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TWiM regularly receives listener email with corrections, comments, suggestions for show topics, requests for clarification, and additional information. A selection of these is archived on this page.
TWiM & TWiV team,
Keep up the excellent work! I am an electronics engineer who has never studied biological sciences, but now in my 50's, I find your podcasts fascinating. I listen to episodes while working out - a good combination of mental & physical exercise ... thank you!
If you haven't already, please read this article in Scientific American, Dec 2013:
What I found interesting:
(1) Fungi have much larger genomes than bacteria or viruses, and this combined with sexual reproduction, gives them a larger arsenal for rapid adaptation.
(2) In the wild, the biggest predators for this fungus are amoebas, therefore it has developed protection mechanisms. If fungus ends up in humans, marcophages look very much like amoebas, and the fungus hitches a ride inside the macrophage, protected from the immune system until it can replicate and do damage.
Maybe you can do a show on virulent fungi? TWiF? Elio should be interested …
Here's an article which describes a TB drug that can be tweaked to target multiple disease-causing bacteria, and also ward off resistance by targeting multiple pathways in organisms.
[here is the paper: http://www.ncbi.nlm.nih.gov/pubmed/24568559]
I have a suggestion for a slightly out-of-the-way article that would be interesting to hear you analyze. I may be wrong but this article seems a little "primitive" and almost designed to continue an "alien origin" scenario. Despite that, this appears to be a genuine phenomenon in need of some specificity.
Personally, I'd love to learn that it is a stratospheric life form that got swept down to earth but I suspect that it is much more likely to be an oceanic life form swept up by a typhoon.
"Morphological and Molecular Analysis Calls for a Reappraisal of the Red Rain Cells of Kerala", Rajkumar Ganagappa, Mark J. Burchell, Stuart I Hogg, Current Microbiology (2014) 68: 192-198.
Regarding episode 72, I have to confess that it was one of those episodes that went, mostly, right over my head. Fortunately, I was saved by a listener's question regarding using beer as a vaccine medium against yeast infections. At least I know a little about beer.
First of all, I don't have any set answers for your querent. I do have some information that might help set the stage.
Yeasts are indeed used in the production of beer but comparing the basic beer yeast (Saccharomyces) with an infectious yeast like, say, Candida is lot like comparing the stomping power of the hyrax versus an elephant. They may be related but they're different beasts. That said, it might be possible and even practical to infect a beer wort with infectious yeasts and have them proliferate. If you could figure out some way to engineer a non-infectious version of that yeast, then I suppose that it might be possible to prime the immune system against infectious strains of that yeast. My guess is that the process is a lot tricker than with, say, polio or people would already be doing it. In addition, it would likely change the taste of the beer which might or might not be a good thing. Fermentation with non-Saccharomyces yeasts is being studied and does have some beneficial properties.
Then there is the question of actually getting the non-infectious infectious yeast or some significant immune-response-inducing part of it into the final product. If you lysed the yeasts and the appropriate vaccinating portions were soluble and smaller than the filter size, then that could work if you didn't denature it with the heating process first.
There might, however, be a simpler way. Europeans and Americans prefer their beer clear and non-yeasty so they heat it up and filter it. There is, however, a class of ancient beers called opaque or sour beers. These are simple beers which are not filtered (hence both yeasty and carbohydraty - a full meal at lunch time). They are also produced by the combined actions of yeasts and lactic acid bacteria (hence the sourness). For the most part, these beer are living beers, made in the home, and drunk within a day or two. They are best-known in Africa.
If the non-infectious infectious yeast could be supplied in a dormant state able to withstand, for instance, the hot african sun, (perhaps in a spray-dried sugar-yeast mix) then the yeast could be added to this sour beer, proliferate, and be drunk live to induce the immune response. Any taste differences would be much less noticeable in this product and it would fit in well and easily with the daily food consumption of some areas of the world.
Of course, if you could get it into a dormant state in sugar, then it might just be easier to distribute it in lollipops.
Interesting idea that probably won't work but it does lead to some interesting possibilities for integrating other medicinal microbes into diets.
