Bacterial weaponry and the ecological factors of competitive success.

Bacteria have evolved complex protein systems known as bacterial weapons to inhibit or kill their competitors. These bacterial weapons are a remarkably diverse arsenal that influence the composition and function of important microbial communities such as the human microbiome. In turn, the spatial constraints, nutrient availability, environmental stressors, and the presence of competitors determine not only whether weapons are expressed, but which weapons provide the greatest advantage. While bacterial weaponry is widespread, the types, mechanisms, and abundance of these systems vary between, and even within, species. Recent research has highlighted the importance of bacterial weaponry in community invasion and pathogenicity. Their potency and narrow killing spectrum have also generated interest in exploiting bacterial weapons to engineer microbial communities or develop therapeutics that avoid the disruption of broad-spectrum antibiotics. Understanding how ecological context affects weapon efficacy could reveal new virulence mechanisms used by pathogens and inform the design of novel treatments and microbiome-based therapies. This review outlines three of the best-studied bacterial weapon systems (protein bacteriocins, the type VI secretion system, and contact-dependent inhibition), highlighting their roles in microbial ecology, pathogenicity and their potential as therapeutics.