Biofilms are structured communities of bacteria that are held together by an extracellular matrix consisting of protein and exopolysaccharide. Biofilms often have a limited lifespan, disassembling as nutrients become exhausted and waste products accumulate. D-amino acids were previously identified as a self-produced factor that mediates biofilm disassembly by causing the release of the protein component of the matrix in Bacillus subtilis. Here we report that B. subtilis produces an additional biofilm-disassembly factor, norspermidine. Dynamic light scattering and scanning electron microscopy experiments indicated that norspermidine interacts directly and specifically with exopolysaccharide. D-amino acids and norspermidine acted together to break down existing biofilms and mutants blocked in the production of both factors formed long-lived biofilms. Norspermidine, but not closely related polyamines, prevented biofilm formation by B. subtilis, Escherichia coli, and Staphylococcus aureus.
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We thank T. Kodger for help with dynamic light scattering, C. Marks and A. Grahame for their help with sample preparation for electron microscopy imaging, and the Harvard Center for Nanoscale Systems for use of its Imaging Facility. I.K.-G. is a fellow of the Human Fronteir Science Program. T.B. was supported by German Academy of Sciences Leopoldina (LPDS 2009-45), Leopoldina Research Fellowship. This work was supported by National Institutes of Health grants GM18568 to R.L., GM58213 and GM82137 to R.K., GM086258 and AI057159 to J.C. and by the BASF Advanced Research Initiative at Harvard University to R.L. and R.K. Harvard University has filed a patent application based on this work.