Heard you mention that you had a competitor by the name of Goggles Optional, so being obsessive about science, I looked them up and tried listening to a few of their podcasts. It's reminiscent of TWIS and no real competition to your in depth science podcasting! Actually, it's a bit aggravating.
Hi, I have some comments regarding your dislike of some choice of words in the microbiology and molecular fields. This discussion should be able to fit both twiv and twim.
First you say that the term prokaryote is wrong, but i think the meaning that it has widely attached to the word is wrong. Usually people think of the word to mean without nucleus, and usually we think of these organisms coming before the eukaryotes (that is another discussion altogether) but i don't find this is correct.
there are two stems pre- and pro- , both of them can be meant to mean before, but in a different way. pre- would mean to me something that happens before the appearance of anything, so cells that appeared before eukaryotes would be prekaryotes. Now, prokaryote would mean to me protokaryote, which people may have chosen to shorten to prokaryote. This fits best with the description of these organisms, since they have a nucleiod or protonucleus, some sort of organization that is not quite a nucleus but it is there. so I think prokaryote fits best if it is explained right.
The other is your dislike to the expression "a protein is expressed in the X", you say that we shouldn't say this but instead the protein is translated and that a only a gene can be expressed, and i think this is wrong as well. A gene is transcribed, a protein is translated. What i mean by wrong is that the word expressed according to (http://dictionary.reference.com/browse/express) can signify to manifest. Following this, a gene is expressed when the DNA is copied and the specific bases of the gene are put together, an mRNA is expressed when the gene is transcribed by RNAPol, and a protein can be expressed when it is translated and when it has reached its final destination.
One other comment is how we are thought about bacteria. It is regarding the fact that bacteria are thought of archaic life forms, and while the first lifeforms might have resembled more single celled organisms, both the lineage that gave rise to humans is as old as that of bacteria since we should have the same primordial ancestor, unless there were independent primordial life forms formations. Everyone should be taught that any extant organism is as "modern" as any since all organisms have to adapt to the changing and current environment. So we can say that current bacteria are the best expression of their lineage, and not that being unicellular organisms they chose to not continue to innovate biologically.
A latest topic of discussion has been the state of science, and it occurred to me that while most people in science say that cutting down the number of PhDs and restructuring, it seems contradictory the fact that there are very active programs of highschoolers and minorities into science with the excuse that we need more scientists, what are your thoughts on this?
Thanks for your discussions, I'm always looking forward for each episode of the Twimvps and also urban agriculture.
Dear TWIM hosts,
I enjoyed episode 76, "Genetic biopixels and a pathogenic sweet tooth". I really enjoyed hearing about the course that Dr. Schaechter teaches and in particular the work his students did in developing the biosensor. I would like to recommend a couple of papers that a classmate in my differential equations class told me about. They can be found at Biomed Central and are open source which is great. The first is "Solving a Hamiltonian Path Problem with a bacterial computer", Jordan Baumgardner et al, J Biol. Engineering 2009, 3:11. The second was also published in the same journal, "Engineering bacteria to solve the Burnt Pancake Problem", Karmella A. Haynes et al, J. Biol. Engineering 2008,2:8.
A Hamiltonian Path Problem involves finding a route in a directed graph that starts at a node ( the beginning node) and visits all of the nodes in the graph exactly one time. Companies like FedEx solve these kinds of problems daily in determining the most economical and efficient routes for their delivery persons. Solutions to these types of problems are very complex and computationally intensive. The authors used E. coli that contained a Hin/hixC recombination system from S. typhimurium to randomly shuffle DNA segments as the computing system. They represented nodes in the graph as linked halves of two different genes encoding red or green fluorescent proteins. The bacterial populations displayed phenotypes that reflected random ordering of the edges of the graph. A Hamiltonian path was reported by fluorescing both red and green, resulting in yellow colonies. The Burnt Pancake Problem involves sorting a stack of distinct objects into proper order and orientation using the minimum number of manipulations. This paper describes a proof-of-concept of "in vivo" computation. volunteer
I enjoy so much listening to all of the TWIV, TWIM and TWIP podcasts. Since I've been working on my math degree I don't really have anyone to talk biology, biochemistry, etc with and I miss it. I'm down to the last 2 course before I'm finished, "Real Analysis" and "Probability". I'm hoping that I can find a lab to volunteer to help out in and I've been looking but so far no one has been too keen on having a 70 year old guy hanging out in the lab. Oh well, I have had been able to take some interesting breadth classes and just finished BIoInformatics. It was a trip to actually do sequence analysis and construct heat maps and run blasts! Anyone working on a machine to reverse aging I'm a willing volunteer.
