Host specificity and action mechanism of algicidal Saprospira.

本研究的目的是分离海洋杀藻微生物，并阐明微生物的杀藻作用机理。本研究取得的成果概述如下：(1)从鹿儿岛湾和仓间对虾养殖池的海水中分离到阿米巴、迷宫、腐霉菌和透明颤菌4种微生物，它们在含硅藻细胞的双层琼脂平板上形成菌斑。(2)从细胞形态、生理特性、生长反应和全细胞脂的脂肪酸组成等方面将腐霉菌株分为3种。(3)沙门氏菌菌株在双层琼脂平板上形成菌斑，但在基础培养基中添加氨基酸或有机酸时，菌斑形成。不同种类的氨基酸或有机酸对藻类的杀藻效果不同。(4)除毛壳藻外，Saprospira菌株对一些硅藻也有一定的杀藻效果。(5)虽然添加Saprospira菌株的细菌细胞降低了藻类培养物的浊度，但藻菌混合培养上清液对硅藻的生长没有抑制作用。这些结果表明，Saprospira spp的杀藻活性主要是分布在细菌细胞表层的大分子，由于细菌细胞与宿主藻细胞的直接接触而作用于藻细胞壁。

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.