Regulation of the tagatose catabolic gene cluster and development of a tagatose-inducible expression system in the probiotic Escherichia coli Nissle 1917.

Abstract

Background: The probiotic Escherichia coli Nissle 1917 (EcN) is a promising microbial chassis for therapeutic and industrial applications. However, its broad utility is limited by a lack of reliable inducible gene expression systems that precisely control gene expression.

Results: We developed a tagatose-inducible expression system in EcN using D-tagatose, a naturally occurring sugar with established safety in humans, as a metabolizable inducer. Through differential RNA sequencing and sequence analysis, we identified the key regulatory elements governing D-tagatose catabolism in EcN and demonstrated that the DeoR family regulator (TagR) functions as a tagatose-responsive repressor. The developed system exhibited a strong dose-dependent response to D-tagatose, ensuring uniform and tunable gene activation across cell populations. Additionally, a catabolite repression-enabled auto-induction strategy facilitated robust biomass accumulation, followed by targeted protein production. This expression system was successfully applied to overexpress recombinant proteins under both aerobic and anaerobic conditions.

Conclusions: D-Tagatose is a naturally occurring low-calorie sugar that can serve as an inducer in vivo, including within the human gut microbiome. Thus, the tagatose-inducible expression system provides EcN with an additional tunable option for gene regulation, which may be valuable in applications such as synthetic biology and metabolic engineering.