Bacterial autoinducer 2 (AI-2) is proposed to be an interspecies mediator of cell-cell communication that enables cells to operate at the multicellular level. Many environmental stimuli have been shown to affect the extracellular AI-2 levels, carbon sources being among the most important. In this report, we show that both AI-2 synthesis and uptake in Escherichia coli are subject to catabolite repression through the cyclic AMP (cAMP)-CRP complex, which directly stimulates transcription of the lsr (for "luxS regulated") operon and indirectly represses luxS expression. Specifically, cAMP-CRP is shown to bind to a CRP binding site located in the upstream region of the lsr promoter and works with the LsrR repressor to regulate AI-2 uptake. The functions of the lsr operon and its regulators, LsrR and LsrK, previously reported in Salmonella enterica serovar Typhimurium, are confirmed here for E. coli. The elucidation of cAMP-CRP involvement in E. coli autoinduction impacts many areas, including the growth of E. coli in fermentation processes.Bacteria have evolved complex genetic circuits to modulate their physiological states and behaviors in response to a variety of extracellular signals. In a process termed quorum sensing, or density-dependent gene regulation, bacteria produce, release, and respond to signaling molecules (autoinducers), which accumulate as a function of cell density. Quorum sensing allows bacteria to communicate with each other and coordinate their activities at a multicellular level. The autoinducers of many gram-positive bacteria are secreted peptides (30, 42), while gram-negative bacteria use small chemical molecules (60). Among gram-negative bacteria, the LuxI/LuxR signal synthase-signal receptor system is the most studied at the molecular level, with the signaling species being a family of N-acylhomoserine lactones. However, the cross-species autoinducer, autoinducer 2 (AI-2), has received intense interest recently because the gene for its terminal synthase, luxS, is present in over 55 bacteria and its activity can be readily assayed biologically (61). It is known that quorum sensing regulates diverse cellular processes, including bioluminescence (19, 34), spore formation (33), motility (18, 22), competence (35), conjugation (20), antibiotic synthesis (2, 17), virulence (38,44,50), and biofilm maturation (13, 45).Our laboratory is interested in understanding and controlling microbial behavior in bioreactors in order to enhance recombinant protein synthesis and yield. Since quorum sensing is emerging as a global regulator of many intracellular processes, including those that influence protein synthesis, efforts to understand this "tunable" controller are essential. In our previous work using chemostat cultures (14), many stimuli were found to affect the level of AI-2. Among these, the pulsed addition of glucose, a common carbon source for recombinant Escherichia coli fermentations, resulted in increased AI-2 levels, but with the dynamic response dependent on the steadystate growth rate (e.g., dil...

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Electroaddressing of biological components at specific device addresses is attractive because it enlists the capabilities of electronics to provide spatiotemporally controlled electrical signals. Here, the electrodeposition of calcium alginate hydrogels at specific electrode addresses is reported. The method employs the low pH generated at the anode to locally solubilize calcium ions from insoluble calcium carbonate. The solubilized Ca2+ can then bind alginate to induce this polysaccharide to undergo a localized sol‐gel transition. Calcium alginate gel formation is shown to be spatially controlled in the normal and lateral dimensions. The deposition method is sufficiently benign that it can be used to entrap the bacteria E. coli. The entrapped cells are able to grow and respond to chemical inducers in their environment. Also, the entrapped cells can be liberated from the gel network by adding sodium citrate that can compete with alginate for Ca2+ binding. The capabilities of calcium alginate electrodeposition is illustrated by entrapping reporter cells that can recognize the quorum sensing autoinducer 2 (AI‐2) signaling molecule. These reporter cells were observed to recognize and respond to AI‐2 generated from an external bacterial population. Thus, calcium alginate electrodeposition provides a programmable method for the spatiotemporally controllable assembly of cell populations for cell‐based biosensing and for studying cell‐cell signaling.