Biotoxin Tropolone Contamination Associated with Nationwide Occurrence of Pathogen Burkholderia plantarii in Agricultural Environments in China

Abstract

Tropolone, a biotoxin produced by the agricultural pathogen Burkholderia plantarii, exerts cytotoxicity toward a wide array of biota. However, due to the lack of quantitative and qualitative approach, both B. plantarii occurrence and tropolone contamination in agricultural environments remain poorly understood. Here, we presented a sensitive and reliable method for detection of B. plantarii in artificial, plant, and environmental matrices by tropolone-targeted gas chromatography-triple-quadrupole tandem mass spectrometry analysis. Limits of detection for B. plantarii and tropolone were 10 colony-forming units (CFU)/mL and 0.017 mu g/kg, respectively. In a series of simulation trials, we found that B. plantarii from 10 to 108 CFU/mL produced tropolone between 0.006 and 107.8 mg/kg in a cell-population-dependent manner, regardless of habitat. Correlation analysis clarified a reliable reflection of B. plantarii density by tropolone level with R-2 values from 0.9201 to 0.9756 (p < 0.01). Through a nationwide pilot study conducted in China, tropolone contamination was observed at 0.014-0.157 mg/kg in paddy soil and rice grains, and subsequent redundancy analysis revealed soil organic matter to be a dominant environmental factor, having a positive correlation with tropolone contamination. In this context, our results imply that potential ecological and dietary risks posed by long-term exposure to trace levels of tropolone contamination are of concern.