This paper reports the codisplay of organophosphorus hydrolase (OPH) and methyl parathion hydrolase (MPH)-green fluorescent protein (GFP) fusion on the cell surface of Escherichia coli using the truncated ice nucleation protein (INPNC) and Lpp-OmpA as the anchoring motifs. The surface localization of both OPH and MPH-GFP was demonstrated by cell fractionation, Western blot analysis, protease accessibility experiment, and immunofluorescence microscopy. Anchorage of the foreign proteins on the outer membrane neither inhibits cell growth nor affects cell viability. The recombinant strain can be used as a whole-cell biocatalyst and showed a broader substrate range than strains expressing either OPH or MPH. A mixture of six organophosphorus pesticides (OPs) (0.2 mM each) could be degraded completely within 5 h. The broader substrate specificity in combination with the rapid degradation rate makes the recombinant strain a promising candidate for detoxification of OPs. The fluorescence of surface-displayed GFP is very sensitive to environmental pH change. Because hydrolysis of OPs by OPH or MPH generates protons, the recombinant E. coli could be used as a whole-cell biosensor for the rapid detection of OPs by evaluating fluorescence changes as a function of OP concentrations.
The twin-arginine translocation (Tat) pathway exports folded proteins across the cytoplasmic membranes of bacteria and archaea. Two parallel Tat pathways (TatAdCd and TatAyCy systems) with distinct substrate specificities have previously been discovered in Bacillus subtilis. In this study, to secrete methyl parathion hydrolase (MPH) into the growth medium, the twin-arginine signal peptide of B. subtilis YwbN was used to target MPH to the Tat pathway of B. subtilis. Western blot analysis and MPH assays demonstrated that active MPH was secreted into the culture supernatant of wild-type cells. No MPH secretion occurred in a total-tat2 mutant, indicating that the observed export in wild-type cells was mediated exclusively by the Tat pathway. Export was fully blocked in a tatAyCy mutant. In contrast, the tatAdCd mutant was still capable of secreting MPH. These results indicated that the MPH secretion directed by the YwbN signal peptide was specifically mediated by the TatAyCy system. The N-terminal sequence of secreted MPH was determined as AAPQVR, demonstrating that the YwbN signal peptide had been processed correctly. This is the first report of functional secretion of a heterologous protein via the B. subtilis TatAyCy system. This study highlights the potential of the TatAyCy system to be used for secretion of other heterologous proteins in B. subtilis.
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