The indigenous gut microbiota in humans possesses the ability to synthesize neurotransmitters that are hypothesized to modulate behavioral, cognitive, and emotional processes of the body via the gut-brain axis (1). Since the emergence of this axis theory, researchers have been interested in genetically modifying probiotics for use as edible delivery vehicles of neurotransmitters to treat a variety of illnesses. There is limited experimental evidence regarding the effectiveness of these probiotics in the gut as this is a relatively novel concept.
Thus, our project is aimed at engineering an effective probiotic capable of producing higher levels of gamma-aminobutyric acid (GABA) to treat patients with anxiety, hypertension and certain bowel disorders. GABA is the neurotransmitter of interest due to its proposed anxiolytic, anti-hypertensive, and digestion-regulating effects (2-4). In order to create an accurate and translational model, we will utilize Lactobacillus plantarum as our probiotic as it is native to the human gut (5). L. plantarum is also commonly found in a wide variety of foods, including yogurt, kimchi, and cheese, allowing us to easily utilize our genetically-modified version to create medicinal food (6-8). Although L. plantarum can naturally synthesize GABA, we intend to expand the GABA-producing potential of the bacteria by characterizing and subsequently optimizing the expression of the gadB gene, which encodes glutamate decarboxylase, the enzyme responsible for converting glutamate into GABA (Fig. 1) (9).
- Mayer E. A. et al. Gut Microbes and the Brain: Paradigm Shift in Neuroscience. J Neurosci.34(46): 15490-96 (2014).
- Bravo, J. A. et al. Ingestion of Lactobacillus strain regulates emotional behavior and central GABA receptor expression in a mouse via the vagus nerve. Proc Natl Acad Sci USA. 108(38): 16050-5 (2011).
- Shimada M. et al Anti-hypertensive effect of gamma-aminobutyric acid (GABA)- rich Chlorella on high-normal blood pressure and borderline hypertension in placebo-controlled double blind study. Clin Exp Hypertens. 21(4): 342-54 (2009).
- Auteri M. et al. GABA and GABA receptors in the gastrointestinal tract: from motility to inflammation. Pharmacological Research. 93: 11-21 (2015).
- De Vries, M. et al. Lactobacillus plantarum - survival, functional and potential probiotic properties in the human intestinal tract. International Dairy Journal. 16(0): 1018-1028 (2006).
- Shan, Y. et al. Evaluation of improved gamma-aminobutyric acid production in yogurt using Lactobacillus plantarum NDC75017. J Dairy Sci. 98(4): 2138-49 (2015).
- Siragusa, S. et al. Synthesis of gamma-aminobutyric acid by lactic acid bacteria isolated from a variety of italian cheeses. Appl Environ Microbiol. 73(22): 7283-90 (2007).
- Yoon, J. H. Lactobacillus kimchii sp. Nov., a new species from kimchi. Int J Syst Evol Microbiol. 50: 1789-95 (2000).
- Yunes, R. A. GABA production and structure of gadB/gadC genes in Lactobacillus and Bifidobacterium strains from human microbiota. Anaerobe. 42: 197-204 (2016).