Catalytic transformation of HODAs using an efficient meta-cleavage product hydrolase-spore surface display system

The accumulation of 2-hydroxy-6-oxohexa-2,4-dienoic acids (HODAs) in the process of aromatics transformation will hinder the mineralization rate. In this study, a novel type of biocatalyst, meta-cleavage product (MCP) hydrolase (MfphA and BphD) displayed on the surface of Bacillus subtilis 168 spores, was developed for the transformation of HODAs. The successful display of CotG-MfphA and CotG-BphD fusion protein on the surface of spore were confirmed by western blot analysis and activity measurement. The optimal transformation conditions by spore surface-displayed MfphA and BphD were found to be 70 °C and pH 7. The thermal and pH stability analysis exhibited that spore surface-displayed MfphA and BphD were stable and retained more than 80% of relative activities even at 80 °C and pH 10. Meanwhile, recycling experiments showed that the conversion percentage of HODA by surface-displayed MfphA and BphD were not significantly decreased throughout the reutilization process, which still retained 45% and 70% at the tenth cycle, respectively. To the best of our knowledge, this is the first report concerning the B. subtilis 168 spore surface-displayed MCP hydrolases. The high activities and good recycle performance suggested that this novel biocatalyst system could serve as a suitable alternative for HODAs transformation.