Abstract
Because cells have the extraordinary ability to sense and respond to even subtle environmental changes by intricately regulating their gene expression patterns, their behaviors can be intentionally “tuned” by altering the state of their environments in a prescribed or rational manner. Rational control of both external and internal molecular stimuli provides a basis for many biotechnological applications including the expression of foreign protein products. This is done by coordinately controlling product synthesis while retaining the cell in a productive state. Quorum sensing (QS), a molecular signaling modality that mediates cell-cell communication, autonomously facilitates both inter- and intra-species gene regulation. This process can be rewired to enable autonomously actuated, but molecularly programmed, genetic control. Recently, even electrical signals, which have long been used to control the most sophisticated of man-made devices, are now employed to alter cell signaling processes enabling computer programmed behavior, particularly in cells suitably engineered to accommodate electrical signals. By minimally engineering these genetic circuits, new applications have emerged for the repurposing of Escherichia coli, from creating innovative sensor concepts to stimulating the emerging field of electrogenetics.
Keywords
- protein expression
- quorum sensing
- autonomous induction
- cell-cell communication
- redox signaling
- electro-induction
- synthetic biology
1. Introduction
Controlling the processes or functioning of biological systems has profound implications in biotechnological and other applications [1]. By controlling gene expression, cell behavior and responses to environmental cues can, in turn, be regulated. Ever since the dawn of biotechnology, scientists have been searching for new and better methods to specifically modulate gene expression. Biological systems, however, possess the ability to sense and respond to internal or environmental changes through tuning their own genetic networks. For example, they are capable of detecting metabolic stress during foreign protein expression, and in response, express genes that brake or facilitate the process. Cells are also able to receive signaling molecules from their ‘neighbors’, to then begin functioning as a ‘collective’ or population by activating certain genetic regulons. In this chapter, gene-regulating technologies of prokaryotes are discussed that intentionally alter the intracellular landscape for protein expression as well as the extracellular microenvironmental state in the vicinity of ‘designer’ production strains in order to program gene expression and behavior. These techniques incorporate the understanding of cell metabolism and the transcriptome, cell-cell communication (previously reviewed by [2, 3]), and biological redox reactions (previously reviewed by [4]). This chapter will mainly focus on recent advances in how actuation of genes is accomplished in
2. Optimizing protein expression: rational control of cell condition
There is no doubt that among the myriads of systems available for heterologous protein expression, the Gram-negative bacterium
2.1. Reducing bottlenecks: protease activity
The reduction in growth rate is particularly problematic, not only does it contribute to segregational plasmid instability, but severe growth rate perturbations at the onset of induced foreign protein synthesis have been shown to inhibit further expression of the desired protein [8]. Therefore, high levels of foreign protein expression are often unsustainable. Moreover, increased protease activity upon induction and overexpression of foreign protein generally leads to increased proteolysis, as described elsewhere [9, 10, 11]. These protease activities with uncharacterized specificity can be considered detrimental to the stability of the recombinant protein. Inefficient cell metabolism during overexpression, as indicated by acetate secretion of host cells, also results in lower protein expression [12]. These cell responses can greatly diminish the genetically-focused efforts to maximize both the final yield and concentration of recombinant proteins by increasing gene expression. In attempting to overcome these hurdles, cell dynamics during induced expression of chloramphenicol acetyl-transferase (CAT) expression have been examined and mathematically modeled in [13], suggesting that induction with an optimized amount of inducer (IPTG) at the onset of stationary phase can avoid growth rate suppression and achieve high expression. However, stimulated protease activity can be still observed. Intracellular proteases of recombinant
2.2. Reducing bottlenecks: transcription factors
Levels of the global heat shock transcription factor, σ32, for example, have been shown to increase rapidly during stress, including the stress associated with heterologous protein overexpression [18, 19, 20, 21, 22, 23]. Indeed, a variety of cellular stresses induce the σ32-mediated stress response, including both ethanol and heat shock [19, 20, 21, 22, 24]. While σ32 accumulation could be mediated by control of transcription and translation, its accumulation following production of recombinant protein is mainly due to an altering of its otherwise chaperone-sequestered state [19, 25]. To facilitate protein expression in recombinant
2.3. Reducing bottlenecks: perspectives
Indeed, there have been countless studies demonstrating techniques to enhance the production of protein over the past 40+ years since recombinant DNA technology was first introduced. Besides choosing the right amount and type of inducer, optimal fermentation conditions have been developed to alleviate the reduction of growth rate during overexpression and enhance yield. Increasing stability of the protein product can also overcome the increased protease activity, this in addition to downregulation of protease-specific regulators. On top of the examples described above, an excellent review by Makrides [28] and a more recent review by Rosano [29] have discussed the various niches within which one can dig deeper in order to achieve higher yield and activity of the desired recombinant protein product.
