Expression of the DisA amino acid decarboxylase from Proteus mirabilis inhibits motility and class 2 flagellar gene expression in Escherichia coli

In Proteus mirabilis, a putative phenylalanine decarboxylase (DisA) acts in a regulatory pathway to inhibit class 2 flagellar gene expression and motility. In this study, we demonstrate that DisA expression in Escherichia coli blocked motility and resulted in a 50-fold decrease in the expression of class 2 (fliA) and class 3 (fliC) flagellar genes. However, the expression of flhDC encoding the class 1 activator of the flagellar cascade was unchanged by DisA expression at both the transcriptional and translational levels. Phenethylamine, a decarboxylation product derived from phenylalanine, was able to mimic DisA overexpression and decrease both motility and class 2/3 flagellar gene expression. In addition, both DisA overexpression and phenethylamine strongly inhibited biofilm formation in E. coli. DisA overexpression and exogenous phenethylamine could also reduce motility in other enteric bacteria, but had no effect on motility in non-enteric Gram-negative bacteria. It is hypothesized that phenethylamine or a closely related compound formed by the DisA decarboxylation reaction inhibits the formation or activity of the FlhD4C2 complex required for activation of class 2 genes.