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Sinorhizobium meliloti 1021 Loss-of-Function Deletion Mutation in chvI and Its Phenotypic Characteristics

February 2010 , Volume 23 , Number  2
Pages  153 - 160

Chunxia Wang,1 Jocelyn Kemp,1 Isabel O. Da Fonseca,1 Raymie C. Equi,1 Xiaoyan Sheng,1 Trevor C. Charles,2 and Bruno W. S. Sobral1

1Virginia Bioinformatics Institute, Virginia Polytechnic Institute and State University, Blacksburg 24061, U.S.A.; 2Department of Biology, University of Waterloo, Waterloo, ON, N2L 3G1, Canada

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Accepted 15 October 2009.

Bacterial two-component regulatory systems (TCS) are common components of complex regulatory networks and cascades. In Sinorhizobium meliloti, the TCS ExoS/ChvI controls exopolysaccharide succinoglycan production and flagellum biosynthesis. Although this system plays a crucial role in establishing the symbiosis between S. meliloti and its host plant, it is not well characterized. Attempts to generate complete loss-of-function mutations in either exoS or chvI in S. meliloti have been unsuccessful; thus, it was previously suggested that exoS or chvI are essential genes for bacterial cell growth. We constructed a chvI mutant by completely deleting the open reading frame encoding this gene. The mutant strain failed to grow on complex medium, exhibited lower tolerance to acidic condition, produced significantly less poly-3-hydroxybutyrate than the wild type, was hypermotile, and exhibited an altered lipopolysaccharide profile. In addition, this mutant was defective in symbiosis with Medicago truncatula and M. sativa (alfalfa), although it induced root hair deformation as efficiently as the wild type. Together, our results demonstrate that ChvI is intimately involved in regulatory networks involving the cell envelope and metabolism; however, its precise role within the regulatory network remains to be determined.

© 2010 The American Phytopathological Society