Mutation in the cobO gene generates auxotrophy for cobalamin and methionine and impairs the symbiotic properties of Sino
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ORIGINAL PAPER
Mutation in the cobO gene generates auxotrophy for cobalamin and methionine and impairs the symbiotic properties of Sinorhizobium fredii HH103 with soybean and other legumes Carlos Medina · Juan Carlos Crespo-Rivas · Javier Moreno · María Rosario Espuny · María Teresa Cubo
Received: 16 April 2008 / Revised: 26 June 2008 / Accepted: 25 July 2008 / Published online: 22 August 2008 © Springer-Verlag 2008
Abstract We report here the isolation of a methionine and cobalamin mutant strain (SVQ336) of Sinorhizobium fredii HH103 obtained by Tn5-lacZ mutagenesis. Sequence analysis showed that the transposon was inserted into a gene homologous to cobO. This gene codes for a cobalamin adenosyltransferase which is involved in the biosynthesis of vitamin B12. Another HH103 cobO mutant (strain SVQ524), was constructed by the insertion of interposon. Both cobO mutants required the addition of methionine because cobalamin acts as a cofactor of the enzyme MetH, which catalyses the last step of the methionine biosynthesis. Mutant SVQ524 failed to nodulate on Vigna radiate but was able to nodulate on Glycine max cvs. Williams and Peking and Cajanus cajan, although the total number of nodules formed was highly reduced in comparison with that of plants inoculated with the wild-type strain
Communicated by Ursula Priefer. Electronic supplementary material The online version of this article (doi:10.1007/s00203-008-0424-0) contains supplementary material, which is available to authorized users. C. Medina · J. C. Crespo-Rivas · M. R. Espuny · M. T. Cubo (&) Department of Microbiology, Faculty of Biology, University of Sevilla, Reina Mercedes, 6, 41012 Seville, Spain e-mail: [email protected] J. Moreno Department of Cellular Biology, Faculty of Biology, University of Sevilla, Reina Mercedes, 6, 41012 Seville, Spain Present Address: C. Medina Área de Microbiología, Centro Andaluz de Biología del Desarrollo, Universidad Pablo de Olavide/CSIC, Ctra. Utrera Km 1, 41013 Seville, Spain
HH103. The roots of these plants did not seem to secrete enough cobalamin and/or methionine to support growth of cobalamin/methionine auxotrophs in the rhizosphere. In all cases, the phenotype of SVQ524 was nearly overcome by the addition of methionine or cobalamin to the plant growth media or by the presence of a copy of the cobO gene in cosmid pMUS756. Keywords Sinorhizobium fredii · Cobalamin · Methionine · Root exudation · Nodulation
Introduction Rhizobia are nitrogen-Wxing bacteria that are able to invade the roots of leguminous plants and trigger the formation of the nodule, a new plant structure that contains the nitrogenWxing microsymbiont. Infection and nodule development are highly speciWc and depend on both partners, the bacterium and the plant, to be eVective. During the symbiotic process, the host plant roots secrete Xavonoids that induce the rhizobial nodulation genes (nod, nol, and noe genes). Many of these genes are involved in the synthesis and secretion of host-speciWc lipooligosaccharide signal molecules that cause root hair curling a
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