Schicho R N, Ma K, Adams M W, Kelly R M
Department of Chemical Engineering, Johns Hopkins University, Baltimore, Maryland 21218.
J Bacteriol. 1993 Mar;175(6):1823-30. doi: 10.1128/jb.175.6.1823-1830.1993.
The bioenergetic role of the reduction of elemental sulfur (S0) in the hyperthermophilic archaeon (formerly archaebacterium) Pyrococcus furiosus was investigated with chemostat cultures with maltose as the limiting carbon source. The maximal yield coefficient was 99.8 g (dry weight) of cells (cdw) per mol of maltose in the presence of S0 but only 51.3 g (cdw) per mol of maltose if S0 was omitted. However, the corresponding maintenance coefficients were not found to be significantly different. The primary fermentation products detected were H2, CO2, and acetate, together with H2S, when S0 was also added to the growth medium. If H2S was summed with H2 to represent total reducing equivalents released during fermentation, the presence of S0 had no significant effect on the pattern of fermentation products. In addition, the presence of S0 did not significantly affect the specific activities in cell extracts of hydrogenase, sulfur reductase, alpha-glucosidase, or protease. These results suggest either that S0 reduction is an energy-conserving reaction, i.e., S0 respiration, or that S0 has a stimulatory effect on or helps overcome a process that is yield limiting. A modification of the Entner-Doudoroff glycolytic pathway has been proposed as the primary route of glucose catabolism in P. furiosus (S. Mukund and M. W. W. Adams, J. Biol. Chem. 266:14208-14216, 1991). Operation of this pathway should yield 4 mol of ATP per mol of maltose oxidized, from which one can calculate a value of 12.9 g (cdw) per mol of ATP for non-S0 growth. Comparison of this value to the yield data for growth in the presence of S0 reduction is equivalent to an ATP yield of 0.5 mol of ATP per mol of S0 reduced. Possible mechanism to account for this apparent energy conservation are discussed.
利用恒化器培养，以麦芽糖作为限制性碳源，研究了嗜热古菌（以前称为古细菌）激烈火球菌中元素硫（S⁰）还原的生物能量作用。在有S⁰存在的情况下，最大产量系数为每摩尔麦芽糖产生99.8克（干重）细胞（cdw），但如果省略S⁰，则每摩尔麦芽糖仅产生51.3克（cdw）。然而，相应的维持系数没有发现显著差异。检测到的主要发酵产物是H₂、CO₂和乙酸盐，当S⁰也添加到生长培养基中时，还会产生H₂S。如果将H₂S与H₂相加来表示发酵过程中释放的总还原当量，S⁰的存在对发酵产物模式没有显著影响。此外，S⁰的存在对氢化酶、硫还原酶、α-葡萄糖苷酶或蛋白酶的细胞提取物中的比活性没有显著影响。这些结果表明，要么S⁰还原是一种能量守恒反应，即S⁰呼吸作用，要么S⁰对产量限制过程具有刺激作用或有助于克服该过程。有人提出，Entner-Doudoroff糖酵解途径的一种变体是激烈火球菌中葡萄糖分解代谢的主要途径（S. Mukund和M. W. W. Adams，《生物化学杂志》266:14208 - 14216，1991）。该途径的运行每氧化一摩尔麦芽糖应产生4摩尔ATP，由此可以计算出非S⁰生长时每摩尔ATP的产量为12.9克（cdw）。将该值与存在S⁰还原时的生长产量数据进行比较，相当于每还原一摩尔S⁰产生0.5摩尔ATP的产量。文中讨论了可能解释这种明显能量守恒的机制。
