TRIFOLITOXIN PRODUCTION IN RHIZOBIUM-ETLI STRAIN CE3 INCREASES COMPETITIVENESS FOR RHIZOSPHERE COLONIZATION AND ROOT NODULATION OF PHASEOLUS-VULGARIS IN SOIL
Ea. Robleto et al., TRIFOLITOXIN PRODUCTION IN RHIZOBIUM-ETLI STRAIN CE3 INCREASES COMPETITIVENESS FOR RHIZOSPHERE COLONIZATION AND ROOT NODULATION OF PHASEOLUS-VULGARIS IN SOIL, Molecular plant-microbe interactions, 10(2), 1997, pp. 228-233
The effect of trifolitoxin (TFX) production by Rhizobium etli on rhizo
sphere colonization and competition for nodulation in soil conditions
was determined. TFX is a potent peptide antibiotic made by Rhizobium l
eguminosarum by. trifolii T24 that inhibits many a-proteobacteria (E.
W. Triplett, B, T. Breil, and G. A. Splitter, Appl. Environ. Microbiol
. 60:4163-4166, 1994). Seeds of Phaseolus vulgaris were inoculated wit
h a TFX-sensitive reference strain and either of two isogenic strains
that differ only in their ability to produce TFX. The pair of strains
were inoculated at different ratios in sterile and nonsterile soil. Th
e representation of the strains in the rhizosphere and nodules was det
ermined at 96 h after inoculation and 3 weeks after planting respectiv
ely. The TFX-producing strain was significantly more competitive for b
oth phenotypes versus the TFX-sensitive strain, compared with the TFX-
nonproducing strain versus the TFX-sensitive strain. These results sho
w that nodule occupancy by inoculant strains, often displaced from the
nodules by indigenous strains, can be increased by addition of the TF
X production phenotype to R. etli in plants grown in either sterile or
nonsterile soil. Also, this work shows the efficacy of the TFX system
for the first time on a legume host with determinant nodules.