The Type VI secretion system in enteric pathogen colonization: molecular mechanisms, ecological dynamics, and...

The Type VI Secretion System (T6SS) is a sophisticated, phage-tail-like contractile nanomachine that mediates contact-dependent protein translocation in a wide range of Gram-negative enteric pathogens. As a primary weapon for interference competition, T6SS enables pathogens like Salmonella and Vibrio cholerae to directly eliminate commensal rivals. This targeted elimination allows pathogens to dismantle microbiota-mediated colonization resistance and seize essential nutritional niches. Beyond interbacterial warfare, the system facilitates "exploitative competition" by secreting effectors for the acquisition of limited micronutrients such as iron and zinc. Furthermore, T6SS acts as a crucial virulence determinant by manipulating host cell signaling, disrupting cytoskeletal integrity, and even enhancing intestinal contractions to physically expel competitors. The expression and activity of T6SS are dynamically regulated by gastrointestinal cues, including bile salts, pH fluctuations, and quorum sensing signals, ensuring its activation is precisely timed during infection. Elucidating these multifaceted roles not only deepens our understanding of microbial ecology in the gut but also highlights T6SS as a promising target for microbiome engineering and the development of customizable, precision antimicrobial therapies.