FIG. 1.

Permissiveness of acidic buffers for C. burnetii metabolism. The metabolic activity of purified C. burnetii in acidic (pH 4.5) buffers was determined by measuring [³⁵S]Cys-Met radiolabel incorporation by bacteria after a 3-h incubation in the indicated buffers without (A and C), or with (B and D) 1 mM glutamate. The level of de novo synthesized protein was determined by scintillation counting (A and B) and SDS-PAGE with autoradiography (C and D). The magnitude of radiolabel incorporation is expressed as the relative increase over incorporation observed in P-25 buffer (pH 7.0) (negative control). Asterisks indicate statistically significant differences (P < 0.05) between the indicated sample and P-25 buffer (pH 7.0). The broken line represents the level of radiolabel incorporation in P-25 buffer (pH 7.0) normalized to 1. Representative autoradiograms are shown. citrate-P, citrate-phosphate; MW, molecular weight (in thousands).