title: Identification of a functional 2-keto-myo-inositol dehydratase gene of Sinorhizobium fredii USDA191 required for myo-inositol utilization.
abstract: Sinorhizobium fredii USDA191 is a Gram-negative bacterium capable of forming nitrogen-fixing nodules on soybean roots. The USDA191 idhA gene encoding myo-inositol dehydrogenase, an enzyme necessary for myo-inositol utilization, is known to be involved in competitive nodulation and nitrogen fixation. In Bacillus subtilis, myo-inositol dehydrogenase catalyzes the first step of the myo-inositol catabolic pathway. Recently iolE was identified as the gene encoding 2-keto-myo-inositol dehydratase, which catalyzes the second step in the pathway. Here we report the presence of 2-keto-myo-inositol dehydratase activity in free-living USDA191 cells cultured in a medium containing myo-inositol. An iolE ortholog was cloned from USDA191. USDA191 iolE was expressed in Escherichia coli as a His(6)-tag fusion and purified to exhibit 2-keto-myo-inositol dehydratase activity. Inactivation of USDA191 iolE led to defective myo-inositol utilization. USDA191 iolE partially complemented a B. subtilis iolE deficient mutant. These results suggest that S. fredii USDA191 utilizes a myo-inositol catabolic pathway, analogous to that of B. subtilis, involving at least idhA and iolE.
authors.affiliation: Department of Biofunctional Chemistry, Kobe University. kenyoshi@kobe-u.ac.jp
authors.forename: Ken-Ichi
authors.initials: K
authors.lastname: Yoshida
authors.forename: Won-Seok
authors.initials: WS
authors.lastname: Kim
authors.forename: Masaki
authors.initials: M
authors.lastname: Kinehara
authors.forename: Rie
authors.initials: R
authors.lastname: Mukai
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Ashida
authors.forename: Hideki
authors.initials: H
authors.lastname: Ikeda
authors.forename: Yasutaro
authors.initials: Y
authors.lastname: Fujita
authors.forename: Hari B
authors.initials: HB
authors.lastname: Krishnan
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D003001:Cloning, Molecular; D017931:DNA Primers; D005798:Genes, Bacterial; D006836:Hydro-Lyases / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D007294:Inositol / Q000378:metabolism*; D008969:Molecular Sequence Data; D017386:Sequence Homology, Amino Acid; D042181:Sinorhizobium fredii / Q000201:enzymology* / Q000235:genetics
chemical_list: D017931:DNA Primers; D007294:Inositol; D006836:Hydro-Lyases