Host specificity and action mechanism of algicidal Saprospira.

本研究的目的是分离海洋溶藻微生物，并阐明其溶藻作用机制。主要研究结果如下：（1）从鹿儿岛湾和日本仓间对虾养殖池的海水中分离到4种能在硅藻细胞（角孢毛藻）双层琼脂平板上形成菌斑的微生物，即变形虫属（Amoeba）、Labelthula、腐螺旋菌属（Saprospira）和玻璃体菌属（Vitrespira）。(2)根据细胞形态、生理特性、生长反应和全细胞脂肪酸组成，将腐螺旋体分为3个种。(3)腐螺旋体菌株在双层琼脂平板上形成噬菌斑，但在基础培养基中添加氨基酸或有机酸时，根据添加的氨基酸或有机酸的种类，发生噬菌斑形成、菌落形成或细菌不生长。(4)腐螺旋体菌株对除角毛藻外的一些硅藻如刺丝藻也有杀藻效果。(5)SaprosSpira菌株的菌体加入虽使藻液浊度降低，但藻菌混合培养上清液对硅藻的生长无抑制作用，说明SaprosSpira菌株的杀藻活性spp.is菌体表面的大分子物质与藻细胞直接接触，作用于藻细胞壁。

The aim of this study is to isolate marine algicidal microorganisms and to clarify the mechanism of algicidal action by the microorganisms. The outline of the results obtained in this study is as follows ;(1) Four kinds of microorganisms including Amoeba, Labyrinthula, Saprospira and Vitreoscilla, which form plaques on double layr agar plates containing diatom cells (Chaetoceros ceratosporum), were isolated from sea water in Kagoshima Bay and Kuruma-prawn culture ponds.(2) Saprospira isolates was classified as 3 species in terms of cellular morphology, physiological properties, growth response and fatty acid composition of whole cell lipids.(3) Saprospira strains formed plaque on double layr agar plates, but on addition of amino acids or organic acids to basal medium, plaque formation, colony formation or no growth of bacteria occurred depending on the kind of amino acids or organic acid added.(4) Saprospira strains were algicidally effective on some diatoms such as Skeletonema sp.besides Chaetoceros sp.(5) Although the addition of bacterial cells of Saprospira strains caused decrease in turbidity of algal culture, the supernatant of mixed culture of algae and bacteria did not inhibit the growth of diatoms.These results suggest that algicidal activity of Saprospira spp.is attributed to macromolecules distributed in surface layr of bacterial cells, which act on algal cell wall as there is direct contact between bacterial cells and host algal cells.