Biodiversity and Biogeography of Rhizobia Associated with Soybean Plants Grown in the North China Plain

Abstract

As the putative center of origin for soybean and the second largest region of soybean production in China, the North China Plain covers temperate and subtropical regions with diverse soil characteristics. However, the soybean rhizobia in this plain have not been sufficiently studied. To investigate the biodiversity and biogeography of soybean rhizobia in this plain, a total of 309 isolates of symbiotic bacteria from the soybean nodules collected from 16 sampling sites were studied by molecular characterization. These isolates were classified into 10 genospecies belonging to the genera Sinorhizobium and Bradyrhizobium, including four novel groups, with S. fredii (68.28%) as the dominant group. The phylogeny of symbiotic genes nodC and nifH defined four lineages among the isolates associated with Sinorhizobium fredii, Bradyrhizobium elkanii, B. japonicum, and B. yuanmingense, demonstrating the different origins of symbiotic genes and their coevolution with the chromosome. The possible lateral transfer of symbiotic genes was detected in several cases. The association between soil factors (available N, P, and K and pH) and the distribution of genospecies suggest clear biogeographic patterns: Sinorhizobium spp. were superdominant in sampling sites with alkaline-saline soils, while Bradyrhizobium spp. were more abundant in neutral soils. This study clarified the biodiversity and biogeography of soybean rhizobia in the North China Plain.

Genetic Diversity and Evolution of Bradyrhizobium Populations Nodulating Erythrophleum fordii, an Evergreen Tree Indigenous to the Southern Subtropical Region of China

“…This result confirmed a previous finding that the symbiotic genes could be spread by lateral gene transfer among different genera and species (49). The lateral gene transfer that occurs in rhizobial strains is an important way of forming novel species, to improve their biodiversity and adaptation capacity, even though lateral transfer happens only rarely (6). These results also suggested that the symbiotic genes had taxonomic values, beyond determination of their host specificity (40), even though they are located on transferable symbiotic islands or plasmids (50,51).…”

“…Intensive research on these symbiotic bacteria has been performed around the world. All the rhizobial strains or populations have been shown to have a specific host spectrum, although the same plant species can form symbiotic relationships with distinct rhizobia in different geographic regions (5,6). Therefore, novel rhizobia or new symbiotic associations between rhizobia and legumes might be found by studying the rhizobia associated with legumes grown in different regions or by investigating legumes in which the rhizobia have not yet been studied.…”

The tRNA arg Gene and engA Are Essential Genes on the 1.7-Mb pSymB Megaplasmid of Sinorhizobium meliloti and Were Translocated Together from the Chromosome in an Ancestral Strain

“…The Sinorhizobium genus is expanding as new root nodule isolates are identified from diverse leguminous plants and geographic regions (14,43,56,(77)(78)(79). It will be interesting to see how the chromosome or megaplasmid location of the engA and tRNA arg genes segregates in these newly identified Sinorhizobium species.…”

Bradyrhizobium daqingense sp. nov., isolated from soybean nodules

“…Previously, B. japonicum, B. elkanii, B. liaoningense, B. yuanmingense, Ensifer fredii and Ensifer sojae (Han et al, 2009;Li et al, 2011a;Man et al, 2008;Wang et al, 2009;Xu et al, 1995) have been isolated from root nodules of soybean grown in different regions of China. Clear biogeographic patterns have been revealed in the soybean rhizobia and soil types seemed to be the main determinant of the biogeography of these bacteria (Han et al, 2009;Li et al, 2011b;Man et al, 2008;Zhang et al, 2011).…”