Research Institute for the Environment and Livelihoods, Ellengowan Drive, Casuarina, Charles Darwin University, Darwin, NT, Australia.
Power and Water Corporation, Water Services, P.O. Box 37471, Winnellie, NT, Australia.
Harmful Algae. 2023 Aug;127:102476. doi: 10.1016/j.hal.2023.102476. Epub 2023 Jul 5.
Cyanobacteria can dominate the algal community in wastewater ponds, which can lead to the production of cyanotoxins and their release into the environment. We applied traditional and molecular techniques to identify cyanotoxin hazards and high-risk periods in a tropical wastewater treatment system. Potentially toxic cyanobacteria were identified by microscopy and amplicon sequencing over the course of a year. Toxin gene levels were monitored and compared to toxin production to identify likely toxin producing species and high-risk periods. Cyanobacteria were persistent in the effluent year-round, with Planktothrix and Microcystis the most abundant genera; Microcystis could not be resolved beyond genus using amplicon sequencing, but M. flos-aquae was identified as a dominant species by microscopy. Microcystin toxin was detected for the first time in treated effluent at the beginning of the wet season (December 2018), which correlated with an increase in Microcystis amplicon sequence abundance and elevated microcystin toxin gene (mcyE/ndaF) levels. Concomitantly, microscopy data showed an increase in M. flos-aquae but not M. aeruginosa. These data informed a refined sampling campaign in 2019 and results showed a strong correlation between mcyE/ndaF gene abundance, microcystin toxin levels and Microcystis amplicon sequence abundance. Microscopy data showed that in addition to M. flos-aquae, M. aeruginosa was also abundant in February and March 2019, with highest levels coinciding with toxin detection and toxin gene levels. M. aeruginosa was the most abundant Microcystis species detected in selected treated effluent samples by metagenomics analysis, and elevated levels coincided with toxin production. All microcystin genes in the biosynthesis pathway were detected, but microcystin genes from Planktothrix agardhii were not detected. Gene toxin assays were successfully used to predict microcystin production in this wastewater system. Changes in amplicon sequence relative abundance were a useful indicator of changes in the cyanobacterial community. We found that metagenomics was useful not just for identifying the most abundant Microcystis species, but the detection of microcystin biosynthesis genes helped confirm this genus as the most likely toxin producer in this system. We recommend toxin gene testing for the early detection of potential toxin producing cyanobacteria to manage the risk of toxicity and allow the implementation of risk management strategies.
蓝藻可以在废水池塘中主导藻类群落，从而导致产生蓝藻毒素并将其释放到环境中。我们应用传统和分子技术来识别热带废水处理系统中的蓝藻毒素危害和高风险期。通过一整年的显微镜检查和扩增子测序，确定了潜在的有毒蓝藻。监测毒素基因水平并将其与毒素产生进行比较，以确定可能产生毒素的物种和高风险期。蓝藻在全年的废水中都很持久，最丰富的属是束丝藻属和微囊藻属；使用扩增子测序无法将微囊藻属进一步解析到种的水平，但通过显微镜检查鉴定出 M. flos-aquae 是优势种。在湿季开始时（2018 年 12 月），首次在处理过的废水中检测到微囊藻毒素，这与微囊藻属扩增子序列丰度增加和微囊藻毒素基因（mcyE/ndaF）水平升高有关。同时，显微镜数据显示 M. flos-aquae 增加，但 M. aeruginosa 没有增加。这些数据为 2019 年的精细化采样活动提供了信息，结果表明 mcyE/ndaF 基因丰度、微囊藻毒素水平和微囊藻属扩增子序列丰度之间存在很强的相关性。显微镜数据显示，除了 M. flos-aquae 外，M. aeruginosa 在 2019 年 2 月和 3 月也很丰富，毒素检测和毒素基因水平最高时 coincide。宏基因组分析检测到在选定的处理过的废水样本中最丰富的微囊藻物种是 M. aeruginosa，并且毒素产生时水平升高。生物合成途径中的所有微囊藻毒素基因都被检测到，但未检测到束丝藻属的微囊藻毒素基因。基因毒素测定成功地用于预测该废水系统中的微囊藻毒素产生。扩增子序列相对丰度的变化是蓝藻群落变化的有用指标。我们发现，宏基因组学不仅有助于识别最丰富的微囊藻物种，而且检测微囊藻生物合成基因有助于确认该属是该系统中最有可能的产毒物种。我们建议进行毒素基因检测，以早期检测潜在的产毒蓝藻，从而管理毒性风险并实施风险管理策略。
