| Co-Investigator(Kenkyū-buntansha) |
IMAI Ichiro Kyoto Univ., Graduate Sschool of Agriculture, , Associate Professor, 農学研究科, 助教授 (80271013)
FURUSAWA Iwao Kyoto Univ., Graduate Sschool of Agriculture, Professor, 農学研究科, 教授 (10026594)
YOSHINAGA Ikuo Kyoto Univ., Graduate Sschool of Agriculture, Instructor, 農学研究科, 助手 (40230776)
SAKO Yoshihiko Kyoto Univ., Graduate Sschool of Agriculture, Associate Professor, 農学研究科, 助教授 (60153970)
UCHIDA Aritsune Kyoto Univ., Graduate Sschool of Agriculture, Professor, 農学研究科, 教授 (50027190)
|
|---|
| Research Abstract |
We enumerated the microorganisms which killed the noxious red tide phytoplankton Heterosigma akashiwo (raphidophyceae) and Gymnodinium mikimotoi, (dinophyceae) ハ 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 increase 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 related to the extinction of H.akashiwo blooms, the algicidal bacteria may play the leading part in the termination of the bloom. We could isolate many strains of H.akashiwo-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 relationsh
… More
ip 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.mikimotoi were silated during the occurrenece 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.mikimotoiopportunistically. Most of the killing bacteria did not affect the growth of three marine diatoms, Skeletonema costatum, Ditylum brighwelli 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.mikimotoi red 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 Skeketonem 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 algal blooming could be prevented by using such microbes as a "microbial pesticide". Less
|
