Functional Surface Display of Laccase in a Phenol-Inducible Bacterial Circuit for Bioremediation Purposes

Phenolic compounds, which are produced routinely by industrial and urban activities, possess dangers to live organisms and environment. Laccases are oxidoreductase enzymes with the ability of remediating a wide variety of phenolic compounds to more benign molecules. The purpose of the present research is surface display of a laccase enzyme with adhesin involved in diffuse adhesion (AIDA-I) autotransporter system on the surface of Escherichia coli cells for bioremediation of phenolic compounds.
The expression of laccase was regulated by a phenol-responsive promoter (a σ54 promoter). The constitutively-expressed CapR transcription activator was able to induce laccase expression in the presence of phenolic compounds.
Western blot analysis showed the expression and correct transfer of the enzyme to the outer membrane of E. coli cells in the presence of phenol. Activity assay confirmed the correct folding of the enzyme after translocation through the autotransporter system. HPLC analysis of residual phenol in culture medium showed a significant reduction of phenol concentration in the presence of cells displaying laccase on the surface.
Our findings confirm that autodisplay enables functional surface display of laccase for direct substrate-enzyme availability by overcoming membrane hindrance.