title: Characterization of a symbiotically defective serine auxotroph of Mesorhizobium ciceri.
abstract: A Tn5-induced mutant strain (TL68) of Mesorhizobium ciceri unable to grow with ammonium as the sole nitrogen source was isolated and characterized. Unlike its wild-type parent (strain TAL620), the mutant had an absolute dependence on serine to grow. Cloning of the DNA region containing Tn5 and sequence analysis showed that Tn5 was inserted into the gene coding for 3-phosphoglycerate dehydrogenase, which catalyses the first step in the serine biosynthetic pathway. The role of serine biosynthesis of M. ciceri in the establishment of nitrogen-fixing symbiosis with chickpea (Cicer arietinum L) was investigated using the mutant TL68. The serA(-) mutant (TL68) was unable to elicit the development of efficient nodules on the roots of Cicer arietinum L. The addition of serine to the plant-growth medium restored the ability of the mutant to nodulate Cicer arietinum, and the nodules were able to fix nitrogen.
authors.affiliation: Institute of Life Sciences, Department of Biotechnology, Bhubaneswar, India. subratkdas@hotmail.com
authors.forename: Subrata K
authors.initials: SK
authors.lastname: Das
authors.forename: Uma Shankar
authors.initials: US
authors.lastname: Gautam
authors.forename: Pran K
authors.initials: PK
authors.lastname: Chakrabartty
authors.forename: Aqbal
authors.initials: A
authors.lastname: Singh
mesh_terms: D020561:Alphaproteobacteria / Q000378:metabolism*; D029863:Cicer / Q000382:microbiology*; D003470:Culture Media; D008969:Molecular Sequence Data; D016254:Mutagenesis, Insertional; D009586:Nitrogen Fixation; D018517:Plant Roots / Q000382:microbiology; D012694:Serine / Q000378:metabolism*; D013559:Symbiosis / Q000235:genetics*
chemical_list: D003470:Culture Media; D012694:Serine