title: Biosynthesis of branched-chain amino acids is essential for effective symbioses between betarhizobia and Mimosa pudica.
abstract: Burkholderia phymatum STM815 and Cupriavidus taiwanensis LMG19424 are betaproteobacterial strains that can effectively nodulate several species of the large legume genus Mimosa. A Tn5 mutant, derived from B. phymatum STM815 (KM60), and another derived from C. taiwanensis LMG19424 (KM184-55) induced Fix(-) nodules on Mimosa pudica. The Tn5-interrupted genes of the mutants showed strong homologies to ilvE, which encodes a branched-chain amino acid aminotransferase, and leuC, which encodes the large subunit of isopropylmalate isomerase. Both enzymes are known to be involved in the biosynthetic pathways for branched-chain amino acids (BCAAs) (leucine, valine and isoleucine). The B. phymatum ilvE mutant, KM60, was not auxotrophic for BCAAs and could grow well on minimal medium with pyruvate as a carbon source and ammonia as a nitrogen source. However, it grew less efficiently than the wild-type (WT) strain when ammonia was substituted with valine or isoleucine as a nitrogen source. The BCAA aminotransferase activity of KM60 was significantly reduced relative to the WT strain, especially with isoleucine and valine as amino group donors. The C. taiwanensis leuC mutant, KM184-55, could not grow on a minimal medium with pyruvate as a carbon source and ammonia as a nitrogen source, but its growth was restored when leucine was added to the medium. The isopropylmalate isomerase activity of KM184-55 was completely lost compared with the WT strain. Both mutants recovered their respective enzyme activities after complementation with the WT ilvE or leuC genes and were subsequently able to grow as well as their parental strains on minimal medium. They were also able to form nitrogen-fixing nodules on M. pudica. We conclude that the biosynthesis of BCAAs is essential for the free-living growth of betarhizobia, as well as for their ability to form effective symbioses with their host plant.
authors.affiliation: Laboratory of Microbiology, Department of Seafood Science, National Kaohsiung Marine University, No. 142, Hai-Chuan Rd, Nan-Tzu, Kaohsiung City 811, Taiwan, ROC.
authors.forename: Wen-Ming
authors.initials: WM
authors.lastname: Chen
authors.affiliation: Soil Ecology, Department of Botany, RWTH Aachen, 52056 Aachen, Germany.
authors.forename: Jurgen
authors.initials: J
authors.lastname: Prell
authors.affiliation: The James Hutton Institute, Invergowrie, Dundee DD2 5DA, UK.
authors.forename: Euan K
authors.initials: EK
authors.lastname: James
authors.affiliation: Department of Marine Biotechnology, National Kaohsiung Marine University, No. 142, Hai-Chuan Rd, Nan-Tzu, Kaohsiung City 811, Taiwan, ROC.
authors.forename: Der-Shyan
authors.initials: DS
authors.lastname: Sheu
authors.affiliation: Department of Marine Biotechnology, National Kaohsiung Marine University, No. 142, Hai-Chuan Rd, Nan-Tzu, Kaohsiung City 811, Taiwan, ROC.
authors.forename: Shih-Yi
authors.initials: SY
authors.lastname: Sheu
mesh_terms: D000597:Amino Acids, Branched-Chain / Q000096:biosynthesis*; D019117:Burkholderia / Q000235:genetics / Q000254:growth & development / Q000378:metabolism / Q000502:physiology*; D003470:Culture Media / Q000737:chemistry; D049921:Cupriavidus / Q000235:genetics / Q000254:growth & development / Q000378:metabolism / Q000502:physiology*; D004251:DNA Transposable Elements; D017353:Gene Deletion; D005798:Genes, Bacterial; D005816:Genetic Complementation Test; D031298:Mimosa / Q000382:microbiology* / Q000502:physiology*; D016254:Mutagenesis, Insertional; D013559:Symbiosis
chemical_list: D000597:Amino Acids, Branched-Chain; D003470:Culture Media; D004251:DNA Transposable Elements