Quorum Sensing via Autoinducer-2 Promotes Colonisation and Host Adaptation in B. bifidum PRL2010.

Autoinducer-2 (AI-2) is a key signalling molecule that in many bacteria facilitates interspecies communication by regulating gene expression in response to population density through a process known as quorum sensing. While this signalling mechanism has been extensively studied in Gram-negative bacteria, its role in the genus Bifidobacterium remains poorly understood. In this study, an in silico analysis was conducted to examine the distribution of the luxS gene, which encodes the enzyme that synthesises the AI-2 precursor, across Bifidobacterium genomes. Our analysis revealed that luxS is ubiquitously present in all publicly available bifidobacterial genomes. To explore the functional implications of luxS, gene expression profiling was performed on the model strain B. bifidum PRL2010 and its isogenic luxS insertion mutant, both grown in a medium simulating the human gut environment. RNA sequencing results indicated that disruption of luxS impairs the mutant strain's ability to (i) interact and communicate with the host, (ii) transport sugars, (iii) internalise potassium and iron, and (iv) cope with stress conditions. Collectively, these findings highlight the crucial role of AI-2 in promoting colonisation and ensuring the persistence of PRL2010 within the competitive ecosystem of the human gut.