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Biofilm structure and modeling, etc.

Veeh, Rick rick_v at erc.montana.edu
Wed Feb 12 13:43:15 EST 1997

	As requested by Julian Wimpenny, I am addressing my response to
the biofilms group at large regarding his concern over limitations to
our views on biofilm and microbial community structure.  First of all,
let me say that as a long-standing student and research associate at the
Center for Biofilm Engineering in Bozeman, I am very familiar with Paul
Stoodley's elegant work in elucidating the "mushroom" structure of the
biofilm with which he worked.  However, I wholeheartedly agree with
Julian that it is a serious mistake to use the model for this biofilm to
describe all biofilms.  I would prefer to call this biofilm model the
"glucose-enhanced, water-unlimited, Pseudomonas aeruginosa
conduit/flat-plate reactor" model (I'm sure that this name will soon be
adopted....Yeah, right!).  Granted, this model/structure may be used to
describe other biofilms existing under similar environmental conditions;
but I definitely believe that a model based on this biofilm would NOT
accurately describe a large number of naturally-occurring biofilms.
	As an example, most of the biofilms existing on concrete that I
have imaged using SEM would probably fall into Category #3 suggested by
Julian.  These biofilms are usually very densely packed cells no more
than a few microns thick (I believe a monolayer in many cases),
discontinuous, and buried in EPS so that just the "backs" of the cells
are visible.  My guess would be that this structure is more the norm in
nature, especially under conditions of moisture/nutrient limitations.
ln fact, these biofilms are probably limited to gleaning moisture from
the humidity in the air and to diffusion as the ONLY means of
substrate/metabolic byproduct exchange.
	Finally, regarding Julian's last question/comment about
accidental (??) purposiveness in biofilm structure, I have a couple of
ideas I'd like to share.  First of all, neither do I believe that
biofilm structure is accidental or purposeful (at least in any
non-spiritual sense).  And I was reminded of an earlier comment by one
of the biofilm group members that bioflims somehow violate the laws
(they are obviously still theories to alot of people) of natural
selection.  To me it seems reasonable that biofilms and the species that
comprise these consortia are continuously subject to natural selection
pressures and, therefore, are dynamic entities that change as
environmental (e.g. seasonal) conditions change.  At any one time a
microbial consortium reflects these conditions and the interdependence
of the organisms present.  I think reminding everyone of the old
Darwinian concept of "niche" is not out of line here.  If there is a
niche that is not occupied (e.g. a carbon/energy source that is not
being utilized), an organism will probably evolve or expand its existing
"territory" to fill it.  Likewise, if a niche is challenged or
eliminated (in a biofilm or in the business community in Bozeman, MT),
some THING will change, move on, or disappear.

I would love to hear any comments back!

Rick Veeh    

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