and still more..
>>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?
>*** I would argue that in many cases it is NOT a subjective opinion. The
>significance of a biofilm being more that one cell is that there is a
>potential for "communication" (genetic or chemical exchange) between the
>cells; that the cells function as a tissue and have behaviors that the
>single cell cannot have. This communication cannot take place if the
>bacteria are not sufficiently close and if there is not a vehicle (matrix,
>pili, etc) for transporting the message . Hence, I would argue that single,
>attached cells that do not have the potential for communication are "single
>attached cells".
Your point about communication is clearly important. Biofilms offer the
advantage of CLOSE communication. However, all the types of communication
you mentioned are known to occur in planktonic cells (and, we would
postulate, single attached cells), so perhaps these factors are not
operable in defining a biofilm - they are operable as advantages of the
biofilm habitat, such as access to nutrients unvailable (or sparsely
available) in the bulk liquid.
Rob Palmer
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