Surface display of cellulases in ethanol producing bacterium Zymobacter palmae.

Lenz F, Tozakidis IEP, Jose J

Abstract

Using lignocellulosic biomass as feedstock for the generation of biofuels by fermentation has for long time been considered a promising approach for the generation of sustainable energy, however its commercial success has since stayed out. Simultaneous saccharification and fermentation (SSF) has become of particular interest due to its potential to reduce the overall process costs of biomass conversion. The ethanologenic bacterium Zymobacter palmae offers several advantages compared to commonly used yeast strains such as higher growth rates and genetic accessibility. To enable Z. palmae for SSF applications, the endocellulase Cel5 from Hahellachejuensis, the exocellulase CelK from Ruminiclostridium thermocellum and the β-glucosidase BglA from Bacillussubtillis were expressed as Maximized AutoTransporter mediated Expression (MATE)-fusion proteins on the surface of Z.palmae. Enzyme displaying cells showed activity towards their specific substrates carboxymethylcellulose (CMC), 4-nitrophenyl-β-D-cellobioside and 4-nitrophenyl-β-D-glucopyranoside. In combination, the cells were able to break down phosphoric acid swollen cellulose (PASC), Avicell and Filterpaper. A low hydrolytic-activity of cells displaying BglA prevented the efficient formation of glucose and hence its fermentation to ethanol.