蓝藻毒素对底栖动物的毒理学研究进展

近年,由于人类活动加剧,大量氮磷等营养物质流入湖泊等缓流水体,导致水体富营养化。而由此引起有害蓝藻水华的频繁爆发,使生态环境和人类健康受到严重威胁。相关研究表明,蓝藻水华的爆发不仅能够使水体水质恶化,其中一些产毒藻类还会产生大量蓝藻毒素,对水生生物产生重要影响。底栖动物作为水体生态系统的重要组成部分,在食物网中有重要作用,同时其中的许多种类又与人类息息相关,因此关于水华蓝藻毒素对淡水底栖动物的毒理学研究具有重要意义。在介绍蓝藻毒素概况的基础上,综述了蓝藻毒素的致毒机理和对底栖动物的影响,展望了研究方向。     

一株囊藻毒素降解辅助菌的发现

太湖、滇池等水体爆发的蓝藻水华,对水体生态环境及人们生活带来了严重的影响,引起了各级政府的高度重视。目前每年从太湖中打捞的水华数以亿吨计,但由于其毒性较大,无法利用,同时大规模发生蓝藻的水体底泥藻毒素含量也在不断提高。微囊藻毒素(Microcystins,MCs)是由淡水藻如微囊藻属、鱼腥藻属、     

蓝藻毒素的类型及其产毒基因

水体富营养化及蓝藻水华的频繁发生,严重破坏水域生态系统,有毒水华蓝藻产生的藻毒素,污染水体且危害水生动物和人类健康。本文综述了水华蓝藻的次级代谢产物藻毒素及藻毒素合成基因的国内外研究进展,介绍了蓝藻毒素的类型、不同毒素毒性机理、产毒基因以及利用产毒基因进行产毒蓝藻的分子生物学检测等,并对研究中存在的问题和未来的研究方向进行了展望,目的是为建立有毒水华蓝藻的预警机制、科学评价产毒蓝藻及其藻毒素的生态、环境危害及生态环境治理提供理论和技术支撑。     

微囊藻毒素生物合成基因及其功能研究进展

水体富营养化加剧,导致了蓝藻水华在世界范围内频发。蓝藻产生的微囊藻毒素是最常见的一种藻毒素,对人类和动物造成了很大的危害甚至导致死亡。微囊藻毒素经非核糖体合成途径由多肽合成酶合成。对微囊藻毒素的结构与性质、微囊藻毒素合成基因的功能及其生物合成、微囊藻毒素的分子生物学检测技术进行了评述,对未来的研究方向进行了展望。     

微囊藻毒素对鱼类的毒性效应

湖泊富营养化导致的蓝藻水华已成为国内外普遍关注的环境问题,它所带来的主要危害之一是产生的藻毒素对鱼类的影响。在已发现的藻毒素中,微囊藻毒素(microcystins,MCs)的分布广、毒性大、危害严重,而备受关注。阐述了MCs对鱼类的影响。微囊藻毒素能干扰胚胎的发育,降低孵化率,增加畸形率,影响存活率,胚胎孵化受微囊藻毒素影响还具有剂量依赖效应;野外室内实验均表明鱼类暴露于微囊藻毒素后不仅可在肝脏中富集还可在肌肉、肠道等组织器官中快速积累;对鱼类进行组织病理检测发现MCs可导致肝脏、肾脏、心脏、脑、鳃等组织受损;MCs在鱼体中的解毒过程可能开始于由谷胱甘肽S-转移酶催化的还原型谷胱甘肽的结合反应;MCs还可影响鱼类的生长、行为和血清生化指标,此外,还具有一定的免疫毒性。MCs的转运机制和分子作用机制以及在食物链中传递过程中对人类造成的潜在影响可能成为今后研究重点。     

微囊藻毒素LR诱导大鼠肾NRK细胞Bax蛋白表达

近年来水体富营养化已成为一个全球性关注的问题,过量的氮、磷使藻类过度生长并产生水华。微囊藻毒素是蓝藻的一些属产生的次生代谢产物,在发生水华的水体中这类毒素普遍存在。微囊藻毒素产生的原因和作用目前还不是很清楚,然而它们对动物和人类都能产生极为严重的影响。       

