Identification of a Novel Matrix Protein That Promotes Biofilm Maturation in Vibrio fischeri

Bacteria form communities, termed biofilms, in which cells adhere to each other within a matrix, typically comprised of polysaccharides, proteins, and extracellular DNA. Biofilm formation by the marine bacteriumVibrio fischerirequires the Syp polysaccharide, but the involvement of matrix proteins is as yet unknown. Here we identified three genes, termedbmpA, -B, and -C(biofilmmaturationprotein), with overlapping functions in biofilm maturation. A triplebmpABCmutant, but not single or double mutants, was defective in producing wrinkled colonies, a form of biofilm. Surprisingly, the triple mutant was competent to form pellicles, another biofilm phenotype, but they generally lacked a three-dimensional architecture. Transmission electron microscopy revealed that the extracellular matrix of thebmpmutant contained electron-dense, thread-like structures that were also present in the wild type but lacking insypmutant strains. We hypothesized that thebmpmutant produces the Syp polysaccharide but fails to produce/export a distinct matrix component. Indeed, a mixture of thebmpandsypmutants produced a wrinkled colony. Finally, BmpA could be detected in cell-free supernatants from disrupted pellicles. Thus, this work identifies a new matrix protein necessary for biofilm maturation byV. fischeriand, based on the conservation ofbmp, potentially other microbes.