Constitutive oxalate-biodegrading Bacillus subtilis for kidney stones

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Project Summary / Abstract Kidney stones (nephrolithiasis) are an extremely painful and debilitating condition. About 12% of people will experience kidney stones in their lifetime, and about 70% of those will have recurrences. The economic burden of kidney stones is estimated to exceed $5 billion per year in the USA alone. Each year, over 3 million workdays are lost in the USA due to kidney stones. 75% of kidney stones consist of calcium oxalate (CaOx), and are caused by excessive urinary oxalate levels. Unfortunately, current treatment options all have serious drawbacks. A low oxalate diet is routinely recommended for CaOx stone patients, but is not very effective by itself. Alkalinizing agents such as potassium citrate can reduce stone recurrence, but are costly and often cause GI distress. Thiazide diuretics come with frequent, potentially life-threatening adverse effects such as hypokalemia. Thus, there remains a strong need for the development of new kidney stone treatment options that are both safe and effective. We propose to develop and test a new kidney stone treatment consisting of a novel Bacillus subtilis strain that overexpresses endogenous oxalate biodegrading enzymes. As bacteria stay in the gut, the spectrum of potential side effects is massively reduced as compared to small molecule drugs. Thus, our innovative approach is designed to result in an affordable, safe, and broadly effective kidney stone treatment option. In this Phase I SBIR project, we will develop new Bacillus subtilis strains engineered to biodegrade oxalate. We will produce and test different strains to optimize oxalate biodegradation capacity. As we will chromosomally overexpress endogenous enzymes in a spore-forming bacterium, our approach avoids key drawbacks of previously developed oxalate- degrading microbes. Finally, we will determine if the best performing engineered strain can effectively reduce urine oxalate levels in a relevant rat model.