微囊藻毒素LR影响人肝细胞HL7702的ERK及JNK的蛋白磷酸化

微囊藻毒素(Microcystin,MCYST)是蓝藻的一些属产生的次级代谢产物,在发生水华的水体中普遍存在。微囊藻毒素LR(MCLR)是微囊藻毒素中存在最为普遍且毒性作用最强的一种。已有研究表明,微囊藻毒素可以诱发肝毒性并且与人群中的肝癌发生密切相关1,2,因此进一步阐明其致毒机理具有重要的意义。       

微囊藻胞内毒素的提取方法

随着全球淡水水体富营养化程度的不断加剧,蓝藻水华及其毒素污染问题已经逐渐威胁到人类饮用水的安全。微囊藻(Microcystis)为常见的水华蓝藻种类,其所产生的微囊藻毒素(Microcystins,MCs)不仅会严重危害水生态系统,并且可能会给人类健康带来威胁1,2。我国云南滇池、江苏太湖和安徽巢湖等淡水湖泊均发生不同程度的蓝藻水华,并检测到了高含量MCs的存在3,4。       

应用高通量实时荧光定量PCR方法筛选FL细胞对低剂量微囊藻毒素LR暴露的应答基因

微囊藻毒素是蓝藻的一些属产生的单环七肽,在发生水华的水体中普遍存在[1]。含有微囊藻毒素的水华能引起野生动物、鱼类、家畜、家禽等中毒和死亡,也对人类健康构成严重威胁[2,3]。流行病学调查发现,人群原发性肝癌、大肠癌发病率与饮水源中的微囊藻毒素有关[4]。其中微囊藻毒素LR是微囊藻毒素中最常见的一种,因其高急性毒性,强促癌活性而受到广泛的关注。有研究结果表明微囊藻毒素LR可引起多种细胞发生凋亡[5],本实验室先前的研究也发现微囊藻毒素LR能激活在凋亡过程中起重要作用的酶Caspase-3[6],及引起P53、Bax、Bcl-2等凋亡相关蛋白…     

加强蓝藻的研究

蓝藻属原核生物一大类,也有研究者把它列为蓝细菌（Cyanobacterium）,它与人类的关系非常密切,既有有益的一面,又有有害的一面。所谓害者,比如人们熟悉的造成湖泊水域“水华”的发生。它的疯长与繁衍,一是毒素蓝藻“水华”造成水域缺氧环境,使水产生物窒息而死;二是产毒素蓝藻,常见的有危害最重的微囊藻（Microcystisaeroginosa）;还有鱼腥藻（如Anabaenacireinalis及A．．flosaquae）、节球藻（Nodalaria）、鞘丝藻（Lyngbya）、水华束丝藻（Aphanizomenonflosaquae）、颤藻（Oscillatoria）等一些种类;三是水华藻体分解后产生大量恶臭有机物,污染环境。这一切会造成家畜、家禽、野生动物、鱼类等中毒致死,同时也给居民生活带来危害。为彻底解决有害水华蓝藻的问题,可以从以下几方面考虑：（1）首先要解决水环境富营养化即氮、磷等的污水流人问题。有关部门需采取综合防治措施,以防止污水流人,避免“水华”爆发。（2）就有害蓝藻本身而言,一是对产毒素蓝藻产毒产品和产毒机制作进一步研究,索取毒素产品以服务于民。     

微囊藻毒素对陆生植物的污染途径及累积研究进展

微囊藻毒素(Microcystins,MCs)是全世界范围内普遍存在、且随着水体污染的加剧而在自然环境中大量积聚的蓝藻毒素之一,对多种生物有着严重的毒性作用.MCs在生物体内富集并通过食物链传递,对人类健康造成威胁.近些年,MCs对陆生植物的毒害作用及累积研究尤为引人关注,取得了一批重要的研究成果.MC-LR(L为亮氨酸)和MC-RR(R为精氨酸)是淡水水体中普遍存在且危害较大的两种MCs异构体.针对这两种毒素,重点介绍其对陆生植物的污染途径、毒性作用及其在作物体内的累积量,对今后的研究进行了展望.     

