Smith Jessica A, Aklujkar Muktak, Risso Carla, Leang Ching, Giloteaux Ludovic, Holmes Dawn E
Department of Microbiology, University of Massachusetts, Amherst, Massachusetts, USA.
Department of Biological Sciences, Towson University, Towson, Maryland, USA.
Appl Environ Microbiol. 2015 Apr;81(8):2735-44. doi: 10.1128/AEM.04038-14. Epub 2015 Feb 6.
The hyperthermophilic archaeon Ferroglobus placidus can utilize a wide variety of electron donors, including hydrocarbons and aromatic compounds, with Fe(III) serving as an electron acceptor. In Fe(III)-reducing bacteria that have been studied to date, this process is mediated by c-type cytochromes and type IV pili. However, there currently is little information available about how this process is accomplished in archaea. In silico analysis of the F. placidus genome revealed the presence of 30 genes coding for putative c-type cytochrome proteins (more than any other archaeon that has been sequenced to date), five of which contained 10 or more heme-binding motifs. When cell extracts were analyzed by SDS-PAGE followed by heme staining, multiple bands corresponding to c-type cytochromes were detected. Different protein expression patterns were observed in F. placidus cells grown on soluble and insoluble iron forms. In order to explore this result further, transcriptomic studies were performed. Eight genes corresponding to multiheme c-type cytochromes were upregulated when F. placidus was grown with insoluble Fe(III) oxide compared to soluble Fe(III) citrate as an electron acceptor. Numerous archaella (archaeal flagella) also were observed on Fe(III)-grown cells, and genes coding for two type IV pilin-like domain proteins were differentially expressed in Fe(III) oxide-grown cells. This study provides insight into the mechanisms for dissimilatory Fe(III) respiration by hyperthermophilic archaea.
嗜热古菌普拉氏铁球菌能够利用多种电子供体，包括碳氢化合物和芳香族化合物，以Fe(III)作为电子受体。在迄今已研究的Fe(III)还原细菌中，这一过程由c型细胞色素和IV型菌毛介导。然而，目前关于古菌中该过程是如何完成的信息很少。对普拉氏铁球菌基因组的计算机分析显示，有30个基因编码假定的c型细胞色素蛋白（比迄今已测序的任何其他古菌都多），其中5个含有10个或更多的血红素结合基序。当通过SDS-PAGE分析细胞提取物，然后进行血红素染色时，检测到了多条对应于c型细胞色素的条带。在以可溶和不溶铁形式生长的普拉氏铁球菌细胞中观察到了不同的蛋白质表达模式。为了进一步探究这一结果，进行了转录组学研究。与以柠檬酸铁（可溶）作为电子受体相比，当普拉氏铁球菌以不溶性Fe(III)氧化物生长时，8个对应于多血红素c型细胞色素的基因上调。在以Fe(III)生长的细胞上还观察到了大量的古菌鞭毛，并且编码两种IV型菌毛样结构域蛋白的基因在以Fe(III)氧化物生长的细胞中差异表达。这项研究为嗜热古菌异化Fe(III)呼吸的机制提供了见解。
