Heterologous expression of geraniol dehydrogenase for identifying the metabolic pathways involved in the biotransformation of citral by <i>Acinetobacter</i> sp. Tol 5

<p>The biotransformation of citral, an industrially important monoterpenoid, has been extensively studied using many microbial biocatalysts. However, the metabolic pathways involved in its biotransformation are still unclear, because citral is a mixture of the <i>trans</i>-isomer geranial and the <i>cis</i>-isomer neral. Here, we applied the heterologous expression of <i>geoA</i>, a gene encoding geraniol dehydrogenase that specifically converts geraniol to geranial and nerol to neral, to identify the metabolic pathways involved in the biotransformation of citral. <i>Acinetobacter</i> sp. Tol 5 was employed in order to demonstrate the utility of this methodology. Tol 5 transformed citral to (1<i>R</i>,3<i>R</i>,4<i>R</i>)-1-methyl-4-(1-methylethenyl)-1,3-cyclohexanediol and geranic acid. Biotransformation of citral precursors (geraniol and nerol) by Tol 5 transformant cells expressing <i>geoA</i> revealed that these compounds were transformed specifically from geranial. Our methodology is expected to facilitate a better understanding of the metabolic pathways involved in the biotransformation of substrates that are unstable and include geometric isomers.</p> <p>Heterologous expression of <i>geoA</i> was applied to identify the metabolic pathways involved in the biotransformation of citral by Acinetobacter sp. Tol 5.</p>