Consumption of toxic cyanobacteria by Potamopyrgus antipodarum (Gastropoda, Prosobranchia) and consequences on life traits and microcystin accumulation

Among the wide range of toxins produced by cyanobacterial blooms, microcystins (MCs) are the most common and are known to accumulate in aquatic organisms. Freshwater gastropods are grazers and likely to ingest toxic cyanobacteria, particularly Planktothrix agardhii, one of the most common species in the northern hemisphere. The study examines (i) the ingestion of toxic P. agardhii by the prosobranch Potamopyrgus antipodarum, (ii) the kinetics of MC accumulation and depuration in snail tissues during and post-exposure, and (iii) the impact of MCs on their life traits (survival, growth and fecundity). We showed that P. antipodarum ingested 71% of cyanobacteria available during the first 24 h in the presence or not of non-toxic food, and accumulated 1.3% of ingested MCs during the 5-week intoxication period. Elimination of MCs was total after 3 weeks of depuration. A decrease of growth and fecundity was observed during the intoxication period, but it was reversible after the end of exposure. Results are discussed in terms of variation of the response between prosobranch and pulmonate gastropods to toxic cyanobacteria exposure, and the negative impact of toxic cyanobacteria on natural communities of freshwater gastropods.     

Depth profiles of cyanobacterial hepatotoxins (microcystins) in three Turkish freshwater lakes

The Turkish freshwater lakes, Sapanca, Iznik and Taskisi (Calticak) have been enriched with nutrients from agriculture and domestic sources for many years. A major bloom of cyanobacteria (blue-green algae) in Lake Sapanca was recorded in May 1997, closely followed by a fish kill. Investigations were subsequently made on the cyanobacteria and water quality of the lakes, including analysis for cyanobacterial hepatotoxins (microcystins) in the filtered particulate fraction. Samples, taken from the beginning of May to end of August 1998, were analysed for microcystins by high–performance liquid chromatography with photodiode array detection (HPLC-PDA), protein phosphatase inhibition assay (PPIA) and an enzyme-linked immunosorbent assay (ELISA). No microcystins were detected in the water column in Lake Sapanca above 10 m, but toxins were found in filtered cyanobacterial samples from 20 m depth at a concentration of 3.65 μg l^?1 microcystin–LR equivalents. Ninety percent of the microcystin pool detected in L. Sapanca was found between depths of 15 and 25 m. The principal microcystin detected by HPLC-PDA was similar to microcystin–RR. Two unidentified microcystin variants were found in Lake Taskisi surface samples at a concentration of 2.43 μg l^?1 microcystin–LR equivalents in the filtered cyanobacterial cell fraction. Although 10 water samples (10 × 5 l) were taken from Lake Iznik (surface to 20 m, 5 m intervals), no microcystins were detected by HPLC-PDA (limit of detection 10 ng). The depth at which microcystins were detected in L. Sapanca coincided with the draw-off depth for the drinking water supply for the city of Sakarya     

Turbulence increases the risk of microcystin exposure in a eutrophic lake (Lake Taihu) during cyanobacterial bloom periods

