Autodisplay of alpha amylase from Bacillus megaterium in E. coli for the bioconversion of starch into hydrogen, ethanol and succinic acid

Abstract

"In this work, the expression of an alpha-amylase from Bacillus megaterium on the cell surface of Escherichia toll strains WDHA (Delta hycA and Delta ldhA) and WDHFP (Delta hycA, Delta frdD and Delta pta) by the autodisplay adhesin involved in diffuse adherence (AIDA) system was carried out with the purpose to confer the ability to E. coli strains to degrade starch and thus produce hydrogen, ethanol and succinic acid. For the characterization of the biocatalyst, the effect of temperature (30-70 degrees C), pH (3-6) and CaCl2 concentration (0-25 mM), as well as the thermostability of the biocatalyst (55-80 degrees C) at several time intervals (15-60 min) were evaluated. The results showed that the biocatalyst had a maximum activity at 55 degrees C and pH 4.5. Calcium was required for the activity as well for the thermal stability of the biocatalyst. The calculated Vmax and Km values were 0.24 U/cm(3) and 5.8 mg/cm(3), respectively. Furthermore, a set of anaerobic batch fermentations was carried out using 10 g/dm(3) of starch and 1 g/dm(3) of glucose as carbon sources in 120 cm(3) serological bottles, using WDHA and WDHFP strains harboring the pAIDA-amyA plasmid. The hydrogen production for WDHA was 1056.06 cm(3)/dm(3) and the succinic acid yield was 0.68 g/g(starch), whereas WDHFP strain produced 1689.68 cm(3)/dm(3) of hydrogen and an ethanol yield of 0.28 g/g(starch). This work represents a promising strategy to improve the exploitation of starchy biomass for the production of biofuels (hydrogen and ethanol) or succinate without the need of a pre-saccharification process."