Rewiring lactobacilli: challenges, opportunities, and the translational path to therapeutics.

Lactobacilli have long been regarded as promising probiotic bacteria due to their safety profile, host compatibility, and beneficial roles in modulating human health. However, the therapeutic efficacy of wild-type probiotics remains constrained by limited target specificity, lack of control over their activity, and variability in clinical responses. Recent advances in synthetic biology have enabled the possibility of overcoming these constraints through precise engineering of bacterial functions, such as therapeutics production. Despite these advances, significant challenges remain in engineering lactobacilli, including limited genetic toolkits, species- and strain-dependent variability, and uncertainty regarding the stability and safety of engineered strains. This review discusses the current landscape of engineering lactobacilli for therapeutic applications, with particular emphasis on candidates undergoing clinical evaluation. Furthermore, it outlines key technical hurdles to overcome and suggests potential solutions to accelerate their translation into clinically effective and reliable microbial therapeutics.