Sulfur globule oxidation in green sulfur bacteria is dependent on the dissimilatory sulfite reductase system
Sulfur globule oxidation in green sulfur bacteria is dependent on the dissimilatory sulfite reductase system
复制标题
DOI：
10.1099/mic.0.044669-0
复制
发表时间：
2011-04-01
期刊：
影响因子：
2.8
通讯作者：
Frigaard, Niels-Ulrik
中科院分区：
文献类型：
--
作者：
Holkenbrink, Carina;Barbas, Santiago Ocon;Frigaard, Niels-Ulrik
绿色硫细菌（GSB）将硫化物和硫代硫酸盐氧化为硫酸盐，细胞外的元素硫球作为中间体。在这里，我们调查了哪些基因参与了这些硫球的形成和消耗的绿色硫细菌Chlorobaculum tepidum。我们表明，硫球氧化是严格依赖于异化亚硫酸盐还原酶（DSR）系统。dsrM/CT 2244或dsrT/CT 2245或两个dsrCABL簇（CT 0851-CT 0854，CT 2247 -2250）的缺失消除了硫球氧化并防止了从硫化物形成硫酸盐，而dsrU/CT 2246的缺失没有影响。DSR系统似乎也参与了硫代硫酸盐的形成，因为硫代硫酸盐在硫化物氧化过程中从野生型细胞中释放，但不是从DSR突变体中释放。不能完全氧化底物的dsr突变体氧化硫化物和硫代硫酸盐的速度大约是野生型的两倍，而生长速度仅略低（野生型的70-80%）。增加的氧化速率似乎补偿了不完全的衬底氧化，以满足生长期间减少当量的要求。一个突变体，其中两个硫化物：醌氧化还原酶（sqrD/CT 0117和sqrF/CT 1087）被删除表现出降低硫化物氧化速率（类似于50%的野生型），但形成和消耗的硫球不受影响。缺乏DSR系统的突变体保持有效生长的观察表明，DSR系统在硫化物浓度足够高的环境中被破坏。因此，GSB中的DSR系统可能是通过水平基因转移获得的，作为对在硫化物限制性生境中增强底物利用的需要的响应。
Green sulfur bacteria (GSB) oxidize sulfide and thiosulfate to sulfate, with extracellular globules of elemental sulfur as an intermediate. Here we investigated which genes are involved in the formation and consumption of these sulfur globules in the green sulfur bacterium Chlorobaculum tepidum. We show that sulfur globule oxidation is strictly dependent on the dissimilatory sulfite reductase (DSR) system. Deletion of dsrM/CT2244 or dsrT/CT2245, or the two dsrCABL clusters (CT0851-CT0854, CT2247-2250), abolished sulfur globule oxidation and prevented formation of sulfate from sulfide, whereas deletion of dsrU/CT2246 had no effect. The DSR system also seems to be involved in the formation of thiosulfate, because thiosulfate was released from wild-type cells during sulfide oxidation, but not from the dsr mutants. The dsr mutants incapable of complete substrate oxidation oxidized sulfide and thiosulfate about twice as fast as the wild-type, while having only slightly lower growth rates (70-80% of wild-type). The increased oxidation rates seem to compensate for the incomplete substrate oxidation to satisfy the requirement for reducing equivalents during growth. A mutant in which two sulfide : quinone oxidoreductases (sqrD/CT0117 and sqrF/CT1087) were deleted exhibited a decreased sulfide oxidation rate (similar to 50% of wild-type), yet formation and consumption of sulfur globules were not affected. The observation that mutants lacking the DSR system maintain efficient growth suggests that the DSR system is dispensable in environments with sufficiently high sulfide concentrations. Thus, the DSR system in GSB may have been acquired by horizontal gene transfer as a response to a need for enhanced substrate utilization in sulfide-limiting habitats.