Toxic cyanobacterial harmful algal blooms (CyanoHABs) have posed serious water use and public health threats because of the toxins they produce, such as the microcystins (MCs). The direct physical effects of turbulence on MCs, however, have not yet been addressed and is still poorly elucidated. In this study, a 6-day mesocosm experiment was carried out to evaluate the effects of wind wave turbulence on the competition of toxic Microcystis and MCs production in highly eutrophicated and turbulent Lake Taihu, China. Under turbulent conditions, MCs concentrations (both total and extracellular) significantly increased and reached a maximum level 3.4 times higher than in calm water. Specifically, short term (∼3 days) turbulence favored the growth of toxic Microcystis species, allowing for the accumulation of biomass which also triggered the increase in MCs toxicity. Moreover, intense turbulence raises the shear stress and could cause cell mechanical damage or cellular lysis resulting in cell breakage and leakage of intracellular materials including the toxins. The results indicate that short term (∼3 days) turbulence is beneficial for MCs production and release, which increase the potential exposure of aquatic organisms and humans. This study suggests that the importance of water turbulence in the competition of toxic Microcystis and MCs production, and provides new perspectives for control of toxin in CyanoHABs-infested lakes.     

Increasing oxygen radicals and water temperature select for toxic Microcystis sp

Pronounced rises in frequency of toxic cyanobacterial blooms are recently observed worldwide, particularly when temperatures increase. Different strains of cyanobacterial species vary in their potential to produce toxins but driving forces are still obscure. Our study examines effects of hydrogen peroxide on toxic and non-toxic (including a non-toxic mutant) strains of M. aeruginosa. Here we show that hydrogen peroxide diminishes chlorophyll a content and growth of cyanobacteria and that this reduction is significantly lower for toxic than for non-toxic strains. This indicates that microcystins protect from detrimental effects of oxygen radicals. Incubation of toxic and non-toxic strains of M. aeruginosa with other bacteria or without (axenic) at three temperatures (20, 26 and 32°C) reveals a shift toward toxic strains at higher temperatures. In parallel to increases in abundance of toxic (i.e. toxin gene possessing) strains and their actual toxin expression, concentrations of microcystins rise with temperature, when amounts of radicals are expected to be enhanced. Field samples from three continents support the influence of radicals and temperature on toxic potential of M. aeruginosa. Our results imply that global warming will significantly increase toxic potential and toxicity of cyanobacterial blooms which has strong implications for socio-economical assessments of global change.     

The cyanotoxin-microcystins: current overview

The monocyclic heptapeptides microcystins (MCs), are a group of hepatotoxins, produced worldwide by some bloom-forming cyanobacterial species/strains both in marine and freshwater ecosystems. MCs are synthesized non-ribosomally by large multi-enzyme complexes consisting of different modules including polyketide synthases and non-ribosomal peptide synthetases, as well as several tailoring enzymes. More than 85 different variants of MCs have been reported to exist in nature. These are chemically stable, but undergo bio-degradation in natural water reservoirs. Direct or indirect intake of MCs through the food web is assumed to be a highly exposed route in risk assessment of cyanotoxins. MCs are the most commonly found cyanobacterial toxins that cause a major challenge for the production of safe drinking water and pose a serious threat to global public health as well as fundamental ecological processes due to their potential carcinogenicity. Here, we emphasize recent updates on different modes of action of their possible carcinogenicity. Besides the harmful effects on human and animals, MC producing cyanobacteria can also present a harmful effect on growth and development of agriculturally important plants. Overall, this review emphasizes the current understanding of MCs with their occurrence, geographical distribution, accumulation in the aquatic as well as terrestrial ecosystems, biosynthesis, climate-driven changes in their synthesis, stability and current aspects on its degradation, analysis, mode of action and their ecotoxicological effects.     

Oxidative stress response of <Emphasis Type="Italic">Synechocystis</Emphasis> sp. (PCC 6803) due to exposure to microcystin-LR and cell-free cyanobacterial crude extract containing microcystin-LR

Cyanobacteria are able to produce a variety of secondary metabolites such as the microcystins. The ecological role of microcystins for the cyanobacteria themselves and in the aquatic ecosystem is not well understood. The aim of this study is to evaluate if microcystins might be used as a communication tool for interspecies cyanobacterial communication via the promotion of oxidative stress. Reactive oxygen species (ROS) are known to be used as plant signals. The main questions relate to the promotion of oxidative stress in Synechocystis sp. via exposure to the cyanobacterial toxins and the physiological effects. This study shows a few markers for oxidative stress, such as the antioxidative enzymes superoxide dismutase, peroxidases and catalases, and cell damage due to extensive generation of ROS leading to lipid peroxidation. End products of lipid peroxidation (malonaldehyde and 4-hydroxynonenal) are conjugated by glutathione S-transferase.     

