Pathogenic neisseriae can use hemoglobin, transferrin, and lactoferrin independently of the tonB locus

Redundant TonB systems which function in iron transport from TonB-dependent ligands have recently been identified in several gram-negative bacteria. W e demonstrate here that in addition to the previously described tonB locus, an alternative system exists for the utilization of iron from hemoglobin, transferrin, or lactoferrin in Neisseria meningitidis and Neisseria gonorrh oeae, Following incubation on media containing hemoglobin, N, meningitidis IR3436 (tonB exbB exbD deletion mutant) and N. gonorrhoeae PD3401 (tonB ins ertional mutant) give rise to colonies which can grow with hemoglobin. Tran sfer of Hb(+) variants (PD3437 or PD3402) to media containing hemoglobin, t ransferrin, and/or Lactoferrin as sole iran sources resulted in growth comp arable to that observed for the wild-type strains. Transformation of N. men ingitidis IR3436 or N. gonorrhoeae PD3401 with chromosomal DNA from the Hb( +) variants yielded transformants capable of growth with hemoglobin. When w e inactivated the TonB-dependent outer membrane hemoglobin receptors (HmbR or HpuB) in the Neisseria Hb(+) variants, these strains could not grow with hemoglobin; however, growth was observed with transferrin and/or lactoferr in. These results demonstrate that accumulation of iron from hemoglobin, tr ansferrin, and lactoferrin in the pathogenic neisseriae can occur via a sys tem that is independent of the previously described tonB locus.