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Membership of a biofilm

Andy Spragg sparge at globalnet.co.uk
Thu Jul 29 01:20:22 EST 1999

I don't seem to be having much joy in getting anyone to bite on this
one, though all sorts of people seem to be happily discussing the
definition of a biofilm. Is it because it is perceived as unimportant,
or difficult?
As I said previously, whilst I think defining a biofilm is important
and interesting, I see it as, so to speak, almost axiomatic (in other
words, as long as most people can agree what is and isn't one most of
the time, that's good enough). Furthermore, if a definition of a
biofilm is good, the definition of membership of a biofilm should more
or less come out in the wash, and with it the answer to the question
"Is this microbe a member of this biofilm, or not?". However, none of
the discussion I've seen so far helps with these questions:
- Are grazing protozoa members of a biofilm? I suspect most people
would say no, but I'd be interested to know why.
- Are motile bacteria (loc cit), which are "facultative planktonic"
(so to speak) and can move from one biofilm to another, members of all
the ones they visit? Of none? Received wisdom would seem to indicate
membership of none.
- Are adventitious microbes members of the biofilm they stumble upon?
Received wisdom seems to say yes - but it seems a bit unjust to
exclude the ones that got there by design, and include the ones that
got there by accident.
Then there is a hypothetical example I dreamed up yesterday which I'd
love to hear opinions on. I have been reading the book "A genetic
switch" about lambda phage. Consider a hypothetical biofilm comprised
of bugs which are lysogens, in an environment which is irradiated with
UV periodically e.g. sunlight. The ones at the top see the UV and
lysis is triggered, the ones further down do not see it and remain
lysogenic. The phage released will in turn infect and lyse some bugs,
and lysogenise others, so the dynamics of the biofilm growth are
critically dependent on the dynamics of the lysis and lysogenisation,
which in turn are driven by the intensity, frequency and duration of
the UV irradiation.
So the phage are either stably and passively integrated into a host
genome or they are dispersed into the environment, I presume they
could not survive long "naked" in the biofilm. Question: do the phage
belong to the biofilm?
Hire a man a car and you transport him into work for a day.
Teach a man to drive and you transform him into an asshole for life.

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