GM bacteria instead of colonoscopy
Researchers from Rice University, working under the leadership of Dr. Jeffrey Tabor, have created genetically modified intestinal bacteria that can respond to the development of colitis – inflammation of the intestine – in mice. The results of this work indicate a new research direction dedicated to the study of the interaction of intestinal bacteria and humans at the molecular level, the end result of which may be the creation of oral bacterial preparations for monitoring the state of the intestine.
As Dr. Tabor says, the intestine is home to billions of microorganisms that influence the state of health and the course of diseases. However, it is a dark and hard-to-reach place, a detailed study of the processes taking place in which is possible with the help of a very limited set of technologies. On the other hand, in the course of evolution, bacteria have acquired tens of thousands of sensors, many of which react to various substances in the intestinal tract. Therefore, genetically modified sensor bacteria have a huge potential for studying the processes occurring in the intestine and diagnosing diseases.
Synthetic biology specialists specialize in programming single-celled organisms, such as bacteria, using approaches similar to those that allow engineers to program robots. In particular, Tabor and his colleagues are working on the creation of bacterial sensors that can register signals of intestinal diseases. Like electrical engineers who create electrical circuits from wires and electronic parts, they use genetic circuits to program single-celled organisms, which as a result acquire the ability to process complex information.
The results of earlier studies by the authors indicate that changes in the gut microbiome, genetic predisposition and various environmental factors may play key roles in the development of inflammatory bowel disease – a fairly common combined condition, including Crohn's disease and ulcerative colitis.
Based on the results of a number of earlier studies, researchers have suggested that the development of colitis is accompanied by an increase in the content of thiosulfate in the intestinal contents. The study of this relationship is currently difficult due to the lack of tools for a reliable assessment of the level of thiosulfate in a living organism. The first goal of the project launched in 2015 was to create such a tool.
The idea taken as a basis was to use sensory bacteria, namely genetically modified E. coli (Escherichia coli) to register thiosulfate and related sulfur-containing compounds, which can also be biomarkers of colitis. The researchers had at their disposal well-developed methods of genetic programming that endow E. coli with the ability to produce a green fluorescent protein in response to specific stimuli, but they did not know which genes make it possible to register thiosulfate and other sulfur-containing compounds.
With the help of a special computer program, such genes were found in the genome of Shewanella bacteria living in marine sediments. The authors believe that chevanelles use sensors of sulfur-containing compounds to activate enzymes specific to them.
It took them about a year to create a genetically modified strain of E. coli expressing the genes of such sensors, validate the functioning of these genes and optimize them, providing a specific response to potential biomarkers, manifested by the expression of a green fluorescent protein. It took another year to confirm the functionality of this system and its ability to detect intestinal inflammation in mice.
As part of the experiments, animals with colitis, as well as healthy mice of the control groups, received orally two drops of a solution containing about a billion sensory bacteria. After six hours, the researchers assessed the activity of sensory bacteria in feces by the brightness of the glow of a green fluorescent protein. This glow is not visible to the naked eye, but is easily detected using a standard laboratory instrument known as a flow cytofluorimeter.
Observations showed that the bacterial sensor was not activated in the intestines of healthy animals, but was activated in the intestines of mice with intestinal inflammation, while the fluorescence brightness was proportional to the degree of inflammation.
According to Dr. Tabor, the data obtained indicate that bacteria carrying genetically engineered sensors can be used for non-invasive detection of certain metabolites in the intestine, which will provide new opportunities in studying the processes occurring in it.
It is obvious that the development of approaches suitable for clinical use will take several more years, and today it is unclear whether thiosulfate is a biomarker of colitis in humans. However, the technology proposed by the authors can be adapted to the detection of other compounds, and the green fluorescent protein can be replaced with an enzyme that ensures the appearance of a specific color of feces. In many cases, such tests can replace a doctor's visit and an expensive invasive colonoscopy procedure.
Article by Kristina N-M Daeffler et al. Engineering bacterial thiosulfate and tetrathionate sensors for detecting gut inflammation is published in the journal Molecular Systems Biology.
Evgenia Ryabtseva
Portal "Eternal youth" http://vechnayamolodost.ru based on the materials of Rice University: Synthetic biologists engineer inflammation-sensing gut bacteria.
12.04.2017