Binding and utilization of human transferrin by Prevotella nigrescens

To survive and multiply within their hosts, pathogens must possess efficien t iron-scavenging mechanisms. In the present study, we investigate the capa city of Prevotella nigrescens and Prevotella intermedia to use various sour ces of iron for growth and characterize the transferrin-binding activity of P. nigrescens. Iron-saturated human transferrin and lactoferrin, but not f erric chloride and the iron-free form of transferrin, could be used as sour ces of iron by P, nigrescens and P. intermedia. Neither siderophore activit y nor ferric reductase activity could be detected in P. nigrescens and P. i ntermedia. However, both species showed transferrin-binding activity as wel l as the capacity to proteolytically cleave transferrin. To various extents , all strains of P, nigrescens and P. intermedia tested demonstrated transf errin-binding activity. The activity was heat and protease sensitive. The c apacity of P. nigrescens to bind transferrin was decreased when cells were grown in the presence of hemin, Preincubation of bacterial cells with hemin , hemoglobin, lactoferrin, fibrinogen, immunoglobulin G, or laminin did not affect transferrin-binding activity. The transferrin-binding protein could be extracted from the cell surface of P. nigrescens by treatment with a zw itterionic detergent. Subjecting the cell surface extract to affinity chrom atography on an agarose-transferrin column revealed that it contained a pro tein having an estimated molecular mass of 37 kDa and possessing transferri n-binding activity. The transferrin-binding activity of P. nigrescens and P . intermedia may permit the bacteria to obtain iron for survival and growth in periodontal pockets.