An <Emphasis Type="Italic">Escherichia coli aer</Emphasis> mutant exhibits a reduced ability to colonize the streptomycin-treated mouse large intestine

The oxygen sensor Aer of Escherichia coli affects the expression level of genes that are involved in sugar acid degradation. Phenotypes of Aer mediated gene regulation, namely growth on sugar acids was tested ‘in vitro’ with Phenotype MicroArrays and colonization of the mouse large intestine was tested ‘in vivo’. The aer mutant did not grow on the sugar acids d-gluconate, d-glucuronate, d-galacturonate, as well as the sugar alcohol d-mannitol. Since sugar acids are the predominant carbon source for E. coli in the intestinal mucosa, the ability of the aer mutant to colonize the streptomycin-treated mouse large intestine was tested. The mutant exhibited a decreased ability to colonize the intestine when compared to wild-type cells. This effect was more pronounced under competitive conditions. The colonization phenotype of the aer mutant was complemented with either of two plasmids. One of them expressed the Aer protein, whereas the other one expressed the sugar acid degradation enzymes that are encoded by edd and eda. The data support the interpretation that decreased expression of edd and eda along with the decreased ability to grow on sugar acids may contribute to the reduced capacity of the aer mutant to colonize the mouse intestine. While Aer seems to be important during the initiation phase of colonization, FlhD/FlhC appears to be of disadvantage during maintenance phase. FlhD/FlhC is the master regulator of all flagellar genes and required for Aer expression. Mutants in flhD exhibited an initial competitive disadvantage during the first 3 days of colonization, but recovered lateron.     

Pleiotropic phenotypes of a <Emphasis Type="Italic">Yersinia enterocolitica flhD</Emphasis> mutant include reduced lethality in a chicken embryo model

Background  

The Yersinia enterocolitica flagellar master regulator FlhD/FlhC affects the expression levels of non-flagellar genes, including 21 genes that are involved in central metabolism. The sigma factor of the flagellar system, FliA, has a negative effect on the expression levels of seven plasmid-encoded virulence genes in addition to its positive effect on the expression levels of eight of the flagellar operons. This study investigates the phenotypes of flhD and fliA mutants that result from the complex gene regulation.     

A novel gene involved in regulating the flagellar gene cascade in Proteus mirabilis

In this study, we identified a transposon insertion in a novel gene, designated disA, that restored swarming motility to a putrescine-deficient speA mutant of Proteus mirabilis. A null allele in disA also increased swarming in a wild-type background. The DisA gene product was homologous to amino acid decarboxylases, and its role in regulating swarming was investigated by examining the expression of genes in the flagellar cascade. In a disA mutant background, we observed a 1.4-fold increase in the expression of flhDC, which encodes FlhD(2)C(2), the master regulator of the flagellar gene cascade. However, the expressions of class 2 (fliA, flgM) and class 3 (flaA) genes were at least 16-fold higher in the disA background during swarmer cell differentiation. Overexpression of DisA on a high-copy-number plasmid did not significantly decrease flhDC mRNA accumulation but resulted in a complete block in mRNA accumulation for both fliA and flaA. DisA overexpression also blocked swarmer cell differentiation. The disA gene was regulated during the swarming cycle, and a single-copy disA::lacZ fusion exhibited a threefold increase in expression in swarmer cells. Given that DisA was similar to amino acid decarboxylases, a panel of decarboxylated amino acids was tested for effects similar to DisA overexpression, and phenethylamine, the product of phenylalanine decarboxylation, was capable of inhibiting both swarming and the expression of class 2 and class 3 genes in the flagellar regulon. A DisA-dependent decarboxylated amino acid may inhibit the formation of active FlhD(2)C(2) heterotetramers or inhibit FlhD(2)C(2) binding to DNA.