Immunological function and antibacterial activity of two ferritin proteins from the freshwater pearl mussel Hyriopsis schlegelii

Ferritin is a conserved iron-binding protein involved in host defense and cellular iron metabolism in most organisms. We investigated the expression profiles of two ferritin genes (designated HsFer-1 and HsFer-2) in the hemocytes, gonad, and hepatopancreas of Hyriopsis schlegelii, when challenged with bacteria and metal ions. HsFer gene transcription increased 1.8-7.7- and 1.9-6.1-fold in these tissues after stimulation with Staphylococcus aureus and Vibrio anguillarum, respectively. In addition, following exposure to Fe³⁺, expression of HsFer-1 and HsFer-2 was elevated by 1.5-6.1- and 3.6-10.1-fold, respectively. Levels of HsFer-1 and -2 mRNA also increased significantly after treatment with Cu²⁺ and Pb²⁺ at certain concentrations. Moreover, recombinant HsFer-1 and -2 were able to inhibit the growth of two strains of bacteria, and the former efficiently chelated Fe³⁺. From these results, we conclude that HsFer-1 and -2 may be involved in iron metabolism and immune defense by inhibiting the growth of bacteria.