Ng K Y, Kamimura K, Sugio T
Division of Science and Technology for Energy Conversion, Graduate School of Natural Science and Technology, Okayama University, 1-1-1 Tsushima Naka, Okayama 700-8530, Japan.
J Biosci Bioeng. 2000;90(2):193-8. doi: 10.1016/s1389-1723(00)80109-7.
When incubated under anaerobic conditions, five strains of Thiobacillus ferrooxidans tested produced hydrogen sulfide (H2S) from elemental sulfur at pH 1.5. However, among the strains, T. ferrooxidans NASF-1 and AP19-3 were able to use both elemental sulfur and tetrathionate as electron acceptors for H2S production at pH 1.5. The mechanism of H2S production from tetrathionate was studied with intact cells of strain NASF-1. Strain NASF-1 was unable to use dithionate, trithionate, or pentathionate as an electron acceptor. After 12 h of incubation under anaerobic conditions at 30 degrees C, 1.3 micromol of tetrathionate in the reaction mixture was decomposed, and 0.78 micromol of H2S and 0.6 micromol of trithionate were produced. Thiosulfate and sulfite were not detected in the reaction mixture. From these results, we propose that H2S is produced at pH 1.5 from tetrathionate by T. ferrooxidans NASF-1, via the following two-step reaction, in which AH2 represents an unknown electron donor in NASF-1 cells. Namely, tetrathionate is decomposed by tetrathionate-decomposing enzyme to give trithionate and elemental sulfur (S4O6(2-)-->S3O6(2-) + S(o), Eq. 1), and the elemental sulfur thus produced is reduced by sulfur reductase using electrons from AH2 to give H2S (S(o) + AH2-->H2S + A, Eq. 2). The optimum pH and temperature for H2S production from tetrathionate under argon gas were 1.5 and 30 degrees C, respectively. Under argon gas, the H2S production from tetrathionate stopped after 1 d of incubation, producing a total of 2.5 micromol of H2S/5 mg protein. In contrast, under H2 conditions, H2S production continued for 6 d, producing a total of 10.0 micromol of H2S/5 mg protein. These results suggest that electrons from H2 were used to reduce elemental sulfur produced as an intermediate to give H2S. Potassium cyanide at 0.5 mM slightly inhibited H2S production from tetrathionate, but increased that from elemental sulfur 3-fold. 2,4-Dinitrophenol at 0.05 mM, carbonylcyanide-m-chlorophenyl- hydrazone at 0.01 mM, mercury chloride at 0.05 mM, and sodium selenate at 1.0 mM almost completely inhibited H2S production from tetrathionate, but not from elemental sulfur.
在厌氧条件下培养时，所测试的五株氧化亚铁硫杆菌在pH 1.5的条件下能从元素硫产生硫化氢（H₂S）。然而，在这些菌株中，氧化亚铁硫杆菌NASF - 1和AP19 - 3在pH 1.5时能够利用元素硫和连四硫酸盐作为产生H₂S的电子受体。用菌株NASF - 1的完整细胞研究了连四硫酸盐产生H₂S的机制。菌株NASF - 1不能利用连二硫酸盐、连三硫酸盐或连五硫酸盐作为电子受体。在30℃厌氧条件下培养12小时后，反应混合物中的1.3微摩尔连四硫酸盐被分解，产生了0.78微摩尔的H₂S和0.6微摩尔的连三硫酸盐。反应混合物中未检测到硫代硫酸盐和亚硫酸盐。根据这些结果，我们提出氧化亚铁硫杆菌NASF - 1在pH 1.5时通过以下两步反应从连四硫酸盐产生H₂S，其中AH₂代表NASF - 1细胞中一种未知的电子供体。即，连四硫酸盐被连四硫酸盐分解酶分解生成连三硫酸盐和元素硫（S₄O₆²⁻→S₃O₆²⁻ + S₀，方程1），由此产生的元素硫被硫还原酶利用来自AH₂的电子还原生成H₂S（S₀ + AH₂→H₂S + A，方程2）。在氩气下从连四硫酸盐产生H₂S的最适pH和温度分别为1.5和30℃。在氩气下，培养1天后连四硫酸盐产生H₂S的过程停止，总共产生2.5微摩尔H₂S/5毫克蛋白质。相比之下，在氢气条件下，H₂S的产生持续了6天，总共产生10.0微摩尔H₂S/5毫克蛋白质。这些结果表明，来自氢气的电子被用于还原作为中间产物产生的元素硫以生成H₂S。0.5毫摩尔的氰化钾对连四硫酸盐产生H₂S有轻微抑制作用，但使元素硫产生的H₂S增加了3倍。0.05毫摩尔的2,4 - 二硝基苯酚、0.01毫摩尔的羰基氰化物 - m - 氯苯腙、0.05毫摩尔的氯化汞和1.0毫摩尔的硒酸钠几乎完全抑制了连四硫酸盐产生H₂S，但不抑制元素硫产生H₂S。
