The Novel Monooxygenase Gene dipD in the dip Gene Cluster of Alcaligenes faecalis JQ135 Is Essential for the Initial Catabolism of Dipicolinic Acid

Dipicolinic acid (DPA), an essential pyridine derivative biosynthesized in spores, constitutes a major proportion of global biomass carbon pool. Alcaligenes faecalis strain JQ135 could catabolize DPA through the "3HDPA (3- ydroxy i icolinic cid) pathway." However, the genes involved in this 3HDPA pathway are still unknown. In this study, a gene cluster responsible for DPA degradation was cloned from strain JQ135. The expression of genes was induced by DPA and negatively regulated by DipR. A novel monooxygenase gene, , was crucial for the initial hydroxylation of DPA into 3HDPA and proposed to encode the key catalytic component of the multicomponent DPA monooxygenase. The heme binding protein gene , ferredoxin reductase gene , and ferredoxin genes were also involved in the DPA hydroxylation and proposed to encode other components of the multicomponent DPA monooxygenase. The O stable isotope labeling experiments confirmed that the oxygen atom in the hydroxyl group of 3HDPA came from dioxygen molecule rather than water. The protein sequence of DipD exhibits no significant sequence similarities with known oxygenases, suggesting that DipD was a new member of oxygenase family. Moreover, bioinformatic survey suggested that the gene cluster was widely distributed in many , , and , including soil bacteria, aquatic bacteria, and pathogens. This study provides new molecular insights into the catabolism of DPA in bacteria. Dipicolinic acid (DPA) is a natural pyridine derivative that serves as an essential component of the spore. DPA accounts for 5 to 15% of the dry weight of spores. Due to the huge number of spores in the environment, DPA is also considered to be an important component of the global biomass carbon pool. DPA could be decomposed by microorganisms and enter the global carbon cycling; however, the underlying molecular mechanisms are rarely studied. In this study, a DPA catabolic gene cluster ( ) was cloned and found to be widespread in , , and . The genes responsible for the initial hydroxylation of DPA to 3-hydroxyl-dipicolinic acid were investigated in Alcaligenes faecalis strain JQ135. The present study opens a door to elucidate the mechanism of DPA degradation and its possible role in DPA-based carbon biotransformation on earth.