A novel filamentous bacterium, strain NAF001, was isolated from suspended water of a domestic wastewater treatment tank. It formed an extremely long filamentous trichome and produced endospores. It formed spore-like resting cells (SLRCs) which were heat-resistant. SLRCs grew by budding to form short filaments resembling the gonidia of filamentous bacteria such as LEUCOTHRIX: This is the first report of a Bacillus species that exhibits budding growth. The filamentous form was neither restricted to any particular growth stage nor dependent on cultural conditions. Phylogenetic analysis of the 16S rRNA gene revealed that this isolate was a member of the genus Bacillus, with no close relatives at the species level (sequence similarity <95.3%). Strain NAF001 thus probably belongs to a new and novel species of Bacillus.