Bacterial biofilms play an important role in the growth of algal communities but the mechanisms involved in their development have been unclear. In November 8 Science, Ian Joint and colleagues at Plymouth Marine Laboratory, UK, show that diffusible signal molecules produced by bacterial biofilms are used by the planktonic phase of a marine eukaryotic organism (the seaweed Enteromorpha) to attach to an optimal surface (Science 298:1207, November 8, 2002).

Joint et al. used Vibrio anguillarum bacterial mutants defective in N-acylhomoserine lactone (AHL – a quorum sensing signaling molecule) production, Escherichia coli strains expressing AHL synthases, and synthetic AHLs. They observed that wild type V. anguillarum biofilms strongly enhanced zoospore settlement compared with controls. However, no density-dependent stimulation of attachment was observed with the vanM mutant that does not produce AHL. In addition, they showed that chemotaxis of Enteromorpha required the ability to detect AHL concentration gradients....