Chan Leong-Keat, Weber Timothy S, Morgan-Kiss Rachael M, Hanson Thomas E
College of Marine and Earth Studies and Delaware Biotechnology Institute, University of Delaware, Rm 127 DBI, 15 Innovation Way, Newark, DE 19711, USA.
Microbiology (Reading). 2008 Mar;154(Pt 3):818-829. doi: 10.1099/mic.0.2007/012583-0.
The specific enzymes employed by Chlorobium tepidum for the anaerobic oxidation of thiosulfate, sulfide and elemental sulfur during anoxygenic photosynthesis are not well defined. In particular, it is unclear how C. tepidum completely oxidizes thiosulfate. A C. tepidum genomic region, encoding a putative quinone-interacting membrane-bound oxidoreductase (Qmo) complex (CT0866-0868), hypothetical proteins (CT0869-0875) and a sulfide : quinone oxidoreductase (SQR) homologue (CT0876), was analysed for its role in anaerobic sulfur oxidation. Transcripts of genes encoding the Qmo complex, which is similar to archaeal heterodisulfide reductases, were detected by RT-PCR only while sulfide or elemental sulfur were being oxidized, whereas the SQR homologue and CT0872 were expressed during thiosulfate oxidation and into early stationary phase. A mutant of C. tepidum was obtained in which the region between CT0868 and CT0876 was replaced by a transposon insertion resulting in the truncation or deletion of nine genes. This strain, C5, was completely defective for growth on thiosulfate as the sole electron donor in C. tepidum, but only slightly defective for growth on sulfide or thiosulfate plus sulfide. Strain C5 did not oxidize thiosulfate and also displayed a defect in acetate assimilation under all growth conditions. A gene of unknown function, CT0872, deleted in strain C5 that is conserved in chemolithotrophic sulfur-oxidizing bacteria and archaea is the most likely candidate for the thiosulfate oxidation phenotype observed in this strain. The defect in acetate assimilation may be explained by deletion of CT0874, which encodes a homologue of 3-oxoacyl acyl carrier protein synthase.
嗜热绿菌在无氧光合作用期间用于厌氧氧化硫代硫酸盐、硫化物和元素硫的特定酶尚未明确界定。特别是，尚不清楚嗜热绿菌如何完全氧化硫代硫酸盐。对嗜热绿菌的一个基因组区域进行了分析，该区域编码一个假定的醌相互作用膜结合氧化还原酶（Qmo）复合物（CT0866 - 0868）、假定蛋白（CT0869 - 0875）和一个硫化物：醌氧化还原酶（SQR）同源物（CT0876），以研究其在厌氧硫氧化中的作用。仅在硫化物或元素硫被氧化时，通过RT - PCR检测到编码与古菌异二硫键还原酶相似的Qmo复合物的基因转录本，而SQR同源物和CT0872在硫代硫酸盐氧化期间及进入稳定早期阶段时表达。获得了嗜热绿菌的一个突变体，其中CT0868和CT0876之间的区域被转座子插入所取代，导致九个基因的截断或缺失。该菌株C5在嗜热绿菌中以硫代硫酸盐作为唯一电子供体生长时完全缺陷，但在以硫化物或硫代硫酸盐加硫化物生长时仅略有缺陷。菌株C5不氧化硫代硫酸盐，并且在所有生长条件下乙酸同化也存在缺陷。在菌株C5中缺失的一个功能未知的基因CT0872，在化能自养硫氧化细菌和古菌中保守，是该菌株中观察到的硫代硫酸盐氧化表型最可能的候选基因。乙酸同化缺陷可能由CT0874的缺失来解释，CT0874编码3 - 氧代酰基酰基载体蛋白合酶的同源物。