We note that the majority of these methodologies have targeted either cell-based genetic regulatory structures, the sequence space and alterations of the protein of interest, or the operating policies of the reactors used to cultivate the overproducing cells. These cells, in turn, have typically been monocultures of an optimized host. Rarely have methodologies appeared in which collectives of cells, either monocultures or controlled co-cultures or consortia, and the exogenous signaling thereof are used to produce products such as recombinant proteins. Particularly useful when the engineering of a particular host overburdens its natural regulatory circuitry, cell consortia or collectives provide an interesting alternative. Co-culture and small consortia concepts have recently emerged. Moreover, new methodologies for orthogonal stimulation of genetic circuits can minimize pleiotropic or off-target effects normally accompanying more common chemical inducers. In the sections that follow, we describe efforts to minimally alter the native bacterial signaling processes of quorum sensing and oxidative stress to repurpose
3. Decipher the bacterial dialog: quorum sensing
Gene expression in bacteria can be regulated by a wide array of intra- and extracellular cues. On top of the common chemical inducers that are most often introduced manually to initiate protein overexpression, bacteria are actually capable of producing their own extracellular signals for intercellular communication. The term “quorum sensing (QS)” was coined by EP Greenberg and colleagues decades ago, to describe the phenomena where the secretion and perception of small signaling molecules are transduced to coordinate behavior of a minimal unit (quorum) of microorganisms. Since then, there’s been an explosion in understanding how bacteria communicate with themselves. In this section, well-characterized quorum-sensing systems and types of signals, receptors, mechanisms of signal transduction, and target outputs of each system are introduced. In addition, since quorum sensing in many bacteria is also shown to control gene expression in a global manner, several regulons will be introduced, again with the focus on
3.1. Quorum sensing and its networks
Quorum sensing bacteria produce and release chemical signal molecules termed autoinducers, whose external concentration increases as a function of increasing cell-population density. Once the bacteria detect that autoinducers have reached a minimal threshold level of stimulatory concentration, they will respond by altering their gene expression and behavior. Autoinducers are the cues by which QS bacteria communicate and synchronize particular behaviors on a population-wide scale, thus gaining the ability to function as a multicellular organism.
3.1.1. LuxIR system of V. fischeri
Quorum sensing mechanisms vary from species to species, and hence here we introduce the first-described QS system of the bioluminescent marine bacterium
Figure 1 illustrates the QS system of
3.1.2. LuxS/AI-2 system of E. coli
While some of the
The
3.2. Global quorum sensing regulons
3.2.1. Global genetic regulation of LuxIR and AI-2/Lsr systems
The dawn of genomic profiling has unveiled that quorum sensing, in many bacteria, controls gene expression in a global manner. QS-mutants of
Interestingly, AI-2 synthesis and signaling levels are linked to the accumulation of protein product expressed from plasmid-encoded genes [44]. This suggests that recombinant
3.2.2. Applications
On top of employing the LuxIR system as a platform for innovative genetic and population regulators, intentional rewiring of
More endeavors have been made [56] to increase protein yield in this autonomous system through a different approach. With the same intention in mind [49, 50], a new study showed that reduced heterogeneity between independent cells could be achieved by inserting an enhanced feedback loop to the
That is, in [59] and as shown in Figure 3,
3.3. Interspecies communication
3.3.1. Universal autoinducer AI-2
Beyond controlling genetic expression on a global scale, quorum sensing allows bacteria to communicate within and between species. This notion arose with the study and discovery of the aforementioned autoinducer AI-2. Derived from SAM as a part of bacterial 1-carbon metabolism, AI-2 is a general term for a family of cyclic furanones utilized in interspecies communication [60]. In LuxS-containing bacteria, SAM is converted into SAH and then broken down by enzymes Pfs and LuxS sequentially into signaling molecule DPD and other byproducts. Due to the high reactivity of DPD, many distinct but related products could be recognized by different bacterial species as AI-2. Though it is postulated that small molecules of similar structure as AI-2 could serve as potential antagonists that halt the bacterial conversation, only a handful are found (compared to a large number of AI-1 inhibitors). In [61], C-1 alkyl analogs of AI-2 that quench QS responses in multiple bacterial species simultaneously were developed and synthesized. Interestingly, addition of a single carbon to the C1-alkyl chain of the analog plays a critical role in determining the effect on quenching the QS response. This analog, isobutyl-DPD, was later used to inhibit maturation of
AI-2 is also one of the several signals used by marine bacteria
