In the present study, we attempt to clarify the taxonomic positions of Picrophilus oshimae and Picrophilus torridus . The 16S rRNA gene sequence similarity between P. oshimae DSM 9789T and P. torridus DSM9790T (99.4 %) was above the threshold value (98.6 %) for bacterial species delineation. The average nucleotide identity (ANI) and digital DNA–DNA hybridization (dDDH) values between P. oshimae DSM 9789T and P. torridus DSM9790T were higher than the threshold values (95–96 % for ANI and 70 % for dDDH) for bacterial species delineation. The present results indicate that Picrophilus torridus Zillig et al. 1996 is a later heterotypic synonym of Picrophilus oshimae Schleper et al. 1996.