A new cyanobacterium of strain 0-77 was isolated from a hot spring at Aso-Kuju National Park, Kumamoto, Japan. According to the phylogenetic analysis determined by 165 rRNA gene sequence, the strain 0-77 belongs to the genus Leptolyngbya, classifying into filamentous non-heterocystous cyanobacteria. The strain 0-77 showed the thermophilic behavior with optimal growth temperature of 55 degrees C. Moreover, we have purified and characterized the oxygen-evolving photosystem II (PSII) from the strain 0-77. The O-2-evolving activity of the purified PSII from strain 0-77 (PSII077) was 1275 +/- 255 mu mol O-2 (mg ChI a)(-1) h(-1). Based on the results of MALDI-TOF mass spectrometry and urea-SDS-PAGE analysis, the purified PSII077 was composite of the typical PSII components of CP47, CP43, PsbO, D2, D1, PsbV, PsbQ, PsbU, and several low molecular mass subunits. Visible absorption and 77 K fluorescence spectra of the purified PSII077 were almost identical to those of other purified PSIIs from cyanobacteria. This report provides the successful example for the purification and characterization of an active PSII from thermophilic, filamentous non-heterocystous cyanobacteria. (C) 2014, The Society for Biotechnology, Japan. All rights reserved.