Friedrich C G
Lehrstuhl für Technische Mikrobiologie, Fachbereich Chemietechnik, Universität Dortmund, Germany.
Adv Microb Physiol. 1998;39:235-89. doi: 10.1016/s0065-2911(08)60018-1.
Reduced inorganic sulfur compounds are oxidized by members of the domains Archaea and Bacteria. These compounds are used as electron donors for anaerobic phototrophic and aerobic chemotrophic growth, and are mostly oxidized to sulfate. Different enzymes mediate the conversion of various reduced sulfur compounds. Their physiological function in sulfur oxidation is considered (i) mostly from the biochemical characterization of the enzymatic reaction, (ii) rarely from the regulation of their formation, and (iii) only in a few cases from the mutational gene inactivation and characterization of the resulting mutant phenotype. In this review the sulfur-metabolizing reactions of selected phototrophic and of chemotrophic prokaryotes are discussed. These comprise an archaeon, a cyanobacterium, green sulfur bacteria, and selected phototrophic and chemotrophic proteobacteria. The genetic systems are summarized which are presently available for these organisms, and which can be used to study the molecular basis of their dissimilatory sulfur metabolism. Two groups of thiobacteria can be distinguished: those able to grow with tetrathionate and other reduced sulfur compounds, and those unable to do so. This distinction can be made irrespective of their phototrophic or chemotrophic metabolism, neutrophilic or acidophilic nature, and may indicate a mechanism different from that of thiosulfate oxidation. However, the core enzyme for tetrathionate oxidation has not been identified so far. Several phototrophic bacteria utilize hydrogen sulfide, which is considered to be oxidized by flavocytochrome c owing to its in vitro activity. However, the function of flavocytochrome c in vivo may be different, because it is missing in other hydrogen sulfide-oxidizing bacteria, but is present in most thiosulfate-oxidizing bacteria. A possible function of flavocytochrome c is discussed based on biophysical studies, and the identification of a flavocytochrome in the operon encoding enzymes involved in thiosulfate oxidation of Paracoccus denitrificans. Adenosine-5'-phosphosulfate reductase thought to function in the 'reverse' direction in different phototrophic and chemotrophic sulfur-oxidizing bacteria was analysed in Chromatium vinosum. Inactivation of the corresponding gene does not affect the sulfite-oxidizing ability of the mutant. This result questions the concept of its 'reverse' function, generally accepted for over three decades.
还原性无机硫化合物可被古菌域和细菌域的成员氧化。这些化合物被用作厌氧光合营养和好氧化学营养生长的电子供体，并且大多被氧化为硫酸盐。不同的酶介导各种还原性硫化合物的转化。它们在硫氧化中的生理功能，（i）大多是从酶促反应的生化特性来考虑的，（ii）很少从其形成的调控方面来考虑，（iii）仅在少数情况下是从突变基因失活及所得突变体表型的特性来考虑的。在这篇综述中，讨论了选定的光合营养和化学营养原核生物的硫代谢反应。这些包括一种古菌、一种蓝细菌、绿硫细菌以及选定的光合营养和化学营养变形菌。总结了目前可用于这些生物的遗传系统，这些系统可用于研究其异化硫代谢的分子基础。硫细菌可分为两类：一类能够利用连四硫酸盐和其他还原性硫化合物生长，另一类则不能。这种区分与它们的光合或化学营养代谢、嗜中性或嗜酸性质无关，可能表明其机制不同于硫代硫酸盐氧化的机制。然而迄今为止，尚未鉴定出连四硫酸盐氧化的核心酶。几种光合细菌利用硫化氢，由于其体外活性，硫化氢被认为是由黄素细胞色素c氧化的。然而，黄素细胞色素c在体内的功能可能不同，因为它在其他硫化氢氧化细菌中不存在，但在大多数硫代硫酸盐氧化细菌中存在。基于生物物理研究以及在编码参与反硝化副球菌硫代硫酸盐氧化的酶的操纵子中鉴定出一种黄素细胞色素，讨论了黄素细胞色素c的一种可能功能。在嗜硫色杆菌中分析了在不同光合营养和化学营养硫氧化细菌中被认为以“反向”发挥作用的腺苷 - 5'-磷酸硫酸还原酶。相应基因的失活并不影响突变体的亚硫酸盐氧化能力。这一结果对三十多年来普遍接受的其“反向”功能的概念提出了质疑。
