Cyanobacterial biomass forecasts currently cannot predict the concentrations of microcystin, one of the most ubiquitous cyanotoxins that threaten human and wildlife health globally. Mechanistic insights into how microcystin production and biodegradation by heterotrophic bacteria change spatially and throughout the bloom season can aid in toxin concentration forecasts. We quantified microcystin production and biodegradation during two growth seasons in two western Lake Erie sites with different physicochemical properties commonly plagued by summer Microcystis blooms. Microcystin production rates were greater with elevated nutrients than under ambient conditions and were highest nearshore during the initial phases of the bloom, and production rates were lower in later bloom phases. We examined biodegradation rates of the most common and toxic microcystin by adding extracellular stable isotope-labeled microcystin-LR (1 μg L⁻¹), which remained stable in the abiotic treatment (without bacteria) with minimal adsorption onto sediment, but strongly decreased in all unaltered biotic treatments, suggesting biodegradation. Greatest biodegradation rates (highest of −8.76 d⁻¹, equivalent to the removal of 99.98% in 18 h) were observed during peak bloom conditions, while lower rates were observed with lower cyanobacteria biomass. Cell-specific nitrogen incorporation from microcystin-LR by nanoscale imaging mass spectrometry showed that a small percentage of the heterotrophic bacterial community actively degraded microcystin-LR. Microcystin production and biodegradation rates, combined with the microcystin incorporation by single cells, suggest that microcystin predictive models could be improved by incorporating toxin production and biodegradation rates, which are influenced by cyanobacterial bloom stage (early vs. late bloom), nutrient availability, and bacterial community composition.

中文翻译：

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伊利湖西部盆地微囊藻毒素产量和生物降解率的量化

蓝藻生物量预测目前无法预测微囊藻毒素的浓度，微囊藻毒素是威胁全球人类和野生动物健康的最普遍的蓝藻毒素之一。对异养细菌的微囊藻毒素生产和生物降解如何在空间上和整个开花季节变化的机制见解有助于预测毒素浓度。我们量化了伊利湖西部两个地点在两个生长季节的微囊藻毒素生产和生物降解，这些地点具有不同的物理化学特性，通常受到夏季微囊藻的困扰绽放。养分升高的微囊藻毒素生产率高于环境条件下，并且在开花的初始阶段近岸最高，而在后期开花阶段的产量较低。我们通过添加细胞外稳定同位素标记的微囊藻毒素-LR (1 μ g L ^-1 )检测了最常见和有毒的微囊藻毒素的生物降解率 ，其在非生物处理（无细菌）中保持稳定，对沉积物的吸附最小，但显着降低在所有未改变的生物处理中，表明生物降解。最大的生物降解率（最高 -8.76 d ^-1，相当于在 18 小时内去除 99.98%）在水华高峰期观察到，而在蓝藻生物量较低的情况下观察到较低的速率。通过纳米级成像质谱从微囊藻毒素-LR 中的细胞特异性氮掺入表明，一小部分异养细菌群落主动降解微囊藻毒素-LR。微囊藻毒素的产生和生物降解率，结合单细胞的微囊藻毒素掺入，表明微囊藻毒素预测模型可以通过结合毒素产生和生物降解率来改进，这受蓝藻开花阶段（早期与晚期开花）、养分可用性和细菌群落组成。