Bacterial type VI secretion system facilitates niche domination

Over the last few decades humanity has experienced a series of tremendous technological advances, especially in the realm of basic science. A plethora of new approaches has allowed us to appreciate life in previously unimaginable detail, prompting the realization that life in the microscopic world is not so different from what we can observe with our naked eyes. Microorganisms, for instance, like any other organism, compete with one another for resources and space. Bacteria often use simple mechanisms to occupy their niche such as rapid growth and biofilm formation. Bacteria also use ingenious strategies to maximize their success. Indeed, to engage in warfare, microorganisms often produce diffusible toxic antimicrobial compounds as well as other more complicated molecular weapons. Secretion systems are a particular kind of molecular weapon as they release or inject molecules and substrates that interact not only with hosts and predators but also with bacterial competitors. Given that the type VI secretion system (T6SS) has been recognized as a frequently used molecular weapon, it is not at all surprising that it is found widely distributed throughout diverse bacterial species (around 25% of all gram-negatives) (1). The T6SS system was discovered in Vibrio cholerae due to its toxicity against the social amoeba Dictyostelium discoideum (2). That same year, it was also suggested to contribute to the pathogenesis of Pseudomonas aeruginosa in cystic fibrosis patients (3). Follow-up studies showed that the T6SS of these two species could also be used against other bacteria (4, 5). Indeed, while being recognized for its involvement in host–pathogen and predator–prey interactions, the principal role of the T6SS is currently thought to be as an antibacterial weapon. In PNAS, Speare et al. (6) explore an accessory T6SS of the symbiotic bacterium Vibrio fischeri and describe how this T6SS contributes to light-organ occupancy within the squid host.