Bacteria-Phytoplankton Interactions: The Influence of Marine Bacteria on Alexandrium spp. Blooms in the Gulf of Maine

有毒的亚历山大属鞭毛藻的大量繁殖已经成为影响缅因湾（GOM）大片地区的慢性问题，几乎每年一次。这些藻类是麻痹性贝类中毒的病原体，这是一种潜在的致命的神经系统疾病。对公众健康的担忧导致了贝类的频繁检疫，永久关闭了一些贝类养殖场，并在墨西哥湾实施了昂贵的PSP毒素监测计划。虽然已经做出了相当大的努力来确定影响墨西哥湾亚历山大菌种群动态的环境因素，但控制亚历山大菌种群原位生长和下降的因素仍然知之甚少。海洋细菌和有毒浮游植物之间的相互作用被认为在控制有毒藻华中起着重要作用，但它们在墨西哥湾的潜在重要作用却很少受到关注。众所周知，在沿海海洋环境中，细菌和浮游植物的动态密切相关，经常观察到细菌和浮游植物生物量之间有很强的联系。此外，细菌对特定有害藻华（HAB）生物的积极和消极影响也有文献记载。最初的研究结果表明，GOM细菌能够在实验室条件下显著刺激亚历山大菌，并且这些相互作用可能随季节而变化。本项目旨在阐明细菌在墨西哥湾亚历山大菌种群动态中的作用。细菌与亚历山大菌相互作用的几个方面将被研究，包括：抑制或促进亚历山大菌生长的细菌的季节和空间分布；细菌-亚历山大菌相互作用的特异性；以及影响细菌群落动态的生物和非生物因素。实地研究将与加拿大合作者在芬迪湾西南部进行。此外，将分析1998年和2000年ECOHAB-GOM采样计划合作从GOM东部和西南部收集的存档细菌群落样本，以确定发现与亚历山大菌相互作用的特定细菌的地理分布。与ECOHAB-GOM团队和DFO HAB项目的密切合作将为研究船提供广泛的数据和访问。分析细菌-亚历山大菌相互作用的实验方法将包括：(1)分子系统发育（PCR-DGGE和MPN-PCR）和基于培养的细菌组合的季节和地理分布分析，抑制或促进亚历山大菌；(2)富集和分离与亚历山大菌密切相互作用的新型菌株；(3)分析促亚历山大菌和抑亚历山大菌对墨西哥湾其他藻类的影响；(4)菌株对混合培养亚历山大菌生长的影响分析。这项研究将深入了解墨西哥湾亚历山大菌和细菌之间的相互作用，并可能最终提高我们在给定水体中模拟和预测亚历山大菌动态的能力。这项研究将确定在GOM中某些细菌组合是否与亚历山大菌有关，并将探索亚历山大菌与细菌之间的相互作用，这种相互作用可能促进或抑制亚历山大菌的生长。

Blooms of the toxic dinoflagellates of the genus Alexandrium have become a chronic problem affecting large areas of the Gulf of Maine (GOM) on a near-annual basis. These algae are the causative agents of paralytic shellfish poisoning, a potentially fatal neurological disorder. Concerns for public health have resulted in frequent shellfish quarantines, permanent closure of some shellfish beds, and the implementation of costly PSP toxin monitoring programs in the GOM. Although considerable effort has been made to determine the environmental factors that influence Alexandrium spp. population dynamics in the GOM, the factors that control in situ growth and decline of Alexandrium populations remain poorly understood. Interactions between the marine bacteria and toxic phytoplankton are thought to play a major role in controlling toxic algal blooms, but their potentially important rolein the GOM has received little attention. It is well known that bacteria and phytoplankton dynamics are tightly linked in coastal marine environments, with strong associations frequently observed between bacterial and phytoplankton biomass. In addition, both positive and negative influences of bacteria on specific harmful algal bloom (HAB) organisms have been documented. Initial research results have indicated GOM bacteria capable of dramatically stimulating Alexandrium under laboratory conditions andthat these interactions may vary seasonally. This project will elucidate the role of bacteria in Alexandrium spp. population dynamics in the GOM. Several aspects of bacteria-Alexandrium interactions will be investigated, including: the seasonal and spatial distribution of bacteria that inhibit or promote Alexandrium growth; the specificity of bacteria-Alexandrium interactions; and the biotic and abiotic factors that influence bacterial community dynamics. Field research will be conducted in the southwestern Bay of Fundy with Canadian collaborators. In addition, archived bacterial community samples that were collected from the eastern and southwestern GOM in collaboration with the ECOHAB-GOM sampling program in 1998 and 2000 will be analyzed to determine the geographic distribution of specific bacteria found to interact with Alexandrium. Close collaboration with the ECOHAB-GOM team and the DFO HAB program will provide an extensive array of data and access to research vessels. Experimental methods to analyze bacteria-Alexandrium interactions will include: (1) molecular phylogenetic (PCR-DGGE and MPN-PCR) and cultivation-based analysis of the seasonal and geographic distribution of bacterial assemblages that inhibit or promote Alexandrium; (2) enrichment and isolation of novel bacterial strains that interact closely with Alexandrium; (3) analysis of the influence of Alexandrium- promoting or Alexandrium-inhibiting bacteria on other algal species present in the GOM; and (4) analysis of the isolates' influence on Alexandrium growth in mixed cultures. The study will provide insight into interactions between Alexandrium and bacteria in the GOM and may ultimately improve our ability to simulate and predict Alexandrium dynamics within a given body of water. This research will determine whether certain bacterial assemblages are associated with Alexandrium spp. in the GOM and will also explore Alexandrium -bacteria interactions that may promote or inhibit Alexandrium growth.