A rapid bioassay for detecting saxitoxins using a Daphnia acute toxicity test

Bioassays using Daphnia pulex and Moina micrura were designed to detect cyanobacterial neurotoxins in raw water samples. Phytoplankton and cyanotoxins from seston were analyzed during 15 months in a eutrophic reservoir. Effective time to immobilize 50% of the exposed individuals (ET₅₀) was adopted as the endpoint. Paralysis of swimming movements was observed between ∼0.5-3 h of exposure to lake water containing toxic cyanobacteria, followed by an almost complete recovery of the swimming activity within 24 h after being placed in control water. The same effects were observed in bioassays with a saxitoxin-producer strain of Cylindrospermopsis raciborskii isolated from the reservoir. Regression analysis showed significant relationships between ET₅₀vs. cell density, biomass and saxitoxins content, suggesting that the paralysis of Daphnia in lake water samples was caused by saxitoxins found in C. raciborskii. Daphnia bioassay was found to be a sensitive method for detecting fast-acting neurotoxins in natural samples, with important advantages over mouse bioassays.     

Assessment of microcystins in lake water and the omnivorous fish (Carassius gibelio, Bloch) in Lake Pamvotis (Greece) containing dense cyanobacterial bloom

Toxin-producing cyanobacteria in lakes and reservoirs form a threat to humans as well as various forms of aquatic life. This study examined the occurrence and distribution of Microcystins (MCYST) in the shallow eutrophic lake Pamvotis (Greece). MCYST concentrations in the tissues (liver, kidneys, intestine, gonads, brain and muscle) of the fish species Carassius gibelio were also examined. Tests were performed with an enzyme-linked immunosorbent assay (ELISA). MCYST concentration in water and in the scum of Lake Pamvotis were highest during the warm period (April–October, 2005). Phytoplankton samples were dominated by the genera Microcystis and Anabaena during the same period. MCYST values were always below the WHO Guide level for recreational waters but much higher than the WHO Guide level for drinking water. It was found that MCYST can accumulate in the fish tissues of C. gibelio. Even though the target organ for MCYST is the liver, in our study MCYST were found also in the rest of C. gibelio tissues in the following order: intestine> kidney> > brain>gonads> muscle. Muscle tissue contained concentrations of microcystins that correspond to 0.096 μg/kg/day well above the recommended limit for human consumption (0.04 μg/Kg/day).     

特殊风场条件对太湖蓝藻水华迁移的影响研究

在高温、微风气象条件下,适宜蓝藻水华形成。在特殊非均一风场的驱动下,太湖蓝藻水华迁移过程与被均匀风场驱动有所不同。选取太湖典型风向进行分析,并采用三维水动力水质模型对表面非均一风场条件下的风生流流场及水质进行模拟,结果表明,在特殊非均一风场的驱动下,当太湖蓝藻浓度较高时,容易在西部湖区特别在竺山湖、梅梁湾湾内、岸边及湾口聚集,形成水华暴发,这有助于研究太湖污染物及蓝藻水华的输移及空间分布和机理。     

Partial characterization,UV-induction and photoprotective function of sunscreen pigment,scytonemin from Rivularia sp. HKAR-4

Scytonemin, located in the extracellular polysaccharide sheath of some cyanobacterial species is considered an efficient natural photoprotectant against lethal doses of ultraviolet (UV) radiations. In the present study, scytonemin from the cyanobacterium Rivularia sp. HKAR-4 was partially characterized and investigated for its induction by UV radiation as well as its role in photoprotection. High-performance liquid chromatography (HPLC) with photodiode-array detection studies revealed the presence of an UV-absorbing compound with absorption maximum at 386 nm. Based on its absorption spectrum and ion trap liquid chromatography/mass spectrometry (LC/MS) analysis, the compound was confirmed as scytonemin. In comparison to photosynthetically active radiation, a significant induction in the synthesis of scytonemin was found under UV-stress. Scytonemin also exhibited efficient photoprotective ability by detoxifying the in vivo reactive oxygen species (ROS) generated by UV radiation and by reducing the formation of thymine dimers. To the best of our knowledge this is the first report on the UV-screening effects of scytonemin on in vivo ROS generation and thymine dimer formation in any cyanobacterial strain. Based on these findings, we conclude that scytonemin may play a vital role in the survival and sustainability of cyanobacterial life in adverse environmental conditions such as under high solar irradiances.     

