Molecular Ecological Studies on the Microorganisms which Kill or Destroy the Harmful and Toxic Microalgae During their Blooms

采用MPN方法，对1995年和1996年发生在日本广岛湾、天南内湾和田边湾的有毒赤潮浮游植物——刺藻异角藻（Heterosigma ak ashiwo）和刺藻裸子藻（Gymnodinium mikimotoi, dinophyceae）爆发期间杀死它们的微生物进行了枚举。两年内广岛湾各采样点在水华终止期均观察到0.8mm以下海水馏分中杀藻微生物数量迅速增加。由于小于0.2mm的海水馏分波动与黄藻华的灭绝关系不大，因此灭藻菌可能在黄藻华的终止中起主导作用。在水花繁殖过程中，我们可以分离出许多H.ak . ashwo -kill细菌（HAKB）菌株。对古查顿菌的抑藻菌数比HAKB的抑藻菌数低一到两个数量级。因此，杀藻细菌的种群动态可能与浮游植物的繁殖有密切的关系。在海洋生态系统中，针对特定浮游植物的杀藻细菌似乎调控着浮游植物群落结构的变化。在田边湾发生巨红潮时，分离出了几株杀死巨红潮菌的海洋细菌。其中弧菌属、黄杆菌属、不动杆菌属和假单胞菌属。它们都生长在经过过滤的天然海水中，没有添加任何营养物质，这表明这些杀灭细菌在海水中普遍存在，并与mikimotoi G.mikimotoi的发生有机会性关系。大部分杀菌菌对costatum、diylum brightwelli和thalassisira sp. 3种海洋硅藻的生长没有影响，部分杀菌菌对catenella亚历山大藻的生长没有影响。在乌拉内湾有毒的g.m himototototototomotototototola潮汐消失后，从海水中获得的一种黄杆菌sp.5N-3细菌对这一物种具有显著的杀藻作用，而对其他赤潮浮游生物如costatum、Heterosigma akashhiwo和Chattonella anitiqua没有作用。这些结果表明，具有物种特异性抑制作用的细菌在浮游植物群落演替中起着重要作用，利用这些微生物作为“微生物农药”可以防止藻华。少

We enumerated the microorganisms which killed the noxious red tide phytoplankton Heterosigma ak ashiwo (raphidophyceae) and Gymnodinium mikimotoi, (dinophyceae)Ha during their blooms which occurred in Hiroshima Bay and Uranouchi Bay or Tanabe Bay, Japan, in 1995 and 1996, using the MPN method.At every sampling site in Hiroshima Bay in both years, the rapid in crease of the algicidal microorganisms in the seawater fractions less than 0.8mm was observed at the termination period of the blooms. Because the seawater fraction less than 0.2mm fluctuated poorly reloted to the extinction of H.ak ashiwo blooms, the algicidal bacteria may play the leading part in the temination of the bloom. We could isolate many strains of H.ak ashiwo-killing bacteria (HAKB) during the blooms. The number of algicidal bacteria against Chattonella antiqua were one or two order of magnitude lower than that of HAKB.Therefore it is suggested that the population dynamics of algicidal bacteria may have a close relatio … More nship to the blooms of the phytoplankton. In marine ecosystem, algicidal bacteria against specific phytoplankton seem to regulate the change of structure of phytoplankton communities.Several strains of the marine bacteria which killed G.mikimotoiwere isolated during the occurrence of the huge red tide of G.mikimotoi in Tanabe Bay. Among them the strains belonged to the genus Vibrio, Flavobacterium, Acinetobacter and Pseudomonas-Alteromonas. The fact that all of them grew in filtered natural seawater without any nutrient supplements suggested that the killing bacteria are ubiquitous in seawter and are related to the occurrence of G.mikimotoi opportunistically. Most of the killing bacteria did not affect the growth of three marine diatoms, Skeletonema costatum, Ditylum brightwelli and Thalassiosira sp., and some of them did not affect the growth of the Alexandrium catenella.A bacterium, Flavobacterium sp.5N-3, obtained from sawater after the disappearance of a noxious G.mikimotoired tide in Uranouchi Bay showed a drastic algicidal effect on this species in particular, while it had no effects on other red tide plankton of Skeletonem costatum, Heterosigma akashiwo, and Chattonella anitiqua.These results suggest that bacteria with species-specific inhibitory effects play an importnat role on the succession of phytoplankton community and algalblooming could be prevented by using such microbes as a "microbial pesticide". Less