Abstract：
Blooms of the red, filamentous cyanobacterium Planktothrix rubescens occur frequently in pre-alpine lakes in Europe, often with concomitant toxic microcystin (MC) production. Trophic transfer of MCs has been observed in bivalves, fish, and zooplankton species, while uptake of MCs into Diptera species could facilitate distribution of MCs into terrestrial food webs and habitats. In this study, we characterized a Planktothrix bloom in summer 2019 in Lake Mindelsee and tracked possible trophic transfer and/or bioaccumulation of MCs via analysis of phytoplankton, zooplankton (Daphnia) and emergent aquatic insects (Chaoborus, Chironomidae and Trichoptera). Using 16 S rRNA gene amplicon sequencing, we found that five sequence variants of Planktothrix spp. were responsible for bloom formation in September and October of 2019, and these MC-producing variants, provisionally identified as P. isothrix and/or P. serta, occurred exclusively in Lake Mindelsee (Germany), while other variants were also detected in nearby Lake Constance. The remaining cyanobacterial community was dominated by Cyanobiaceae species with high species overlap with Lake Constance, suggesting a well-established exchange of cyanobacteria species between the adjacent lakes. With targeted LC-HRMS/MS we identified two MC-congeners, MC-LR and [Asp3]MC-RR with maximum concentrations of 45 ng [Asp3]MC-RR/L in lake water in September. Both MC congeners displayed different predominance patterns, suggesting that two different MC-producing species occurred in a time-dependent manner, whereby [Asp3]MC-RR was clearly associated with the Planktothrix spp. bloom. We demonstrate an exclusive transfer of MC-LR, but not [Asp3]MC-RR, from phytoplankton into zooplankton reaching a 10-fold bioconcentration, yet complete absence of these MC congeners or their conjugates in aquatic insects. The latter demonstrated a limited trophic transfer of MCs from zooplankton to zooplanktivorous insect larvae (e.g., Chaoborus), or direct transfer into other aquatic insects (e.g. Chironomidae and Trichoptera), whether due to avoidance or limited uptake and/or rapid excretion of MCs by higher trophic emergent aquatic insects.
摘要：
绽放的红色，欧洲高山湖泊中经常出现丝状蓝藻浮游蓝藻，通常伴随有毒微囊藻毒素（MC）的产生。在双壳类动物中观察到MC的营养转移，鱼,和浮游动物物种，而将MC吸收到双翅目物种中可以促进MC在陆地食物网和栖息地中的分布。在这项研究中,我们在2019年夏季在Mindelsee湖进行了浮游生物开花的特征，并通过浮游植物的分析跟踪了MC可能的营养转移和/或生物积累，浮游动物（水蚤）和新兴水生昆虫（Chaoborus，Chironomidae和毛翅目）。使用16SrRNA基因扩增子测序，我们发现了Planktothrixspp的五个序列变体。负责2019年9月和10月的水华形成，这些产生MC的变体，暂时鉴定为P.isothrix和/或P.serta，仅发生在明德尔湖（德国），而在附近的康斯坦茨湖也检测到其他变异。剩余的蓝藻群落以与康斯坦茨湖高度重叠的蓝藻科物种为主，表明相邻湖泊之间蓝藻物种的良好交换。通过靶向LC-HRMS/MS，我们确定了两个MC同源物，9月湖水中MC-LR和[Asp3]MC-RR的最大浓度为45ng[Asp3]MC-RR/L。两种MC同源物显示出不同的优势模式，表明两种不同的MC产生物种以时间依赖性的方式发生，其中[Asp3]MC-RR与Planktothrixspp明显相关。bloom.我们展示了MC-LR的独家转让，但不是[Asp3]MC-RR，从浮游植物到浮游动物达到10倍的生物富集，但在水生昆虫中完全不存在这些MC同源物或其缀合物。后者证明了MC从浮游动物到浮游动物昆虫幼虫的营养转移有限（例如，Chaoborus),或直接转移到其他水生昆虫中（例如摇蚊科和毛翅目），是否由于较高营养性的水生昆虫对MC的避免或有限的吸收和/或快速排泄。
