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Wondering about the Mechanics of Bacterial Death

0. I was idly thinking about the current H1N1 flue pandemic, and the following things occurred to me. Please note, I know very little about this subject matter. So, please consider descriptions in the following as, at best, tentative.

1. There is a basic difference between how alcohol kills viruses and how salt-water kills bacteria. [Alcohol is used in the hand-cleaners they use in hospitals. Girgling with salt-water is the first line of defense (and an unexpectedly highly effective one) which is well known for millenia.]

But the mechanisms involved are different.

Alcohol, I guess, oxidizes organic material that comes in physical contact with it. When the "organic material" is a virus, the extent of the oxidation is sufficient that the virus gets completely burnt. (BTW, is oxidation the reason why you see white patch on your hand after handling alcohol or kerosene?)

On the other hand, in the case of bacteria in salt-water, osmotic pressure results in diffusion of water molecules across the permeable bacterium skin. As water moves inside, it bloats the bacterium. Eventually, the bacterium becomes so bloated that, like an inflated baloon, its skin cannot take the mechanical stress, and so it bursts open. I don't know, but this is what I had heard from a biophysicist friend once. (And, the entry for "cytolysis" on Wikipedia tells something similar.) If the explanation is correct, then what ultimately kills bacteria in salt-water is the mechanical stress.

A few questions:

(i) By any chance, is there any way that not just bacteria but also viruses could get killed due to mechanical stress?

One way I imagine it might come to happen is if the van der Waals forces cause a few surrounding particles to get a grip on the skin of the virus, and then if these particles, for any reason, move across sufficiently differently that high stresses get induced within the virus skin/body. ... Yet, one has never heard of such a mechanism of killing viruses. The action almost always is chemical in nature. (Or radiational. Radiation gets absorbed and heats up the virus body, or it can cause breakages in the RNA strands). Is the virus skin too tough, and the relevant van der Waals forces too weak, or the gradients in the shear forces in the surrounding fluid too small, that the virus may break open mechanically? Any idea?

(ii) Has anyone done any modeling, preferably computational modeling, of the phenomenon of bloating of bactria? Also: Can the model explain why bacteria do survive in sea-water? How about fruit juices?

Comments

Dear Kaushik,

Hmmm.... Looks like Prof. Subra Suresh has been going into many interdisciplinary researches!

... But, Kaushik, mine was an idle wondering. Partly, an amusing take, really speaking... After all, what good would such a nanomechanical  model of a bacterium do? What's the point of modeling its various stages of bloating? Predict that the poor thing would burst open? (LOL!)

On a more serious note, designer-drug molecules and their surface interactions with viruses/bacteria are one thing... But this one was quite another! (LOL!!)

(But I did give a hint about it, didn't I? I did ask whether the nano-mechanical model would predict the survival of a bacterium in sea-water :) )

[Never mind!]

Cheers,

Ajit

PS: If someone has actually done up some model like that, then I would have to nominate it for an Ig-Nobel!

U r thinking is very innovative and a very fresh idea, i feel very exiting to read what u say. I became ur fan now! gr8 and beautifull mind ur havng!!!!

If you want me to notice that your profile ID carries parts such as "Shubham" (Sanskrit for auspicious), SRK (acronymn for Shah Rukh Khan?), etc., then sure, I did notice these.

But what I noticed didn't stop only at that... I also noticed that you would be known to many mechanicians from the USA, perhaps also a few (or all) of them from this page.

Welcome to iMechanica, shall I say to you! (And how many seconds did it take for you to become a posting member here? (And no, I am not interested in your answer/replies.))

-- Ajit R. Jadhav

Jayadeep U. B.'s picture

Hi Ajit,

I think the following statement given in your original post is not correct:

"On the other hand, in the case of bacteria in salt-water, osmotic
pressure results in diffusion of water molecules across the permeable
bacterium skin. As water moves inside, it bloats the bacterium.
Eventually, the bacterium becomes so bloated that, like an inflated
baloon, its skin cannot take the mechanical stress, and so it bursts
open. I don't know, but this is what I had heard from a biophysicist
friend once. (And, the entry for "cytolysis" on Wikipedia tells
something similar.) If the explanation is correct, then what ultimately
kills bacteria in salt-water is the mechanical stress."

In salt water, the bacteria should loss water due to osmosis, and dry up, rather than bloat and explode, which might happen in fresh water.  It seems that organisms have some active mechanisms to prevent the happening of such things.  These might make the studies (modeling?) more complicated...

Regards,

Jayadeep

 

But I distinctly remember that that's what a biophysicist friend had happened to tell us one day... Who knows... Referring to your link, both hypo and hyper tonicities are possible, you know...

