Information on the geoA and 2-MIB synthase genes involved in the biosynthesis of geosmin and 2-MIB is lacking. In this study, we analysed the geoA and 2-MIB synthase genes of the cyanobacterial isolates and environmental samples from water resources. In most isolates, the sequence similarities to those of already reported strains exceeded 99%, however in some isolates, sequence similarities were less than 90%. All geoA genes detected in the environmental samples affiliated with the geoA gene of Dolichospermum , showing geosmin producing Dolichospermum widespread in Japan. 2-MIB synthase genes detected from environmental samples affiliated with 2-MIB synthase genes of Pseudanabaena , Planktothricoides and Microcoleus , and were devided into 7 lineages in the phylogenetic tree. The development of a database of musty odor-causing substance synthase gene sequences will lead to the identification of the causative species and their habitats by analyzing the sequences in tap water source samples. This will be useful in predicting musty odor-causing substances and taking countermeasures in the future.

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