Interkingdom communication was also shown to be mediated by AI-2. In [66], transcriptomic effects of bacterial secretions from two nonpathogenic
3.3.2. Applications
This discovery suggests that AI-2 QS manipulation might find application in guiding human physiology and that ‘smart’ bacteria, those making heterologous proteins such as drugs or essential nutrients and that otherwise serve as decision makers, might find application in a variety of other fields. As an extension, Lentini et al. [67] engineered minimal ‘artificial’ cells capable of expressing AI-2 synthesizing fusion protein His6-LuxS-Pfs-Tyr5 (HLPT) [68] wherein newly synthesized AI-2 was proven to induce luminescence in nearby cells, particularly an AI-2 reporter strain of
Developing, silencing, or intervening with the communication between cells has revolutionized the way we control gene expression. In [69], communication between cells is developed further by modifying the biological ‘nanofactories’ proposed by LeDuc et al. [70] to trigger QS responses in the absence of autoinducers. They are self-assembled and comprised of four functional modules: a targeting module (an antibody), a material sensing module, an assembly module, and a synthesis module (fusion protein His6-Protein G-LuxS-Pfs-Tyr5, HGLPT, (Figure 4). Protein G (assembly module) allows the chimeric enzyme to attach to a targeting antibody
Perhaps next generation antimicrobials can be created by intercepting bacterial communication and creating ‘smart’ bacteria. Instead of targeting the viability of pathogenic strains, interruption of their communication is proposed, as it is hypothesized that there will be less selective pressure to develop resistance if instead one targets the mechanisms keyed to pathogenicity [72]. As a global autoinducer, inhibition of the signal AI-2 could possibly lead to decreased virulence in a variety of bacterial species. Many parts of the AI-2/LuxS system, from signal generators (Pfs and LuxS) to signal receptors are all likely targets for inhibition, especially as there are many synthesized AI-2 analogs that are available for quorum quenching [61, 62, 63, 73]. In another case [74], probiotic
In addition to potential for therapeutic synthesis and delivery,
4. Bridging the bio-electro interface: Redox signaling and electrogenetic systems
In addition to quorum sensing, bacteria use numerous other small chemical molecules to build up conversations between themselves and with the environment. It is well known that redox reactions and redox based signaling pervade living cells and are extremely crucial to both anabolic and catabolic metabolism. Redox-based molecular systems, however, are also leveraged by bacteria for communication. Cells must detect a variety of oxidative stressors and quickly respond so as to avoid oxidative damage and maintain redox balance in order to survive. In this section, several redox signaling pathways will be introduced, yet emphasis will be on how redox signaling and electrochemistry help connect communication and information transfer between biological systems and electronic devices. In this way, redox molecules can serve as exogenous and electronically-programmed controllers of biological function.
4.1. Redox signaling in biological systems
In response to redox imbalance, new metabolic pathways are initiated, the repair or bypassing of damaged cellular components is coordinated and systems that protect the cell from further damage are induced. Throughout the years, many studies have revealed a vast repertoire of elegant solutions that have evolved to allow bacteria to sense and respond to different redox signals [78]. Below, two oxidative stress sensors, SoxR and OxyR, and their corresponding signaling pathway will be introduced. These systems are later shown to enable electrical control of gene expression in
4.1.1. SoxR: [Fe-S]-cluster based, superoxide/nitric oxide stress sensor
The
4.1.2. OxyR: thiol-based, peroxide stress sensor
The
4.2. Redox capacitor and bio-electrode interface communication
To probe bio-related redox reactions/signaling simply and readily, recently developed redox-capacitor films can serve as a bio-electrode interface. These are well-described and have been reviewed [82]. In brief, these electrochemical tools are capable of accepting, storing and donating electrons from mediators commonly used in electrochemistry and also in biology. Biofabricated from catechol and the polysaccharide chitosan, the former can be readily (and reversibly) oxidized. When catechol is oxidized, quinone is formed and it can be covalently grafted onto chitosan. In addition, chitosan can be easily ‘electro-assembled’ onto electrodes owing to its pH-responsive properties. That is, when a voltage is applied to an electrode submersed in an aqueous solution containing chitosan, the pH near the electrode can be controlled. When basic (above the pKa of chitosan, ~6.5), chitosan will form a hydrophobic network and assemble onto the electrode as a film or hydrogel, depending on the application of the electronic charge. When the catechol/quinone redox couple is integrated into the film, it can serve as a source or sink of electrons. Diffusible redox mediators can be added as they can exchange electrons (‘charge/discharge’) with the redox-active films. Common biology-related mediators include molecules such as ascorbate and NADH, which can charge and discharge the film. Pyocyanin, a toxin secreted by
