Type VI secretion systems (T6SSs) and their effectors can function in both pathogenesis and interbacterial competition. Vibrio alginolyticus, a marine pathogen that can infect humans, encodes two T6SSs, but only a single antibacterial effector, Va02265, had been described for these systems. Of note, Va02265 has a MIX domain, which was recently identified as a marker of five 'clans' of T6SS effectors with diverse toxin domains. Salomon et al. used proteomics in deletion mutants to identify an additional six antibacterial effectors secreted by T6SSs in V. alginolyticus, including two additional toxins with MIX domains. A comparative genomic analysis indicated that MIX effectors from clan V, which includes Va02265, are horizontally transferred between Vibrionales species, suggesting that T6SSs can secrete newly acquired toxins. In agreement with this, the antibacterial activity of the V. alginolyticus toxin Va02265 was retained when exogenously expressed in a related species, Vibrio parahaemolyticus.