Table 2. Protective antigen secretion (μg/ml) of Vollum or VollumΔatxA under different growth conditions.

	VollumΔatxA	Vollum	Atmosphere	Supplements
PA μg/ml	-	-	Ambient	-
	-	+++	Ambient	10% NRS
	-	-	10% CO2	-
	-	+++	10% CO2	10% NRS
	-	+++	10% CO2	0.75% HCO3-

- <0.1, + 0.1–0.5, ++ 0.5–1.5, +++ 1.5–10