Interbacterial Biofilm Competition through a Suite of Secreted Metabolites.

Polymicrobial biofilms are ubiquitous, and the complex interspecies interactions within them are cryptic. We discovered the chemical foundation of antagonistic interactions in a model dual-species biofilm in which Pseudomonas aeruginosa inhibits the biofilm formation of Agrobacterium tumefaciens . Three known siderophores produced by P. aeruginosa (pyoverdine, pyochelin, and dihydroaeruginoic acid) were each capable of inhibiting biofilm formation. Surprisingly, a mutant that was incapable of producing these siderophores still secreted an antibiofilm metabolite. We discovered that this inhibitor was N 5 -formyl- N 5 -hydroxy-l-ornithine (fOHOrn)─a precursor in pyoverdine biosynthesis. Unlike the siderophores, this inhibitor did not appear to function via extracellular metal sequestration. In addition to this discovery, the compensatory overproduction of a new biofilm inhibitor illustrates the risk of pleiotropy in genetic knockout experiments. In total, this work lends new insight into the chemical nature of dual-species biofilm regulation and reveals a new naturally produced inhibitor of A. tumefaciens biofilm formation.