IUBio

Membership of a biofilm

Jan Kreft Kreft at cardiff.ac.uk
Thu Jul 29 05:31:02 EST 1999


Andy,

I think your questions boil down to whether "biofilm" is a
habitat/biotope/ecosystem or only the main trophic level constituting an
ecosystem that would be in search of a name.

If it's a habitat/biotope like a savannah, then bacteria, grazers and
every critter that lives there (not merely passing-by), belongs to that
habitat as much as grass, gnus and lions belong to a savannah.

If it's a trophic level like herbivores, then protozoa wouldn't belong as
much as lions are not members of the herbivore trophic level. Only if we
view a biofilm as a trophic level, could we justify excluding protozoa
from membership.

Clearly, biofilms must be seen as biotopes and every creature living there
belongs to (is a member of) the biofilm.

We have to draw a border, though only a fuzzy one, regarding the meaning
of living there. The presence of an organism in the biofilm must have an
effect on the biofilm and on the organism itself to qualify as biofilm
membership. And if it's only passive, taking up space and being protected.
A passer-by doesn't change anything in the biofilm or itself by
passing-by.

Phage would belong to the biofilm, whether dead or alive.

Looking forward to comments,

Jan.

On 28 Jul 1999, Andy Spragg wrote:
 > 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?
 > Andy
 > 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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