Dietary exposure of Daphnia to microcystins: no in vivo relevance of biotransformation.
Dietary exposure of Daphnia to microcystins: no in vivo relevance of biotransformation.
复制标题
DOI：
10.1016/j.aquatox.2014.02.017
复制
发表时间：
2014-05
影响因子：
4.5
通讯作者：
Thomas Sadler;E. von Elert
中科院分区：
文献类型：
--
作者：
Thomas Sadler;E. von Elert
人为的营养物输入湖泊导致有毒蓝藻华的频率增加。水蚤种群已被证明在当地适应有毒的蓝藻，并能够抑制水华的形成；人们对这种现象背后的生理学知之甚少。微囊藻毒素（microcytin - lr， MCLR）是最广泛存在的蓝藻毒素，基于体外实验，假设谷胱甘肽- s -转移酶（GST）可能通过将MCLR与谷胱甘肽偶联作为解毒的第一步。在本研究中，研究人员用100%铜绿微囊藻（microcystis aeruginosaPCC7806）喂养水蚤，这是一种含有大量MCLR （4.8-5.6 fg cell - 1）的蓝藻菌株，以测试体内MCLR与GST水蚤的可能结合。我们使用高分辨率LCMS分析了孵育水、蓝藻细胞和水蚤组织中存在的MCLR偶联产物和未偶联的MCLR。在组织和培养水中均未检测到新形成的偶联产物。此外，与不含水蚤的对照相比，放牧导致蓝藻细胞部分中未结合的MCLR下降，这在相应的孵育水中的MCLR也有类似的增加。因此，在整个实验设置中，MCLR的含量并没有因为daphni的存在而改变。综上所述，daphni摄入MCLR既不会导致偶联产物的形成，也不会导致未偶联MCLR的减少。因此，gst介导的结合似乎与微囊藻毒素（MC）在体内的耐受性无关。这一发现得到了以下事实的支持：GST活性在含mc的野生型或不含mc的m突变体上发生。与不含蓝藻菌的饮食相比，aeruginosaPCC7806显示出相同的特定活性增加。因此，暴露于有毒蓝藻后经常观察到的GST活性诱导不是特定的MC效应，而是一般的蓝藻效应。这表明GST参与了氧化应激反应，而不是MCs的特异性解毒。此外，我们的研究结果表明，存在一种有效的转运机制，可以有效地从水蚤组织中去除未结合的MCLR。需要进一步的研究来阐明这种转运机制的性质。
Anthropogenic nutrient input into lakes has contributed to the increased frequency of toxic cyanobacterial blooms.Daphniapopulations have been shown to be locally adapted to toxic cyanobacteria and are able to suppress bloom formation; little is known about the physiology behind this phenomenon. Microcystin-LR (MCLR) is the most widespread cyanobacterial toxin, and, based onin vitroexperiments, it is assumed that the enzyme glutathione-S-transferase (GST) might act as the first step of detoxification inDaphniaby conjugating MCLR with glutathione.In the present studyDaphnia magnawas fed a diet of 100%Microcystis aeruginosaPCC7806, a cyanobacterial strain that contains MCLR in high amounts (4.8–5.6 fg cell−1), in order to test for a possible conjugation of MCLR with GST inDaphnia in vivo. We used high-resolution LCMS to analyze incubation water, cyanobacterial cells andDaphniatissue for the presence of MCLR conjugation products as well as unconjugated MCLR.Newly formed conjugation products were detected neither inDaphniatissue nor in the incubation water. Moreover, the presence ofDaphnialed to a decrease in unconjugated MCLR in the cyanobacterial cell fraction due to grazing, in comparison to a control without daphnids, which was well reflected by a similar increase of MCLR in the respective incubation water. As a consequence, the MCLR content did not change due toDaphniapresence within the entire experimental setup. In summary, MCLR ingestion byDaphnialed neither to the formation of conjugation products, nor to a decrease of unconjugated MCLR.GST-mediated conjugation thus seems to be of minor relevance for microcystin (MC) tolerance inDaphnia in vivo. This finding is supported by the fact that GST activity inDaphniafeeding on the MC-containing wildtype or a MC-free mutant ofM. aeruginosaPCC7806 revealed an identical increase of specific activity in comparison to a cyanobacteria-free diet. Therefore, the frequently observed induction of GST activity upon exposure to toxic cyanobacteria is not a specific MC effect but a general cyanobacterial effect. This suggests that GST inDaphniais involved in an oxidative stress response rather than in the specific detoxification of MCs. Furthermore, our results indicate the presence of an efficient transport mechanism which efficiently removes unconjugated MCLR from theDaphniatissue. Further studies are needed to elucidate the nature of this transport mechanism.