Role of the extracytoplasmic function sigma factor CarQ in oxidative response of Bradyrhizobium japonicum

Anchana Thaweethawakorn; Dylan Parks; Jae-Seong So; Woo-Suk Chang

doi:10.1007/s12275-015-5308-9

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Role of the extracytoplasmic function sigma factor CarQ in oxidative response of Bradyrhizobium japonicum: Anchana Thaweethawakorn ¹, Dylan Parks ¹, Jae-Seong So ², Woo-Suk Chang ^1,3; Journal of Microbiology 2015;53(8):526-534.
DOI: https://doi.org/10.1007/s12275-015-5308-9
Published online: July 31, 2015

¹Department of Biology, University of Texas, Arlington, Texas 76019, USA, ²Department of Biological Engineering, Inha University, Incheon 402-751, Republic of Korea, ³Division of Biotechnology, College of Environmental and Bioresource Sciences, Chonbuk National University, Iksan 570-752, Republic of Korea¹Department of Biology, University of Texas, Arlington, Texas 76019, USA, ²Department of Biological Engineering, Inha University, Incheon 402-751, Republic of Korea, ³Division of Biotechnology, College of Environmental and Bioresource Sciences, Chonbuk National University, Iksan 570-752, Republic of Korea

Corresponding author: Woo-Suk Chang , Tel: +1-817-272-3280,

Received: 17 June 2015 • Revised: 17 July 2015 • Accepted: 21 July 2015

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Abstract

As a nitrogen-fixing bacterium, Bradyrhizobium japonicum can establish a symbiotic relationship with the soybean plant (Glycine max). To be a successful symbiont, B. japonicum must deal with plant defense responses, such as an oxidative burst. Our previous functional genomics study showed that carQ (bll1028) encoding extracytoplasmic function (ECF) sigma factor was highly expressed (107.8-fold induction) under oxidative stress. Little is known about the underlying mechanisms of how CarQ responds to oxidative stress. In this study, a carQ knock-out mutant was constructed using site-specific mutagenesis to identify the role of carQ in the oxidative response of B. japonicum. The carQ mutant showed a longer generation time than the wild type and exhibited significantly decreased survival at 10 mM H2O2 for 10 min of exposure. Surprisingly, there was no significant difference in expression of oxidative stress-responsive genes such as katG and sod between the wild type and carQ mutant. The mutant also showed a significant increase in susceptibility to H2O2 compared to the wild type in the zone inhibition assay. Nodulation phenotypes of the carQ mutant were distinguishable compared to those of the wild type, including lower numbers of nodules, decreased nodule dry weight, decreased plant dry weight, and a lower nitrogen fixation capability. Moreover, desiccation of mutant cells also resulted in significantly lower percent of survival in both early (after 4 h) and late (after 24 h) desiccation periods. Taken together, this information will provide an insight into the role of the ECF sigma factor in B. japonicum to deal with a plant-derived oxidative burst.

Keywords: symbiotic nitrogen fixation;oxidative stress;desiccation;soybean;ECF sigma factor;CarQ

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Role of the extracytoplasmic function sigma factor CarQ in oxidative response of Bradyrhizobium japonicum

J. Microbiol. 2015;53(8):526-534. Published online July 31, 2015

DOI: https://doi.org/10.1007/s12275-015-5308-9

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