Characterization of Porphyromonas gingivalis FeoB transporters

Porphyromonas gingivalis has been implicated as one of the major aetiological agents of chronic periodontitis, a bacterial-associated inflammatory disease of the supporting tissues of the teeth. P. gingivalis is a black-pigmented, anaerobic, asaccharolytic, Gram-negative bacterium that has an obligate requirement for iron. A unique transporter, FeoB, has been demonstrated to be the major iron transport system in Escherichia coli and Helicobacter pylori. A search of the P. gingivalis genome using the predicted sequence of E. coli FeoB unexpectedly identified two potential FeoB homologues encoded by this bacterium. Objective: To determine the function of P. gingivalis FeoB transporters using FeoB1- (W50FB1) and FeoB2- (W50FB2) isogenic mutants. Methods: The growth of these mutants was compared to the wild-type W50 in the presence of different iron sources, and found to be similar. The transport of radiolabelled ferrous iron was determined in washed, energized P. gingivalis cells. P. gingivalis W50FB2 transported Fe2+ at a rate similar to the wild-type W50, thus indicating that FeoB2 is not involved in iron transport. From radiolabelled iron uptake assays and intracellular iron determination, FeoB1 was shown to be involved in ferrous iron transport. The intracellular metal contents of P. gingivalis W50, W50FB1 and W50FB2 were determined using inductively-coupled plasma mass spectrometry. Results: The metal content of W50 and W50FB2 was similar for iron, magnesium, nickel, zinc, copper and molybdenum. However the manganese content of W50FB2 was approximately one third of that of the wild-typeW50, indicating that it was deficient in manganese transport, thereby suggesting a novel role for FeoB2 in the accumulation of manganese. Conclusions: This is the first time that a FeoB analogue has been implicated in the transport of a metal other than iron in a bacterium. This study was supported by NHMRC grant no. 145831 and an ADRF summer scholarship for LK.