Biological Weapons in the Ladybug Wars

"Human activities, particularly international trade,

promote the spread of invasive species that cause

extensive economic losses and negatively affect native

species."

"The harlequin ladybird Harmonia axyridis, introduced

for biological pest control, has become an invader that

is outcompeting indigenous ladybird species in many

countries."

- A. Vilcinskas, K., Stoecker, H. Schmidtberg, C. R. Rohrich,

and H. Vogel, Science, 2013, 340(6134), 862-863.

Harmonia axyridis - the invasive harlequin ladybird.

    In my May 7th post, I discussed a study that revealed an interesting mutualistic relationship between termites and fungi that resulted in the discovery of new compounds, the tyroscherins, that showed some potential use as new antifungals.  Then, in my May 22nd post, we acknowledged that our bodies are, among other things, giant growth vessels for trillions of microbial cohabitants, referred to collectively as the human microbiota.  All of these worlds collide in a recent publication in the journal Science, where Andreas Vilcinskas and co-workers have uncovered a microbe at the crux of an ongoing war that spans multiple continents, is having negative socioeconomic impacts, and could possibly even explain the sometimes funky terroir of wine.  The combatants?  Ladybugs.  Specifically, the invasive central Asian species Harmonia axyridis, AKA the harlequin ladybird, is wreaking havoc on the native European and American ladybug populations.  The study revealed that harlequin ladybirds carry a pathogenic fungal microsporidian closely related to Nosema thompsoni that is functioning as a biological WMD against Coccinella septempunctata, the indigenous ladybird species.  This study reveals yet again that biology we see unfolding at the macroscale (i.e. one ladybug kills another) has, at its core, a microscale explanation. 

    Prior to this study, it was thought that the lethality of the harlequin ladybird towards Coccinella was derived from the exceptionally high levels of harmonine - a foul tasting, stinky, antibacterial, antiparasitic, wine-spoiling alkaloid - in harlequin ladybird hemolymph (ladybug blood).  This study unequivocally showed that this was, in fact, not the case.  Indeed, you could shoot up Coccinella with high concentrations of harmonine, and they'd survive just fine.  However, after identifying the Nosema parasite using microscopy and nucleic acid analysis, the group was able to purify the pathogen from harlequin hemolymph and show that they were the causative agent of sickness and death in the Coccinella victims.  This exposes an entirely new set of questions regarding the biological relationships seen here, and there are several:

1. Nosema kills Coccinella septempunctata (a parasitic relationship).
2. Nosema requires a host, Harmonia axyridis, to survive. 
3. Nosema is not parasitic to Harmonia axyridis.
4. Harmonia axyridis uses Nosema to conquer new territory.

On its face, the paper clearly establishes point #1, as was discussed above.  This raises very interesteing, and perhaps more important, things to consider with respect to points 2-4, and harmonine may be controlling - at least in part - the entire situation.  Harmonine is a known antimicrobial, and it is found in high concentrations in the hemolymph of the harlequin ladybird, but is not present in the hemolymph of the defenseless Coccinella.  It was found in this report that the microsporidia, while living in the harlequin ladybird, were essentially deadbeats - metabolically inactive, non-disease causing cells - that were apparently just along for the ride.  The authors proposed the possibility that the high concentration of harmonine keeps these potential pathogens in check, but were careful to point out that Harmonia axyridis also produces unusually high levels of antimicorbial peptides.  So, to really get to the bottom of Nosema immunity in harlequin ladybirds, more studies will need to be conducted.  Nevertheless, the Harmonia beetles must be employing a system to harbor and control their microsporidian WMDs (points 2 & 3) until they are ready to deliver the deadly payload (point 4) on unsuspecting Coccinella.  The authors think that this system may be a glimpse at a common evolutionary mechanism of successful invasive species: if you amp up your immune system (with compounds like harmonine and antimicrobial peptides), you will be able to resist the new and strange pathogens you are bound to encounter in your new territory, while simultaneously introducing a deadly dose of pathogen to your soon-to-be conquered lands.  In a fascinating perspective piece that served as a lead-in to this article, Stuart Reynolds compares the Harmonia-Coccinella-Nosema relationship to the European-Native American-smallpox scenario that played out horrifically in the 16th century conquest of the Americas.  It may not be a pretty comparison, but it doesn't make it less biologically pertinent. 

