Genetic and Biochemical Characterization of a Gene Operon for -Aconitic Acid, a Novel Nematicide from .

-Aconitic acid (TAA) is an isomer of -aconitic acid (CAA), an intermediate of the tricarboxylic acid cycle that is synthesized by aconitase. Although TAA production has been detected in bacteria and plants for many years and is known to be a potent inhibitor of aconitase, its biosynthetic origins and the physiological relevance of its activity have remained unclear. We have serendipitously uncovered key information relevant to both of these questions. Specifically, in a search for novel nematicidal factors from , a significant nematode pathogen harboring many protein virulence factors, we discovered a high yielding component that showed activity against the plant-parasitic nematode and surprisingly identified it as TAA. Comparison with CAA, which displayed a much weaker nematicidal effect, suggested that TAA is specifically synthesized by as a virulence factor. Analysis of mutants deficient in plasmids that were anticipated to encode virulence factors allowed us to isolate a TAA biosynthesis-related () operon consisting of two genes, and We expressed the corresponding proteins, TbrA and TbrB, and characterized them as an aconitate isomerase and TAA transporter, respectively. Bioinformatics analysis of the TAA biosynthetic gene cluster revealed the association of the TAA genes with transposable elements relevant for horizontal gene transfer as well as a distribution across bacteria and other strains, suggesting a general role for TAA in the interactions of group bacteria with nematode hosts in the soil environment. This study reveals new bioactivity for TAA and the TAA biosynthetic pathway, improving our understanding of virulence factors employed by pathogenesis and providing potential implications for nematode management applications.