title: Artificial citrate operon and Vitreoscilla hemoglobin gene enhanced mineral phosphate solubilizing ability of Enterobacter hormaechei DHRSS.
abstract: Mineral phosphate solubilization by bacteria is mediated through secretion of organic acids, among which citrate is one of the most effective. To overproduce citrate in bacterial systems, an artificial citrate operon comprising of genes encoding NADH-insensitive citrate synthase of E. coli and Salmonella typhimurium sodium-dependent citrate transporter was constructed. In order to improve its mineral phosphate solubilizing (MPS) ability, the citrate operon was incorporated into E. hormaechei DHRSS. The artificial citrate operon transformant secreted 7.2 mM citric acid whereas in the native strain, it was undetectable. The transformant released 0.82 mM phosphate in flask studies in buffered medium containing rock phosphate as sole P source. In fermenter studies, similar phenotype was observed under aerobic conditions. However, under microaerobic conditions, no citrate was detected and P release was not observed. Therefore, an artificial citrate gene cluster containing Vitreoscilla hemoglobin (vgb) gene under its native promoter, along with artificial citrate operon under constitutive tac promoter, was constructed and transformed into E. hormaechei DHRSS. This transformant secreted 9 mM citric acid under microaerobic conditions and released 1.0 mM P. Thus, incorporation of citrate operon along with vgb gene improves MPS ability of E. hormaechei DHRSS under buffered, microaerobic conditions mimicking rhizospheric environment.
authors.affiliation: Molecular Microbial Biochemistry Laboratory, Department of Biochemistry, Faculty of Science, The M. S. University of Baroda, Vadodara, 390002, Gujarat, India.
authors.forename: Kavita
authors.initials: K
authors.lastname: Yadav
authors.forename: Chanchal
authors.initials: C
authors.lastname: Kumar
authors.forename: G
authors.initials: G
authors.lastname: Archana
authors.forename: G Naresh
authors.initials: GN
authors.lastname: Kumar
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D019343:Citric Acid / Q000378:metabolism; D004754:Enterobacter / Q000235:genetics* / Q000378:metabolism*; D004926:Escherichia coli / Q000235:genetics; D060847:Metabolic Engineering; D009876:Operon; D010710:Phosphates / Q000378:metabolism*; D012988:Soil Microbiology; D054793:Truncated Hemoglobins / Q000235:genetics* / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D010710:Phosphates; D054793:Truncated Hemoglobins; C082613:hemoglobin protein, Vitreoscilla; D019343:Citric Acid