Weather in Orange CA this week has been hot and dry. Today was 98 F, 37 C, 4% humidity, dew point 4 F, winds 20 - 30 mph. We have more of the same predicted for tomorrow and into the weekend. To windy to sail, to hot to just lay around at the beach, and with the winds the surf sucks. So good time to hole up inside in the air-conditioning and enjoy some episodes of TWIM.
Dr. Robert Kelley (Bob)
Dear TWiM team,
I am currently studying for my Biology degree second year exams in the UK and have listened to my first TWiM podcast today. Id like to quickly thank you as the zombie plant topic made perfect outside reading for my plant exam in a few days! I’m about to tackle the paper now.
I will continue listening for more interesting topics!
Thanks so much,
I'm giving a final exam right now, then flying out to Boston for ASMCUE/ASM. Maybe I will see some of you there!
I adore this concept of parasites/pathogens/symbionts altering the behavior of their hosts. Sounds like you all do, too!
Elio had some interesting ideas about viruses and behavior.
I know that folks are short on time, but the SF writer David Brin has an old story about this, called "The Giving Plague." It's online here:
Here you have a virus that causes altruistic behavior! It reminds me of the story (I'm sure it's not true) about the fellow who survives rabies. After he recovers, he is asked why he tried to bite people. He thinks for a moment and replies "It seemed like a good idea at the time."
Even though the virology may make you wince (I love SF, but the authors sometimes...well...play a little fast and loose with the actual world of science), I think you and your readers might enjoy Dave Brin's story.
I will be teaching a freshman writing course on symbioses and parasitism this Fall at my small liberal arts college, and you can rest assured I will be discussing this and related issues with them (including TWiP!). Happy for any suggestions or assistance out there!
As always, I so enjoy listening to your podcasts.
Mark O. Martin, Ph.D.
Department of Biology
University of Puget Sound
Dear Drs. Racaniello, Schaecter and Schmidt,
Thanks for the great episode on swabbing the environment around hospitals to check for prevalence of antibiotic resistant microbes. The idea of resistance spreading out from health care facilities seems very intuitive after hearing about it but I'd never thought of this before. It got me thinking about the number of other livestock farmers I know who have a family member that works in health care as well as helping on the farm. Could this be leading to increases in antibiotic resistant organisms in livestock or obviously vice versa?
I also found the practice of using antibiograms interesting. I had not known how doctors make decisions on which first course antibiotics to use. I will have to ask my veterinarian friends if there is an antibiogram equivalent in animal medicine.
Thanks again for another great episode and also for the TWIV bump for our AgSciToday podcast. It was much appreciated by Steph and I. Hope that nice late spring early summer weather has rolled in where you all are and that you have a few chances to get out and enjoy it. It's a balmy 18 C here in MN and finally not raining for once although it did just rain 1.25" the other day so we were due some decent weather. I'll also add a planting progress report despite that not being a typical feature on the show - we have around 60% of our hay fields seeded, 0% of our corn and 0% of our pasture ground interseeded. Usually those numbers would all be around 100% at this time. It's been another wet spring to say the least.
I first found TWiP, which led me to TWiV which led me here (Hey Vincent- get on Dickson for more TWiP episodes!). I love all three shows. I work as a research technician at a medical/veterinary entomology lab, and spend several hours of my day counting and identifying mosquitoes caught in traps in rice paddies (when I'm not sitting in a makeshift african hut...) Your podcasts have saved my sanity on multiple occasions! While I work closely with vectors of many of the parasites/pathogens you discuss, it is great to learn about the mechanisms of infection and disease, a subject which I feel I am slightly lacking in.
