Type VI secretion system-associated effectors from the termite gut as a means of symbiont-meditated pathogen protection

The symbionts of the eastern subterranean termite, Reticulitermes flavipes, have been associated with digestion, pathogen protection, and mediating other host physiologies. While several anti-fungal mechanisms have been described from symbionts in the termite gut no antibacterial defenses have been characterized. Recently, our lab described a type VI secretion system (T6SS) in a member of the termite gut normal flora. T6SSs are molecular machines embedded in the cell wall of some gram-negative bacteria used to target nearby bacteria. Using a combination of bioassays and genomics, we have identified a Serratia isolate from the termite gut that 1) kills the termite pathogen, Serratia marcescens, in co-culture and 2) has twenty-two putative effectors encoded in its genome. These effectors were identified using the SecReT6 v.3 prediction tool which identifies putative T6SS-associated genes using sequence homology. Here we describe the expression patterns and antibacterial toxicity of several putative effectors from this termite symbiont. Characterizing these effectors is important to understand the demonstrated congeneric toxicity leading to host protection and to explore the potential to exploit these effectors in novel pest control and antibacterial applications.