Characterizing the role of the Sit and Hemolysin proteins in high affinity iron acquisition in the tsetse symbiont Sodalis glossinidius

Sodalis glossinidius is a gram-negative facultative symbiont of the tsetse fly. Sodalis is unique among symbionts in that it can be cultured outside of its host. Iron is critical for the growth and survival of almost all bacteria, including Sodalis. Because the bioavailability of iron is low, bacteria have evolved high affinity iron acquisition systems. These systems are used to obtain iron when free iron is limited. The Sodalis genome contains several putative high affinity iron acquisition systems. Among these are the sitABCD and SG1998 hemolysin genes. Addition of the Sodalis Sit system to an Escherichia coli strain lacking Sit increased growth of the E. coli in iron limited conditions, though growth enhancement due to Sit was low relative to a siderophore system. Mutation of the Sodalis Sit system reduced the growth of Sodalis in iron-limited conditions. E. coli and Sodalis strains with and without Sit grew equivalently in iron replete conditions. This suggests that the Sit system has an active, though limited, role in acquisition of iron and bacterial growth in low iron conditions. Cloning of the Sodalis hemolysin gene was performed and preliminary characterization studies are described in the appendix