Coral microbial flora has been attracting attention because of their potential to protect corals from environmental stresses or pathogens. Although coral-associated bacteria are considered to be acquired from seawater, little is known about the relationships between microbial composition in corals and its surrounding seawater. Here, we tested several methods to identify coral-associated bacteria in coral and its surrounding seawater to detect specific types of Ruegeria species, some of which exhibit growth inhibition activities against the coral pathogen Vibrio coralliilyticus. We first isolated coral-associated bacteria from the reef-building coral Galaxea fascicularis collected at Sesoko Island, Okinawa, Japan, via random colony picking, which showed the existence of varieties of bacteria including Ruegeria species. Using newly constructed primers for colony PCR, several Ruegeria species were successfully isolated from G. fascicularis and seawater. We further investigated the seawater microbiome in association with the distance from coral reefs. By seasonal sampling, it was suggested that the seawater microbiome is more affected by seasonality than the distance from coral reefs. These methods and results may contribute to investigating and understanding the relationships between the presence of corals and microbial diversity in seawater, in addition to the efficient isolation of specific bacterial species from coral or its surrounding seawater.

珊瑚微生物菌群因其保护珊瑚免受环境压力或病原体侵害的潜力而备受关注。虽然珊瑚相关细菌被认为是从海水中获得的，但人们对珊瑚中微生物组成与其周围海水之间的关系知之甚少。在这里，我们测试了几种方法来识别珊瑚及其周围海水中的珊瑚相关细菌，以检测特定类型的Ruegeria物种，其中一些对珊瑚病原体Vibrio coralliilyticus具有生长抑制活性。我们首先从造礁珊瑚Galaxea fascicularis 中分离出珊瑚相关细菌在日本冲绳 Sesoko 岛通过随机菌落挑选收集到的，这表明存在多种细菌，包括Ruegeria物种。使用新构建的菌落 PCR 引物，成功从G. fascicularis 中分离出几种Ruegeria物种和海水。我们进一步研究了与珊瑚礁距离相关的海水微生物组。通过季节性采样，有人认为海水微生物群受季节性的影响大于与珊瑚礁的距离。除了从珊瑚或其周围海水中有效分离特定细菌物种外，这些方法和结果可能有助于调查和理解珊瑚的存在与海水中微生物多样性之间的关系。