The marine environment is remarkably diverse and harbors a wide variety of organisms that have acquired novel metabolic functions and corresponding genes through evolutionary adaptation. We have screened many useful material such as UV-A resistance molecule, antibiotics, polysaccharide, from our culture collection containing cyanobacteria and photosynthetic bacteria isolated from marine environment. We introduce our research for screening of useful material from marine photosynthetic microorganisms. Furthermore, genetic manipulation for the purpose of metabolic engineering in marine microorganisms is described as the application of marine genomes. The uses of molecular approaches for analyzing microbial diversity have enhanced our knowledge of their population and lead the fact of abundant unculturable microbes. The isolation of novel bioactive compounds from environmental sources has been carried out by molecular approaches where the metagenomic libraries are constructed with directly extracted DNA from environmental samples.