Toxin secreted by the H1 type VI (H1-T6SS) secretion system into the periplasm of recipient cells. Degrades peptidoglycan via muramidase activity thereby helping itself to compete with other bacteria (PubMed:21776080). To protect itself, the bacterium synthesizes immunity protein Tsi3 that specifically interacts with and inactivates cognate toxin (PubMed:24025333). Hydrolysis of (1->4)-beta-linkages between N-acetylmuramic acid and N-acetyl-D-glucosamine residues in a peptidoglycan and between N-acetyl-D-glucosamine residues in chitodextrins. Enzymatic activity depends on membrane binding. Forms an heterotetramer with Tsi3 consisting of two Tse3 dimers and two Tsi3 dimers. Formation of the complex inactivates Tse3 enzymatic activity. Delivered to the target cell periplasm by the H1 type VI (H1-T6SS) secretion system.