4.3. Electrical process modulation and gene induction
Many researchers have endeavored finding new ways to control cell processes. The use of optical means to regulate gene expression has garnered significant attention and resulted in an entire field of optogenetics [83]. Genetic switches that operate on optical signals (even small changes in wavelength or color) have been shown to be powerful exogenous controllers of cell function [84, 85]. More recently, researchers have turned to electronic devices to directly control biochemical reactions. In [86], a transistor-like device is engineered to control glucose metabolism of yeast (
Even more recently, a synthetic, mammalian electro-genetic transcription circuit was created [88]. This was done by linking the electrochemical oxidation of ethanol to acetaldehyde, triggering an acetaldehyde-inducible gene expression circuit. While an indirect outcome of the applied voltage, this was the first study whereby specifically intended gene expression was induced by electronic means. A more direct methodology recently appeared [89] in which the engineered genetic circuit responds directly to the electrode-oxidized signal molecule, opening an entirely new modality for bioelectronic control (Figure 6). Again, pyocyanin was used in their system, it is responsible for translating electrical signals into a biochemical redox signal that, in turn, can be sensed by SoxR and in sequence, initiate the expression from
5. Conclusion
Researchers in biotechnology are constantly seeking novel platforms or techniques from which to address problems: those that in a broad sense, have enhanced efficacy, while maintaining or intensifying specificity. In this chapter, innovative means that focus on controlling environmental cues to regulate gene expression are introduced. To optimize heterologous protein expression, methods seeking to repress stress responses and retain cells in a ‘productive’ state are carried out by carefully engineering host cells to respond to various cues that are either introduced exogenously or endogenously. QS systems have appeared that provide targets for controlling bacterial behavior. They are also shown to report on the prevailing metabolic state of a product-producing cell. Early methodologies such as RNAi, genetic mutation, product protein-directed evolution, all successful means to enhance yield, can be reexamined based on new understanding of how cells communicate with one another. That is, QS systems enable the rewiring of endogenous metabolism for the coordinated control of entire populations of cells. This ushers in a new way of viewing protein or product-producing cells as a cell ‘collective’ rather than as individual cells each identical to one another, responding to cues or inducers such as IPTG for the controlled overexpression of heterologous proteins. QS systems enable autonomous global gene regulation based on cell density. That is, instead of direct interrogation and control of genetic circuits, QS-based cell-cell communication allows indirect gene regulation through self-secretion and uptake of small signaling molecules. Further, exogenous and orthogonal signals, such as those provided by optical and electrical means can be interfaced with cells, providing exquisite control of gene expression. Importantly, in host cells were synthetic components contribute minimal perturbation to native systems, exogenously signaled protein expression can be coupled with exogenously controlled cell behavior (e.g., swimming or decision making). Electrochemistry, along with the invention of redox capacitors, thusly opens a new niche for genetic induction. That is, by leveraging the ability of mediators to translate electrical signals into chemical cues, researchers can cue changes in environmental electrical state that, in turn, are capable of inducing gene expression. These innovative methods will no doubt continue to generate impactful applications in fields such as biotechnology and biosensing.
Acknowledgments
This work was supported by DTRA (HDTRA1-13-0037) and NSF (DMREF #1435957) and by the National Institutes of Health (R21EB024102).
Conflict of interest
We declare that we have no conflicts of interest associated with the submitted work.
References
- 1.
Kitano H. Systems biology: A brief overview. Science. 2002; 295 (5560):1662-1664 - 2.
Fuqua C, Parsek MR, Greenberg EP. Regulation of gene expression by cell-to-cell communication: Acyl-homoserine lactone quorum sensing. Annual Review of Genetics. 2001; 35 :439-468 - 3.
Bassler BL. How bacteria talk to each other: Regulation of gene expression by quorum sensing. Current Opinion in Microbiology. 1999; 2 (6):582-587 - 4.
Dalton TP, Shertzer HG, Puga A. Regulation of gene expression by reactive oxygen. Annual Review of Pharmacology and Toxicology. 1999; 39 :67-101 - 5.
Betenbaugh MJ, Beaty C, Dhurjati P. Effects of plasmid amplification and recombinant gene expression on the growth kinetics of recombinant E. coli . Biotechnology and Bioengineering. 1989;33 (11):1425-1436 - 6.
Goff SA, Goldberg AL. An increased content of protease La, the lon gene product, increases protein degradation and blocks growth in Escherichia coli . The Journal of Biological Chemistry. 1987;262 (10):4508-4515 - 7.
