Host specificity and action mechanism of algicidal Saprospira.

本研究的目的是分离海洋杀藻微生物，并阐明其杀藻作用机制。本研究得到的结果概要如下：(1)从鹿儿岛湾和库鲁玛对虾养殖池海水中分离到在含硅藻细胞（Chaetoceros ceratosporum）的双层琼脂板上形成斑块的变形虫（Amoeba）、迷路虫（迷路虫）、腐坏螺旋体（Saprospira）和玻璃体振荡菌（玻璃体振荡菌）4种微生物。(2)从细胞形态、生理特性、生长反应和全细胞脂质脂肪酸组成等方面将分离菌分为3种。(3)腐生螺旋体菌株在双层琼脂板上形成菌斑，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不同，菌斑形成、菌落形成或细菌不生长。(4)除毛藻外，腐殖质螺旋体菌株对部分硅藻有除藻效果，如对骨骼肌等硅藻有除藻效果。(5)虽然腐殖质螺旋体细菌细胞的加入降低了藻培养物的浊度，但藻菌混合培养的上清液对硅藻的生长没有抑制作用。这些结果表明，腐生螺旋体的杀藻活性与分布在细菌细胞表层的大分子有关，这些大分子在细菌细胞与宿主藻细胞直接接触时作用于藻类细胞壁。

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.