State Key Joint Laboratory of Environment Simulation and Pollution Control, School of Environment, Tsinghua University, Beijing 100084, China.
BMC Microbiol. 2013 Nov 25;13:267. doi: 10.1186/1471-2180-13-267.
The completion of genome sequencing in a number of Shewanella species, which are most renowned for their metal reduction capacity, offers a basis for comparative studies. Previous work in Shewanella oneidensis MR-1 has indicated that some genes within a cluster (mtrBAC-omcA-mtrFED) were involved in iron reduction. To explore new features of iron reduction pathways, we experimentally analyzed Shewanella putrefaciens W3-18-1 since its gene cluster is considerably different from that of MR-1 in that the gene cluster encodes only four ORFs.
Among the gene cluster, two genes (mtrC and undA) were shown to encode c-type cytochromes. The ΔmtrC deletion mutant revealed significant deficiencies in reducing metals of Fe2O3, α-FeO(OH), β-FeO(OH), ferric citrate, Mn(IV) and Co(III), but not organic compounds. In contrast, no deficiency of metal reduction was observed in the ΔundA deletion mutant. Nonetheless, undA deletion resulted in progressively slower iron reduction in the absence of mtrC and fitness loss under the iron-using condition, which was indicative of a functional role of UndA in iron reduction.
These results provide physiological and biochemical evidences that UndA and MtrC of Shewanella putrefaciens W3-18-1 are involved in iron reduction.
Shewanella 属的许多物种的基因组测序已经完成，这些物种以其金属还原能力而闻名，为比较研究提供了基础。Shewanella oneidensis MR-1 的先前研究表明，簇内的一些基因（mtrBAC-omcA-mtrFED）参与了铁还原。为了探索铁还原途径的新特征，我们对 Shewanella putrefaciens W3-18-1 进行了实验分析，因为其基因簇与 MR-1 的基因簇有很大的不同，后者的基因簇只编码四个 ORF。
在基因簇中，两个基因（mtrC 和 undA）被证明编码 c 型细胞色素。ΔmtrC 缺失突变体在还原 Fe2O3、α-FeO(OH)、β-FeO(OH)、柠檬酸铁、Mn(IV)和 Co(III)等金属方面表现出明显的缺陷，但不能还原有机化合物。相比之下，ΔundA 缺失突变体在金属还原方面没有缺陷。然而，在没有 mtrC 的情况下，undA 缺失导致铁还原速度逐渐变慢，在铁利用条件下适应性丧失，这表明 UndA 在铁还原中具有功能作用。
这些结果提供了生理和生化证据，表明 Shewanella putrefaciens W3-18-1 的 UndA 和 MtrC 参与了铁还原。
