Beschreibung:
<jats:p>By screening for restoration of multicellular migration in a non‐swarming but motile <jats:italic>Proteus mirabilis</jats:italic> mutant lacking the FlgN facilitator of flagella assembly, we identified four distinct genes that, <jats:italic>in trans</jats:italic> and multicopy, increased flagella production and cell length. Each of the genes upregulated expression of the <jats:italic>flhDC</jats:italic> master operon that controls flagellar biogenesis, cell division and swarming, not only in the mutant but also in the wild type. The genes were named <jats:italic>umoA</jats:italic>, <jats:italic>umoB</jats:italic>, <jats:italic>umoC</jats:italic> and <jats:italic>umoD</jats:italic>. Disruption of each of the wild‐type chromosomal <jats:italic>umo</jats:italic> genes caused corresponding reductions in swarming and cell elongation, which correlated with decreased expression of the <jats:italic>flhDC</jats:italic> operon. The <jats:italic>umoA</jats:italic>, <jats:italic>umoB</jats:italic>, <jats:italic>umoC</jats:italic> and <jats:italic>umoD</jats:italic> genes are not closely linked, and only <jats:italic>umoB</jats:italic> is part of an operon. The sequences of the calculated gene products, UmoA (20.6 kDa), UmoB (78.0 kDa), UmoC (15.2 kDa) and UmoD (19.2 kDa), contain putative N‐terminal secretion signals and predict a location in the cell membranes or periplasm. UmoB and UmoD have sequence similarity to the <jats:italic>Escherichia coli</jats:italic> uncharacterized open reading frames YrfF and YcfJ respectively; UmoA and UmoC have no known homologues. The <jats:italic>umoB</jats:italic> and <jats:italic>umoC</jats:italic> gene transcripts were present at very low levels, but <jats:italic>umoA</jats:italic> and <jats:italic>umoD</jats:italic> expression was similar to that of <jats:italic>flhDC</jats:italic> and increased in parallel with <jats:italic>flhDC</jats:italic> expression during differentiation into elongated hyperflagellated swarm cells. Like <jats:italic>flhDC</jats:italic>, <jats:italic>umoA</jats:italic> and <jats:italic>umoD</jats:italic> expression was subject to negative feedback in a flagellar assembly mutant lacking the FlhA inner membrane component of the export machinery. Assays of <jats:italic>umo</jats:italic> gene expression and cross‐complementation indicated that the <jats:italic>umo</jats:italic> genes do not act in sequence within a pathway to upregulate <jats:italic>flhDC</jats:italic>, but revealed that <jats:italic>umoA</jats:italic> and <jats:italic>umoD</jats:italic> are reciprocally upregulated by FlhDC. Our findings strengthen the picture of the <jats:italic>flhDC</jats:italic> master operon as a major assimilatory checkpoint in <jats:italic>Proteus mirabilis</jats:italic> and other Gram‐negative bacteria and expand the view of a complex regulatory network coupled to flagellar biogenesis.</jats:p>