Adaptation to disruption of the electron transfer pathway for Fe(III) reduction in Geobacter sulfurreducens
Adaptation to disruption of the electron transfer pathway for Fe(III) reduction in Geobacter sulfurreducens
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DOI：
10.1128/jb.187.17.5918-5926.2005
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发表时间：
2005-09-01
影响因子：
3.2
通讯作者：
Lovley, DR
中科院分区：
文献类型：
--
作者：
Leang, C;Adams, LA;Lovley, DR
以往的研究表明，外膜C型细胞色素OmcB参与了硫还原地杆菌对Fe(III)的还原。一个OmcB缺陷突变株在还原可溶性和不溶性Fe(III)的能力上受到了极大的损害。重新引入omcb使还原Fe(III)的能力恢复到与omcb生产水平成比例的水平。在这里，我们报告了OmcB缺陷突变株逐渐适应在可溶性Fe(III)上生长，而不是在不溶性Fe(III)上生长。在稳态培养条件下，OmcB缺失突变体对可溶性Fe(III)的还原速率与野生型相当，但其细胞产量仅为野生型的60%左右。蛋白质和转录水平的分析表明，适应突变体中几种膜相关细胞色素的表达高于野生型。用全基因组DNA微阵列进一步比较柠檬酸铁稳定生长过程中的转录水平，发现基因表达发生了显著的变化，这显然是为了使新陈代谢适应铁(HI)电子传递的受损。这些结果表明，尽管硫还原革兰氏菌中还有许多其他膜结合的c型细胞色素，但这些细胞色素的表达增加并不能完全弥补OmcB的损失。外膜细胞色素是功能可互换的混杂还原酶的概念似乎是不正确的。此外，研究结果还表明，硫还原菌对可溶性Fe(III)和不溶性Fe(III)氧化物的电子转移可能存在不同的机理，强调了对环境友好的Fe(III)氧化物进行电子转移研究的重要性。
Previous studies demonstrated that an outer membrane c-type cytochrome, OmcB, was involved in Fe(III) reduction in Geobacter sulfurreducens. An OmcB-deficient mutant was greatly impaired in its ability to reduce both soluble and insoluble Fe(III). Reintroducing omcB restored the capacity for Fe(III) reduction at a level proportional to the level of OmcB production. Here, we report that the OmcB-deficient mutant gradually adapted to grow on soluble Fe (III) but not insoluble Fe(III). The adapted OmcB-deficient mutant reduced soluble Fe(III) at a rate comparable to that of the wild type, but the cell yield of the mutant was only ca. 60% of that of the wild type under steady-state culturing conditions. Analysis of proteins and transcript levels demonstrated that expression of several membrane-associated cytochromes was higher in the adapted mutant than in the wild type. Further comparison of transcript levels during steady-state growth on Fe(HI) citrate with a whole-genome DNA microarray revealed a significant shift in gene expression in an apparent attempt to adapt metabolism to the impaired electron transport to Fe(HI). These results demonstrate that, although there are many other membrane-bound c-type cytochromes in G. sulfurreducens, increased expression of these cytochromes cannot completely compensate for the loss of OmcB. The concept that outer membrane cytochromes are promiscuous reductases that are interchangeable in function appears to be incorrect. Furthermore, the results indicate that there may be different mechanisms for electron transfer to soluble Fe(III) and insoluble Fe(III) oxides in G. sulfurreducens, which emphasizes the importance of studying electron transport to the environmentally relevant Fe(III) oxides.