The role of <scp>FlhF</scp> and <scp>HubP</scp> as polar landmark proteins in <scp><i>S</i></scp><i>hewanella putrefaciens</i> <scp>CN</scp>‐32

<jats:title>Summary</jats:title><jats:p>Spatiotemporal regulation of cell polarity plays a role in many fundamental processes in bacteria and often relies on ‘landmark’ proteins which recruit the corresponding clients to their designated position. Here, we explored the localization of two multi‐protein complexes, the polar flagellar motor and the chemotaxis array, in <jats:styled-content style="fixed-case"><jats:italic>S</jats:italic></jats:styled-content><jats:italic>hewanella putrefaciens</jats:italic> <jats:styled-content style="fixed-case">CN</jats:styled-content>‐32. We demonstrate that polar positioning of the flagellar system, but not of the chemotaxis system, depends on the GTPase <jats:styled-content style="fixed-case">FlhF</jats:styled-content>. In contrast, the chemotaxis array is recruited by a transmembrane protein which we identified as the functional ortholog of <jats:styled-content style="fixed-case"><jats:italic>V</jats:italic></jats:styled-content><jats:italic>ibrio cholerae</jats:italic> <jats:styled-content style="fixed-case">HubP</jats:styled-content>. Mediated by its periplasmic <jats:styled-content style="fixed-case">N</jats:styled-content>‐terminal <jats:styled-content style="fixed-case">LysM</jats:styled-content> domain, <jats:italic>Sp</jats:italic>HubP exhibits an <jats:styled-content style="fixed-case">FlhF</jats:styled-content>‐independent localization pattern during cell cycle similar to its <jats:italic>Vibrio</jats:italic> counterpart and also has a role in proper chromosome segregation. In addition, while not affecting flagellar positioning, <jats:italic>Sp</jats:italic>HubP is crucial for normal flagellar function and is involved in type <jats:styled-content style="fixed-case">IV</jats:styled-content> pili‐mediated twitching motility. We hypothesize that a group of <jats:styled-content style="fixed-case">HubP</jats:styled-content>/<jats:styled-content style="fixed-case">FimV</jats:styled-content> homologs, characterized by a rather conserved <jats:styled-content style="fixed-case">N</jats:styled-content>‐terminal periplasmic section required for polar targeting and a highly variable acidic cytoplasmic part, primarily mediating recruitment of client proteins, serves as polar markers in various bacterial species with respect to different cellular functions.</jats:p>