AN INQUIRY INVESTIGATION INTO THE BIODIVERSITY
I, along with (from left to right) Susan Smer, Young Chun and Kelly
Jewett, tried to isolate extremophilic bacteria from the environment.
Extremophiles are organisms
that live in conditions that we would consider harsh. High salinity
(approaching saturation), temperatures above 55 C, and pH below 4 are all
environments in which extremophiles may thrive. Scientists have isolated
extremophiles from harsh environments like Old Faithful and "Black Smokers,"
sulfur vents deep in the ocean and volcanoes.
Yellowstone National Park
Black Smoker, Juan de Fuca Ridge
Dr. Michael Perfit, University of Florida
However, do we have to go to
exotic locations to see extremophiles? We cultured materials that
may provide extreme microhabitats and tried to grow these organisms in
enriched nutrient broth. We cultured ham and bologna which are both
high in salt, milk that has been pasteurized (possibly leaving thermophilic
organisms after pasteurization), hot tap water, vinegar, skin (where sweat
makes it a saline environment), and soil to see if extremophiles were present.
Extremophiles and there products
have a lot of scientific and industrial applications. For instance,
extremophiles affected OJ Simpson's life: PCR, a technique used in
DNA fingerprinting, relies on Taq polymerase, which is an enzyme
derived from thermophilic bacteria. Detergents, used at high temperatures,
may also benefit from enzymes found in thermophilic organisms.
We prepared nutrient broth and enriched the broth
to make solutions of 15% salinity using NaCl to culture halophiles, and
high acidity using HCl and titrated to pH 3 to culture acidophiles.
We then swabbed each sample with a sterile swab and inoculated the various
broths with swabs from each sample. We incubated acid and saline
broth at room temperature for 72 hours. We also inoculated unenriched
nutrient broth and incubated it at 55 C for 72 hours to culture thermophiles.
We performed a Gram stain analysis on each culture to determine the presence
We did see evidence of bacterial
growth in extreme environments. We saw growth in an acidic environment
in cultures from milk, soil, and ham. We saw growth in a saline environment
in cultures from skin, and we saw growth at 55 C in cultures from ham and
milk. Click on the pictures below to see the full size image.
Ham culture in acid medium
Ham culture incubated at 55 C
Milk culture incubated at 55 C
We did find some evidence
of extremophiles in our samples. However, our results were not what
we expected. We expected to see halophiles growing on ham and bologna,
because they are saline environments. We also expected to see some
thermophiles growing in tap water, which can sit in a storage tank for
long periods of time.
The incubator we used did
not maintain 55 C, but usually settled at 49-51 C. This temperature
range will promote mesophilic (normal range) bacterial growth and, therefore,
the bacteria we saw may not have been thermophilic. An additional
difficulty we had was that, when heat fixing the saline enriched samples
for Gram staining, the salt crystallized and obstructed our view under
the microscope. We might have had more success enriching agar plates
To continue our investigation
of extremophiles, the next question that we may want to answer is, "What
is growing in the cultures?" While the Gram stain may help up identify
the organisms, it is in no way a definitive indicator. In order to
do so, we would have to isolate the bacteria and grow a pure culture.
Once we have a pure culture, we would perform a battery of biochemical
tests, such as tests for various sugar digestion, or casein digestion.
I see many ways of integrating
this activity into a general biology class. First, any microbiology
activity must emphasize basic lab techniques, such as measuring, lab safety,
following directions, formulating hypotheses and observation.
It will also introduce students to more sophisticated lab procedures, like
aseptic technique and Gram staining.
By having students conduct
an investigation like this, they will develop their own understanding of
microbial diversity. While microbial diversity is not a common unit
in high school general biology classes, unity and diversity among species
is. By studying the rain forest, a popular theme among high school
students, as well as other biomes, students may understand biodiversity.
But, what better way for them to learn than by observation and self discovery?
If they can see that some organisms can live in one environment but not
another or that some can digest a sugar but another cannot, they
have shown themselves biodiversity. Of course, after such a project,
we could have a discussion about the why and how of biodiversity, incorporating
I would not begin a microbiology
unit with this lab. I would introduce my students to microbiology
with a much more simple investigation, like rubbing their fingers on agar
to see bacterial growth. I would also have students stain known cultures
to train them to look at stained organisms.
back to top
Woodrow Wilson National Fellowship Foundation
CN 5281, Princeton NJ 08543-5281 - Tel:(609)452-7007 - Fax:(609)452-0066
Technical contact: firstname.lastname@example.org