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Appl. Environ. Microbiol., Feb 1995, 623-629, Vol 61, No. 2
P van Berkum, RE Tully and DL Keister
The legume genus Aeschynomene is unusual, since many species develop stem
nodules and the bradyrhizobia isolated from these nodules produce
bacteriochlorophyll (Bchl). Evidence is presented that the bradyrhizobia of
Aeschynomene indica have wide distribution throughout the world, since A.
indica was nodulated when grown in 58 soils collected in 14 different
countries. Only 38 of 79 isolates tested synthesized Bchl and carotenoids
during heterotrophic growth. Nine isolates produced Bchl constitutively,
and cultures were pigmented after growth in the dark. The other isolates
required light for Bchl production. The DNA from seven pigmented and three
nonpigmented bradyrhizobia hybridized with a DNA probe containing the genes
for the photosynthetic apparatus of Rhodobacter capsulatus, but DNA from
two other nonpigmented isolates did not hybridize with this probe. A
relationship between pigmentation in culture and symbiotic phenotype was
not evident, since bradyrhizobia of both Bchl phenotypes nodulated stems of
A. indica and formed nitrogen-fixing symbioses. Several isolates, which
were ineffective on A. indica, probably do belong to the proposed
cross-inoculation group 3 (D. Alazard, Appl. Environ. Microbiol.
50:732-734, 1985), since they did not nodulate Aeschynomene americana or
Macroptilium atropurpureum. Since it has been suggested that extant
rhizobia arose from photosynthetic ancestors (J. I. Sprent, p. 45-54, in P.
M. Gresshoff, L. E. Roth, G. Stacey, and W. E. Newton, ed., Nitrogen
Fixation: Achievements and Objectives, 1990), we propose that the
nonpigmented isolates may represent an extant lineage of an intermediate
evolutionary stage.
Copyright © 1995, American Society for Microbiology
Nonpigmented and Bacteriochlorophyll-Containing Bradyrhizobia Isolated from Aeschynomene indica
Soybean and Alfalfa Research Laboratory, Agricultural Research Service, U.S. Department of Agriculture, Beltsville, Maryland 20705
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