The Escherichia coli uhp two-component system functions as a sensory channel for hexose phosphates secreted by Bifidobacterium.

The human gut microbiota relies on inter-species communication for stability, yet interactions between non-dominant taxa like Pseudomonadota (Escherichia coli) and Actinomycetota (Bifidobacterium) remain poorly understood. We demonstrate that E. coli repurposes its Uhp two-component system as a specialized sensory channel to monitor Bifidobacterium metabolic activity. Screening 54 transport systems revealed that uhpT and idnT genes are specifically induced by Bifidobacterium supernatants, a response absent in members of the Bacteroidota. Using an enzymatic "kinetic trap" approach with a slow-acting Zwf mutant (D177N), we provide biochemical evidence that glucose-6-phosphate (G6P) is the primary signaling molecule. Experimental validation using Modified Garche's Medium confirms that G6P secretion is a consistent byproduct of bifidobacterial metabolism occurring during growth on diverse human milk oligosaccharide (HMO) constituents, including galactose. Furthermore, idnT activation occurs independently of Uhp-mediated transport, suggesting the secretion of a multifaceted metabolic cocktail. We propose these molecular links form a "non-dominant network" enabling low-abundance species to coordinate metabolism and maintain stability alongside the dominant majority. These findings redefine the physiological role of the Uhp system and offer a new perspective on the regulatory networks governing the human microbiome. (183 words).