Thioesterase YbgC affects motility by modulating c-di-GMP levels in Shewanella oneidensis

Because of ubiquity of thioesters, thioesterases play a critical role in metabolism, membrane biosynthesis, signal transduction, and gene regulation. In many bacteria, YbgC is such an enzyme, whose coding gene mostly resides in the tol-pal cluster. Although all other proteins encoded in the tol-pal cluster are clearly involved in maintaining cell envelope integrity and cell division, little is known about the physiological role of YbgC. In this study, we identify in Shewanella oneidensis, a γ-proteobacterium used as a research model for environmental microbes, YbgC as a motility regulator. The loss of YbgC results in enhanced motility, which is likely due to the increased rotation rate of the flagellum. The regulatory function of YbgC requires its thioesterase activity but could not be replaced by YbgC homologues of other bacteria. We further show that the regulation of YbgC is mediated by the second message c-di-GMP.