Recombinant expression and antibacterial activities of two I-type lysozymes from Ruditapes philippinarum

Lysozyme is an important immune effector present in phylogenetically diverse organisms, and plays important roles in bacteria elimination. In this study, two I-type lysozymes from Ruditapes philippinarum (designated as VpILYZ-1 and VpILYZ-2, respectively) were recombinantly expressed in Escherichia coli BL21 (DE3). The recombinant proteins rVpILYZ-1 and rVpILYZ-2 showed broad spectrum of antimicrobial activities. Especially, the rVpILYZ-1 displayed high lytic activities against V. parahaemolyticus, V. splendidus and M. luteus, while rVpILYZ-2 showed strong microbicidal activities against V. parahaemolyticus. The antibacterial activities of rVpILYZs may be performed by both the enzymatic way and non-enzymatic ways. The optimum pH and temperature for the lytic activities of rVpILYZ-1 were 6.5 and 20 °C, and the highest antimicrobial activities of rVpILYZ-2 was detected at pH 4.5 and 10 °C. Moreover, both rVpILYZ-1 and rVpILYZ-2 possessed the opsonic activities, and the phagocytic activities of hemocytes were boosted after being incubated with rVpILYZ-1 or rVpILYZ-2. These results suggested that VpILYZ-1 and VpILYZ-2 played important roles in the immune responses of R. philippinarum.