Grazing rates on toxic and non-toxic strains of cyanobacteria by Hypophthalmichthys molitrix and Oreochromis niloticus

The tilapia Oreochromis niloticus and the silver carp Hypophthalmichthys molitrix were exposed to toxic and non-toxic strains of the cyanobacterium Microcystis aeruginosa in order to determine if cells of the toxic strain were ingested and, if not, by what mechanism they were excluded. Enumeration of cyanobacterial particles before and after exposure to fish showed that there were no significant differences (P<0.05) at the end of the trial between the toxic treatment and the control consisting of toxic M. aeruginosa with no fish. Fish exposed to the non-toxic strain increased opercular beat rate, elevating the volumes of water and food material passed over the gills whereas those that were held in the toxic strain did not. Of the cyanobacterial toxins (microcystins) presented to the fish, most were in the cyanobacterial cells, toxin levels in the water being below the level of detectability (<250 ng l⁻¹), The ability of the fish to differentiate between toxic and non-toxic cyanobacterial strains may thus be determined by very low levels of extracellular microcystins or/and other features which distinguish toxic from non-toxic M. aeruginosa strains, such as cell surface components.     

Incidence of microcystin‐producing cyanobacteria in Lake Tana,the largest waterbody in Ethiopia

The occurrence of toxic cyanobacterial blooms is a serious problem for fast‐developing countries in Africa, such as Ethiopia, that are struggling with significant degradation of the natural environment and limited access to water of good quality. Research undertaken on Lake Tana in Ethiopia between 2009 and 2011 was intended to assess the seasonal threat from cyanobacteria and to select methods for tracking of this threat in the future. The cyanobacterial genus Microcystis was found to be present throughout the monitoring period, and M. aeruginosa was determined as the dominant species. Moreover, in all samples, toxigenic cyanobacteria with the potential to produce microcystins were detected. High levels of microcystins, ranging from 0.58 to 2.65 μg L^?1, were detected each November, which indicates that in the postrainy season, water usage should be limited. The correlation between concentrations of chlorophyll‐a and microcystins suggested that chlorophyll‐a could be used as an indicator of the potential presence of cyanobacterial‐derived hepatotoxins in Lake Tana in the future. Furthermore, for quick quantitative confirmation of the presence of microcystins, a simple and rapid ELISA test was recommended.     

Potent toxins in Arctic environments – Presence of saxitoxins and an unusual microcystin variant in Arctic freshwater ecosystems

Cyanobacteria are the predominant phototrophs in freshwater ecosystems of the polar regions where they commonly form extensive benthic mats. Despite their major biological role in these ecosystems, little attention has been paid to their physiology and biochemistry. An important feature of cyanobacteria from the temperate and tropical regions is the production of a large variety of toxic secondary metabolites. In Antarctica, and more recently in the Arctic, the cyanobacterial toxins microcystin and nodularin (Antarctic only) have been detected in freshwater microbial mats. To date other cyanobacterial toxins have not been reported from these locations. Five Arctic cyanobacterial communities were screened for saxitoxin, another common cyanobacterial toxin, and microcystins using immunological, spectroscopic and molecular methods. Saxitoxin was detected for the first time in cyanobacteria from the Arctic. In addition, an unusual microcystin variant was identified using liquid chromatography–mass spectrometry. Gene expression analyses confirmed the analytical findings, whereby parts of the sxt and mcy operon involved in saxitoxin and microcystin synthesis, were detected and sequenced in one and five of the Arctic cyanobacterial samples, respectively. The detection of these compounds in the cryosphere improves the understanding of the biogeography and distribution of toxic cyanobacteria globally. The sequences of sxt and mcy genes provided from this habitat for the first time may help to clarify the evolutionary origin of toxin production in cyanobacteria.