Hi Bob,
Good points, especially for those just getting into the field and for
proposal/paper reviewers on the fringes of the field. My 2 cents worth:
>1) Does one adherent microorganism constitute a biofilm?
Absolutely, especially if you are working with pure cultures. Many of us
believe the suite of physiological changes that constitute "the biofilm
phenotype" begins at attachment. What happens later in time and space
depends on what other organisms (those of the same phenotype or of
different phenotpyes) enter the equation. Also, as I stated in the
Biofilms Workshop at ASM last May, we need to start thinking about
interfaces rather than adherence to substrata - any interface that will
allow aggregation and (most importantly) activity of biomass. The
community that develops there, whether of a single phenotype or of multiple
phenotypes, constitutes a "biofilm". It would be interesting to compare
the sorts of physiological changes that take place through simple
aggregation (clumps of bacteria that are not really adherent to a
substratum) with those that occur through aggregation at an interface or
through true adherence to a substratum.
>2) If not, then how many do we need to start referring to an adherent
>population as a biofilm?
Question of scale, observers's perspective and all that. If you are
examining an event at the community level, then there had better be a
community present. I have made my case for single-cell studies above.
>3) At what point would the term "microcolony" apply?
Colony implies discrete units. Microcolony implies small discrete units.
Discrete units implies some sort of discretion. Psuedomonads in flowing in
vitro systems form tiny clumps of cell before these clumps coalesce into a
carpet of cells. Here the definition might best be approached by a spatial
equation: growth (or accumulation, in the case of motile cells) in Z must
be greater than growth in XY. Only a time-resolved approach can yield
reliable data here.
>4) Do biofilms require metabolically active organisms?
What's your definition of "metabolically active"?
>5) If metabolism is required, then what type of metabolism should be
>essential (proton motive force, respiration, biosynthesis, etc)?
I'd vote for minimal metabolism (repair). Now we are delving into the
definition of alive vs dead. Start thinking about spores and desiccated
cells. Cases exists where cyanobacterial cells from botanical specimens
(dried sheets, like pressed flowers) have been recultured after nearly a
century....
As you can tell, I'm an extremist. If you are concerned about the impact
of biofilms in real-world processes such as corrosion, infection, etc.,
then perhaps the metabolic bar ought to be raised a bit.
>6) On the lighter side, has anyone given their lab a good nickname? (My
>lab at Southwest Texas State University has adopted the name "Slime Gang")
>It is sometimes tempting to get confrontational during some of these
>discussions. I have a lot of respect for the participants in this
>discussion group, both on a personal and a professional level. I would
>encourage people to enjoy the science (including my first five comments)
>and when possible have fun (my comment 6).
I prefer stodgy names like "Biofilm Imaging Facility" that can be converted
to lighter-sounding acronyms (BIF).
Rob Palmer
CEB/UT
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