Biodegradation of quinolinic acid by a newly isolated bacterium Alcaligenes faecalis strain JQ191

Quinolinic acid (QA) is a pyridine derivative that can be found in many organisms and is widely used in the chemical industry. However, QA possesses excitotoxic properties. To date, the catabolism of QA mediated by microorganisms has rarely been reported. In this study, a QA-degrading strain (JQ191) was isolated from sewage sludge. Based on phenotypic and 16S rRNA gene phylogenetic analysis, the strain was identified as Alcaligenes faecalis. Strain JQ191 was able to utilize QA as the sole source of carbon and nitrogen for growth. QA-cultured cells of JQ191 completely degrade 200 mg/L QA within 2 days in a mineral salt medium, whereas the LB-cultured cells experienced a 2-day lag period before degrading QA, indicating that the catabolic enzymes involved in QA degradation were induced by QA. 6-Hydroxypicolinic acid (6HPA) was identified as an intermediate of QA degradation by strain JQ191. A 6HPA monooxygenase gene picB was cloned, genetically disrupted, and heterologously expressed, and the results show that picB was responsible for catalyzing 6HPA to 3,6DHPA in JQ191. A new QA mineralization pathway was proposed. This study identifies a new bacterium candidate that has a potential application prospect in the bioremediation of QA-polluted environment, as well as provides new insights into the bacterial catabolism of QA.