Characterization and expression of the Pseudomonas putida bacterioferritinalpha subunit gene

The root-colonizing pseudomonad Pseudomonas putida (Pp) appears to produce two subunits, alpha and beta, of the iron-binding protein, bacterioferritin . A gene encoding the alpha-bacterioferritin subunit was located adjacent t o the major catalase in Pp. The deduced protein sequence of the Pp bfr alph a gene had a very high identity with other alpha-subunits, possessing conse rved amino acids responsible for ferroxidase activity. The gene also lacked a deduced methionine at residue 52, associated with heme binding in beta-s ubunits. An antibody generated toward the Escherichia coli (E. coli) multif unctional single subunit bacterioferritin recognized two proteins in the Pp extract, a 22 kDa protein likely to be a beta-subunit and, to a lesser ext ent, a 23 kDa band. The 23 kDa band was absent in a Pp mutant in which the bfr alpha gene was disrupted. Loss of alpha-bacterioferritin stimulated pro duction of fluorescent siderophore. Growth on media and on root surfaces wa s not impaired by deletion of the alpha-bacterioferritin. Transcription of bfr alpha was independent of the catalase gene and was dependent on iron. T he transcript levels from bfr alpha decreased in iron deficiency experience d during stationary-phase or upon treatment during growth with an iron chel ator. (C) 2000 Published by Elsevier Science B.V. All rights reserved.