GROWTH PHASE-DEPENDENT VARIATIONS IN THE OUTER-MEMBRANE PROTEIN PROFILE OF BRUCELLA-MELITENSIS

Changes in Brucella cell envelope protein profiles were investigated w ith batch cultures of B. melitensis strain 16M in a 2-litre fermenter. Analysis of expression of outer membrane proteins (OMP) (apparent mol ecular masses of 10, 16.5, 19, 25-27, 31-34, 36-38 and 89 kDa) and hea t-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 detecte d. Variations in profiles of some OMPs, i.e. 25-27-kDa and 31-34-kDa m ajor proteins and 16.5-kDa minor protein, occurred during growth stage s, principally at the end of the exponential growth phase. These varia tions consisted of shifts in apparent molecular masses for the 25-27-k Da and 31-34-kDa OMPs and of peptidoglycan association for the 16.5-kD a OMP. Therefore, whereas the strong association of major OMPs with pe ptidoglycan was confirmed, results suggested that the 16.5-kDa minor O MP is also a peptidoglycan-associated protein.