HP0018 Has a Potential Role in the Maintenance of the Cell Envelope.

is a bacterial pathogen that colonizes the human stomach, where it can cause a variety of diseases. uses a cluster of sheathed flagella for motility, which is required for host colonization in animal models. The flagellar sheath is continuous with the outer membrane and is found in most species identified to date. HP0018 is a predicted lipoprotein of unknown function that is conserved in species that have flagellar sheaths but is absent in species that have sheath-less flagella. Deletion of in B128 resulted in the formation of long chains of outer membrane vesicles, which were most evident in an aflagellated variant of the Δ mutant that had a frameshift mutation in . Flagellated cells of the Δ mutant possessed what appeared to be a normal flagellar sheath, suggesting that HP0018 is not required for sheath formation. Cells of the Δ mutant were also less helical in shape compared to wild-type cells. A HP0018-superfolder green fluorescent fusion protein expressed in the Δ mutant formed fluorescent foci at the cell poles and lateral sites. Co-immunoprecipitation assays with HP0018 identified two enzymes involved in the modification of the cell wall peptidoglycan, AmiA and MltD, as potential HP0018 interaction partners. HP0018 may modulate the activity of AmiA or MltD, and in the absence of HP0018, the unregulated activity of these enzymes may alter the peptidoglycan layer in a manner that results in an altered cell shape and hypervesiculation.