Bioluminescent monitoring of recombinant lactic acid bacteria and their products

Biotherapeutic strategies to promote health, including the application of engineered microbes to deliver therapeutic molecules, hold strong promise. However, without precision tools to detect therapeutic microbes and their products, we are hampered in our ability to monitor and fine-tune therapeutic delivery. Here, we adapted a bioluminescent peptide tagging system for use in lactic acid bacteria, a group of organisms whose members are commonly exploited as delivery vehicles of therapeutics and vaccines. As a proof of concept, we developed various Limosilactobacillus reuteri strains that each produced a recombinant therapeutic protein with an 11 amino acid tag, which is essential to yield a luminescent signal. Luminescent-based quantification of recombinant protein was more sensitive than commercially available immunoassays. In addition, we demonstrated that the bioluminescent peptide tagging system allows in situ recombinant protein detection in a continuous-culture parallel bioreactor system. This presents an exciting opportunity to determine recombinant protein production dynamics in response to different stimuli. Finally, following oral administration of recombinant microbes, luminescence in intestinal and fecal samples allowed for rapid detection of microbes with equal sensitivity to conventional plate count. Because we demonstrated the functionality of this bioluminescent peptide tagging system in 12 species encompassing nine genera, our approach will create previously unexplored opportunities in lactic acid bacteria research. IMPORTANCE: Lactic acid bacteria constitute a genetically diverse group of microorganisms with significant roles in the food industry, biotechnology, agriculture, and medicine. A core understanding of bacterial physiology in diverse environments is crucial to select and develop bacteria for industrial and medical applications. However, there is a lack of versatile tools to track (recombinant) protein production in lactic acid bacteria. In this study, we adapted a peptide-based bioluminescent tagging system that is functional across multiple genera and species. This system enables tracking of tagged proteins both in vitro and in situ, while it also can be used to enumerate recombinant bacteria from the mouse gastrointestinal tract with accuracy comparable to that of conventional plate counts. Our work expands the lactic acid bacteria genetic toolbox and will facilitate researchers in industry and academia with opportunities to monitor microbes and proteins under different physiologically relevant conditions.