Horizontal Transfer of Nodulation Genes in Soils and Microcosms from Bradyrhizobium japonicum to B. elkanii.

Abstract

We investigated the horizontal transfer of nodulation (nod) genes to a Bradyrhizobium elkanii strain, lacking common nod genes as a recipient, in soils and microcosms using selection systems of antibiotic resistance and legume nodulation. We observed the horizontal transfer of nod genes at 4°C in Nakazawa soil where peculiar strains (HRS strains) of B. japonicum harboring high copy numbers of insertion sequences dominated. In microcosms containing HRS strains as donors, we detected a similar horizontal transfer from B. japonicum HRS strain NK5 to the B. elkanii recipient more efficiently at 4°C, which was verified by examining hybridization, nodulation and Nod factor production. These traits were, however, gradually lost during successive cultures. Plasmid analysis indicated that this event was not due to the simple transfer of plasmid carrying common nod genes. These results suggest the potential for horizontal transfer of nod genes among bradyrhizobia and other bacterial populations in soil environments.

Stress Tolerance and Symbiotic and Phylogenic Features of Root Nodule Bacteria Associated with Medicago Species in Different Bioclimatic Regions of Tunisia

“…This mechanism is also responsible for speciation and sub-speciation in bacteria (6). In the case of rhizobia, Minamisawa et al (22) suggested the potential horizontal transfer of nod genes among bradyrhizobia and other bacterial populations in soil environments. Similarly, Bailly et al (2) suggested that during the evolution of Medicago symbionts, horizontal transfer of nod genes might have occurred either to the common ancestor of the two Ensifer species or to one Ensifer species followed by the other.…”

Symbiotic Bradyrhizobium japonicum Reduces N 2 O Surrounding the Soybean Root System via Nitrous Oxide Reductase

“…The surface-sterilized soybean seeds (Glycine max cv. Enrei) were germinated and transplanted to a Leonard jar (25,48), which contained sterile vermiculite and nitrogen-free sterilized nutrient solution (31,39). The cell suspension of B. japonicum (1 ml) was used for inoculation at 1 ϫ 10 7 cells per seed.…”

“…For the nitrogen fixation experiment, soybeans were grown in pots (1 liter) filled with vermiculite in a phytotron (Koitotron type KC; Koito Industries, Tokyo, Japan). A nitrogen-free sterilized nutrient solution was periodically supplied to the pots (31,39). N 2 O uptake, 15 N-N 2 emission, and 15 N incorporation by nodules.…”

“…The whole root system of 32-day-old soybean plants was inserted into a 51-ml test tube (19.4 mm in diameter by 176 mm in height) containing 20 ml nitrogenfree nutrient solution (31,39). The test tube was sealed with a silicon rubber stopper with a gas sampling port and a hole in the center.…”

Genome Analysis Suggests that the Soil Oligotrophic Bacterium Agromonas oligotrophica (Bradyrhizobium oligotrophicum) Is a Nitrogen-Fixing Symbiont of Aeschynomene indica

“…The seeds were then immersed in 0.5% (vol/vol) sodium hypochlorite for 1 min and washed 10 times with sterile distilled water. Finally, the seeds were placed in sterilized plates containing tissue paper wetted with sterile distilled water for 2 days at 30°C in the dark and then transplanted to a Leonard jar (CUL-JAR300; Asahi Glass Co., Ltd., Tokyo, Japan) containing sterile vermiculite and nitrogen-free nutrient solution (28). After transplantation, the seedlings were inoculated with bacteria at 1 ϫ 10 8 cells per plant.…”