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

一些海洋浮游植物物种产生天然生物毒素。滤食性贝类摄取这些浮游植物没有任何明显的负面影响。然而，贝类肉中毒素的生物积累使浓度达到足够高的水平，可能对摄入贝类的人类造成严重的健康后果。麻痹性贝类中毒（PSP）是世界上最严重的贝类中毒综合征。PSP是由甲藻属亚历山大藻产生的强效神经毒素（石房蛤毒素）引起的。PSP在世界范围内发生，英国沃茨中贝类的毒性特征是频繁的低水平毒性（监测计划表明每年发生100次）和零星的重大毒性事件。导致物种的开花在空间和时间上都有变化，我们对控制它们的环境因素还知之甚少。由食品安全当局运作的政府生物毒素和浮游植物监测计划保障了人类健康，但对经济造成了重大损失。在亚历山大藻的各种物种中，塔玛亚历山大藻的物种复合体在英国沃茨特别受到关注。无毒，第三组，A.tamarense历史上曾在法国，西班牙和葡萄牙发现，其最北端是英国南部。相比之下，毒性细胞组I.塔玛阿氏是北纬度的特点。然而，最近的研究表明，分布正在发生变化，无毒的第三组细胞现在被发现，北至设得兰群岛。已知英国周围的沃茨正在变暖，这表明这一点或其他相关的环境变化（例如局部盐度，pH值或光照条件）允许III组细胞“入侵”北方沃茨，在那里它们现在与I组竞争。这与近年来PSP事件减少的监测观测结果一致，但塔玛阿龙的总丰度没有显着变化。对塔玛海鞘分布变化驱动因素的研究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沃茨海洋浮游植物的分布。最近，我们已经分离到实验室培养菌株的组I和组III塔玛曲霉，提供了第一次，文化的有毒和无毒菌株的生物体从一个单一的地区。我们将研究环境条件对菌株生长和毒性的影响，包括单独和竞争。此外，由于A.tamarense形成越冬休眠期（包囊），它沉降到海底，只有在条件有利时才发芽，因此我们将研究环境条件对包囊发芽的影响。由于两种塔玛曲霉菌株都属于单一物种，因此不可能根据形态学区分它们。因此，我们将利用最近开发的寡核苷酸探针塔玛曲霉。用这些分子探针处理后，在荧光显微镜下紫外光下观察，无毒的III组细胞发绿色光，而有毒的I组细胞发金色光，即使当细胞组合生长以研究它们的竞争时，也可以容易地进行区分和计数。最后，我们将使用我们的实验结果来推导和参数化的数学模型为A. tamarense。这些模型将用于模拟我们目前在一些地点收集的不同塔玛曲霉菌株丰度的原位数据。一旦开发出来，这些模型将提高我们根据环境条件的知识预测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.