The Escherichia coli flagellar transcriptional activator flhD regulates cell division through induction of the acid response gene cadA

Abstract

FlhD is a positive regulator of cadA. A mutant with a transposon-mediated lacZ fusion to cadA exhibited a cell division phenotype similar to that of the flhD mutant and had FlhD-dependent ␤-galactosidase activity. Under different growth conditions, the cell division rate correlated with the level of expression of cadA.In a previous study (13), we demonstrated that Escherichia coli flhD is involved in a process other than flagellar expression, namely, reducing the cell division rate as cells enter stationary phase. It was demonstrated that flhD mutant cells grown in tryptone broth (TB) (1% tryptone, 1% NaCl) continued to divide at a rate that is typical for mid-exponential growth at a time when wild-type cells started to reduce their cell division rate. flhD mutant cells were smaller than wild-type cells as they entered stationary phase, and it was demonstrated that this characteristic correlated with their inability to sense the depletion of serine from the medium, which signals wild-type cells to reduce their cell division rate. It was discussed that the signal cascade probably included phosphorylation of OmpR (15) by acetyl phosphate (14). It was unclear how the expression of flhD led to the reduction of the cell division rate.We now demonstrate that the effect of FlhD upon the cell division rate is mediated through induction of cadA. The cad operon consists of cadB and cadA, encoding the lysine/cadaverine antiporter CadB and the enzyme lysine decarboxylase CadA. Expression of this operon is dependent on the regulator CadC, whose gene is located upstream of cadA. The expression from the p cad promoter is induced by low pH, low oxygen, rich medium, and excess lysine. All of these signals activate cadBA expression via a cadC-dependent pathway (10)(11)(12)18).Construction of the cadA transposon mutant. All strains, plasmids, and phage used in this study are listed in Table 1. Plasmid pPB10 was constructed by cloning the flhD gene, obtained from plasmid pPM61 (1) by PCR, into the arabinoseinducible plasmid pKB130 (17), kindly provided by L. Katz (Abbott Laboratories, Chicago, Ill.). pcnB1 zad-981::mini-Kn from strain RP7947 (8), kindly provided by J. S. Parkinson (University of Utah, Salt Lake City), was used to reduce the plasmid copy number and the background expression. The resulting strain BP78 exhibited complementation of the flhD mutation in the presence of arabinose. The cadA::Tn10-lacZ fusion was obtained by transposon mutagenesis. Cells of strain BP78 were infected with phage lysate TnphoAЈ-2 (19), kindly provided by B. Wanner (Purdue University, West Lafayette, Ind.). Cells were plated on tetracycline to identify chromosomal insertions. One tetracycline-resistant colony was blue in the presence of arabinose and white in its absence. This strain was designated BP87 and is characterized in this report. cadA::Tn10-lacZ was transduced by P1 transduction into the wild-type strain YK410 and the flhD mutant strain YK4131. In Luria-Bertani medium (LB) (TB plus 0.5% yeast extract) and late-exponential phase, the ...

The Ability ofProteus mirabilisTo Sense Surfaces and Regulate Virulence Gene Expression Involves FliL, a Flagellar Basal Body Protein

“…More significantly, the flhDC operon is strongly upregulated during P. mirabilis swarming (29) and contributes to virulence factor expression in several pathogens (4,25,42,80). In addition, microarray comparisons of mRNA levels from E. coli wild-type and flhDC mutant strains have suggested that the flagellar master operon regulates several nonflagellar genes, particularly those involved in cell division (52)(53)(54)(55)(56)67). Thus, the phenotype of the fliL mutation found in this study is likely a consequence of FliL directly or indirectly affecting flhDC expression.…”

Bacterial Cell-to-Cell Signaling in the Gastrointestinal Tract

“…Transcription of these genes, as well as motility, could be restored by addition of signals exogenously, further confirming that regulation of flagellum expression and motility is controlled by a quorum sensing signaling mechanism (74,75). QS regulation of flhDC expression has far-reaching implications beyond flagellum expression, given that FlhDC has been shown to also regulate bacterial cell division (57,58) and several metabolic processes (56). QS regulation of the LEE-encoded TTS system and the flagellum regulon in EHEC is dependent on the AI-3 signal; the role of AI-2 signaling in EHEC remains to be established (75).…”

Lateral Flagellar Gene System of Vibrio parahaemolyticus

“…The master flagellar operon flhDC also directs transcription of many nonflagellar genes (65). It has been implicated in the regulation of cell division (66,67), and overproduction is known to induce swarming in many enteric bacteria (22). Although the V. parahaemolyticus lateral gene system encodes proton-powered peritrichous flagella that are upregulated in response to growth on a surface, as are the flagella of E. coli and S. enterica, we have discovered that the hierarchy of the laf system is unlike the system of these enteric bacteria.…”