Okita B, Arcuri E, Turner K, Sharr D, Del Tito B, Swanson J, et al. Effect of induction temperature on the production of malaria antigens in recombinant E. coli . Biotechnology and Bioengineering. 1989;34 (6):854-862 - 8.
Bentley W. Effects of plasmid-mediated activity on bacterial metabolism and culture stability [thesis]. Boulder, CO: University of Colorado; 1989 - 9.
Gottesman S, Maurizi MR. Regulation by proteolysis: Energy-dependent proteases and their targets. Microbiological Reviews. 1992; 56 (4):592-621 - 10.
Maurizi MR. Proteases and protein degradation in Escherichia coli . Experientia. 1992;48 (2):178-201 - 11.
Grossman AD, Taylor WE, Burton ZF, Burgess RR, Gross CA. Stringent response in Escherichia coli induces expression of heat shock proteins. Journal of Molecular Biology. 1985;186 (2):357-365 - 12.
Ko YF, Bentley WE, Weigand WA. The effect of cellular energetics on foreign protein production. Applied Biochemistry and Biotechnology. 1995; 50 (2):145-159 - 13.
Bentley WE, Davis RH, Kompala DS. Dynamics of induced CAT expression in E. coli . Biotechnology and Bioengineering. 1991;38 (7):749-760 - 14.
Harcum SW, Bentley WE. Response dynamics of 26-, 34-, 39-, 54-, and 80-kDa proteases in induced cultures of recombinant Escherichia coli . Biotechnology and Bioengineering. 1993;42 (6):675-685 - 15.
Gill RT, DeLisa MP, Valdes JJ, Bentley WE. Genomic analysis of high-cell-density recombinant Escherichia coli fermentation and “cell conditioning” for improved recombinant protein yield. Biotechnology and Bioengineering. 2001;72 (1):85-95 - 16.
Gill RT, Valdes JJ, Bentley WE. A comparative study of global stress gene regulation in response to overexpression of recombinant proteins in Escherichia coli . Metabolic Engineering. 2000;2 (3):178-189 - 17.
Gill RT, DeLisa MP, Shiloach M, Holoman TR, Bentley WE. OmpT expression and activity increase in response to recombinant chloramphenicol acetyltransferase overexpression and heat shock in E. coli . Journal of Molecular Microbiology and Biotechnology. 2000;2 (3):283-289 - 18.
Blaszczak A, Zylicz M, Georgopoulos C, Liberek K. Both ambient temperature and the DnaK chaperone machine modulate the heat shock response in Escherichia coli by regulating the switch between sigma 70 and sigma 32 factors assembled with RNA polymerase. The EMBO Journal. 1995;14 (20):5085-5093 - 19.
Kanemori M, Mori H, Yura T. Induction of heat shock proteins by abnormal proteins results from stabilization and not increased synthesis of sigma 32 in Escherichia coli . Journal of Bacteriology. 1994;176 (18):5648-5653 - 20.
Lesley SA, Thompson NE, Burgess RR. Studies of the role of the Escherichia coli heat shock regulatory protein sigma 32 by the use of monoclonal antibodies. The Journal of Biological Chemistry. 1987;262 (11):5404-5407 - 21.
Straus DB, Walter WA, Gross CA. The heat shock response of E. coli is regulated by changes in the concentration of sigma 32. Nature. 1987;329 (6137):348-351 - 22.
Straus DB, Walter WA, Gross CA. The activity of sigma 32 is reduced under conditions of excess heat shock protein production in Escherichia coli . Genes & Development. 1989;3 (12A):2003-2010 - 23.
Tilly K, Spence J, Georgopoulos C. Modulation of stability of the Escherichia coli heat shock regulatory factor sigma. Journal of Bacteriology. 1989;171 (3):1585-1589 - 24.
Parsell DA, Lindquist S. The function of heat-shock proteins in stress tolerance: Degradation and reactivation of damaged proteins. Annual Review of Genetics. 1993; 27 :437-496 - 25.
Neidhardt FC, Curtiss R. Escherichia coli and Salmonella: Cellular and Molecular Biology. Vol. 2. 2nd ed. Washington, DC: ASM Press; 1996. (xx, 2822 p.) p - 26.
Zhou YN, Kusukawa N, Erickson JW, Gross CA, Yura T. Isolation and characterization of Escherichia coli mutants that lack the heat shock sigma factor sigma 32. Journal of Bacteriology. 1988;170 (8):3640-3649 - 27.
Srivastava R, Cha HJ, Peterson MS, Bentley WE. Antisense downregulation of sigma(32) as a transient metabolic controller in Escherichia coli : Effects on yield of active organophosphorus hydrolase. Applied and Environmental Microbiology. 2000;66 (10):4366-4371 - 28.
