Bradyrhizobium elkanii rtxC Gene Is Required for Expression of Symbiotic Phenotypes in the Final Step of Rhizobitoxine Biosynthesis

Shin Okazaki, Masayuki Sugawara, Kiwamu Minamisawa

Research output: Contribution to journalArticlepeer-review

26 Citations (Scopus)

Abstract

We disrupted the rtxC gene on the chromosome of Bradyrhizobium elkanii USDA94 by insertion of a nonpolar aph cartridge. The rtxC mutant, designated ΔrtxC, produced serinol and dihydrorhizobitoxine but no rhizobitoxine, both in culture and in planta. The introduction of cosmids harboring the rtxC gene into the ΔrtxC mutant complemented rhizobitoxine production, suggesting that rtxC is involved in the final step of rhizobitoxine biosynthesis in B. elkanii USDA94. Glycine max cv. Lee inoculated with ΔrtxC or with a null mutant, Δrtx::Ω1, showed no foliar chlorosis, whereas the wild-type strain USDA94 caused severe foliar chlorosis. The two mutants showed significantly less nodulation competitiveness than the wild-type strain on Macroptilium atropurpureum. These results indicate that dihydrorhizobitoxine, the immediate precursor of the oxidative form of rhizobitoxine, has no distinct effect on nodulation phenotype in these legumes. Thus, desaturation of dihydrorhizobitoxine by rtxC-encoded protein is essential for the bacterium to show rhizobitoxine phenotypes in planta. In addition, complementation analysis of rtxC by cosmids differing in rtxC transcription levels suggested that rhizobitoxine production correlates with the amount of rtxC transcript.

Original languageEnglish
Pages (from-to)535-541
Number of pages7
JournalApplied and environmental microbiology
Volume70
Issue number1
DOIs
Publication statusPublished - 2004 Jan

ASJC Scopus subject areas

  • Biotechnology
  • Food Science
  • Applied Microbiology and Biotechnology
  • Ecology

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