Exposure of P. furiosus mutants lacking SOR, FdpA, and Rd to O2 challenge. Cultures (40 mL) in 100-mL bottles were grown at 95 °C in medium containing 5 g/L maltose, 0.5 g/L yeast extract, and no sulfide on a shaking platform (150 rpm). Cultures parent (circles) or mutant (squares) were grown anoxically (black) or were exposed to 8% O2 (vol/vol in headspace) after 4 h of growth (gray). Total H2 production was measured throughout growth. (A) SOR1, (B) FdpA1, (C) SOR FdpA1, and (D) Rd1.