Makrides SC. Strategies for achieving high-level expression of genes in Escherichia coli . Microbiological Reviews. 1996;60 (3):512-538 - 29.
Rosano GL, Ceccarelli EA. Recombinant protein expression in Escherichia coli : Advances and challenges. Frontiers in Microbiology. 2014;5 :172 - 30.
Nealson KH, Hastings JW. Bacterial bioluminescence: its control and ecological significance. Microbiological Reviews. 1979; 43 (4):496-518 - 31.
Waters CM, Bassler BL. Quorum sensing: Cell-to-cell communication in bacteria. Annual Review of Cell and Developmental Biology. 2005; 21 :319-346 - 32.
Miller MB, Bassler BL. Quorum sensing in bacteria. Annual Review of Microbiology. 2001; 55 :165-199 - 33.
March JC, Bentley WE. Quorum sensing and bacterial cross-talk in biotechnology. Current Opinion in Biotechnology. 2004; 15 (5):495-502 - 34.
Lenz DH, Mok KC, Lilley BN, Kulkarni RV, Wingreen NS, Bassler BL. The small RNA chaperone Hfq and multiple small RNAs control quorum sensing in Vibrio harveyi andVibrio cholerae . Cell. 2004;118 (1):69-82 - 35.
Lee J, Zhang XS, Hegde M, Bentley WE, Jayaraman A, Wood TK. Indole cell signaling occurs primarily at low temperatures in Escherichia coli . The ISME Journal. 2008;2 (10):1007-1023 - 36.
Li J, Attila C, Wang L, Wood TK, Valdes JJ, Bentley WE. Quorum sensing in Escherichia coli is signaled by AI-2/LsrR: Effects on small RNA and biofilm architecture. Journal of Bacteriology. 2007;189 (16):6011-6020 - 37.
Kamaraju K, Smith J, Wang J, Roy V, Sintim HO, Bentley WE, et al. Effects on membrane lateral pressure suggest permeation mechanisms for bacterial quorum signaling molecules. Biochemistry. 2011; 50 (32):6983-6993 - 38.
Graff SM, Bentley WE. Mathematical model of LsrR-binding and derepression in Escherichia coli K12. Journal of Bioinformatics and Computational Biology. 2017;15 (1):1650039 - 39.
Quan DN, Tsao CY, Wu HC, Bentley WE. Quorum sensing desynchronization leads to bimodality and patterned behaviors. PLoS Computational Biology. 2016; 12 (4):e1004781 - 40.
Herzberg M, Kaye IK, Peti W, Wood TK. Ydg G (Tqs A) controls biofilm formation in Escherichia coli K-12 through autoinducer 2 transport. Journal of Bacteriology. 2006;188 (2):587-598 - 41.
Gonzalez Barrios AF, Zuo R, Hashimoto Y, Yang L, Bentley WE, Wood TK. Autoinducer 2 controls biofilm formation in Escherichia coli through a novel motility quorum-sensing regulator (Mqs R, B3022). Journal of Bacteriology. 2006;188 (1):305-316 - 42.
DeLisa MP, Wu CF, Wang L, Valdes JJ, Bentley WE. DNA microarray-based identification of genes controlled by autoinducer 2-stimulated quorum sensing in Escherichia coli . Journal of Bacteriology. 2001;183 (18):5239-5247 - 43.
Wang L, Li J, March JC, Valdes JJ, Bentley WE. luxS-dependent gene regulation in Escherichia coli K-12 revealed by genomic expression profiling. Journal of Bacteriology. 2005;187 (24):8350-8360 - 44.
DeLisa MP, Valdes JJ, Bentley WE. Quorum signaling via AI-2 communicates the “metabolic burden” associated with heterologous protein production in Escherichia coli . Biotechnology and Bioengineering. 2001;75 (4):439-450 - 45.
Ha JH, Hauk P, Cho K, Eo Y, Ma X, Stephens K, et al. Evidence of link between quorum sensing and sugar metabolism in Escherichia coli revealed via cocrystal structures of LsrK and HPr. Science Advances. 2018;4 (6):eaar7063 - 46.
DeLisa MP, Bentley WE. Bacterial autoinduction: Looking outside the cell for new metabolic engineering targets. Microbial Cell Factories. 2002; 1 (1):5 - 47.
Yokobayashi Y, Weiss R, Arnold FH. Directed evolution of a genetic circuit. Proceedings of the National Academy of Sciences of the United States of America. 2002; 99 (26):16587-16591 - 48.
