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Journal of Bacteriology, January 2009, p. 220-230, Vol. 191, No. 1
0021-9193/09/$08.00+0     doi:10.1128/JB.00925-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

RpoHII Activates Oxidative-Stress Defense Systems and Is Controlled by RpoE in the Singlet Oxygen-Dependent Response in Rhodobacter sphaeroides{triangledown} ,{dagger}

Aaron M. Nuss,{ddagger} Jens Glaeser,{ddagger}* and Gabriele Klug

Institut für Mikrobiologie und Molekularbiologie, Universität Giessen, Heinrich-Buff-Ring 26, D-35392 Giessen, Germany

Received 6 July 2008/ Accepted 21 October 2008

Photosynthetic organisms need defense systems against photooxidative stress caused by the generation of highly reactive singlet oxygen (1O2). Here we show that the alternative sigma factor RpoHII is required for the expression of important defense factors and that deletion of rpoHII leads to increased sensitivity against exposure to 1O2 and methylglyoxal in Rhodobacter sphaeroides. The gene encoding RpoHII is controlled by RpoE, and thereby a sigma factor cascade is constituted. We provide the first in vivo study that identifies genes controlled by an RpoHII-type sigma factor, which is widely distributed in the Alphaproteobacteria. RpoHII-dependent genes encode oxidative-stress defense systems, including proteins for the degradation of methylglyoxal, detoxification of peroxides, 1O2 scavenging, and redox and iron homeostasis. Our experiments indicate that glutathione (GSH)-dependent mechanisms are involved in the defense against photooxidative stress in photosynthetic bacteria. Therefore, we conclude that systems pivotal for the organism's defense against photooxidative stress are strongly dependent on GSH and are specifically recognized by RpoHII in R. sphaeroides.

* Corresponding author. Mailing address: Institut für Mikrobiologie und Molekularbiologie, Heinrich-Buff-Ring 26, 35392 Giessen, Germany. Phone: (49) 641 99 355 57. Fax: (49) 641 99 355 49. E-mail: Jens.Glaeser{at}mikro.bio.uni-giessen.de

{triangledown} Published ahead of print on 31 October 2008.

{dagger} Supplemental material for this article may be found at http://jb.asm.org/.

{ddagger} These authors contributed equally to this work.

Journal of Bacteriology, January 2009, p. 220-230, Vol. 191, No. 1
0021-9193/09/$08.00+0     doi:10.1128/JB.00925-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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