Magnetic bacteria such as those in the Geobacter family (the
first-discovered ones being G. metalloreducens) "breathe" rust
(Fe(OH)2) and reduce it to magnetite. Rust is the electron acceptor
for these organisms' cellular respiration, analogous to the way we
must breathe oxygen and reduce it to water and carbon dioxide in order
to survive.
These bacteria will undergo magnetotaxis at minimal Earth-surface
magnetic field levels (about 0.3 G), so whatever the threshold level
is, it must be less than this. Most experiments have been done with
constant magnetic fields of 0.5 G. So, essentially, the answer is
"only a very small, 'ambient' magnetic field is required." The effect
of this field on a cell, of course, will be dependent on the cell's
magnetic moment, which will vary on the cell's size and the
organization of magnetic particles within it.
A classic, massive review of this material can be found in R.B.
Frankel (1984), Annual Reviews of Biophysical Bioengineering. The
PubMed citation is here:
http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=6378076 |
Request for Answer Clarification by
snesprogrammer-ga
on
15 May 2004 00:32 PDT
I read your answer and the paper you linked to. Unfortunately I was
dissappointed. Hopefully you can clear some stuff up for me.
The first paragraph of your answer apparently was taken from some
place other than the paper you pointed out. Because that paper
(contrary to what you wrote), says that Fe+2 (ie Fe(OH)2 dissolved) is
actually oxidized (not reduced) to hydrous F2O3. Then, after some
dehydration, partially reduced to Fe3O4. Overall, the Fe(OH)2 is NOT
accepting electrons, but giving them up.
The paper explains ways to measure the cells magnetic moment, but
doesn't give any values from actual measurements (unless I somehow
overlooked them?). It also explains how to calculate the "average
direction" depending on the magnetic moment, magnetic field, and the
temperature. You even write:
"The effect of this field on a cell, of course, will be dependent on the cell's
magnetic moment, which will vary on the cell's size and the
organization of magnetic particles within it."
All you did was tell me what intermediate information needs to be
found ... and not the answer. So, to answer the question, maybe you
could find what the range of typical values are for the cell's
magnetic moment. Then along with the info you already gave me, I can
easily calculate how "directed" the motion is at any temperature.
Also, the paper you gave me seems to contradict itself. Look at this:
pg16
"Fe+2 is reoxidized and accumulated as the low density hydrous iron
oxide. ... this oxidation step might involve molecular oxygen, which
is required for Fe3O4 precipitation in A. magnetotacticum."
pg17
"... low O2 environment appears to be a requirement for Fe3O4 precipitation."
Hopefully I just dreadfully misunderstood the mechanism the paper was
proposing, which could explain why it seems to contradict with itself
and even with your answer. But I'm also worried by the fact that the
paper was written in 1984. Maybe their proposal was wrong? Either
way, surely there is newer and better info about how these particles
are made (the paper didn't even explain several steps of the process).
I am a patient person. I am not upset, just disappointed with the results so far.
Please keep trying.
- find the range of typical values for the magnetic moment of these cells
- find info (hopefully more recent) that explains the magnetite
particle production, to clear up the contradictions in your first
answer
Thank you.
|
Clarification of Answer by
rxrfrx-ga
on
15 May 2004 14:47 PDT
The first part of my answer was taken off the top of my head, and I
actually only examined the part of the paper that had to do with
magnetotaxis, not iron respiration. I will examine the paper more
carefully and get back to you within a day or two, as you seem to be
in no rush to obtain clarification of this answer.
|
Request for Answer Clarification by
snesprogrammer-ga
on
01 Jun 2004 14:41 PDT
Did you forget about this question? It's been quite a few days, and
the question is going to expire soon.
|
Clarification of Answer by
rxrfrx-ga
on
01 Jun 2004 15:32 PDT
Sorry! I'll post something soon...
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Request for Answer Clarification by
snesprogrammer-ga
on
14 Jun 2004 04:00 PDT
Did you forget again?
I originally thought that there would be a paper or a good collection
of information on these things that would answer everything. Since
that appears to not be true this has kind of turned into two
questions.
So to adjust for that I'll give a tip of $10 to finish the answer.
Thanks.
|
Request for Answer Clarification by
snesprogrammer-ga
on
16 Jun 2004 21:00 PDT
I saw that you added another comment saying you didn't have time to
finish. But now the comment is removed. Did you change your mind?
Or did some moderator remove that?
|
Clarification of Answer by
rxrfrx-ga
on
17 Jun 2004 06:28 PDT
Moderator removed it.
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Request for Answer Clarification by
snesprogrammer-ga
on
01 Jul 2004 18:30 PDT
Well Moderator, I'd appreciate it if you didn't remove posts by your
workers as it is not constructive in the least (especially if you
don't at least put a comment in its place).
Moderator, since you apparently didn't like what rxrfrx-ga suggested.
What exactly do you suggest? (feel free to finish the question if you
wish)
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