YuaB functions synergistically with the exopolysaccharide and TasA amyloid fibers to allow biofilm formation by Bacillus subtilis.

During biofilm formation by Bacillus subtilis, two extracellular matrix components are synthesized, namely, the TasA amyloid fibers and an exopolysaccharide. In addition, a small protein called YuaB has been shown to allow the biofilm to form. The regulatory protein DegU is known to initiate biofilm formation. In this report we show that the main role of DegU during biofilm formation is to indirectly drive the activation of transcription from the yuaB promoter. The N terminus of YuaB constitutes a signal peptide for the Sec transport system. Here we show that the presence of the signal peptide is required for YuaB function. In addition we demonstrate that upon export of YuaB from the cytoplasm, it localizes to the cell wall. We continue with evidence that increased production of TasA and the exopolysaccharide is not sufficient to overcome the effects of a mutation in yuaB, demonstrating the unique involvement of YuaB in forming a biofilm. In line with this, YuaB is not involved in correct synthesis, export, or polymerization of either the TasA amyloid fibers or the exopolysaccharide. Taken together, these findings identify YuaB as a protein that plays a novel role during biofilm formation. We hypothesize that YuaB functions synergistically with the known components of the biofilm matrix to facilitate the assembly of the biofilm matrix.

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