Ecology and molecular phylogenetic analysis of marine algicidal labyrinthulids

众所周知，迷宫藻类生活在海洋大型藻类和水生植物的表面，是鳗草腐烂病的病原体。此外，它们被认为从硅藻或细菌细胞中摄取有机物质，而硅藻或细菌细胞通过其裂解活动在细胞外裂解。本研究以含硅藻细胞的双层琼脂平板为菌斑生物，从海洋大型藻类和水生植物中分离出杀藻微生物，并对其分布、生长反应和分子系统发育进行了研究。作为扩张的斑块形成生物，观察到阿米巴、迷路和丝状细菌。迷路分离物在硅藻双层琼脂平板上形成菌斑，在含有加热细菌细胞的双层琼脂平板上形成菌落。显然，从硅藻、细菌或血清中提取的磷脂可以刺激迷路分离株的菌落生长。迷宫分离株细胞脂中的二十二碳六烯酸(DHA)含量很高(60%~70%)，根据18S rDNA序列对迷宫分离株L95-1和L95-2进行了分子系统发育分析，发现它们与迷宫霉属的亲缘关系较近。An-1565(同源性87%)，属于迷路系统发育群。

Labyrinthulids are known to live on the surface of marine macroalgae and aquatic plants and to be causative organisms for eelgrass wasting disease. Furthermore, they are considered to intake organic matters from the diatom or bacteria cells which are lysed extracellularly by their lytic activities. In this study, distirbution, growth response, and molecular phylogeny of marine labyrinthulids were investigated.Algicidal microorganisms were isolated by using double layered agar plates containing diatom cells as plaque-forming organisms from marine macroalgae and aquatic plants. As the expanding plaque-forming organisms, amoeba, labyrinthulids, and filamentous bacteria were observed. Labyrinthulid isolates formed plaques on the diatom double layered agar plates and colonies on the double layered agar plates containing heated bacterial cells. It was clear that phospholipids derived from diatom, bacteria, or serum stimulate colony growth of labyrinthulid isolates. Docosahexaenoic acid (DHA) content was very high (60-70%) in cellular lipids of labyrinthulid isolates.From molecular phylogenetic analysis of labyrinthulids L95-1 and L95-2 based on 18s rDNA sequences, they were found to be close to Labyrinthula sp. AN-1565 (87% homology) and belong to labyrinthulid phylogenetic group.