E Over-expression of SiaCT68A restored the ability of ΔsiaA to form biofilm. The biofilm formation of the indicated strains was displayed with crystal violet staining (up) and quantified with optical density measurement (down). F Deletion of ΔsiaB in the ΔsiaA background strain restored the ability of ΔsiaA to form biofilm. The biofilm formation of the indicated strains was displayed with crystal violet staining (up) and quantified with optical density measurement (down). 