Research Article: Physiological Roles of ArcA, Crp, and EtrA and Their Interactive Control on Aerobic and Anaerobic Respiration in Shewanella oneidensis

Date Published: December 28, 2010

Publisher: Public Library of Science

Author(s): Haichun Gao, Xiaohu Wang, Zamin K. Yang, Jingrong Chen, Yili Liang, Haijiang Chen, Timothy Palzkill, Jizhong Zhou, Pierre Cornelis.

Abstract: In the genome of Shewanella oneidensis, genes encoding the global regulators ArcA, Crp, and EtrA have been identified. All these proteins deviate from their counterparts in E. coli significantly in terms of functionality and regulon. It is worth investigating the involvement and relationship of these global regulators in aerobic and anaerobic respiration in S. oneidensis. In this study, the impact of the transcriptional factors ArcA, Crp, and EtrA on aerobic and anaerobic respiration in S. oneidensis were assessed. While all these proteins appeared to be functional in vivo, the importance of individual proteins in these two major biological processes differed. The ArcA transcriptional factor was critical in aerobic respiration while the Crp protein was indispensible in anaerobic respiration. Using a newly developed reporter system, it was found that expression of arcA and etrA was not influenced by growth conditions but transcription of crp was induced by removal of oxygen. An analysis of the impact of each protein on transcription of the others revealed that Crp expression was independent of the other factors whereas ArcA repressed both etrA and its own transcription while EtrA also repressed arcA transcription. Transcriptional levels of arcA in the wild type, crp, and etrA strains under either aerobic or anaerobic conditions were further validated by quantitative immunoblotting with a polyclonal antibody against ArcA. This extensive survey demonstrated that all these three global regulators are functional in S. oneidensis. In addition, the reporter system constructed in this study will facilitate in vivo transcriptional analysis of targeted promoters.

Partial Text: Depending on the availability of electron donors and acceptors, facultative anaerobes such as Escherichia coli adopt three different metabolic modes: aerobic respiration, anaerobic respiration, and fermentation [1]–[2]. Aerobic respiration with oxygen as the terminal electron acceptor (EA) is the most productive mode due to complete oxidation of a growth substrate while anaerobic respiration can only oxidize a substrate partially with alternative electron acceptors, such as nitrate. Fermentation is the least productive process because only substrate level phosphorylation occurs. As a result, aerobic respiration is preferred over anaerobic respiration, which in turn is preferred over fermentation [3].

S. oneidensis MR-1 is an intriguing microorganism in terms of its metabolic pathways. Its genome contains genes encoding many enzymes of mixed acid fermentation but it is not able to ferment [8], [28]. Thus the bacterium can only grow by means of aerobic and anaerobic respiration, in which it is renowned for its versatility. However, the mechanism by which S. oneidensis controls the transition from aerobiosis to anaerobiosis remains elusive despite several investigations since the predicted major player, EtrA, was identified 16 years ago [14]. It has become apparent that the function of major global regulators, such as ArcA, Crp, and EtrA, is altered in S. oneidensis compared to E. coli[9], [11], [13], [21]. Recently, such an alteration has been clearly demonstrated in regulation of arsenate respiration pathway in Shewanella sp. strain ANA-3 [29]. Crp, rather than EtrA or ArcA, is an essential regulator for arsenate respiration.