Role offlhDC in the expression of the nuclease genenucA, cell division and flagellar synthesis inserratia marcescens

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Abstract
We investigated inSerratia marcescens the functions of theflhDC operon, which controls motility and cell division in enteric bacteria. Included in our evaluations were investigation of cell division, flagellar synthesis and regulation of the expression of nuclease (encoded by thenucA Sm gene, one of the virulence factors). Interruption of the chromosomalflhDC operon inS. marcescens CH-1 resulted in aberrant cell division and loss of nuclease and flagella. Expression ofnucA Sm and other mutated phenotypes was restored in theflhDC mutant by the induction of overexpression offlhDC in a multicopy plasmid. MulticopiedflhDC also induced the formation of differentiated cells (polyploid aseptate cells with oversynthesis of peritrichous flagella) in broth culture using minimal growth medium. Expression of theflhDC operon showed positive autoregulation, and was growth phase dependent (upregulated in early log phase). In addition,flhDC expression was inhibited when the temperature increased from 30 to 37°C, and when osmolarity was increased, but was not influenced by glucose catabolite repression. These results show that FlhD/FlhC is a multifunctional transcriptional activator involved in the process of cell differentiation, swarming and virulence factor expression.