Molecular cloning, nucleotide sequence, and occurrence of a 16.5-kilodalton outer membrane protein of Brucella abortus with similarity to pal lipoproteins

Cloning and sequencing of the bacterioferritin gene of Brucella melitensis 16M strain

The 40 N-terminal amino acids of the 20 kDa antigen A2 from Brucella melitensis were sequenced and showed important similarities with 4 bacterioferrins. A monoclonal antibody raised against this antigen cross-reacted with Escherichia coli bacterioferritin. Hybridization of two sets of degenerate primers with B. melitensis HindIII-digested genomic DNA identified a 3.8 kb fragment. This fragment was shown to contain a bacterioferritin gene (bfr) encoding a 161-amino acid protein. The sequence of the Brucella bacterioferritin is 69% similar to that of E. coli, and many of the ferroxidase centre and haem-ligation residues are conserved.

Growth phase-dependent variations in the outer membrane protein profile of Brucella melitensis

Changes in Brucella cell envelope protein profiles were investigated with batch cultures of B. melitensis strain 16M in a 2-litre fermenter. Analysis of expression of outer membrane proteins (OMP) (apparent molecular masses of 10, 16.5, 19, 25-27, 31-34, 36-38 and 89 kDa) and heat-shock protein DnaK (73 kDa) was performed with monoclonal antibodies (mAb) and immunoblotting techniques. Synthesis of the 89-kDa OMP and the heat-shock protein DnaK was invariant during B. melitensis growth. Expression of the 10-, 19- and 36-38-kDa minor OMPs was never detected. Variations in profiles of some OMPs, i.e. 25-27-kDa and 31-34-kDa major proteins and 16.5-kDa minor protein, occurred during growth stages, principally at the end of the exponential growth phase. These variations consisted of shifts in apparent molecular masses for the 25-27-kDa and 31-34-kDa OMPs and of peptidoglycan association for the 16.5-kDa OMP. Therefore, whereas the strong association of major OMPs with peptidoglycan was confirmed, results suggested that the 16.5-kDa minor OMP is also a peptidoglycan-associated protein.