The competitive dynamics of toxic and non toxic ribotypes of the harmful dinoflagellate Alexandrium tamarense

许多种类的海洋浮游植物产生天然的生物毒素。滤食性贝类摄取这些浮游植物而没有任何明显的负面影响。然而，毒素在贝类肉中的生物积累使其浓度达到足够高的水平，从而可能对摄入贝类的人造成严重的健康后果。麻痹性贝类中毒（PSP）可能是全球最重要的贝类中毒综合征，其症状严重且可能致命。PSP是由甲藻属Alexandrium产生的强效神经毒素引起的。PSP发生在世界各地，英国水域贝类毒性的特点是经常出现低水平毒性（监测程序表明每年发生100次）和零星的主要毒性事件。致病物种的大量繁殖在空间和时间上都是不同的，到目前为止，我们对控制它们的环境因素知之甚少。政府的生物毒素和浮游植物监测方案由食品安全当局实施，以保障人类健康，但对经济造成重大损失。在各种各样的亚历山大菌中，tamarense亚历山大菌是英国水域特别关注的物种。无毒，III类，A.tamarense历史上在法国，西班牙和葡萄牙被发现，其最北的范围是英国的南部。与此相反，A.tamarense I群的毒性细胞是北纬地区的特征。然而，最近的研究表明，它们的分布正在发生变化，现在在北部的设得兰群岛也发现了无毒的III族细胞。众所周知，英国周围的水域正在变暖，这表明，这一变化或其他相关的环境变化（例如，局部盐度、pH值或光照条件）使III类细胞“入侵”了北部水域，现在它们在那里与i类细胞竞争。这与近年来监测到的PSP事件减少的情况一致，但A.tamarense的总丰度没有显著变化。研究柽柽树分布变化的驱动因素将有助于更好地理解和预测PSP事件。这将使生物毒素监测更有针对性，更好地保障人类健康。此外，这样的研究将使我们能够调查气候变化如何影响英国水域海洋浮游植物的分布。最近，我们在实验室培养中分离出了I群和III群的塔玛氏A.tamarense菌株，这是第一次从一个地区同时培养出有毒和无毒菌株。我们将从个体和竞争两方面研究环境条件对菌株生长和毒性的影响。此外，由于tamarense形成一个越冬休息阶段（囊），它沉降到海底，只有在条件有利时才发芽，我们将研究环境条件对囊萌发的影响。由于这两种塔玛氏A.tamarense菌株都是一个物种，因此不可能根据形态来区分它们。因此，我们将利用最近开发的tamarense寡核苷酸探针。用这些分子探针处理后，在紫外显微镜下观察，无毒的III组细胞发出绿色的光，而有毒的I组细胞发出金色的光，即使在细胞组合生长以研究它们的竞争时，也可以很容易地区分和计数。最后，我们将利用我们的实验结果来推导和参数化塔玛莲的数学模型。这些模型将用于模拟我们目前在许多地点收集的不同菌株tamarense丰度的原位数据。一旦发展起来，这些模型将提高我们基于环境条件知识预测PSP事件可能性的能力。

A number of species of marine phytoplankton produce natural biotoxins. Filter feeding shellfish ingest these phytoplankton without any apparent negative effects. However, bio-accumulation of the toxins in the shellfish flesh allows concentrations to reach sufficiency elevated levels that serious health consequences may result for humans that ingest the shellfish. Owing to the severity and possible fatality of the symptoms, paralytic shellfish poisoning (PSP) is perhaps the globally most important shellfish poisoning syndrome. PSP is caused by potent neurotoxins (saxitoxins) produced by the dinoflagellate genus Alexandrium. PSP occurs worldwide, with toxicity of shellfish in UK waters being characterised by frequent low level toxicity (monitoring programs indicating 100's of occurrences annually) and sporadic major toxicity events. Blooms of the causative species vary both spatially and temporally, and as yet we have very little understanding of the environmental factors that govern them. Human health is safeguarded by government biotoxin and phytoplankton monitoring programmes operated by Food Safety Authorities at significant cost to the economy. Of the various species of Alexandrium, the species complex Alexandrium tamarense is of particular concern in UK waters. Non toxic, group III, A.tamarense have historically been found in France, Spain and Portugal with their northernmost extent being the south of the UK. In contrast, toxic cells of group I A.tamarense are characteristic of northerly latitudes. However, recent studies have indicated changing distributions, with the non toxic group III cells now being found as far north as Shetland. Waters around the UK are known to be warming, suggesting that this, or other associated environmental changes (e.g. localised salinity, pH or light conditions), have allowed group III cells to 'invade' northern waters, where they now compete with group I. This is consistent with monitoring observations of reduced PSP events in recent years, but with no significant change in the total abundance of A.tamarense. Study of the factors driving the changing distributions of A.tamarense will provide better understanding and predictive ability of PSP events. This will allow more targeted biotoxin monitoring and better safeguard human health. Furthermore, such study will allow us to investigate how climate change is influencing the distribution of marine phytoplankton in UK waters. Recently we have isolated into laboratory culture strains of both group I and group III A.tamarense providing, for the first time, cultures of both toxic and non toxic strains of the organism from a single region. We shall study the influence of environmental conditions on strain growth and toxicity both individually and in competition. In addition, as A.tamarense forms an overwintering resting stage (a cyst) which settles to the sea floor and only germinates when conditions are favourable, we shall study the effect of environmental conditions on cyst germination. As both A.tamarense strains are of a single species, it is not possible to discriminate between them based on morphology. We will therefore utilise recently developed oligonucleotide probes for A.tamarense. After treatment with these molecular probes, and viewed under ultra violet light on a flourescence microscope, the non-toxic group III cells glow green and the toxic groups I cells glow gold, allowing for easy discrimination and enumeration even when cells are grown in combination to study their competition. Finally, we shall use our experimental results to derive and parameterise mathematical models for A.tamarense. These models will be used to simulate in situ data on the abundance of the different strains of A.tamarense we are currently collecting at a number of sites. Once developed, these models will increase our ability to predict the likelihood of a PSP event based on knowledge of the environmental conditions.