Journal of Bacteriology · 2019 · 23 citations · 45 references
Picolinic acid (PA) is a natural toxic pyridine derivative. Microorganisms can degrade and utilize PA for growth. However, the full catabolic pathway of PA and its physiological and genetic foundation remain unknown. In this study, we identified a gene cluster, designated <i>picRCEDFB4B3B2B1A1A2A3</i>, responsible for the degradation of PA from <i>Alcaligenes faecalis</i> JQ135. Our results suggest that PA degradation pathway occurs as follows: PA was initially 6-hydroxylated to 6-hydroxypicolinic acid (6HPA) by PicA (a PA dehydrogenase). 6HPA was then 3-hydroxylated by PicB, a four-component 6HPA monooxygenase, to form 3,6-dihydroxypicolinic acid (3,6DHPA), which was then converted into 2,5-dihydroxypyridine (2,5DHP) by the decarboxylase PicC. 2,5DHP was further degraded to fumaric acid through PicD (2,5DHP 5,6-dioxygenase), PicE (<i>N</i>-formylmaleamic acid deformylase), PicF (maleamic acid amidohydrolase), and PicG (maleic acid isomerase). Homologous <i>pic</i> gene clusters with diverse organizations were found to be widely distributed in <i>Alpha</i>-, <i>Beta</i>-, and <i>Gammaproteobacteria</i> Our findings provide new insights into the microbial catabolism of environmental toxic pyridine derivatives.<b>IMPORTANCE</b> Picolinic acid is a common metabolite of l-tryptophan and some aromatic compounds and is an important intermediate in organic chemical synthesis. Although the microbial degradation/detoxification of picolinic acid has been studied for over 50 years, the underlying molecular mechanisms are still unknown. Here, we show that the <i>pic</i> gene cluster is responsible for the complete degradation of picolinic acid. The <i>pic</i> gene cluster was found to be widespread in other <i>Alpha</i>-, <i>Beta</i>-, and <i>Gammaproteobacteria</i> These findings provide a new perspective for understanding the catabolic mechanisms of picolinic acid in bacteria.
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