Precursors and metabolic pathway for guaiacol production by Alicyclobacillus acidoterrestris

• Guaiacol can't be produced from catechol, ferulic acid, phenylalanine and tyrosine.
• Vanillin was reduced to vanillyl alcohol by NADPH-dependent vanillin reductase.
• Vanillin was oxidized to vanillic acid by NAD(P)+-linked vanillin dehydrogenases.
• The vanillic acid decarboxylase was inducible, reversible and oxygen insensitive.

Alicyclobacillus acidoterrestris has recently received much attention due to its implication in the spoilage of pasteurized fruit juices, which was manifested by the production of guaiacol. Vanillic acid and vanillin have been accepted as the biochemical precursors of guaiacol in fruit juices. The purpose of this study was to try to find other precursors and elucidate details about the conversion of vanillic acid and vanillin to guaiacol by A. acidoterrestris. Four potential substrates including ferulic acid, catechol, phenylalanine and tyrosine were analyzed, but they could not be metabolized to guaiacol by all the thirty A. acidoterrestris strains tested. Resting cell studies and enzyme assays demonstrated that vanillin was reduced to vanillyl alcohol by NADPH-dependent vanillin reductase and oxidized to vanillic acid by NAD(P)+-dependent vanillin dehydrogenases in A. acidoterrestris DSM 3923. Vanillic acid underwent a nonoxidative decarboxylation to guaiacol. The reversible vanillic acid decarboxylase involved was oxygen insensitive and pyridine nucleotide-independent.