Xanthobacter flavus 301T (T = type strain) and other strains, including H4-14, both of which were previously described as nonmotile, were reproducibly motile and peritrichously flagellated during the log phase when they were cultured in medium lacking tricarboxylic acid cycle intermediates. Therefore, the species description is emended to include motility and flagellation. Similarly, Xanthobacter autotrophicus was found to be flagellated and motile, but this finding was not consistently reproducible and was mainly found with the mutant strain 7cSF [corrected].