INVOLVEMENT OF N-ACYL-L-HOMOSERINE LACTONE AUTOINDUCERS IN CONTROLLING THE MULTICELLULAR BEHAVIOR OF SERRATIA-LIQUEFACIENS

Several bacterial species possess the ability to differentiate into hi ghly motile swarmer cells capable of rapid surface colonization. In Se rratia liquefaciens, we demonstrate that initiation of swarmer-cell di fferentiation involves diffusible signal molecules that are released i nto the growth medium. Using high-performance liquid chromatography (H PLC), high resolution mass spectrometry and nuclear magnetic resonance (NMR) spectroscopy, we identified N-butanoyl-L-homoserine lactone (BH L) and N-hexanoyl-L-homoserine lactone (HHL) in cell-free Serratia cul ture supernatants. BHL and HHL are present in a ratio of approximately 10:1 and their structures were unequivocally confirmed by chemical sy nthesis. The swrl (swarmer initiation) gene, the predicted translation product of which exhibits substantial homology to the LuxI family of putative N-acyl homoserine lactone (AHL) synthases is responsible for directing synthesis of both BHL and HHL, In an swrl mutant, swarming m otility is abolished but can be restored by the addition of an exogeno us AHL, These results add swarming motility to the rapidly expanding l ist of phenotypes known to be controlled through quorum sensing.