Glycerol utilization by Rhizobium leguminosarum requires an ABC transporter and affects competition for nodulation

• Published in: Microbiology (Society for General Microbiology) 2012-05, Vol.158 (Pt 5), p.1369-1378
• Main Authors: HAO DING, YIP, Cynthia B, GEDDES, Barney A, ORESNIK, Ivan J, HYNES, Michael F
• Format: Article
• Language: English
• Subjects: Agrobacterium; Agronomy. Soil science and plant productions; ATP-Binding Cassette Transporters - genetics; ATP-Binding Cassette Transporters - metabolism; Bacterial Proteins - genetics; Bacterial Proteins - metabolism; Bacteriology; Biological and medical sciences; Computational Biology; DNA, Bacterial - genetics; Economic plant physiology; Escherichia coli; Fundamental and applied biological sciences. Psychology; Gene Expression Regulation, Bacterial; Genes, Bacterial; Glycerol - metabolism; Glycerol Kinase - metabolism; Glycerophosphates - metabolism; Microbiology; Miscellaneous; Mutagenesis, Insertional; Operon; Pisum sativum - microbiology; Plant Root Nodulation; Plasmids; Pseudomonas aeruginosa; Repressor Proteins - metabolism; Rhizobium etli; Rhizobium leguminosarum; Rhizobium leguminosarum - genetics; Rhizobium leguminosarum - metabolism; Rhizobium leguminosarum - physiology; Sequence Analysis, DNA; Sinorhizobium; Symbiosis (nodules, symbiotic nitrogen fixation, mycorrhiza...)
• ISSN: 1350-0872; 1465-2080
• DOI: 10.1099/mic.0.057281-0

Plasmid curing has shown that the ability to use glycerol as a carbon source is plasmid-encoded in Rhizobium leguminosarum. We isolated the locus responsible for glycerol utilization from plasmid pRleVF39c in R. leguminosarum bv. viciae VF39. This region was analyzed by DNA sequencing and mutagenesis. The locus encompasses a gene encoding GlpR (a DeoR regulator), genes encoding an ABC transporter, and genes glpK and glpD, encoding a kinase and dehydrogenase, respectively. All the genes except the regulatory gene glpR were organized into a single operon, and were required for growth on glycerol. The glp operon was strongly induced by both glycerol and glycerol 3-phosphate, as well as by pea seed exudate. GlpR repressed the operon in the absence of inducer. Mutation of genes encoding the ABC transporter abolished all transport of glycerol in transport assays using radiolabelled glycerol. This confirms that, unlike in other organisms such as Escherichia coli and Pseudomonas aeruginosa, which use facilitated diffusion, glycerol uptake occurs by an active process in R. leguminosarum. Since the glp locus is highly conserved in all sequenced R. leguminosarum and Rhizobium etli strains, as well as in Sinorhizobium spp. and Agrobacterium spp. and other alphaproteobacteria, this process for glycerol uptake is probably widespread. Mutants unable to use glycerol were deficient in competitiveness for nodulation of peas compared with the wild-type, suggesting that glycerol catabolism confers an advantage upon the bacterium in the rhizosphere or in the infection thread.