Protein Engineering of the Quorum-Sensing Regulator SdiA of Escherichia coli

The Escherichia coli quorum-sensing regulator, SdiA, belongs to the LuxR family of transcriptional regulators and is responsible for detecting signals from other bacteria. Previously we found that SdiA is necessary for E. coli to control its biofilm formation with indole just as SdiA is necessary for E. coli to alter its biofilm formation in the presence of N-acylhomoserine lactones (AHLs). Here we engineered SdiA by random mutagenesis to further control biofilm formation in the presence of indole and AHLs. After screening of 477?? mutants with indole and two AHLs (N-butyryl-DL-homoserine lactone, and N-(3-oxooctanoyl)-L-homoserine lactone, C6HSL), five SdiA variants were obtained that altered biofilm with and without signals of indole and AHLs. Two truncation variants (1E11 and 14C3) lacking the C-terminal DNA-binding domain of SdiA showed the reduction of biofilm formation by 5-fold and 10-fold in LB and LB glu, respectively. DNA microarrays show that the evolved SdiA (1E11) compared to wild-type SdiA influences indole synthesis genes, AI-2 uptake genes, acid-resistance genes, motility related genes, cold-shock protein genes, and several regulatory protein genes. Corroborating DNA microarrays, SdiA variants produced various amounts of indole which led to different survivals in low pH and influenced swimming motility and final cell density. Also, an AHL sensitive variant (2D10) 2-fold increased biofilm formation in the presence of C6HSL, while another variant (6B12) lowered biofilm formation in the presence of C6HSL. Hence, the results clearly showed that mutation of SdiA itself directly controls biofilm formation and SdiA variants could be further recognized by the inter-species signal AHLs. This is the first random protein engineering to control biofilm formation.

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Lee J, Maeda T, Hong SH, Wood TK