I See Your Smart Phone and Raise You Smart Bacteria

“Smart” bacteria that sense, track, pursue, fight and defeat infectious and other biological agents afflicting the warfighter might be closer to reality.

Building on earlier work focused on understanding how bacteria sense their nearest neighbors (including pathogens), a DTRA CB/JSTO-funded research team managed by DTRA CB’s Dr. Ilya Elashvili and led by Dr. William E. Bentley has paired with the Italian synthetic biology team headed by Dr. Sheref Mansy. The joint team created artificial cells that translate non-native signals into native signals that manipulate a local bacterial population.

These new tools have the potential to offer a means to localize bacteria and take actions to identify pathogens, other maladies (e.g., cancer cells), and synthesize drugs for local delivery and treatment.

Synthetic biology holds great promise to enable the engineering of “smart” bacteria that execute high order functions, such as those needed to sense, track, pursue, and fight pathogens. The Bentley lab focuses on minimally rewiring native cell processes so as not to “over engineer” these designer cells.

For example, they have built modules that recognize a pathogen’s signals and that rewire metabolic pathways to synthesize a pathogen-targeted drug. However, as these modules are pieced together and new modules are added, they impede other needed functions, such as swimming to or away from desired locales.

One way to counter unanticipated “side effects” is to employ small populations of orchestrated cells that act collectively to accomplish their task. Their plans, for example, call for “sentinel” and “dirigible” cells that find pathogens and call for backup.

In a recent Nature Communications article, “Integrating artificial with natural cells to translate chemical messages that direct E. coli behaviour,” the American-Italian joint team showed they were able to induce desired activity of native cells through communication with artificial cells.

The artificial cells, in turn, read a chemical cue foreign to the native cells and synthesized another compound recognized by the native cells. In this way, the artificial cells served as a translator. To the authors’ knowledge, this is the first artificial, cell-like system capable of translating unrecognized signals into a chemical language that natural cells can recognize.

The artificial non-living cell was built with a phospholipid vesicle containing isopropyl β-D-1-thiogalactopyranoside (IPTG), DNA, and transcription–translation machinery. The DNA template codes for a previously selected ribo-switch that activates translation in response to the presence of a model chemical signal molecule, theophylline.

Theophylline is added to the mixture, diffuses into the vesicle, and triggers the synthesis of the pore forming protein α-hemolysin (αHL). Therefore, only in the presence of theophylline a pore forms that releases entrapped IPTG.

Released IPTG will increase the transcription of a variety of genes induced by the lac operon in E. coli. IPTG is a model signal molecule in the current study, but it is a surrogate for a pathogen-modulating compound that would otherwise be held in abeyance in the vesicle in future studies.

E. coli alone does not respond to theophylline, and IPTG does not cross the vesicle membrane of the artificial cell in the absence of the pore. The ability of E. coli to receive the chemical message (IPTG) sent by the artificial cells was assessed in two ways.

First, a recombinant E. coli transformed with a plasmid, synthesized green fluorescent protein in response to IPTG; this was assayed using flow cytometry. Second, a natural or “wild type” E. coli was tested via reverse transcription quantitative polymerase chain reactions (RT-qPCR) that confirmed the up-regulation of the lac operon genes (more than a 20-fold increase).

The integration of artificial translator cells with natural cells represents a new strategy to introduce synthetic features to a biological system and at the same time, lessens the need for direct genetic manipulation.

These expanded capabilities to create “smart” cells that survey the local environment and decide whether or not to initiate gene expression represents a new area in synthetic biology that would be useful for both Department of Defense and civilian applications.

From the Defense Threat Reduction Agency’s Chemical & Biological Technologies Department
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