Browsing by Author "Buhlers, Deborah"

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    Genetics of Ribitol Catabolism in Rhizobium leguminosarum
    (2019-09-20) Buhlers, Deborah; Hynes, Michael F.; Gieg, Lisa M.; Wong, Sui-Lam; Oresnik, Ivan; Niu, Dongyan
    Rhizobium leguminosarum bv. viciae strain VF39SM contains six plasmids; a strain cured of both pRleVF39c and pRleVF39d is unable to grow on ribitol, whereas strains cured of only one of the plasmids can grow on this substrate. BLAST database searches and previous work show that the pRleVF39d plasmid ribitol catabolic genes are widely distributed among many R. leguminosarum strains. The less common pRleVF39c plasmid locus contains genes encoding a DeoR transcriptional regulator (rlcR), an ATPase component of an ABC transporter (rlcB), a periplasmic binding protein of an ABC transporter (rlcA), two ABC transporter permease components (rlcC, rlcF), a glycerophosphoryl diester phosphodiesterase (rlcG), a hydrolase (rlcH), a ribitol dehydrogenase (rlcD) and a ribulokinase (rlcK). The pRleVF39d locus contains genes encoding a reductase (rldE), a ribitol-2-dehydrogenase (rldD), an ABC transporter permease (rldC), the ATPase of an ABC transporter (rldB), the periplasmic binding protein of an ABC transporter (rldA), and an AraC-like regulator (rldR). Mutagenesis of the genes of these two loci showed that rlcK, rlcD, rldD, rldA, and rldR are required for the catabolism of ribitol. Three c and d plasmid double mutants, rlcK-rldA, rlcK-rldD and rlcK-rldR, were also unable to grow in the presence of ribitol as sole carbon and energy source. The d plasmid ribitol catabolic genes comprise as single operon, while the c plasmid ribitol catabolic genes are in multiple operons, with rlcR and rlcB comprising a divergently transcribed operon, and the remaining c plasmid ribitol catabolic genes making up additional transcripts. The c plasmid ribitol catabolic genes are induced by ribitol and seed exudates of peas, beans and lentils. Nodulation competition assays using ribitol catabolic gene single and double mutants, demonstrated that ribitol catabolism is required for nodulation competitiveness on peas (cv. Little Marvel) and lentils (cv. Marble), but not for vetch or faba beans (cv. Windsor). Ribitol catabolic gene induction during interaction of R. leguminosarum VF39SM with lentils and vetch seedlings also showed that rldR, but not rlcA was induced during early stages of interaction with the roots of lentil seedlings, and that rlcA is induced within the nodules of vetch.