Bacterial symbionts in oral niche use type VI secretion nanomachinery for fitness increase against pathobionts

Microbial ecosystems experience spatial and nutrient restrictions leading to the coevolution of cooperation and competition among cohabiting species.To increase their fitness for survival, bacteria exploit machinery to antagonizing rival species upon close contact.As such, the bacterial type VI secretion system (T6SS) nanomachinery, typically expressed by pathobionts, can transport proteins directly into eukaryotic or prokaryotic cells, consequently killing cohabiting competitors.Here, we demonstrate for the first time that oral symbiont Aggregatibacter aphrophilus possesses a T6SS and can eliminate its close relative oral pathobiont Aggregatibacter actinomycetemcomitans using its T6SS.These findings bring nearer the antibacterial prospects of symbionts against cohabiting pathobionts while introducing the presence of an active T6SS in the oral cavity.