FIG. 6.

Comparison of PA and capsule production in parent and mutated B. anthracis strains. (a) Immunoprecipitation of PA produced by colonies of B. anthracis Ames 35 (pXO1⁺; left side) and the isogenic double mutant MSLL35 (pXO1⁺; center), with Ames 34 (pXO1⁻; right side) as a negative control. The cultures were grown for 18 h on CA agar supplemented with 0.8% (wt/vol) sodium bicarbonate, 5% (vol/vol) horse serum, and 5% (vol/vol) PA antiserum (from sheep) in a 20% CO₂ environment at 37°C. (b) B. anthracis double mutant MSLL34 (pXO2⁺) produces less capsule (right side) than the parent Ames 34 strain (pXO2⁺; left side). The Ames 35 strain (pXO2⁻) was used as a negative control (center). The cultures were grown for 18 h in bicarbonate agar supplemented with 0.8% (wt/vol) bicarbonate and 10% (vol/vol) horse serum in 20% CO₂ at 37°C. Cells were removed from the colonies shown, and capsule was visualized with India ink (bottom panel). Bar, 5 μm.