Microcystins produced during harmful cyanobacterial blooms are a public health concern. Although patterns are emerging, the environmental cues that stimulate production of microcystin remain confusing, hindering our ability to predict fluctuations in bloom toxicity. In earlier work, growth at cool temperatures relative to optimum (18°C vs. 26°C) was confirmed to increase microcystin quota in batch cultures of Microcystis aeruginosa NIES-843. Here, we tested this response in M. aeruginosa PCC 7806 using continuous cultures to examine temporal dynamics and using RNA-sequencing to investigate the physiological nature of the response. A temperature reduction from 26 to 19°C increased microcystin quota ∼2-fold, from an average of ∼464 ag μm^–3 cell volume to ∼891 ag μm^–3 over a 7–9 d period. Reverting the temperature to 26°C returned the cellular microcystin quota to ∼489 ag μm^–3. Long periods (31–42 d) at 19°C did not increase or decrease microcystin quota beyond that observed at 7–9 d. Nitrogen concentration had little effect on the overall response. RNA sequencing indicated that the decrease in temperature to 19°C induced a classic cold-stress response in M. aeruginosa PCC 7806, but this operated on a different timescale than the increased microcystin production. Microcystin quota showed a strong 48- to 72-h time-lag correlation to mcy gene expression, but no correlation to concurrent mcy expression. This work confirms an effect of temperature on microcystin quota and extends our understanding of the physiological nature of the response.

有害蓝藻繁殖期间产生的微囊藻毒素是公共卫生问题。尽管出现了各种模式，但刺激微囊藻毒素产生的环境提示仍然令人困惑，从而阻碍了我们预测水华毒性波动的能力。在较早的工作中，相对于最佳温度（18°C），在低温下生长与 已确认26°C）可增加分批培养的微囊藻毒素配额 铜绿微囊藻NIES-843。在这里，我们在铜绿假单胞菌PCC 7806使用连续培养来检查时间动态，并使用RNA测序来研究响应的生理特性。从26到19℃升高微囊配额的温度降低〜2倍，从平均~464 AG微米^-3细胞体积~891 AG微米^-3在7-9 d周期。如果还原温度至26℃下返回的蜂窝微囊配额~489 AG微米^-3。在19°C的长时间（31–42 d），未增加或减少7–9 d观察到的微囊藻毒素配额。氮浓度对总体响应影响很小。RNA测序表明温度降低到19°C会引起典型的冷应激反应。铜绿假单胞菌PCC 7806，但其操作时间与增加的微囊藻毒素产量不同。微囊藻毒素配额显示出与48-72小时的强烈时滞相关性cy 基因表达，但与并发无关 cy表达。这项工作证实了温度对微囊藻毒素配额的影响，并扩展了我们对反应的生理本质的理解。