It is well recognized that uncultured or uncultivable microbes account for more than 99% of total microbes existing in environment, hence, it would be impossible to overview the microbial world by conventional methods in microbiology. We are analyzing diversity of microorganisms in natural and engineered ecosystems using molecular approaches and histological methods. We are also attempting to cultivate microbes yet-to-be-cultured by classical methods combined with new techniques to uncover the unseen majority on the earth.