Bob wrote:
> On Wed, 9 Feb 2011 22:14:55 -0800, Lina Dances <lsc.dancing from gmail.com>
> wrote:
>>> Hi
>> I am in grade 10 and would like to do a science fair experiment using agar
>> dishes and a simple culture from staph epidermidis and have strong magnets
>> (north and south) in each side of the petri dish, to see if the bacteria
>> chooses to align with the magnets.
>> I am unsure if this will show any changes at all, please tell me if this is
>> not a good idea, and if there are other ideas to see effects of the magnetic
>> fields in cellular life.
>> Thank you!!!
>> Lina
> There are some very interesting bacteria that are known to respond to
> magnetic field. Google on
> magnetic bacteria
> and look around. There is a Wikipedia article, perhaps to start. But
> explore.
The magnetotactics can be difficult to culture...and may be hard
for a 10 grade student to source. (To say nothing of expensive...
last time I purchased from the ATCC the Matsunaga Magnetospi-
rillum strain was over $200/specimen.)
> I suspect you can isolate some -- if you have access to some good mud.
> Then you could compare with "ordinary" bacteria.
They're not easily isolated out of soil though, given that they
lurk at the oxic-anoxic transition zone...which, depending on the
soil, can be fairly far down (depending on the depth of the humic
layer). The odds would be better in a water column, but again,
such may be beyond the financial and instrumental reach of a
high school student. (And there's always the risk, when "culturing
wild" of also ending up with bugs that are less than user-friendly
from a biosafety standpoint.)
Lina doesn't give a location, but if she's in the Northern Hemi-
sphere...particularly if she's in the American middle-west, field
collection might be problematic right now given temperatures
and/or snow and ice cover over much of the terrain.
> Note that these are bacteria that orient in the magnetic field of the
> earth; you don't even need an added magnet. So this is a little
> different than your orig idea. Also note that these bacteria take a
> little care to grow. They don't like much air -- which is relevant to
> their magnetism.
Roughly 2%, so you'll need sealed serum vials with an Eh indicator
like Resasurin in your media so you can determine approximate O2
concentration. Given that sealed vials require syringes, my sense
is that these particular bugs might be outwith the safety levels al-
lowed by most high schools.
With all due respect, I'd be inclined to use S. epi as originally sug-
gested...it's considerably more robust than the magnetotactics for
a beginner and there's been research which seems to indicate in-
creased levels of ferric chloride have an effect on the expression
of Fe-linked genes...as well as differences between planktonic and
sessile cultures. Whether or not there's any visually discernible
effect in a magnetic field, I'd not like to conjecture, but it might be
interesting to run multiple cultures with varying amounts of FeCl3
in the media and see if there's anything to distinguish between
them. It also might be worth trying to balance a petri dish directly
upon a magnet (centrally located) and seeing if there's a preferen-
tial selection _away_ from the edges.
Speaking for myself, I think you've come up with a very good...
testable...idea, Lina...especially if this is your first independent foray
into microbial behaviour. It's a single culture, controlled environment
which can easily done with limited materials. One thing I would
suggest is that the bugs be cultured as pour, rather than streak
plates, so that the initial inoculation is more homogeneous. Don't
forget to add some control plates (inoculated the same way but
grown without a magnetic field) so you have something to com-
pare them to.
Oops...and one thing more...even if there's no obvious growth
near (or away) from the magnets, you still have a result and you
can discuss the _absence_ of preferential growth (and why that
may be) rather than the presence of it. It's all a matter of per-
spective...:-)
Have fun...and if you think of it and have time, would you return
to post what happens? I'd be interested to see what results you
get.
Deirdre