Increasing nitrogen limitation in the Bothnian Sea,potentially caused by inflow of phosphate-rich water from the Baltic Proper

The study showed that the open water of the Bothnian Sea (BS) is likely to have shifted from altering nitrogen and phosphorous limitations of the spring bloom to more nitrogen-limited conditions during the last 20 years. This is affected by the by inflow of phosphate-rich and oxygen-depleted water from depths near the halocline in the northern Baltic Proper, where severe oxygen conditions currently cause extreme phosphate concentrations in the deep water. The change in relation between inorganic nitrogen and phosphorous in the BS occurs first in the deep water and then progresses to the surface water. The change can potentially cause increased production in the BS and more frequent cyanobacterial blooms. There does not appear to be any immediate concern in the short-term perspective for the state of the BS, but a progression of the processes may lead to a more eutrophic state of the BS.

Electronic supplementary material

The online version of this article (doi:10.1007/s13280-015-0675-3) contains supplementary material, which is available to authorized users.     

微囊藻毒素毒理学研究综述

微囊藻毒素常见于富营养化的水体中，结构是单环多肽链，其中均含有特殊的必要需活性氨基酸基团。ＭＣＹＳＴ的化学性质稳定，但可被生物降解和ＵＶ光解。利福平等化学保护剂可预防其毒作用。该文就ＭＣＹＳＴ的理化性质，暴露剂量，毒作用及机理，预防等各方面的研究，作一综述。     

Modelling the effect of planktivorous fish removal in a reservoir on the biomass of cyanobacteria

In 2002, a “top-down” biomanipulation (reduction of biomass of planktivorous fish Carassius auratus) had been successfully carried out in a small reservoir of the river Bugach (Krasnoyarsk, Russia), after which the cyanobacterial blooming ceased. However, the reservoir ecosystem was absolutely free of Daphnia – the main link of trophic cascade. As supposed, the reduction of blooming was the result of suppression of a direct stimulation effect of planktivorous fish on cyanobacteria, revealed earlier in laboratory experiments. The question arose as to whether the effect of stimulation of cyanobacteria revealed in laboratory may lead to the changes in biomass of cyanobacteria in the reservoir, observed after the biomanipulation.To test this supposition, a mathematical model describing growth of cyanobacteria in the reservoir was developed. The modelling results and field data on biomass of cyanobacteria in summer closely coincided. Modelling calculations showed that direct influence of planktivorous fish could cause the second summer peak of water blooming by Microcystis. On the contrary, removal of crucian carp from the reservoir will not affect the level of water blooming caused by cyanobacteria Anabaena, as this species’ growth is not stimulated by fish.     

巢湖蓝藻重度发生时的水质特征分析

通过2004~2006年以来气象卫星观测和现场实时的水质监测结果,得出巢湖蓝藻重度发生时的水质特征,并对预警蓝藻发生的监测点位以及利用卫片解译蓝藻时应注意的问题提出建议。     

Cyanobacterial bloom dynamics in Lake Taihu

<正>Lake Taihu is the third largest freshwater lake in China and serves as an important drinking water source for the local populace;however,decades of excessive nutrient loading fueled by anthropogenic activities have resulted in hypertrophic conditions,promoting the annual formation of nuisance phytoplankton blooms(Chen et al.,2003;Duan et al.,2009)     

Influence of zeta potential on the flocculation of cyanobacteria cells using chitosan modified soil

Using chitosan modified soil to flocculate and sediment algal cells has been considered as a promising strategy to combat cyanobacteria blooms in natural waters. However, the flocculation efficiency often varies with algal cells with different zeta potential (ZP) attributed to different growth phases or water conditions. This article investigated the relationship between ZP of Microcystis aeruginosa and its influence to the flocculation efficiency using chitosan modified soil. Results suggested that the optimal removal efficiency was obtained when the ZP was between -20.7 and -6.7 mV with a removal efficiency of more than 80% in 30 min and large floc size of >350 μm. When the algal cells were more negatively charged than -20.7 mV, the effect of chitosan modified soil was depressed (<60%) due to the insufficient charge density of chitosan to neutralize and destabilize the algal suspension. When the algal cells were less negative than -6.7 mV or even positively charged, a small floc size (<120 μm) was formed, which may be difficult to sink under natural water conditions. Therefore, manipulation of ZP provided a viable tool to improve the flocculation efficiency of chitosan modified soil and an important guidance for practical engineering of cyanobacteria bloom control.