Escherichia coli genes regulated by cell-to-cell signaling

Abstract

Utilizing the bicistronic reporter transposon mini-Tn5 lacZ-tet͞1, we have identified lacZ fusions to four Escherichia coli genes͞operons that are strongly activated by the accumulation of self-produced extracellular signals. These fusions were designated cma9, cma48, cma113, and cma114 for conditioned medium activated. Each of the cma fusions was expressed in a growth phase-dependent manner, and the presence of conditioned medium from a stationary phase E. coli culture resulted in the premature activation of these fusions in cells at early to mid-logarithmic phase. The cma48 and cma114 fusions were dependent on RpoS for growth phase expression and response to extracellular factors. The extracellular factors that activated the cma9, cma48, and cma114 fusions were produced in both rich complex and defined minimal media. The cma fusions were shown to be within the cysK (cma9), astD (cma48), tnaB (cma113), and gabT (cma114) genes. These genes function in the uptake, synthesis, or degradation of amino acids that yield pyruvate and succinate.Bacteria are capable of regulating gene expression in response to a variety of extracellular signals. When the signal is produced by the bacterium itself, this type of regulation is termed autoinduction or quorum sensing (1-4). The composition of signaling molecules can include mixtures of amino acids, peptides, fatty acids, and acyl derivatives of homoserine lactone (1-4, 5-7). These signaling molecules can regulate gene expression by a number of mechanisms, including modulating the activity of members of the LuxR family, interacting with two-component systems, and inhibiting phosphatases (1,3,(8)(9)(10). The cellular processes regulated by quorum sensing are diverse, and some examples include spore formation, activation of luminescence, competence, conjugal transfer of plasmid DNA, regulation of virulence genes, regulation of peptidoglycan O-acetylation, and biofilm maturation (11)(12)(13)(14)(15)(16)(17)(18)(19)(20).In Escherichia coli, the regulation of gene expression by extracellular signals has also been established. Expression of the rpoS gene, encoding the alternate sigma factor S ( 38 ) involved in stationary-phase and osmoregulated gene expression is stimulated by the presence of a factor in conditioned medium (21,22). Studies by Huisman and Kolter (23) indicate that rpoS expression is decreased in a thrA, metL, lysC triple mutant that is defective in production of homoserine, and expression could be restored by exogenous homoserine lactone. However, the role of homoserine lactone or an acylated derivative in RpoS expression is unclear. Additional E. coli genes subject to regulation by extracellular factors include sdiA and the ftsQAZ cell division gene cluster (22,24). Recent studies by Surette and Bassler (25) have revealed that E. coli produces a signal that can substitute for AI-2, one of two Vibrio harveyi signals that control luminescence gene expression. The E. coli signal was heat labile, produced at mid-exponential phase of growth, and degraded at sta...

Indole induces the expression of multidrug exporter genes in Escherichia coli

“…Thus, the induction of E. coli drug exporter genes by indole is not likely to be a result of the envelope stress response. Recently, it was reported that indole acts as an extracellular signal like N-acyl homoserine lactone and AI-2 (Baca- DeLancey et al, 1999;Fuqua et al, 2001;Wang et al, 2001;Bassler, 2002;Chen et al, 2002). The indole concentration increases with cell growth as a byproduct of pyruvate production in E. coli cells (Wang et al, 2001).…”

Diffusible signals and interspecies communication in bacteria

“…Indole is generated through the degradation of tryptophan by tryptophanase, the product of the tnaA gene, and can reach levels up to 340 mM in stationary-phase cultures of E. coli. The role of indole as a potential signal molecule in E. coli was first revealed through analysis of factors required for the induction of the astD, tnaB and gabT genes by E. coli conditioned medium (Baca-DeLancey et al, 1999;Wang et al, 2001). Although indole itself acted as an inducer, conditioned medium from a tnaA mutant was still able to induce these genes, albeit to a lower extent than the wild-type.…”

A quantitative study of gene regulatory pathways in Bacillus subtilis for virulence and competence phenotype by quorum sensing

“…Bacillus subtilis has become the best studied grampositive model organism for a number of reasons which includes its relative ease of handling in wet lab experiments, its growth rate is relatively fast (comparable to that of Escherichia coli), it possesses a natural competence system and the machinery for homologous recombination (Baca-DeLancey et al 1999). In Gram positive bacteria signal molecule is a post-translationally processed secreted peptide for the communication.…”