Isoprenoid quinones in an aerobic hyperthermophilic archaeon, Aeropyrum pernix

Aeropyrum pernix is the first strictly aerobic hyperthermophile known to grow heterotrophically at neutral pH and at temperatures up to 100°C. Using a simple and sensitive frit-fast atom bombardment liquid chromatography/mass spectrometry quinone analysis method, we analyzed the quinones in A. pernix. This organism contained demethylmenaquinone analogs (DMK-6(H_n)) and methionaquinone analogs (MTK-6(H_n)) when it was grown under vigorous shaking in the presence of air. The quinones were partially or fully saturated with six isoprenyl units. Although DMK and MTK are the quinones found in eubacteria, this is the first report to demonstrate the simultaneous occurrence of DMK and MTK in archaea. The effect of Na₂S₂O₃ on the quinone composition was studied at concentrations of 0, 0.1 and 0.5% under aerobic growth conditions with shaking. The total quinone content was highest (83.4 μg g⁻¹ dry cell weight) at 0.1% Na₂S₂O₃. In the absence of Na₂S₂O₃, only DMK-6 analogs were detected. While DMK analogs such as DMK-6(H₁₂), DMK-6(H₁₀) and DMK-6(H₈) were the major quinones at 0.1% Na₂S₂O₃, MTK analogs such as MTK-6(H₁₂) and MTK-6(H₁₀) were also detected. When the Na₂S₂O₃ concentration was increased to 0.5%, both DMK-6(H₈) and MTK-6(H₁₀) disappeared, while MTK-6(H₁₂) increased to approximately 20% of the total quinone content. When A. pernix was grown under oxygen limitation in a tightly closed bottle without gas phase, MK-6(H₁₀) appeared.