Properly interpret metabolic inhibition results to identify primary mercury methylating microbes

Distinguishing the respective contributions of various microbes to methylmercury (MeHg) production is critical for predicting MeHg bioaccumulation and exposure risk. Metabolic inhibitors have been commonly used to block the activity of specific microbial groups and identify primary Hg methylating microbes. By reviewing literatures and our empirical data, we demonstrate how multiple factors, including (1) the addition of inappropriate amounts of inhibitors, (2) a tendency to overlook microbial syntrophy, and (3) the absence of comprehensive proxy systems of Hg methylation, would impact result interpretation of this approach. We thus suggest that the design of inhibition assays should consider the environmental properties, e.g., background levels of electron acceptors, concentrations of metabolic substrates, and abundances of Hg methylating microbes. We also recommend that inhibitors should be added at multiple concentrations and that observed changes in Hg methylation should be assessed with comprehensive indicators. Revealing the key factors responsible for the improper usage of this method and inadequate interpretation of the results would help optimize inhibition assays for robust predictions of MeHg production in nature.

Automated summary

Distinguishing the contributions of different microbes to methylmercury production is crucial for predicting bioaccumulation and exposure risk. However, there are several factors that can impact the interpretation of inhibition assays, including the addition of inappropriate amounts of inhibitors, overlooking microbial syntrophy, and the absence of comprehensive proxy systems. To improve the accuracy of inhibition assays, environmental properties and concentrations of inhibitors should be considered, and comprehensive indicators should be used to assess changes in methylmercury production.