How animals in the hydrothermal vent can live with the high temperature.

Davin C. Enigl enigl at aol.com
Sun Mar 31 16:50:50 EST 2002

On 31 Mar 2002 11:40:54 -0800, rgregoryclark at yahoo.com (Robert Clark)

>  This spore retains 10% viability even after heating for 2.5 hours at
>150 C. 

So, that would be a 150 minute D-value at 150C.  It would be even more
interesting to know the z-value because then you could predict the
survival time at 600C and 1000C, there *will* be some sort of time
value, you might need 10^9 to measure it however.

>Then much higher survival would be expected at only 5 to 15

Well, sure witha D-value of 150, this is a merely a first order
reaction.  Of course there is an initial non-linear bump, explained by
A. Douglas King's work at the USDA.

>Given the much higher survivability of this spore than other
>bacteria it would be expected some fraction could survive exposure 370
>C for several minutes.

Sure, that merely depends on initial counts.  That is my initial
point, the D-value is more important than the temperature.

> In the refs. I cited in the post there was still an unresolved
>question of how the spores were able to survive these high

I guess they have not heard of D-value -- it is only about 120 years
old (Hunt Brothers meat canning validation used to convince the US
government safe commercial canning could take place. I was a senior
microbiologist at Hunt's).   

>One possibility could be the unusual honeycombed coat
>possessed by the spore.

The standard explanation is just that we have a thermodynamic
first-order reaction.  The interesting thing is the growth curve:  

1) Lag, 
2) log-growth, 
3) stationary, then 
4) log-death phase.  

Bacteria live and die logarithmically.  In fact, the log death happens
with thing other than heat.  Cosmetic (chemical) preservatives also
kill with a characteristically linear logarithmic decline.  There are
some rather interesting causes for exceptions to this, however.

>If the interior of the spore is encased in
>this coat shaped somewhat like a buckyball then heat might be
>communicated to the interior only through the thin sides of the coat,

Interesting, but there is no experimental data supporting this as far
as I know.  When we did spore clumping  experiments and looked at SEMs
of the spore coat destruction, there was no significant effect on the
D-values from this factor.  The IR radiation seemed to penetrate
straight through even the biggest clumps we tested.  The inner cells
did not have a lower probability to die over the ones on the outside
of the clump, as far as we could tell.  This may not have been good
enough method to tell, however.  

>thus limiting the amount of heat communicated to the interior.
> I'm thinking here of the case for example of space shuttle tiles that
>can be held at the edges while white hot at the interior.

Ok, that is dry.  We tested most things wet, that is a big difference
-- deep sea vents are presumably wet in this ng thread.  Dry heat
always takes longer.  And, we had this discussion a few months ago on
heating anthrax spores with microwaves -- heat-loss calculations are
needed.  It is amazing how much energy is needed to heat something up
when it is "dry" and not touching anything else.


More information about the Microbio mailing list

Send comments to us at biosci-help [At] net.bio.net