An aphid - food for Harmonia

    In a Science and Tech highlight of this article in Chemical and Engineering News, another interesting layer of this story was introduced.  You see, the harlequin ladybird didn't diabolically opt to conquer Europe and the US.  We brought it here on purpose.  It turns out that Harmonia have a voracious appetite for aphids, tiny little insect pests that are notorious for eating, regurgitating on, transmitting diseases to, and otherwise raining hell upon important agricultural crops.  The harlequin ladybird will happily feast upon 100s of the insects a day, far more than the native Coccinella, making them an attractive, all-natural, non-chemical, "pesticide".  (What could possibly go wrong!?  Fast-forward to today...)  Since the Harmonia beetles are now taking over, is there a way to get the population back under control?  The secret may lie in the aphid itself - specifically the aphid gut, where a bacterial symbiont, Staphylococcus sciuri, lives and produces a chemical attractant for the ladybugs, one of which is called farnesene.  The ladybugs smell the farnesene, locate the aphids, and then chow down.  So now that the Harmonia population is out of control, folks are throwing around the idea of using farnesene as bait in ladybug traps!  Why not... what could possibly go wrong...!?

 

    Herein lies a great and complex system of multispecies symbioses.  Nosema is willing to live in the chemically hostile, harmonine laced blood of Harmonia axyridis until they can find a Coccinella septempunctata to infect.  Once the Coccinella die at the hands of Nosema, the harlequins can take over new turf.  Once they do that, they need something to eat, so they follow their noses - via a farnesene signal - to a tasty meal of aphids.  And here is the craziest symbiosis yet.  The symbiont (Staphylococcus sciuri) of the prey (the aphid) attracts the predator (Harmonia).  Essentially, "Hey, come eat my host!"  Like most complex host/microbe relationships, I wouldn't be surprised if there's more here - chemically - than meets the eye.  At any rate, these stories have exposed yet another example of macroscopic biology depending on microscopic biology, which ultimately relies on unique and specialized chemistry.  Am I a biased chemist talking here?  Probably, but it's still cool, isn't it?

- @EJDimise

 

You and 100 Trillion of Your Best Friends

"... we would do well to begin regarding the 
human body as 'an elaborate vessel optimized 
for the growth and spread of our microbial inhabitants.'"
- Dr. Justin Sonnenburg (Stanford Microbiology) quoted
in "Some of My Best Friends Are Germs" by Michael Pollan
of the New York Times 

    Has it come to your attention lately that you aren't pooping on a regular enough or comfortable enough basis?  Has Jamie Lee Curtis convinced you that the answers to all of your problems can be found in a cup of Activia yogurt?  What, not crazy about eating yogurt multiple times a day?  Maybe you need to swallow some Phillips' Colon Health, Bayer's somewhat expensive offering; no yogurt, just pop a pill!  These and other products promise to deliver "probiotics" that will tend to your less than perfect defecation situation.  Sounds good, right?  Take this stuff with your vitamins in the morning and it will straighten you out.  But what is the it that is doing the straightening?  Thanks to the New York Times Sunday Magazine this last weekend, you can learn all about it in one easily digestible article.  And that's great, because it has had the attention of the scientific community for a while now, and it's only becoming a hotter and hotter topic.

    In, "Some of My Best Friends Are Germs", Michael Pollan provides a great survey of the current state of research into the human microbiota - the trillions upon trillions of bacteria that live on you and in you - all the time.  But wait, aren't bacteria bad?  Don't they cause illness?  Aren't they to be feared and fought off with soaps, sanitizers, cleaning sprays, and antibiotics?  The answer is yes, but only sometimes, and just the troublemakers (read: pathogens - the disease causers).  It's true, whether you like it or not, you always have been, and always will be, populated by microbes, head to toe, inside and out.  And that's a good thing!  Your resident microbes help you digest food, they help keep your immune system up to snuff, and they help out-compete the disease causing bugs when they try to take over the turf of our friendly cohabitants.  The way research is moving, there's likely a study linking your microbial friends to the most mundane bodily functions.

"SYMBIOSIS - any close physical association between two

organisms, usually from different species.  This includes

mutualism, commensalism and parasitism.  The term originates

from the Greek words syn (together) and bio (life)."

Nature Reviews Microbiology, Felix Sommer & Fredrik Backhed,

2013, Vol. 11, 227-238.