I just finished reading a couple books about the history and discovery of prions, and while I am not sure they can be classified as microbes, I would love to hear a show on the subject. I've become slightly obsessed! Keep up the great podcasting - I have several thousand more mosquitoes to go!
Look forward to all the TWi* discussions. Last months TWiM on Salmonella, with its reference to Typhoid Fever, reminded me of Bertolucci's twenty year old film masterpiece, The Sheltering Sky in which Port played by John Malkovich contracts Typhoid.
The story written by Paul Bowles, is interesting by itself in that Bowles lives in Tangiers - - where the story plays out - - and for his friendship with William Burroughs. Debra Winger is magnificent as Kit, Malkovich's wife. At the end of the film the viewer struggles with moral issues and whether or not Kit lost her sanity. Reading the book doesn't help.
The photography and the acting are superb. The progression of the Typhoid Fever in Port is accurately portrayed. The source of Port's infection is only hinted at. As one of the World's great films, the film was grossly underrated by film reviewers. Nevertheless, most people with a scientific background will appreciate the film and likely give it the highest ratings.
After listening to the second portion of TWiM 78, talking about the presence of gram-negative nosocomials around Brooklyn, I noticed a several people wearing scrubs while at lunch near a hospital in Houston, TX. Then a thought occured to me; disease! Disease everywhere! Might part of the problem, if these microbes are moving out from the hospital, be that they're carried from a day's worn clothes? I realize I'm asking to speculate, but think this might be a good consideration for hospital policy. Houston is currently 27 C at a low 50% humidity.
P.S. I finished my sandwich. It was a pastrami ruben.
"Ideas" with Paul Kennedy on the Canadian Broadcast Corp site recently ran a 54 min program about invasive species that included a short reference to rock snot. At the link find the title, "Bioinvasion: Attack of the Alien Species!," right-click (here or there) "Download Bioinvasion: Attack of the Alien Species!" to download it. I thought it, along with Prof Schmidt's comment about furry teeth, are a good intro to any program for kids about bio-films.
You have spoken before on TWiM about the potential risks of triclosan-resistant pathogens developing through its over use.
A recent open-access article from the the University of Michigan, published in mBio, looks like it may be worth a mention. The researchers conducted a study that examined the nasal passages of healthy adults, 41% of those sampled had traces of triclosan in their nasal secretions and the presence of triclosan in the secretions also correlated positively with nasal colonization by Staphylococcus aureus.
When grown in the presence of triclosan, Staphylococcus aureus was was found to be better able to attach to human proteins.
Additional experiments found that that rats exposed to triclosan were also more susceptible to nasal colonization by Staphylococcus aureus.
Del writes: (re: episode 77)
I was looking forward to this discussion, after hearing you hint about it in a previous podcast. As a practicing ID doc, I have been fascinated by the difference in pain induced by cellulitis from presumed or proven Staph or Strep infections. I see some patients whose pain resolves in a day or so after antibiotics, and some fewer patients who have a much more protracted course of pain, with tenderness to minimal touch or change in position. I have suspected that different isolates produce different toxins to explain these clinical differences, as my clinical judgement and experience argues that patient personality differences or 'pain thresholds' are simply not enough explanation for the variation I see. It also seems to "be there, or not be there," more distinctly than a simple continuum would explain. I am grateful for the basic science work being done in the field at present, and for your discussion.
Thanks to you all for the work you put into this podcast. I am learning every week, and finding connections in areas I would have never before considered.
All the best,
Del DeHart MD FACP
Associate Professor of Medicine
Michigan State University
I realize that this is a bit behind the times but I have two questions related to beta-lactamase (hope I got that right) form episode 6 - "Antibacterial Therapy with Bacteriophage".
1) We all know that the proliferation of bacterial resistance to antibiotics has a direct influence on infection recovery in humans and animals. What I'm pretty sure most people forget is that most antibiotics began their "careers" as part of microbial defense systems. Are you folks aware of any studies looking at the effects of increasing antibiotic resistance in environmental microbiomes? I would think that this human-induced change has got to be skewing microbial populations and interactions. Indeed, I'm having trouble even imagining what the impacts on the microbial and, therefore macrobial world might be.
