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Analysis for Life

Todd Stevens tstevens at oneworld.owt.com
Thu May 18 18:04:39 EST 2000

No. Most bacteria will not grow on a simple plate of rich medium.  Besides, if it
were that simple, what would be the point of the exhibit?

I guess the answer would really depend on what point you ARE trying to get across,
and who the target audience is.

Some off-the-cuff examples:

A simple illustration of the difficulty of detecting microorganisms might be a
microscopic view (even a photograph) of a soil sample.  You see a lot of
strange-looking stuff, but you can't really tell what it is.  A side-by-side view
of the same sample (that has been stained with a specific fluorescent stain) under
epifluorescent illumination shows where the bacteria were "hiding' in the first

Another point that might be worth illustrating is that there are many different
kinds of metabolism (to kids: adaptations to different worlds, maybe.) and you
only see what you look for.  A sample that contains only E.coli, or the like
would yield colonies on the previously mentioned agar plates, while a sample that
contains far greater numbers of Clostridium or a Methanogen, for instance, would
appear "sterile."  Yet when the same samples are subjected to a different test
(e.g. anaerobic grownth) the results would be completely different.  You have to
learn something about the environment that the sample came from, guess what kind
of metabolism might be possible there, and design tests accordingly.

Another point, ala Viking,  or ALH84001, would be that  organisms make a living by
chemistry, and one must be careful to determine that non-biological chemistry
doesn't give the same result.  (i.e. you have to use controls.)  For example,
samples with a lot of reduced iron (or say highly oxidized iron, & peroxides, as
per Viking) will react with some culture media in ways similar to microorganisms.
One could probably think up a colorimetric reaction that would show this.

"Hiranya S. Roychowdhury" wrote:

> You don't need "elaborate" "biochemical" analyses for this. A simple LB
> and/or McConkey's (sp?) plate should be enough to show the presence or
> absence of bacterial population. To show presence of fungi, you need a
> general VM type medium (low pH). I am not sure about protozoans.
> Whether ET life behaves the same way is another matter, and is anybody's guess.
> At 03:44 PM 5/18/00 +0100, Martin Weiss wrote:
> >
> >       Has anyone developed or know of straight forward activities
> >with which students can use to differentiate between microbial life
> >in sterile and non sterile soil with out involving elaborate
> >biochemical analysis that I might be able to adapt for a museum
> >exhibition on detection of Extraterrestrial Life?
> >
> >Cheers,
> >
> >Martin
> >
> >
> >
> >Sorry for the cross posting.
> >
> >
> >
> >Martin Weiss, Ph.D.
> >Director of Biology
> >New York Hall of Science
> >47-01 111th Street
> >Flushing Meadows-Corona Park
> >New York 11368
> >voice mail 718 699 0005 x 356
> >facsimile  718 699 1341
> >mweiss at nyhallsci.org
> >http://www,nyhallsci.org
> >---
> >
> Dr. Hiranya Sankar Roychowdhury
> New Mexico State University
> Las Cruces, NM 88003
> Ph. (505) 646-5785
> hroychow at nmsu.edu
> ---

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