And, regarding the hardiness of certain bacteria / microorganisms, the Discovery channel once (actually, many times) showed how some of them manage to live right deep down on ocean floors, right next to those live underwater volcanoes (i.e. in the regions of fairly high temperatures). One part of their hardiness is that they are anerobic. In fact, they thrive at relatively higher temperatures. And then, there is some evidence that microorganisms manage to survive interstellar spaces too (including high radiation, extreme temperature variations, etc.)... 

But if you are going to do a micromechanical modeling of bacterial bloating+bursting or drying+possible implosion, I still feel, the effort would deserve nothing less than an Ig-Nobel!

k1suthar's picture

Deaar Ajit:

This can be solved using FEA, Provided you know the mechanical characteristic of the membrane. 

Any osmosis can be defined by two equations one is Nernst Planck (along with the reaction term) 
and second one is Poisson's equation, depend on electrical interaction between
molecules and membrane, the Poisson's equation can be used.

Solving these two equations will give you concentration difference, which
will be driving force for expansion. If you know physical properties of
the membrane, you can apply mechanical field equation and estimate the required
osmotic pressure to break the membrane.

At the end, you are talking about the external solution to be so
concentrated that will rapidly exchange the ions and break the membrane.

This is about becteria. 

 

For the virus, I am limited by my knowledge. I do not think they have any membrane, (which can be penetrated) other than actively binding surface (multiplies with DNA type generation). It would be a molecular dynamics problem.

Dear Kamlesh,

1. My comments in this point roughly follow the order of the various points you make

Yes, FEA can be used for nano/micro-modeling of the mechanical response of membranes. Perhaps, also for nonlinear vibrations that arise as it bursts. ... I still maintain, it all would qualify for an Ig-Nobel.

Probably, Poisson's would be too simplistic for higher concentrations.

What, precisely, would constitute an MD problem here? Mechanical?

2. Since this is the third time that I am emphasizing the light nature of my initial comment, as exemplified by my above references to the Ig-Nobel, but nevertheless have been drawn into serious topics again and again, allow me some real seriousness here.

2.1 My intial comment does not deny that there may be a lot of issues that are fine for serious research when it comes to membranes, diffusion, fracture, etc.

A lot of chemistry and chemical engineering is concerned with membranes and diffusion. As to bio-chemistry, Bert Sakmann and Erwin Neher won the 1991 Nobel in Physiology & Medicine for their work inter alia on "the function of single ion channels in cells;" see Wiki. Certainly, they did not deserve the Ig-Nobel, IMHO.

2.2 Since they have already diffracted buckyballs (e.g. see here), I wonder if they also diffract viruses and/or bacteria these days. No, seriously. I am seriously interested in the wave-particle duality, and have had something to say about it (viz. its resolution). As to the large "clusters" of molecules like viruses and bacteria, I gather from the relevant Wiki page that quantum decoherence could form one of important motivations for people to seriously pursue such a line of research. Viruses, I suppose, do have definite crystal structures.

So, if not Schrodinger's cat, it would at least be Schrodinger's virus/bacterium!!

[And, once again, noticing what serious Nobel laureates themselves, in the course of their serious physics research (not to mention everyone else in every other way) have had to say on this matter, I can't now stop beginning to LOL!]

Light... That, was the tone of the matter, initially, here.

k1suthar's picture

Hi,

Well FEA works, so does Poisson's equation for any concentration; you can also try boltzman equation for near boundary potential. 

Sorry for not getting your LIGHT tone. It would have saved my time.

By the way, Bert Sakmann and Erwin Neher's research have solved many problem (almost all) of biology related to ion transport, which has lead to revolutionary drug design.

Regards,

 

 

 

FEA works halfway through for Poisson's equation worse (in a more complicated manner) than FDM does. (Why do I say half-way? Consider the ansatz-dependent behavior for gradients fundamentally built into FEM, but not in FDM, in case you haven't noticed it (and more likely: have not been taught) already). And, let me reiterate my reservations for Poisson's in case there are interactions.

Never feel too sorry for it; I am not unhappy that my reply helps you save your time in future at least.

That was one of the consequent reasons why I thought they certainly didn't deserve the Ig-Nobel (which, incidentally, was not awarded to them)... Might as well add, among the things more core to their research, it showed, e.g., why people with BP are well advised to eat less salt and more bananas---banana is rich in K (potassium), and so, eating it shifts the dynamic balance towards lesser Na+, and that, in turn, helps control BP. ... Also, explaining the athlete's high... A whole mind-boggling range of phenomena.... In a world where insularity in science gets rewarded, the committee did themselves a favor in awarding them the Nobel. 

And, before closing, let me remind you: Do save your time! (LOL!)

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