EVIDENCE OF AUTOINDUCER ACTIVITY IN NATURALLY-OCCURRING BIOFILMS

N-Acyl homoserine lactone (AHL) molecules have been shown to act as me diators of population density-dependent production in Vibrio fischeri, expression of virulence factors in Pseudomonas aeruginosa, and conjug ation in Agrobacterium tumefaciens. In nature, bacteria often grow as surface-adherent biofilm communities, As biofilms typically contain hi gh concentrations of cells, AHL activity and quorum-sensing gene expre ssion have been proposed as essential components of biofilm physiology . However, proof of AHL production within biofilms has heretofore been lacking. In this study we have employed a cross-feeding assay, using A. tumefaciens A136 (traI::lacZ) as an AHL-responsive reporter strain, to show the presence of naturally occurring AHL production in aquatic biofilms growing on submerged stones. AHL was detected in living biof ilms and biofilm extracts, but was not present in rocks lacking a biof ilm. This represents the first report of AHL activity in naturally occ urring biofilms.