     In this great piece by Pollan, we see the popular press providing an in depth look at the many aspects of health and modern research that is dedicated to understanding the bacterial symbionts that we live with.  In fact, in the scientific community, it is becoming less chic and more mundane to view the human body as an ecosystem unto itself - a veritable superorganism - composed of our human cells and no less than 10X that number in bacterial cells, representing many hundreds of different species.  Their presence can be weighed, literally, in pounds.  (Trying to shed some weight?  Sorry to say, but several of those pounds don't even belong to you.)  Hence, the title of this post.  You literally have 100 trillion "other", non-human, cells living in and on you.  And why not?  You're a great place to live.  Your exposed surfaces, inside and out, provide so many different habitats to adapt to.  Your immune system keeps the trouble makers at bay.  You provide food and water multiple times a day.  You are very efficient at delivering oxygen, at least to those bugs that bother to breath it in the first place.  For those that don't - and, by the way, most of your symbionts don't - most of your digestive tract is really great at keeping that poisonous gas far far away (yeah, oxygen is actually poisonous to them). 

    Symbiosis is at the center of this story.  Life often works better when different species live and interact with one another.  Our commensal bacteria - the ones that have something to gain from us, but we could care less about them - are often written off as "along for the ride".  This may be so, but the more we learn, the more difficult it is likely to become to draw the line between these free-riders and our bona fide mutualists - we provide a benefit for them and they return the favor.  These are the probiotics we hear so much about in TV commercials (though there are many many more that aren't included in your probiotic pills!).  Your body gives them food and shelter, and they make sure you poop on time and that the experience is as good as it can be.  Most of the time when we think about microbes, we think about the ones that cause disease - the pathogens - but they comprise a small yet horribly troublesome minority.  So when you think about you and your 100 trillion little friends, there's no need to be grossed out.  They need you and you need them.  Anyway, it's how life works, and there's no amount of Purell or penicillin that can change it.

We'll talk more about this soon,
- @EJDimise

Compounds from Bugs that Live on Other Bugs

"...social insects have evolved... beneficial 
associations with microbes that provide colonies 
with antimicrobial agents."
- C. Nirma, V. Eparvier, D. Stien

    Both the mainstream and scientific media frequently report on the urgency of discovering new antibiotics to combat the increasing health threat posed by antibiotic-resistant disease-causing bacteria.  The importance of finding new chemical compounds to treat fungal infections gets slightly less attention from the press, but is nevertheless very important.  The mid 20th century saw a boom in new antibiotic discovery, but as the century progressed, the usual sources of antibiotics - often bacteria and fungi from soils - appeared to be tapped out.  Researchers were growing new strains of bacteria, but kept "re-discovering" old compounds.  More recently, it has become evident that one way to discover new compounds is to search for antibiotic-producing bacteria from new and interesting environments.  A novel environment ought to provide a unique niche for the bacteria that inhabit it, resulting in the evolution of specialized chemical compounds that serve a role specific to that habitat.

    Enter the social insects.  Ants, wasps, and termites are three kinds of bugs that live together in large numbers within colonies of their own construction.  Just like human societies, different members play different roles, all working for the betterment of the community (OK, maybe not totally like human society...).  And also just like humans, the social insects have to be able to deal with the occasional infectious disease outbreak, with the major difference being that there are no members of their community specialized to write prescriptions or administer drugs.  Instead, the insects outsource the work of drug development and production to some powerful microbial allies.  Thus emerges a beautiful and fascinating mutualistic symbiosis - a mutually beneficial relationship between different species of living things - wherein the insects provide the microbes with a home and food and the microbes produce antibiotic or antifungal compounds to protect the insects from infection.  Essentially, the microbes play the role of the pharmaceutical chemist in the insect society.  This has previously been seen with ant and wasp colonies, for example.  Currently available as an advanced online publication in the Journal of Natural Products, C. Nirma, V. Eparvier and D. Stien report the discovery of N-methyltyroscherin from a fungus named Pseudoallescheria boydii that was isolated from a colony of the Amazonian termite Nasutitermes sp.  A slightly different version of the compound, called tyroscherin, had previously been discovered by Watanabe and coworkers by virtue of its toxicity towards breast cancer cells.

  

    The structure was determined using normal Nuclear Magnetic Resonance (NMR) and Mass Spectrometry (MS) based techniques.  The N-methyl group was assigned via chemical methylation of tyroscherin using methyl iodide.  Although the de-methyl analog of the compound (lacking a CH3 group on the N atom) was already known (Watanabe ref. above), what is most fortuitous about this study is that N-methyltyroscherin was isolated based on its ability to kill disease causing fungi.  Thus, although this may seem on the surface to harken back to our theme of "molecular re-discovery", a new and potentially useful function - antifungal activity - was revealed.  The termites would likely agree that the fungus-killing activity of N-methyltyroscherin is useful.  Perhaps more importantly, this study reveals yet again that the microbial members of social insect communities are likely to be a unique and useful source of chemical compounds that could help treat important infections, whether you are a human or a bug.

- @EJDimise