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

用MPN法对1995年和1996年在日本广岛湾、浦内湾和田边湾发生的赤潮有害浮游植物异形异形藻(Heterosigma AK Ashiwo)和三叶裸藻(Gymnodium mikimotoi(Dinophyceae)Ha)水华期间的致死微生物进行了计数。在这两年广岛湾的每个采样点，都观察到水华终止期小于0.8 mm的海水中含藻微生物的迅速增加。由于海水中0.2 mm以下的海水波动较小，导致赤潮的消亡，因此杀藻细菌可能在赤潮的形成过程中起主导作用。我们可以在水华期间分离到许多菌株(HAKB)。杀藻细菌数量比…少1~2个数量级。因此，杀藻细菌的种群动态可能与HAKB有密切关系更多的是与浮游植物的繁盛有关。在海洋生态系统中，针对特定浮游植物的杀藻细菌似乎调节着浮游植物群落结构的变化。在田边湾发生大规模赤潮期间，分离到了几株杀死三本藻的海洋细菌。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，没有任何营养补充剂，这表明杀死细菌在海水中随处可见，并与G.mikimotoi的发生机会性地有关。大部分致死细菌不影响中肋骨条藻、亮斑藻和海链藻三种海洋硅藻的生长，部分不影响链状亚历山大藻的生长。乌拉努奇湾有毒米氏藻潮消退后从海水中获得的一株细菌黄杆菌5N-3对该物种有强烈的杀痛作用，而对其他赤潮浮游生物中的中肋骨条藻、赤潮异形藻和赤潮生物没有影响。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的演替中起着重要作用，利用这种微生物作为“微生物杀虫剂”可以防止藻华的发生。较少

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