MICROBIAL BIOFILMS

Direct observations have clearly shown that biofilm bacteria predomina te, numerically and metabolically, in virtually all nutrient-sufficien t ecosystems. Therefore, these sessile organisms predominate in most o f the environmental, industrial, and medical problems and processes of interest to microbiologists. If biofilm bacteria were simply plankton ic cells that had adhered to a surface, this revelation would be unimp ortant, but they are demonstrably and profoundly different. We first n oted that biofilm cells are at least 500 times more resistant to antib acterial agents. Now we have discovered that adhesion triggers the exp ression of a sigma factor that derepresses a large number of genes so that biofilm cells are clearly phenotypically distinct from their plan ktonic counterparts. Each biofilm bacterium lives in a customized micr oniche in a complex microbial community that has primitive homeostasis , a primitive circulatory system, and metabolic cooperativity, and eac h of these sessile cells reacts to its special environment so that it differs fundamentally from a planktonic cell of the same species.