2) During your discussion of beta-lactamase gene development in the environment, I thought of a possible counter that might help us continue to use beta-lactam antibiotics a little longer. Are you aware of any groups who are researching anti-beta-lactamase drugs that could be added to antibiotics allowing the beta-lactams to retain some effectiveness against resistant microbes? If someone developed a low-toxicity drug that had a significantly higher and, one would like, non-reversible affinity for beta-lactamase than beta-lactam. then one could, presumably, administer it along with beta-lactam and it would inactivate the beta-lactamase while leaving the beta-lactam free to do it's work. Such a system probably wouldn't be effective within a microbe but it should be effective for running interference at cell membranes.
Thanks for the interesting shows,
Dr. Schmidt's viral illness would be quite serious if there was consolidation as was asserted.
Consolidation refers to the gross characteristics of the lung when it turns from fluffy and pliant into solid as the air spaces become filled with cellular and proteinaceous exudates in pneumonias. Bad enough with bacteria and the antibiotic resistance problem; if it is a viral pneumonia, the treatment modalities are mostly supportive care.
It's been found that nasal carriage of Staphylococcus aureus is associated with increased risk of infection due to dispersal of SA from the nose while breathing and by nose-picking and not washing your hands. Some individuals are colonized with SA and are more prone to infection. Now there's a lot of research on how best to decolonize the nose of SA, because it survives antibiotics and quickly recolonizes the body. Mupirocin is typically used, but results are not good and resistance is likely. Seems to me that the aim of decolonization is stupid, since it is impossible to kill every last cell in and on the body, and even if you could there's plenty more in an individual's environment (which can survive for months on surfaces) to recolonize them anyway. Surely a better aim is to find out why some people do not become colonized and reproduce whatever they have in colonized people. Presumably, there's something about uncolonized peoples' immune systems and/or microbiomes which makes it hard for SA to become a problem. Maybe it's like the problems some people have with gut bacteria, where gut bacteria (shit) transplants have been shown to be effective. Maybe similar transplants of bacteria from the skin and/or nose of uncolonized individuals would be as effective for SA depopulation? It's a revolting idea, but no more disgusting than a poo-transplant!
Didn't recognize "Speak friend and enter!" and "NIN" ?!? What kind of barbarians do you invite on this show?!
Just kidding. TWIM # 73 was another amazing and wonderful podcast. I am only a geologist, so I can sometimes only vaguely hum along with yours, Michele's, and Michael's biochemistry arias. Nonetheless, TWIM is one of my favorite podcasts. When I listen on my walking commute from my home to my office in Seattle, I arrive smarter!. And grateful. I am always grateful after listening. Thank you!
Hello Twim team,
After reading the Pasteur lecture.
It seems that the idea of using the Pseudomonas aer, "coal & septicemia" came from a demonstration that the "bactericidie" in the blood from animal with anthrax ("sang charbonneux") was the only origin of the disease.
It was a point of contention in the fight against the last supporters of the spontaneous generation.
When use the "sang charbonneux" from death animals collected at a rendering facility was shown to kill rabbit, but without the presence of the bactericidie in the rabbit blood.
Pasteur was able to demonstrate that was due to contamination of the corps blood between the time of death & the collection, by the "virions" causing "septicemie". And that's was causing the destruction of the "coal virulence" (virulence charbonneuse). For him it was of therapeutic interest, but it seems he has never used it on human (only on guineapigs).
He has developed instead the vaccination against anthrax by selection of an attenuated variant.
By the way fun coincidence with Michael remarque to Elio about the LON & E coli turning to snakes.
In the same lecture Pasteur also observed that outside of the blood in septicemia killed guinea pigs, the bactericidies form long snake like filament "creeping, sinuous, and separating the blood cells as a snake separate the grass in the bushes".
I have never been as excited about a podcast as I was when I saw the title of the latest episode of TWIM (#51, Cave science with Hazel Barton), and it definitely did not disappoint! I listened to it twice right away. I'm trying to specialize in metagenomics, and I love caves and caving. If someone had asked me to design my dream TWIM, it would have been exactly like this. I had actually thought about suggesting the antibiotic resistance in cave microbes -paper for discussion, but I didn't think anyone else would find it interesting - probably because I come from a country with no proper caves, where you only get blank stares when you mention caving. Thank you so much for this episode!
