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Journal of Bacteriology, August 2005, p. 5683-5690, Vol. 187, No. 16
0021-9193/05/$08.00+0     doi:10.1128/JB.187.16.5683-5690.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

Biochemical Characterization of RssA-RssB, a Two-Component Signal Transduction System Regulating Swarming Behavior in Serratia marcescens

Jun-Rong Wei,¹ Yu-Huan Tsai,¹ Po-Chi Soo,¹ Yu-Tze Horng,¹ Shang-Chen Hsieh,¹ Shen-Wu Ho,^1,2 and Hsin-Chih Lai^1,2*

Department of Clinical Laboratory Sciences and Medical Biotechnology, National Taiwan University College of Medicine, Taipei, Taiwan, Republic of China,¹ Department of Laboratory Medicine, National Taiwan University Hospital, Taipei, Taiwan, Republic of China²

Received 17 February 2005/ Accepted 16 May 2005

Our previous study had identified a pair of potential two-component signal transduction proteins, RssA-RssB, involved in the regulation of Serratia marcescens swarming. When mutated, both rssA and rssB mutants showed precocious swarming phenotypes on LB swarming agar, whereby swarming not only occurred at 37°C but also initiated on a surface of higher agar concentration and more rapidly than did the parent strain at 30°C. In this study, we further show that the predicted sensor kinase RssA and the response regulator RssB bear characteristics of components of the phosphorelay signaling system. In vitro phosphorylation and site-directed mutagenesis assays showed that phosphorylated RssA transfers the phosphate group to RssB and that histidine 248 and aspartate 51 are essential amino acid residues involved in the phosphotransfer reactions in RssA and RssB, respectively. Accordingly, while wild-type rssA could, the mutated rssA(H248A) in trans could not complement the precocious swarming phenotype of the rssA mutant. Although RssA-RssB regulates expressions of shlA and ygfF of S. marcescens (ygfF_Sm), in vitro DNA-binding assays showed that the phosphorylated RssB did not bind directly to the promoter regions of these two genes but bound to its own rssB promoter. Subsequent assays located the RssB binding site within a 63-bp rssB promoter DNA region and confirmed a direct negative autoregulation of the RssA-RssB signaling pathway. These results suggest that when activated, RssA-RssB acts as a negative regulator for controlling the initiation of S. marcescens swarming.

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* Corresponding author. Mailing address: Department of Clinical Laboratory Sciences and Medical Biotechnology, National Taiwan University College of Medicine, No. 1. Chang-Der Street, Taipei 100, Taiwan, Republic of China. Phone: 886 2 2312-3456, ext. 6931. Fax: 886 2 2371-1574. E-mail: hclai{at}ha.mc.ntu.edu.tw.

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Journal of Bacteriology, August 2005, p. 5683-5690, Vol. 187, No. 16
0021-9193/05/$08.00+0     doi:10.1128/JB.187.16.5683-5690.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

This article has been cited by other articles:

• Soo, P.-C., Horng, Y.-T., Wei, J.-R., Shu, J.-C., Lu, C.-C., Lai, H.-C. (2008). Regulation of Swarming Motility and flhDCSm Expression by RssAB Signaling in Serratia marcescens. J. Bacteriol. 190: 2496-2504 [Abstract] [Full Text]  
• Wei, J.-R., Tsai, Y.-H., Horng, Y.-T., Soo, P.-C., Hsieh, S.-C., Hsueh, P.-R., Horng, J.-T., Williams, P., Lai, H.-C. (2006). A Mobile Quorum-Sensing System in Serratia marcescens. J. Bacteriol. 188: 1518-1525 [Abstract] [Full Text]