The genesis of our inquiry traces back to an ordinary moment when one of our team members, while conversing with a friend, noticed the friend's refusal of an invitation to share milk tea. Upon further inquiry, the friend revealed that he had lactose intolerance. This surprising discovery of a lactose-intolerant individual in our immediate circle sparked our investigation. Lactose intolerance arises from insufficient lactase production in the intestines, leading to excessive lactose accumulation in the gut. This disrupts the intestinal microbiota, causing symptoms such as bloating and diarrhea. Furthermore, it may impair the absorption of vitamins and calcium, hinder development, and potentially serve as a contributing factor to colon cancer. Globally, approximately 70% of adults are or have been affected by lactose intolerance. In Central Asia, this figure can exceed 90%, while in densely populated East Asia, it stands at around 70%. A survey conducted in the United States reported a prevalence rate of 30%, indicating that nearly 100 million individuals in the U.S. alone require assistance. Current treatment approaches for lactose intolerance also face significant challenges. According to a U.S.-based study, 70% of healthcare providers recommend reducing or avoiding dairy consumption—a strategy that fails to address the root cause and necessitates additional nutritional guidance to mitigate potential deficiencies. While oral lactase supplements offer temporary relief, they do not provide a long-term solution. Moreover, they impose additional financial burdens and diminish quality of life due to the need for frequent medication. As for lactose-free dairy alternatives, they often alter the original flavor profiles and cannot comprehensively cover all lactose-containing foods—particularly those integral to the cultural heritage of ethnic minorities.

To effectively decompose excess lactose in the patient's gut, we aimed to engineer a synthetic biology-based system using engineered bacteria. A highly efficient lactose metabolism system is crucial for this purpose. We introduced the bgaB gene, encoding lactase from Geobacillus stearothermophilus, into the engineered bacteria to enhance their lactose-metabolizing capacity. Additionally, to prevent limited lactose uptake from hindering the decomposition process, we incorporated the LacY protein to improve lactose absorption. This ensures rapid breakdown of dietary lactose in the patient's intestine. Through dry lab simulations, we further optimized the lactase enzyme to enhance therapeutic efficiency. Our computational models successfully generated a more efficient variant of lactase, promising even greater performance. For detailed insights, please refer to the Model section of our work.

In terms of biosafety, Lacbutler utilizes Bifidobacterium longum as the engineered chassis. As an obligate anaerobe, this bacterium struggles to survive outside the gut environment, significantly reducing the risk of environmental release and ensuring containment.

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{% raw %}[8] Ridolo, E., Baiardini, I., Meschi, T., Peveri, S., Nouvenne, A., Dall Aglio, P., & Borghi, L. (2013). HRQoL questionnaire evaluation in lactose intolerant patients with adverse reactions to foods. Internal and Emergency Medicine, 8(6), 493-496. https://doi.org/10.1007/s11739-011-0630-7