3'UTR-derived small RNA couples acid resistance to metabolic reprogramming of Salmonella within macrophages.

Acid resistance is crucial for enterobacteria to withstand host acidic environments during infection, including the gastrointestinal tract and macrophage phagosomes. A key acid resistance mechanism of the facultative intracellular pathogen Salmonella is the expression of the arginine decarboxylase AdiA. While AdiA confers acid resistance via an H+-consuming reaction, we discover that the 3'-untranslated region (UTR) of adiA mRNA is processed by RNase E into a regulatory small RNA, AdiZ. Through RNA-RNA interactome profiling and transcriptomic analysis, followed by in vitro structural probing and in vivo validations, we demonstrate that AdiZ directly base-pairs with and negatively regulates ptsG, pykF, and dmsA mRNAs involved in glucose uptake, glycolysis, and anaerobic respiration, respectively. Intriguingly, AdiZ is induced and facilitates Salmonella survival within macrophages, where acidic and hypoxic stresses prevail. Thus, simultaneous expression of AdiA and AdiZ from a single mRNA ties arginine-dependent acid resistance to metabolic reprogramming of Salmonella in the host intracellular niches.