in such a way as to cause or speed up corrosion. This can involve changing the pH or producing corrosive compounds like hydrogen sulfide and iron phosphide.


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