Identification and characterization of the vanillin dehydrogenase YfmT in Bacillus subtilis 3NA

With vanillin as one of the most important flavoring agents, many efforts have been made to optimize its biotechnological production from natural abundant substrates. However, its toxicity against the hosts results in rather low yields and product concentrations. Bacillus subtilis as a soil-dwelling bacterium is a possible lignin-derived compound-degrading microorganism. Therefore, its vanillin and ferulic acid metabolism was investigated. With a rather high tolerance for vanillin up to 20 mM, it is a promising candidate to produce natural vanillin. In this study, the well-studied phenolic acid decarboxylases PadC and BsdBCD could be ascribed to function as the only enzymes in B. subtilis 3NA converting ferulic acid to 4-vinylguaiacol and vanillic acid to guaiacol, respectively. As vanillin also becomes converted to guaiacol, a previous conversion to vanillic acid was assumed. Usage of bioinformatic tools revealed YfmT, which could be shown to function as the only vanillin dehydrogenase in B. subtilis 3NA. Thus, YfmT was further characterized regarding its temperature and pH optima as well as its substrate range. Vanillin and ferulic acid metabolic routes in the tested B. subtilis strain were revealed, a direct conversion of ferulic acid to vanillin, however, could not be found.