The type VI secretion system (T6SS) is a contact-dependent bacterial nanomachine that delivers toxic effectors into neighboring cells. T6SS-positive (T6SS+) cells prevent self-intoxication by co-expressing immunity proteins that neutralize toxins. This project identifies toxin diversity among T6SS+ Vibrio fischeri strains, which form multi-strain symbioses with the squid Euprymna scolopes. Specifically, we investigate the impact of AHH nucleases on growth between non-isogenic T6SS+ strains to better understand how different T6SS+ strains can occupy the same habitat.