I also have a question. Dr. Barton mentioned they have tried to do 454 sequencing, but apparently they haven't published anything about that yet? Do any of you know of any sequencing-based cave microbiome papers, particularly about "normal" karst caves? I've been unable to find anything on my own.
Thank you once more for the most awesome podcast episode ever,
(your subway-driving fan from Finland)
[I asked Hazel. She wrote:]
Yeah, unfortunately we've done a ton, but the papers aren't done.
Here's some good references though:
Making a living while starving in the dark: metagenomic insights into the energy dynamics of a carbonate cave. Ortiz et al, ISME J, 2013 (1-14).
Life in the dark: metagenomic evidence that a microbial slime community is driven by inorganic nitrogen metabolism. Tetu et al, ISME J, 2013(7), 1227-1236
One of the other podcasts I listen to is CBC Radios' Quirks and Quarks. I find it always interesting, and often profound.
The segment I was just blown away by was this one: http://www.cbc.ca/quirks/2014/03/15/2014-03-15-1/.
It put together many of the keywords I have heard from your podcasts, and added a new one- "host-defence peptides".
It even made me consider what are "biofilms", a term I have heard you use but never thought significant.
So. as something different, would you consider reviewing this radio segment as you do a paper? You could bring into the discussion regular papers that are relevant, too.
And, a final question, what ARE biofilms and what are their significance?
Thanks for doing what you do (even though I understand 25% of it).
Dear Dr. Racaniello,
In your latest TWIM (#72?), I heard you wonder out loud why a virus such as polio managed just fine without virulence whereas one such as norovirus seemed to relish it.
Might the answer have something to do with the work of Dr. Graham Rook at University College, London? His Old Friends hypothesis (a re-formulated hygiene hypothesis) distinguishes between microbes that inhabited hunter-gatherer hominids before we lived in cities (like hepatitis A and H/ pylori, which protect against allergies/asthma/autoimmune diseases) and those more recently evolved to infect humans living in sufficient population densities to support epidemics (like measles, which does NOT protect against a/a/a).
Maybe virulence evolved as an adaptation to crowds?
Just a thought,
P.S. My mother's family has the name Ianiello, which means--maybe 500 years ago or so--our families may have known each other. Just another thought.
I just got around to listening to episode 12 “Photothermal Nanoblades and Genome Engineering”. Your comment that it would need to be scaled up before it was practical for some of you to use intrigued me. I did a quick Google search and I didn’t see any recent articles addressing scaling up the process though I’m sure that there are groups working on it. In my own amateur fashion, I’d like to suggest an approach to such a process.
I believe that technology applying microfluidic flow cells to single cell streaming is reasonably well-developed currently and improving all the time. If you installed the insertion capillary tube into a microfluidic flow cell and added a photo-sensitive trigger to the capillary tube, then it should be fairly practical to mass insert bubbles of materials into cells fed through the flow cell and collected on the other side. Although flow cells would, most likely be tailored to particular cell sizes, it might be possible to make the insertion point slightly generic (i.e., slightly larger) by using laser forceps to automatically direct and immobilize the cells during insertion.
The main restriction would likely be finding a cell culture that would support the microbe in question with sufficiently low viscosity so as to flow through the cell with ease while prevented undesirable cellular effects (such as clumping or lysing) while the cells are waiting to inject. High cell density at the input reservoir could probably be achieved by centrifuging the initial culture then micro-diluting up the resulting pellet.
Although this may not prove to be the most efficient way to mass-process cells, I do see another potential advantage in using a microflow cell. With additional solvent input channels before and after the insertion point it might be possible to chemically manipulate the cell’s immediate environment for periods of milliseconds to seconds in such a way as to make them momentarily more amenable to insertion without long-term consequences to cell survival. Such manipulations would be easy to study, cell species by species in these flow cells until a manual of cells and optimum manipulation conditions could be generated.
Anyway, thanks again for the fascinating look at research that I don’t get a chance to look at very closely often (or understand).
