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Definition of a biofilm - Again

David B. Hedrick davidbhedrick at icx.net
Thu Jul 22 03:42:33 EST 1999

Dear Robert and all:
I'd like to suggest that the term "biofilm" be used to distinguish 
attached microbes from free-living or planktonic organisms. A single 
bacterium (AKA "lonely") still derives benefits from attachment - often 
higher carbon availability, not being swept away, etc. How many 
"lonely" bacteria are there in a square centimeter? Isn't it just a 
matter of degree, and a subjective opinion at that, whether 2 bacteria 
are close enough together to qualify as a biofilm? People like Robert 
with his lovely laser confocal microscope can routinely measure the 
distance between organisms. But those of us using chemical or molecular 
techniques have no way of determining whether the organisms are disperse 
or clustered on the surface. Short of hiring Rob, that is. 
The purpose of a semantic discussion should be to obtain the simplest 
usable definition, so that we can go on to use it. 
Problems in definition I've run into are with things that look like 
biofilms but are free-floating in water. Methanosarcina grow in clumps 
under most cultural conditions, and are more resistant to toxins (oxygen 
in this case) when clumped. Many aqueous systems have solid particles 
such as silt and clay which are often colonized. Do the bacteria 
colonizing a clay particle many times their size act like planktonic or 
biofilm organisms? Then what about the flocs that the bioreactor people 
are always complaining about? 
> I don't think anyone is reinventing the wheel here. Bob brought up some 
> points that are frequently raised WITHIN the biofilm community, and as such 
> are even more pertinent to those entering a burgeoning field. 
> For example, does a single cell qualify as a biofilm by your definition? 
> I would suggest not, but only by virtue of the wording that requires 
> "accumulation". However a single cell can be immobilized and can produce 
> extracellular material. Let's say it divides. Do those two cells now 
> constitute a biofilm as an "accumulation"? They certainly fit all the 
> other requirements of either of your definitions. The Characklis-edited 
> magnum opus (to which many individuals made very important contributions) 
> is still the Bible of biofilm research despite its heavy emphasis on 
> engineering aspects and desptite our recognition that biofilms are NOT 
> black boxes whose physical (and physiological) characteristertics can be 
> modeled like a bomb blast. 
> I too am a bit bothered by all this worry about what constitutes a biofilm 
> - it has been and always will be an operating definition subject to 
> interpretation and "waffle". Discussion certainly does a minimal amount of 
> damage, and open discussion in this (and other) forums helps clarify to 
> which camps we all belong. 
> Rob Palmer 
> >I don't want to sound as though I am older than I am, but why do we need 
> >another definition of a biofilm? Perhaps the first review of biofilm 
> >engineering and biology was published 16 years ago by the late Bill 
> >Characklis and I. In it we defined a biofilm in the following way : 
> >....immobilized cells grow, reproduce, and produce extracellular polmer 
> >substances that frequently extend from the cell, forming a tangled mass of 
> >fibers lending structure to the entire assemblage which shall be termed a 
> >biofilm. The term biofilm does not necessarily imply a surface accumulation 
> >that is uniform in time and/or space. 
> >We dveloped this into a shorter version that defines a biofilm as "the 
> >accumulation of microbial cells , their products and inorganic particles at 
> >a wetted surface ".[ to take into the account that natural biofilms 
> >accumulate lots of silt]. 
> >Let's not re-invent the wheel! 
> >Keith Cooksey, Research Professor 
> >As part of the final part of the review we mentioned 13 areas that we felt 
> >were in need of further work. It is interesting to see how many of these 
> >STILL need further work! 
> >The reference is Adv in Appl. Microbiol. 29 93-137 [1983] 
> > 

Technical writing, literature search, and data analysis at the interface 
of chemistry and biology. 
davidbhedrick at icx.net
David B. Hedrick 
P.O. Box 16082 
Knoxville, TN 37996

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