Chen W, Kallio PT, Bailey JE. Construction and characterization of a novel cross-regulation system for regulating cloned gene expression in Escherichia coli . Gene. 1993;130 (1):15-22 - 49.
You L, Cox RS 3rd, Weiss R, Arnold FH. Programmed population control by cell-cell communication and regulated killing. Nature. 2004; 428 (6985):868-871 - 50.
Danino T, Mondragon-Palomino O, Tsimring L, Hasty J. A synchronized quorum of genetic clocks. Nature. 2010; 463 (7279):326-330 - 51.
Glass L. Synchronization and rhythmic processes in physiology. Nature. 2001; 410 (6825):277-284 - 52.
Tsao CY, Hooshangi S, Wu HC, Valdes JJ, Bentley WE. Autonomous induction of recombinant proteins by minimally rewiring native quorum sensing regulon of E. coli . Metabolic Engineering. 2010;12 (3):291-297 - 53.
Studier FW. Protein production by auto-induction in high density shaking cultures. Protein Expression and Purification. 2005; 41 (1):207-234 - 54.
Studier FW, Moffatt BA. Use of bacteriophage T7 RNA polymerase to direct selective high-level expression of cloned genes. Journal of Molecular Biology. 1986; 189 (1):113-130 - 55.
Tsao CY, Wang L, Hashimoto Y, Yi H, March JC, DeLisa MP, et al. LuxS coexpression enhances yields of recombinant proteins in Escherichia coli in part through posttranscriptional control of GroEL. Applied and Environmental Microbiology. 2011;77 (6):2141-2152 - 56.
Zargar A, Quan DN, Bentley WE. Enhancing intercellular coordination: Rewiring quorum sensing networks for increased protein expression through autonomous induction. ACS Synthetic Biology. 2016; 5 (9):923-928 - 57.
Zargar A, Quan DN, Emamian M, Tsao CY, Wu HC, Virgile CR, et al. Rational design of ‘controller cells’ to manipulate protein and phenotype expression. Metabolic Engineering. 2015; 30 :61-68 - 58.
Servinsky MD, Terrell JL, Tsao CY, Wu HC, Quan DN, Zargar A, et al. Directed assembly of a bacterial quorum. The ISME Journal. 2016; 10 (1):158-169 - 59.
Wu HC, Tsao CY, Quan DN, Cheng Y, Servinsky MD, Carter KK, et al. Autonomous bacterial localization and gene expression based on nearby cell receptor density. Molecular Systems Biology. 2013; 9 :636 - 60.
Singh V, Lee JE, Nunez S, Howell PL, Schramm VL. Transition state structure of 5′-methylthioadenosine/S-adenosylhomocysteine nucleosidase from Escherichia coli and its similarity to transition state analogues. Biochemistry. 2005;44 (35):11647-11659 - 61.
Roy V, Smith JA, Wang J, Stewart JE, Bentley WE, Sintim HO. Synthetic analogs tailor native AI-2 signaling across bacterial species. Journal of the American Chemical Society. 2010; 132 (32):11141-11150 - 62.
Roy V, Meyer MT, Smith JA, Gamby S, Sintim HO, Ghodssi R, et al. AI-2 analogs and antibiotics: A synergistic approach to reduce bacterial biofilms. Applied Microbiology and Biotechnology. 2013; 97 (6):2627-2638 - 63.
Gamby S, Roy V, Guo M, Smith JA, Wang J, Stewart JE, et al. Altering the communication networks of multispecies microbial systems using a diverse toolbox of AI-2 analogues. ACS Chemical Biology. 2012; 7 (6):1023-1030 - 64.
Quan DN, Bentley WE. Gene network homology in prokaryotes using a similarity search approach: Queries of quorum sensing signal transduction. PLoS Computational Biology. 2012; 8 (8):e1002637 - 65.
Xavier KB, Bassler BL. LuxS quorum sensing: More than just a numbers game. Current Opinion in Microbiology. 2003; 6 (2):191-197 - 66.
Zargar A, Quan DN, Carter KK, Guo M, Sintim HO, Payne GF, et al. Bacterial secretions of nonpathogenic Escherichia coli elicit inflammatory pathways: A closer investigation of interkingdom signaling. MBio Journal. 2015;6 (2):e00025 - 67.
Lentini R, Martin NY, Forlin M, Belmonte L, Fontana J, Cornella M, et al. Two-way chemical communication between artificial and natural cells. ACS Central Science. 2017; 3 (2):117-123 - 68.
Fernandes R, Bentley WE. AI-2 biosynthesis module in a magnetic nanofactory alters bacterial response via localized synthesis and delivery. Biotechnology and Bioengineering. 2009; 102 (2):390-399 - 69.
