Kim Byoung-Chan, Postier Bradley L, Didonato Raymond J, Chaudhuri Swades K, Nevin Kelly P, Lovley Derek R
Department of Microbiology, University of Massachusetts, 639 North Pleasant Street, Amherst, MA 01003, USA.
Bioelectrochemistry. 2008 Jun;73(1):70-5. doi: 10.1016/j.bioelechem.2008.04.023. Epub 2008 Apr 29.
Geobacter sulfurreducens effectively produces electricity in microbial fuel cells by oxidizing acetate with an electrode serving as the sole electron acceptor. Deletion of the gene encoding OmcF, a monoheme outer membrane c-type cytochrome, substantially decreased current production. Previous studies demonstrated that inhibition of Fe(III) reduction in the OmcF-deficient mutant could be attributed to poor transcription of the gene for OmcB, an outer membrane c-type cytochrome that is required for Fe(III) reduction. However, a mutant in which omcB was deleted produced electricity as well as wild type. Microarray analysis of the OmcF-deficient mutant versus the wild type revealed that many of the genes with the greatest decreases in transcript levels were genes whose expression was previously reported to be upregulated in cells grown with an electrode as the sole electron acceptor. These included genes with putative functions related to metal efflux and/or type I secretion and two hypothetical proteins. The outer membrane cytochromes, OmcS and OmcE, which previous studies have demonstrated are required for optimal current generation, were not detected on the outer surface of the OmcF-deficient mutant even though the omcS and omcE genes were still transcribed, suggesting that the putative secretion system could be involved in the export of outer membrane proteins necessary for electron transfer to the fuel cell anode. These results suggest that the requirement for OmcF for optimal current production is not because OmcF is directly involved in extracellular electron transfer but because OmcF is required for the appropriate transcription of other genes either directly or indirectly involved in electricity production.
硫还原地杆菌通过以电极作为唯一电子受体氧化乙酸盐，在微生物燃料电池中有效地产生电流。编码单血红素外膜c型细胞色素OmcF的基因缺失，会大幅降低电流产生。先前的研究表明，OmcF缺陷型突变体中Fe(III)还原的抑制可归因于OmcB基因转录不佳，OmcB是一种外膜c型细胞色素，是Fe(III)还原所必需的。然而，一个缺失omcB的突变体产生电流的情况与野生型一样。对OmcF缺陷型突变体与野生型进行微阵列分析发现，转录水平下降幅度最大的许多基因，是先前报道在以电极作为唯一电子受体生长的细胞中表达上调的基因。这些基因包括与金属外排和/或I型分泌相关的推定功能基因以及两种假设蛋白。先前的研究表明，外膜细胞色素OmcS和OmcE是最佳电流产生所必需的，但即使omcS和omcE基因仍在转录，在OmcF缺陷型突变体的外表面也未检测到它们，这表明推定的分泌系统可能参与了将电子转移到燃料电池阳极所必需的外膜蛋白的输出。这些结果表明，最佳电流产生对OmcF的需求，不是因为OmcF直接参与细胞外电子转移，而是因为OmcF是直接或间接参与发电的其他基因进行适当转录所必需的。
