A Transposable Partitioning Locus Used To Stabilize Plasmid-Borne Hydrogen Oxidation and Trifolitoxin Production Genes in a Sinorhizobium Strain

Abstract

Improved nitrogen-fixing inoculum strains for leguminous crops must be able to effectively compete with indigenous strains for nodulation, enhance legume productivity compared to the productivity obtained with indigenous strains, and maintain stable expression of any added genes in the absence of selection pressure. We constructed a transposable element containing the tfx region for expression of increased nodulation competitiveness and the par locus for plasmid stability. The transposon was inserted into tetA of pHU52, a broad-host-range plasmid conferring the H2 uptake phenotype. The resulting plasmid, pHUTFXPAR, conferred the plasmid stability, trifolitoxin production, and H2 uptake phenotypes in the broad-host-range organism Sinorhizobiumsp. strain ANU280. The broad applications of a transposon conferring plasmid stability are discussed.

Significant Yield Increase in Phaseolus vulgaris Obtained by Inoculation with a Trifolitoxin-producing, Hup+ Strain of Rhizobium leguminosarum bv. phaseoli

“…The plasmid used in this work, pHUTFXPAR, was constructed and inserted in Rhizobium leguminosarum bv. phaseoli 127K105a as described by Kent et al (7). The strains used in this work were Rhizobium leguminosarum bv.…”

“…phaseoli 127K105a(pHUTFXPAR). Trifolitoxin production by 127K105a (pHUTFXPAR) was confirmed using the bioassay described previously (7). Bacterial cultures were stored as frozen stock solutions at -75°C in 15% glycerol.…”

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The construction of a stably maintained, broad host range plasmid (pHUTFXPAR) carrying genes that enhance nodulation competitiveness through trifolitoxin production and efficient nitrogen fixation by oxidation of the H 2 evolved from nitrogenase was reported by Kent et al (7). Here the field testing of the efficacy of this construct is reported.

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“…Under field conditions, an inoculum strain that produces this peptide is capable of inducing more nodules than strains that do not produce this peptide (9). Kent et al (7) reported the construction of plasmid pHUTFXPAR that possesses genes coding for increased nodulation competitiveness through trifolitoxin production and increased yield through the Hup + phenotype. Here, the pHUTFXPAR plasmid is added to Rhizobium leguminosarum bv.…”

“…Kent et al (7) reported the construction of plasmid pHUTFXPAR that possesses genes coding for increased nodulation competitiveness through trifolitoxin production and increased yield through the Hup + phenotype. Here, the pHUTFXPAR plasmid is added to Rhizobium leguminosarum bv.…”