Characterization of the Nicotinic Acid and 6‐Hydroxynicotinic Acid Dehydrogenase Complexes in Bacillus niacini

Abstract

N‐Heteroaromatic compounds (NHACs) are prominent environmental contaminants that have cytotoxic, mutagenic, and carcinogenic effects on organisms. NHACs are highly persistent within the environment and strategies to remove these contaminants from aquatic environments have been largely ineffective. Therefore, more research regarding bioremediation is warranted. Several bacteria have been discovered to degrade NHACs, such as Pseudomonas, Bordetella, and Bacillus. These organisms can also catabolize nicotinic acid providing a model NHAC pathway to investigate. The nicotinic acid degradation mechanisms in P. putida and B. pertussis have largely been determined. The pathway of nicotinic acid catabolism and the catalysts in B. niacini are not established. Elucidating this mechanism will allow for optimizing bioremediation applications. Interestingly, all three organisms share a common first hydroxylation step catalyzed by nicotinic acid dehydrogenase. The pathway in B. niacini then diverges with a second hydroxylation step catalyzed by 6‐hydroxynicotinic acid dehydrogenase. Through genome sequencing, a novel gene cluster has been identified, putatively suggesting that four proteins are involved in the two‐hydroxylation steps: NicA1, NicA‐2, NicB1, and NicB2. It is further hypothesized that these proteins form multi‐subunit complexes known as NicAB, perhaps similar to the nicotinate dehydrogenase complex in Eubacterium barkeri. To confirm the gene annotations and determine the oligomerization of the functional NicAB complex in B. niacini, specific deletion mutants will be constructed and analyzed for their ability to survive on minimal media supplemented with nicotinic acid or 6‐hydroxynicotinic acid.Support or Funding InformationThis work was funded by the Department of Chemistry and the Henry J. Copeland Fund for Independent Study at The College of Wooster.