Autotransporter mediated esterase display on Zymomonas mobilis and Zymobacter palmae

Autodisplay, i.e. surface expression of recombinant proteins by virtue of the autotransporter secretion pathway, has been used predominantly with Escherichia coli as host organism, which often limits the applicability of this technique to laboratory purposes and scales. The aim of this study was to investigate if the fermentative bacteria Zymomonas mobilis and Zymobacter palmae, representing attractive candidates for industrial applications, can serve as host organisms for autodisplay. We therefore used the carboxylesterase EstA from Burkholderia gladioli as an autotransporter passenger to display it on the surfaces of Z. palmae and Z. mobilis. Expression and outer membrane localization of the EstA-autotransporter fusion protein were verified by SDS-PAGE, and surface display of the enzyme was demonstrated by ELISA and flow cytometer analysis. Whole-cell activity assays revealed that EstA retained its activity on the cell surface. Recombinant Z. palmae cells exhibited significant higher esterase activity (294mU/mL/OD 1) in comparison to Z. mobilis (88mU/mL/OD 1) and the control E. coli (113mU/mL/OD 1). This appears even more noteworthy, as about 30% of EstA was released from the cell surface of Z. palmae. Nevertheless, our results indicate that both species are suitable autodisplay hosts, in particular Z. palmae for displaying esterase, opening up new horizons for biocatalytic applications.