Production of Toxic Shock Syndrome Toxin 1 by Staphylococcus aureus Requires Both Oxygen and Carbon Dioxide

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Abstract
The effect of O 2 and CO 2 on expression of toxic shock syndrome toxin 1 (TSST-1) by Staphylococcus aureus was investigated under controlled growth conditions with continuous-culture techniques. To stimulate TSST-1 production, air and anaerobic gas were premixed before delivery to the culture vessel. At a growth rate—or mass doubling time ( t d )—of 3 h, production of specific TSST-1 (expressed as micrograms per milligram of cell dry weight) was 5.9-fold greater at an O 2 concentration of 4% than under anaerobic conditions. Increasing the O 2 concentration to 11% did not result in a significant increase ( P > 0.05) in the rate of toxin production over that during growth in 4% O 2 but did result in a significant increase (4.9-fold; P < 0.001) in the rate of toxin production over that during anaerobic growth. At a t d of 9 h, addition of 3.5% O 2 resulted in a 7.6-fold increase in specific TSST-1 production. When room air was sparged through a culture growing at a t d of 9 h, TSST-1 production increased significantly (by 3.4-fold) over that during anaerobic growth. When a growth environment of 4% O 2 –remainder N 2 was studied, no increase in TSST-1 production was observed; this was also the case with 8% O 2 at gas-flow rates of 0.1, 0.2, and 0.4 liters/min. In all experiments, production of biomass (expressed as milligrams of cell dry weight per milliliter) increased, indicating that O 2 was metabolized by S. aureus . Addition of CO 2 to the gas mix (4% O 2 , 10% CO 2 , 86% N 2 ) resulted in a 5.1- to 6.8-fold increase in TSST-1 production over that during anaerobic growth and a 3.6-fold increase over that during growth in an environment of 4% O 2 –remainder N 2 . The agr mutant strain tested produced 6.1-fold more specific TSST-1 in a growth environment of 4% O 2 –10% CO 2 –86% N 2 than during anaerobic growth. These data suggest that in this system, O 2 alone does not trigger production of TSST-1; rather, both CO 2 and O 2 are required.