Fernandes R, Roy V, Wu HC, Bentley WE. Engineered biological nanofactories trigger quorum sensing response in targeted bacteria. Nature Nanotechnology. 2010; 5 (3):213-217 - 70.
Leduc PR, Wong MS, Ferreira PM, Groff RE, Haslinger K, Koonce MP, et al. Towards an in vivo biologically inspired nanofactory. Nature Nanotechnology. 2007; 2 (1):3-7 - 71.
Hebert CG, Gupta A, Fernandes R, Tsao CY, Valdes JJ, Bentley WE. Biological nanofactories target and activate epithelial cell surfaces for modulating bacterial quorum sensing and interspecies signaling. ACS Nano. 2010; 4 (11):6923-6931 - 72.
Hung DT, Shakhnovich EA, Pierson E, Mekalanos JJ. Small-molecule inhibitor of Vibrio cholerae virulence and intestinal colonization. Science. 2005;310 (5748):670-674 - 73.
Roy V, Adams BL, Bentley WE. Developing next generation antimicrobials by intercepting AI-2 mediated quorum sensing. Enzyme and Microbial Technology. 2011; 49 (2):113-123 - 74.
Hwang IY, Koh E, Wong A, March JC, Bentley WE, Lee YS, et al. Engineered probiotic Escherichia coli can eliminate and preventPseudomonas aeruginosa gut infection in animal models. Nature Communications. 2017;8 :15028 - 75.
Virgile C, Hauk P, Wu HC, Shang W, Tsao CY, Payne GF, et al. Engineering bacterial motility towards hydrogen-peroxide. PLoS One. 2018; 13 (5):e0196999 - 76.
McKay R, Hauk P, Quan D, Bentley WE. Development of cell-based sentinels for nitric oxide: Ensuring marker expression and unimodality. ACS Synthetic Biology. 2018; 7 (7):1694-1701 - 77.
Terrell JL, Wu HC, Tsao CY, Barber NB, Servinsky MD, Payne GF, et al. Nano-guided cell networks as conveyors of molecular communication. Nature Communications. 2015; 6 :8500 - 78.
Green J, Paget MS. Bacterial redox sensors. Nature Reviews. Microbiology. 2004; 2 (12):954-966 - 79.
Demple B. Redox signaling and gene control in the Escherichia coli soxRS oxidative stress regulon—A review. Gene. 1996;179 (1):53-57 - 80.
Zheng M, Wang X, Templeton LJ, Smulski DR, LaRossa RA, Storz G. DNA microarray-mediated transcriptional profiling of the Escherichia coli response to hydrogen peroxide. Journal of Bacteriology. 2001;183 (15):4562-4570 - 81.
Lu C, Albano CR, Bentley WE, Rao G. Quantitative and kinetic study of oxidative stress regulons using green fluorescent protein. Biotechnology and Bioengineering. 2005; 89 (5):574-587 - 82.
Kim E, Leverage WT, Liu Y, White IM, Bentley WE, Payne GF. Redox-capacitor to connect electrochemistry to redox-biology. The Analyst. 2014; 139 (1):32-43 - 83.
Fenno L, Yizhar O, Deisseroth K. The development and application of optogenetics. Annual Review of Neuroscience. 2011; 34 :389-412 - 84.
Levskaya A, Chevalier AA, Tabor JJ, Simpson ZB, Lavery LA, Levy M, et al. Synthetic biology: Engineering Escherichia coli to see light. Nature. 2005;438 (7067):441-442 - 85.
Schmidl SR, Sheth RU, Wu A, Tabor JJ. Refactoring and optimization of light-switchable Escherichia coli two-component systems. ACS Synthetic Biology. 2014;3 (11):820-831 - 86.
Song Y, Wang J, Yau ST. Controlled glucose consumption in yeast using a transistor-like device. Scientific Reports. 2014; 4 :5429 - 87.
Gordonov T, Kim E, Cheng Y, Ben-Yoav H, Ghodssi R, Rubloff G, et al. Electronic modulation of biochemical signal generation. Nature Nanotechnology. 2014; 9 (8):605-610 - 88.
Weber W, Luzi S, Karlsson M, Sanchez-Bustamante CD, Frey U, Hierlemann A, et al. A synthetic mammalian electro-genetic transcription circuit. Nucleic Acids Research. 2009; 37 (4):e33 - 89.
Tschirhart T, Kim E, McKay R, Ueda H, Wu HC, Pottash AE, et al. Electronic control of gene expression and cell behaviour in Escherichia coli through redox signalling. Nature Communications. 2017;8 :14030