IUBio

Membership of a biofilm

Doug Caldwell caldwell at skyway.usask.ca
Fri Jul 30 02:22:33 EST 1999


Jan,
A biofilm is most likely the inheritance of a constructed niche.
The concept of niche construction was put forth by Odling-Smee and Laland
in their paper titled "Niche Construction and Gaia" (Abstracts of Gaia in
Oxford III - Gaia and Natural Selection. St. Anne's College. Oxford
University, April 3-7, 1999).
Applying their principles to biofilms, it would follow that the lifetime of
a constructed biofilm is longer than the life of the cells of which it is
constructed. The biofilm is thus inherited by the next generation of
cells. Consequently, the structure of the biofilm is inherited from one
generation to the nextjust as the structure of DNA is inherited from one
generatoin to the next.
This raises the possibility that DNA may not be the sole form of evolving
information. DNA could be just one of many evolving forms of functionality
that are inherited from one generation to the next. Thus the emergent
chemical, physical, and biological properties of all environments could
conceivably represent the construction and evolution of heritable niches
like biofilms.
DNA is not a prerequisite for evolution. If it were, it could not have
emerged through chemical evolution. The emergence of information and
functionality thus seem to be intrinsic in all space/time relationships
between matter/energy objects. Consequently, the most fundamental unit of
life may actually be the space/time continuum rather than DNA, cells, or
organisms.
Instead of focusing and finishing, sometimes it is important to unfocus and
understand before you can refocus and then finish. Thus to really
appreciate what a biofilm is, you have to question the precepts of
chemistry, biology, and physics (the precepts of natural science). That is
the nature and necessity of post-modern ecology.
Best Wishes - Doug Caldwell
p.s. for more info see "Post-Modern Ecology - Is the Environment the
Organism?" which should appear in the August issue of Environmental
Microbiology (not Appl. and Envion. Micro but the new journal published by
Blackwell).
-----------------------------------


 >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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*********************************************************
Doug Caldwell
Microbial Colonization Laboratory
Department of Applied Microbiology and Food Science
51 Campus Drive, University of Saskatchewan
Saskatoon, Saskatchewan, S7N 5A8, Canada
Voice: (306) 966-5026 (office), -5042 (colonization lab), -7704 (laser
imaging facility), 934-0711 (home)
Fax: 306-966-8898
Email: caldwell at sask.usask.ca
**********************************************************



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