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Biofilm structure

Julian Wimpenny wimpennyj at cf.ac.uk
Wed Feb 12 08:54:57 EST 1997


A couple of points, first about the newsgroup. I am alarmed at the small
number of items that seem to get onto the Newsgroup. Also at the short
length of time they stay. I seem(ed) to get lots of items as direct
email which should have been up on the net. I've had items from Doug
Caldwell that were really addressed to everyone, yet they never appeared
on the Newsgroup. I realise that there is some method in this since
replies default to the author and not to the group.

Please try to ensure that items for the gropu are addressed to the group
-not the originator! And can items stay up longer??? Until we really get
into our stride!

I want to reply to Pauls definition of biofilms. He is probably aware of
what I think! With the greatest possible respect, I believe that his
definitions define the Universal Standard American Bozeman biofilm!!

My own view is that there are three separate types of biofilm (at
least.........!) based on the single variable, substrate concentration
and Paul ignores two of these. They are:

1. The heterogeneous mosaic biofilm described and defined by Bill
Keevil.I'm not sure that this is the best name but it defines stacks of
microcolonies *separated frome one another* but all built on a thin (1-5
micron) layer.

2. The USAB biofilm which I haven't a proper name for. I refer to it as
a 'channeled biofilm' but it has been described as a mushroom structure,
at any rate penetrated by holes and channels. OK come up with a decent
name someone!

3. A dense biofilm. This has as its limit (the limit to a biofilm
structure) as a dense uniform structure with no significant pores,
spaces, voids or channels.

I have considered, and, with Ric Colasanti modelled using cellular
automata that these structures represent stages in a continuum
determined by prevailing substrate concentration which we have
considered can vary by ~1 million fold from distilled water up to the
types chewing candy bars and drinking Coca Cola as far as dental plaque
communities are concerned. Come on! You kmow it makes sense! At the
lower concentrations a microcolony will deplete a zone around it of
nutrient. This becomes a no go (grow) area so that at the lowes possible
substrate concentration only stacks can form. As food increases so these
fuse leaving voids or channels. At the highest concentrations all the
voids are filled with bacteria since substrate concentration is not
limiting.

So Paul you seemed to say that these channels or voids have some
SIGNIFICANCE to a biofilm structure!! On the basis of our model I would
be forced to dispute this.

Nothing I have said mitigates, or should in any way be taken as a
criticism of the fine work done by Paul and others at Bozeman. The
'mapping of the mushroom structure is amazing and eleegant. My quarrel
is the interpretation and the fact thay they seem to ignore at least two
other (extreme) forms of biofilm. Also that they endow these structures
(channels etc) with a kind of teleological purposiveness which to me may
simply be a response to environment in this case substrate availability.

Finally though I must say that communities of microbes have an
accidental (??) purposiveness. Where the environment dictates something
communities can exploit the results if they are beneficial!

Julian.

PLEASE POST REPLIES TO THE GROUP UNLESS THEY ARE TOO RUDE............!



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