Dear Rob and others,
true, when we get down into details, we need to be more precise with those
distinctions I outlined. But for the moment, the developmental perspective
you have added is more important.
If we talk about the growth of a biofilm, then it makes perfect sense to
refer to the whole sequence of stages from the single attached cell (and
even earlier, the not-yet-attached cell) to the ageing biofilm as a
growing biofilm. And call a torn-off streamer a torn-off streamer rather
than a floc, after all, this torn-off piece is clearly related to the
structure it was torn-off from. This is even clearer with arms, as
torn-off arms can't live on their own and will always remain torn-off arms
while the streamers might give rise to other structures after having been
washed into the waste carboy eventually.
But, still, if we look at a stage in a developmental cycle as such, it is
clearer to use a specific term, e.g. single attached cell.
To use another analogy, the development of a frog from the fertilized egg
to the adult frog. Clearly, the fertilized egg is going to be a frog, but
is not a frog itself (it is just that: a fertilized egg of a frog), only
the last stage is what we call a frog.
Thus, the developmental view doesn't invalidate "static" definitions, but
links a set of defined static objects (snapshots as you call them) into a
sequence in time (movie), which can represent a succession of ecosystems
or the ontogeny of an organism. The link will be a causal one in those
The developmental perspective is very useful but should not be seen as an
argument for broadening definitions in order to incorporate
developmentally related stages.
PS: Whatever happens to the empty lines in our mails? Where do they get
On 23 Jul 1999, Robert J. Palmer Jr. wrote:
> Now we're getting somewhere...
> >Hi all,
> >I would rather prefer Keith Rose's suggestion that in order to qualify as
> >a biofilm, the structure must have a micro-environment that is different
> >from the bulk phase. Let's take trees and forests as an analogous example.
> >Now, we all have a pretty good idea of what a forest is and wouldn't call
> >a single tree a forest. We would call a tree a tree. A forest is an
> >assembly of trees that creates a habitat that differs from the habitat
> >that a single tree can create. Of course, the difference is gradual, but
> >nevertheless, we can have no doubt that there is a qualitative difference
> >between a tree and a forest, however fuzzy the borderline might be.
> >I would like to suggest that we have to make several independent
> But there are no unattached trees :) :)
> >1. Single organisms versus aggregates. Biofilms would be a special case of
> >microbial aggregates, namely those that arise from attachment of cells to
> >a surface. Other special cases would be colonies on agar plates, lake
> >snow, sludge flocs, digester granules, and consortia in the original sense
> >of the term (referring to well-organized symbiotic aggregates of different
> >species, e. g. "Chlorochromatium aggregatum").
> But where is the distinction? Chlorochromatium is clear (I think..., and
> may be the extreme example of a microcolonial biofilm), but digester
> granules and sludge flocs frequently have a substratum, however small,
> associated with them, much as rain drops have solid nucleation particles.
> Also, don't these flocs, consortia, and aggregates fulfill all the other
> definitions we've heard so far (communication, contact, matrix, etc)?
> >2. Attached to a surface versus planctonic. Biofilms would be attached to
> >a surface, but some of the other abovementioned aggregates wouldn't be
> >(flocs etc.).
> The surface is in the middle of the floc. Tthe digestor is the solar system
> and the flocs are planets and the bug (biofilms) are Earth's biosphere
> (pardon the overly simplistic analogy). Does the substratum have to be big
> and hard? Skin is not hard (usually); leaf surfaces are not hard (although
> they certainly are from the bacterium's standpoint). So, are clay
> particles (or aggregations of clay particles) or colloids within a
> bioreactor that support the aggregation (colonization?) of cells substrata?
> Just being the Devil's advocate here - that's what discussion groups are
> >3. Coming back to Paul Stoodley's primary versus higher order structure
> >distinction, I think that micro-colonies or cell-clusters are a more basic
> >structural unit than biofilms and flocs etc. as these are clearly
> >structures at a higher hierarchal level. So we have cells at the lowest
> >level of structural organization (maybe call it primary structure?), then
> >micro-colonies/cell-clusters as well as consortia at the next level
> >(secondary structure), and sludge flocs and biofilms etc. one level higher
> >(tertiary structure). And maybe stromatolites comprising several layers of
> >biofilm, dead and alive, as quaternary structures.
> >I guess the point I'm trying to make is that if we adopt a definition of
> >biofilms that includes everything under the sun, it will loose its
> >meaning. We need clearly defined terms, based on qualitative distinctions.
> >That's my two cents.
> That was several dollars (pounds, guilders) worth! Here's another point to
> consider. Many here are making a case for narrowing the definition based
> on attachment to a substratum or these putative "higher order" structures.
> However, the biofilm is a temporal phenomenon. Even biochemistry is to
> some extent temporal (whaen is quaternary structure achieved, when is the
> protein folded?). I don't like the discrete-step approach. I prefer the
> developmental approach. To make another simplistic analogy, an arm is an
> arm regardless of whether it is attached to a four-year-old child or to a
> seventy-year-old woman. We all have no problems accepting the definition
> of an arm, and I would venture to say we have several definitions that are
> spatiotemporally intertwined: where the arm starts in time (limb
> formation) or space (it is the armpit from the external perspective, but
> the shoulder joint from a skeletal perspective). All this means that
> "biofilm" will continue to be an operating definition and that the
> "distinct" higher-order structures exist primarily as an artifact of our
> "snapshot" approach to examining biofilms. This is not to say that a
> morphometric approach yields no information: the stromatolite analogy being
> the most extreme arguement. However, stromatolites develop only under a
> very unique set of circumstances. Other assemblages e.g.,
> Farbstreifensandwatt (there's a mouthfull!) is less ordered but still
> clearly recognizable as structures. Pure-culture P.a. biofilms also have
> structures initially (microclonies or whatever you'd care to call tham)
> that then coalesce and loose their definition to a large extent (at least
> morphologically, but how about physiologically!?).
> Maybe the next Biofilms Bible will be a multivolume work with an entire
> volume dedicated to different perspectives on "what is a biofilm"......
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