25c in Palo Alto, California.
I think humans (us) are so enthralled by the idea and stories of symbiosis because we see it as unusual. Even though our world is full of symbionts, life relies on symbiosis, we are blind to it most of the time until extraordinary examples are pointed out to us. These make great examples of the "precision", depth and complexity of evolution and of life.
It's easiest to make a headline in our mind when we see "small" examples of tightly woven systems than to keep the whole ecosystem of metabolism in our minds.
Thanks as always for the amazing education and entrainment,
Tarwin - Developer / Designer
Just wanted to make a point about organelles vs symbionts.
You suggested that the difference might be that if all cells in the organism have it then it is an organelle; however not all plant cells have chloroplasts.
Might the difference be just how high up the taxonomic tree the symbiosis goes?
TWIM 74, about 26 minutes in.
the difference between enbosymbionts and organelles is:
1. WHEN it happened and
2. how much it increased fitness.
the endosymbioses that resulted in mitochondria and chloroplasts happened many billion years ago and apparently conferred selective advantage to recipients cells (future eukaryotes) over nonrecipients (future prokaryotes). we only have to wait a few billion years to see if the same is true for the endosymbionts discussed.
Dear Twim team,
Thank you for all the great episodes; I'm loving every single one of them!
I'm very pleased to hear more discussions on fungi-related subjects, being from Lithuania myself, I wait every year for the mushroom season, so that I could go and collect them. We even have national competitions for who can collect the largest number of mushrooms or find the biggest variety of them :)
On the mushroomy note, I would like to draw your attention on a recent paper describing the first fully sequenced genome of arbuscular mycorrhizal fungus, I think it's worth discussing.
"Genome of an arbuscular mycorrhizal fungus provides insight into the oldest plant symbiosis" http://www.pnas.org/content/110/50/20117.full .
The second paper that caught my eye, was describes how S. aureus "intentionally" induces pain through neurone stimulation, in order to suppress immune system's response to the infection. I think it very much makes one think about systemic control of the immune system and, as ever, the unexpected ways that bacteria have evolved to evade it.
"Bacteria activate sensory neurons that modulate pain and inflammation"http://www.nature.com/nature/journal/v501/n7465/full/nature12479.html
Hello TWiMsters! I recently discovered the trifecta that is the TWi series, and now I can’t get enough of your discussions of all things micro. For graduate students like myself, keeping up with the scientific literature can all too easily become just a means for cramming information into our brains that we feel we “should” know. Not only do your shows keep my mind stimulated and expose me to scientific papers that I might not otherwise read, but the informal and enthusiastic nature of the programs are just the slap in the face I need to crawl out from under the stack of papers, and remind me that I actually love to learn about science and to think about the various implications that a particular finding or result might have. After listening to your conversational discussion format and your fantastic insights that tie together the biology of the organism (or virus – are viruses organisms?) with the environment, host, experimental techniques etc., I am finding new clarity in the way that I think about scientific problems and evaluate scientific papers. I can’t commend you enough for what you do. Formal presentations of scientific findings are a dime a dozen - listening to world-class scientists “chat” amongst themselves about current topics in microbiology is an invaluable resource that few people really ever get a chance to do, until now. THANK YOU!
On a scientific note, I was recently listening to TWIM #43 and your discussion on the stable formation of caveolae in in E. coli. It was mentioned that it had previously been thought that stable caveolae formation in eukaryotic cells requires cholesterol, to which Michael replied that “there is [no cholesterol] in our friends the bacteria”. Although this was and is true in the context of E. coli and the paper’s findings, I think it is worth pointing out that there are several described examples of free cholesterol and cholesterol-containing glycolipids in bacterial outer membranes – namely in Helicobacter, Mycoplasma, Ehrlichia, Anaplasma, Brachyspira, and Borrelia species. In Borrelia burgdorferi, cholesterol containing compounds have been shown to form organized lipid rafts both in culture and in animal-derived organisms, with physical properties similar to that in eukaryotic membranes. A recent paper published in PLOS Pathogens in January of 2013 utilized fluorescent and radiolabeled cholesterol to demonstrate that B. burgdorferi extracts cholesterol from the plasma membrane of eukaryotic cells, and that prokaryotic cholesterol-glycolipids can be transferred to epithelial cell membranes through both a contact dependent mechanism (using direct attachment) and a contact independent method (through released outer membrane vesicles). I highly recommend looking in to this story (maybe as a TWIM topic?), as it provides a shift in the thinking about lipid rafts, expanding their biological relevance to prokaryotes, and could have implications for the evolution of the eukaryotic cell membrane structure. Additionally, transfer of antigenic lipids from bacteria to host cells could play a role in pathogenesis - having multiple consequences for the host immune response and potentially contributing to heightened inflammation, and perhaps even direct targeting of the cells themselves by immune effectors. I’ve provided the citations and Pubmed links to a few papers on the B. burgdorferi story below, but also recommend digging into the story for H. pylori.
