Sulfur oxidation in mutants of the photosynthetic green sulfur bacterium Chlorobium tepidum devoid of cytochrome c-554 and SoxB
Sulfur oxidation in mutants of the photosynthetic green sulfur bacterium Chlorobium tepidum devoid of cytochrome c-554 and SoxB
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DOI：
10.1007/s11120-009-9426-2
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发表时间：
2009-05-01
影响因子：
3.7
通讯作者：
Oh-oka, Hirozo
中科院分区：
文献类型：
--
作者：
Azai, Chihiro;Tsukatani, Yusuke;Oh-oka, Hirozo
一种缺乏细胞色素c-554 （CT0075）的tepidum （Chlorobium tepidum）突变体与野生型相比生长速度下降，但生长产量正常。从培养基中硫化合物的定量测定中发现，突变体比野生型更慢地氧化硫代硫酸盐，但与野生型一样完全氧化硫酸。这表明细胞色素c-554作为一种有效的电子载体会增加硫代硫酸盐氧化的速率，但对硫代硫酸盐氧化本身并不是必不可少的。另一方面，部分soxB基因（CT1021）被aacC1卡带取代的突变体在仅含硫代硫酸盐作为电子源的培养基中根本不能生长。与野生型相比，它们在仅含硫化物的培养基中表现出部分生长产量。这表明SoxB不仅是硫代硫酸盐氧化所必需的，而且还负责硫化物氧化。因此，在缺乏细胞色素c-554的突变体中，在Sox体系和反应中心之间可能存在另一种电子载体或电子转移途径。细胞色素c-554可能在任何其他途径以及硫代硫酸盐氧化途径中发挥作用，因为即使是不能氧化硫代硫酸盐的绿硫细菌也含有编码这种电子载体的cycA基因。
A mutant devoid of cytochrome c-554 (CT0075) in Chlorobium tepidum (syn. Chlorobaculum tepidum) exhibited a decreased growth rate but normal growth yield when compared to the wild type. From quantitative determinations of sulfur compounds in media, the mutant was found to oxidize thiosulfate more slowly than the wild type but completely to sulfate as the wild type. This indicates that cytochrome c-554 would increase the rate of thiosulfate oxidation by serving as an efficient electron carrier but is not indispensable for thiosulfate oxidation itself. On the other hand, mutants in which a portion of the soxB gene (CT1021) was replaced with the aacC1 cassette did not grow at all in a medium containing only thiosulfate as an electron source. They exhibited partial growth yields in media containing only sulfide when compared to the wild type. This indicates that SoxB is not only essential for thiosulfate oxidation but also responsible for sulfide oxidation. An alternative electron carrier or electron transfer path would thus be operating between the Sox system and the reaction center in the mutant devoid of cytochrome c-554. Cytochrome c-554 might function in any other pathway(s) as well as the thiosulfate oxidation one, since even green sulfur bacteria that cannot oxidize thiosulfate contain a cycA gene encoding this electron carrier.