Termite symbionts utilize type VI secretion system during in vitro contact with an opportunistic pathogen

The complexity of the termite gut microbiome has been observed for the past hundred years. The diversity of microorganisms within termites have been implicated in beneficial interactions ranging from nitrogen metabolism, lignocellulose degradation, and pathogen protection. Perturbations of the natural gut flora, like insecticide and antibiotic treatments, result in increased mortality from opportunistic pathogens, like Serratia marcescens. In addition, many competitive bacteria-bacteria interactions, like those between pathogens and normal flora in animal guts, are mediated by type VI secretion system (T6SS). We propose that natural gut bacteria that use T6SS to combat potential pathogens and maintain status quo within the gut. To test this idea, we have performed co-culture bioassays revealing that the outcome of competitions between gut isolates and S. marcescens is predictable based on whether the termite gut isolate has genetic signatures of a T6SS. These results indicate a novel mechanism for symbiont-mediated pathogen protection in termites. This finding has important implications for our understanding not only of termite-bacterial interactions, but also the potential to exploit these bacteria-bacteria interactions in biotechnology, pest control, and conservation.