I’ve rambled enough for now, I should run – I’ve got to get to iTunes to write a good review or two…
LaRocca TJ, Crowley JT, Cusack BJ, Pathak P, Benach J, et al. (2010) Cholesterol lipids of Borrelia burgdorferi form lipid rafts and are required for the bactericidal activity of a complement-independent antibody. Cell Host Microbe 8: 331–342.http://www.ncbi.nlm.nih.gov/pubmed/20951967/
Crowley JT, Toledo AM, LaRocca TJ, Coleman JL, London E, et al. (2013) Lipid Exchange between Borrelia burgdorferi and Host Cells. PLoS Pathog 9(1): e1003109. http://www.ncbi.nlm.nih.gov/pubmed/23326230
Department of Veterinary Microbiology and Pathology
Washington State University
“The truth is incontrovertible. Malice may attack it, ignorance may deride it, but in the end, there it is.”
- Winston Churchill
During TWiM#46 it was discussed that spores are able to sense peptidoglycan that has been shed by other bacteria. I would like to know, are the spores able to differentiate between the peptidoglycan that is shed by growing bacterial neighbours and the peptidoglycan lost during lysis.
University of Victoria, BC, Canada
Jon Dworkin answers:
Excellent question! If this any indication, your listeners are really paying attention!
Spores are able to differentiate between peptidoglycan fragments generated from growth and those generated by lysis since these processes in fact produce different PG fragments. Those resulting from lysis are thought to be produced largely by lytic transglycosylases which generate PG fragments containing an anhydro (non-reducing) end, whereas fragments produced in growth do not contain this group. In collaboration with Shariar Mobashey, an excellent PG chemist at Notre Dame, we demonstrated that synthetic muropeptides containing an anhydro group do not stimulate growth but synthetic muropeptides that lack this group are able to stimulate spore germination. Thus, spores can differentiate between cells in the milieu that are lysing versus those that are growing.
Finally, I can send an intelligent comment (re: TWiM #51) ...
Dear esteemed doctors,
I am sincere in this appellation as one of your many listeners who depend upon your unbiased fact finding and enlightening delivery to both educate and debunk with the latest information.
You have often remarked on the contradiction of the numerous pathogenic bacteria in common public areas while you as individuals do not feel endangered. In commenting on a letter read on TWIM 72 you mentioned the "cloud" of toilet-originating microbes created with every flush, yet a lack of evidence of resulting disease. It comes up also in regular mentions of door knobs, railings, phones and other public conveniences. Often this is attributed to the protection provided by a healthy immune system.
My question is whether the mechanism of microbial balance achieved in the human microbiome should be applied to understanding the forces at work in these external environments. Might our Linus-like microbial cloud function like the often mischaracterized schmutzdecke which purifies much of our drinking water?
Analyzing the potential health affects of environmental microbes apart from the greater human and environmental microbiomes seems a bit like analyzing the path of stars orbiting the earth. Am I wrong to assume that the microbial community of the toilet, room air, hands, nose and mouth have a significant impact on the danger from most of the individual microbes within those communities?
It's 252 degrees absolute, (or minus cold aught six on the Retrograde scale) this morning in sunny Connecticut.
A sincere thanks to you all for your dedication to TWIX. The world is listening to you more intently every day, and better for it.