novel Sinorhizobium meliloti operon encodes and alpha-glucosidase and a periplasmic-binding-protein-dependent transport system for alpha-glucosides

• Published in: Journal of Bacteriology 1999-07, Vol.181 (14), p.4176-4184
• Main Authors: Willis, L.B, Walker, G.C
• Format: Article
• Language: English
• Subjects: active transport; alpha-glucosidase; alpha-Glucosidases - genetics; alpha-Glucosidases - metabolism; amino acid sequences; atp-dependent inner membrane permease; bacterial proteins; Bacterial Proteins - genetics; Bacterial Proteins - metabolism; Bacteriology; Base Sequence; binding proteins; Biological Transport, Active; carbohydrate metabolism; Carrier Proteins - genetics; Carrier Proteins - metabolism; Chromosome Mapping; Cosmids - genetics; Cupriavidus necator - genetics; Cupriavidus necator - growth & development; Disaccharides - metabolism; DNA Transposable Elements; esterases; genbank/af045609; gene transfer; Genes; Genes, Bacterial; genetic transformation; Glucosides - metabolism; Gram-negative bacteria; maltose; Medicago sativa; Metabolism; Molecular Sequence Data; Mutagenesis; mutants; nitrogen fixation; nucleotide sequences; Operon; Periplasm - metabolism; phosphogluconolactonase; Plant Microbiology; plasma membrane; Proteins; Ralstonia eutropha; regulator genes; repetitive sequences; Rhizobiaceae; Sequence Analysis, DNA; Sinorhizobium meliloti; Sinorhizobium meliloti - enzymology; Sinorhizobium meliloti - genetics; sucrose; Sucrose - metabolism; Sugar; transcription factors; trehalose; uptake
• ISSN: 0021-9193; 1098-5530; 1067-8832
• DOI: 10.1128/jb.181.14.4176-4184.1999

The most abundant carbon source transported into legume root nodules is photosynthetically produced sucrose, yet the importance of its metabolism by rhizobia in planta is not yet known. To identify genes involved in sucrose uptake and hydrolysis, we screened a Sinorhizobium meliloti genomic library and discovered a segment of S. meliloti DNA which allows Ralstonia eutropha to grow on the alpha-glucosides sucrose, maltose, and trehalose. Tn5 mutagenesis localized the required genes to a 6.8-kb region containing five open reading frames which were named agl, for alpha-glucoside utilization. Four of these (aglE, aglF, aglG, and aglK) appear to encode a periplasmic-binding-protein-dependent sugar transport system, and one (aglA) appears to encode an alpha-glucosidase with homology to family 13 of glycosyl hydrolases. Cosmid-borne agl genes permit uptake of radio-labeled sucrose into R. eutropha cells. Analysis of the properties of agl mutants suggests that S. meliloti possesses at least one additional alpha-glucosidase as well as a lower-affinity transport system for alpha-glucosides. It is possible that the Fix+ phenotype of agl mutants on alfalfa is due to these additional functions. Loci found by DNA sequencing to be adjacent to aglEFGAK include a probable regulatory gene (aglR), zwf and edd, which encode the first two enzymes of the Entner-Doudoroff pathway, pgl, which shows homology to a gene encoding a putative phosphogluconolactonase, and a novel Rhizobium-specific repeat element.