Citation:

Duan, X., C. Zhang, I. Struewing, X. Li, Hubert Allen, AND J. Lu. Cyanotoxin-encoding genes as powerful predictors of cyanotoxin production during harmful cyanobacterial blooms in an inland freshwater lake: Evaluating a novel early-warning system. SCIENCE OF THE TOTAL ENVIRONMENT. Elsevier BV, AMSTERDAM, Netherlands, 830:154568, (2022). https://doi.org/10.1016/j.scitotenv.2022.154568

Impact/Purpose:

1) Public concern over cyanobacterial blooms has increased due to their higher frequency of occurrences and their potential ecological and health impacts. 2) Investigation of MCer population compositions, their correlations, dominance, toxin gene expressions and relationships between MC and MCers with extant and expressed toxin genes was conducted using a panel of qPCR assays targeting mcyA, E and G on weekly water samples in an Ohio inland lake. Further validated early warning of MC exceeding a US EPA Health Advisory cutoff value (>0.3µg L-1) was also made based on signaling of qPCR and RT-qPCR using receiver operating characteristic curves.3) This information can be used to aid in toxin measurements and aid in making management decisions related to harmful algal blooms. 4) OW, regional offices, scientists and water quality managers could be interested in the results.

Description:

Freshwater harmful cyanobacterial blooms (HCBs) potentially produce excessive cyanotoxins, mainly microcystins (MCs), significantly threatening aquatic ecosystems and public health. Accurately predicting HCBs is thus essential to developing effective HCB mitigation and prevention strategies. We previously developed a novel early-warning system that uses cyanotoxin-encoding genes to predict cyanotoxin production in Harsha Lake, Ohio, USA, in 2015. In this study, we evaluated the efficacy of the early-warning system in forecasting the 2016 HCB in the same lake. We also examined potential HCB drivers and cyanobacterial community composition. Our results revealed that the cyanobacterial community was stable at the phylum level but changed dynamically at the genus level over time. Microcystis and Planktothrix were the major MC-producing genera that thrived in June and July and produced high concentrations of MCs (peak level 10.22 μg·L−1). The abundances of the MC-encoding gene cluster mcy and its transcript levels significantly correlated with total MC concentrations (before the MC concentrations peaked) and accurately predicted MC production as revealed by logistic equations. When the Microcystis-specific gene mcyG reached approximately 1.5 × 103 copies·mL−1 or when its transcript level reached approximately 2.4 copies·mL−1, total MC level exceeded 0.3 μg L−1 (a health advisory limit) approximately one week later (weekly sampling scheme). This study suggested that cyanotoxin-encoding genes are promising predictors of MC production in inland freshwater lakes, such as Harsha Lake. The evaluated early-warning system can be a useful tool to assist lake managers in predicting, mitigating, and/or preventing HCBs.

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