Carbon eaters

David Kafkewitz kafkwtz at ANDROMEDA.RUTGERS.EDU
Tue Mar 19 13:38:19 EST 1996

A week of so ago there was posted a question about  whether there are
bacteria that can grow by oxidizing elemental carbon. There have been no
responses to this interesting question. In the interest of stimulating
discussion, I will take a shot at it.
I know of no such bacteria and I doubt that it is possible. The oxidation of
C to carbon dioxide should have more than enough energy to support growth.
There are many bacteria that grow by oxidizing carbon monoxide to carbon
dioxide.  Oxidation of carbon  atoms with a valence state of zero should be
more exergonic than CO. The problem, I think is, activation energy.
Elemental carbon does not exist as single atoms or small groups of atoms.
Carbon exists as sheets (graphite) or crystals (diamond) which are
exceedingly stable.  There are also exceedingly insoluble, which I assume is
related to the stability. Stability means much energy was given up when the
structure was formed, and thererfore must be added back to crack into the
structure.  My guess is that it is not possible  (probable ?) for this
amount of activation energy to be added by a biological system. Nitrogen
fixation is another example along these lines. If  I rememeber correctly the
reduction of dinitrogen by hydrogen is actually exergonic; yet  biological N
fixation has an enormous energy requirement. The triply bonded N atoms are
so close to each other  and the electron density is so high that much energy
has to be added to get into these bonds.  Activation is costly but possible
for nitrogen, but probably too costly for carbon.

That's my best guess. Somone correct me if i've got it all wrong.
David Kafkewitz, Department of Biological Sciences,
 Rutgers University, Newark N.J. 07102, U.S.A.
 201 648 5865; fax: 201 648 1007
kafkwtz at andromeda.rutgers.edu

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