Genetic diversity of rhizobia isolated from Caragana intermedia in Maowusu sandland, north of China

Abstract

Aims: Thirty-three rhizobial strains isolated from nodules of Caragana intermedia in Maowusu sandland were examined for their genetic diversity and putative phylogenetic position. Methods and Results: Isolates from Caragana intermedia were classified into 12 genotypes by 16S rDNA polymerase chain reaction-restriction fragment length polymorphism (RFLP), which showed no distinct relationships with those of the reference strains. The genotypes of rhizobia were not related to geographical location. Thr 16S rDNA sequence of representative strain GH2001 from dominant genotype 2 shared high homologuey with some Rhizobium species: Rh. giardinii (96AE4%), Rh. huautlense (95AE3%), Rh. galegae (95AE7%), Rh. yanglingense (95AE2%), Rh. mongolense (95AE6%), Rh. radiobacter (99%) and Rh. rubi (98AE3%). Conclusions: A high degree of genetic diversity existed among rhizobia nodulating Caragana intermedia in Maowusu sandland. Most of the new isolates might belong to Rhizobium. Significance and Impact of the Study: The results suggest that the rich diversity of rhizobia might have contributed to the adaptation of the arid region. These strains could be valuable at the economic and ecosystem level.

Mesorhizobiumspp. are the main microsymbionts ofCaraganaspp. grown in Liaoning Province of China

“…grown in Liaoning Province were grouped into the genera Mesorhizobium (109 isolates), Rhizobium (one isolate) and Burkholderia (two isolates) by ARDRA and sequencing of 16S rRNA gene. These results were different from those of Gao et al (2002), who reported that agrobacteria-related strains were the most abundant (42.4%) bacteria in the root nodules of C. intermedia grown in Maowusu sandland (Inner Mongolia, China). Previously, many Agrobacterium strains have been isolated from root nodules and most of them failed to nodulate their hosts of origin (examples are Han et al, 2005;Liu et al, 2005).…”

“…Therefore, the symbiotic characteristic of the Agrobacterium strains of Gao et al (2002) could be questioned as the nodulation ability of their strains was not confirmed by the inoculation and reisolation procedure. If the Agrobacterium strains of Gao et al (2002) were real symbiotic bacteria, the difference between the present results and their results might be related to the geographic origins of the test bacteria, possibly the soil nutrition and pH. The differences among isolation frequencies and richness of protein clusters might also reflect the effects of environmental factors on the rhizobial populations.…”

Genetic diversity and phylogeny of rhizobia isolated from Caragana microphylla growing in desert soil in Ningxia, China

“…These results differed from those of a previous report, in which agrobacteria-related strains were found to be the most abundant bacteria in the root nodules of Caragana intermedia growing in the Maowusu sandland (Inner Mongolia, China) (Gao et al, 2002), as well as a report that Mesorhizobium spp are the main microsymbionts of Caragana spp growing in the Liaoning Province of China (Yan et al, 2007). Caragana sp have the capability for stringent selection of rhizobia symbiotic genotype rather than genomic background, even though lateral transfer of symbiotic genes has been observed in Caragana rhizobia and their biogeography exhibit a clear correlation between rhizobial genospecies and eco-regions (Lu et al, 2009).…”

“…A growing body of evidence has focused on the exploration of Caragana plants for pharmaceutical compounds and bioremediation potential. However, few studies have focused on the symbiotic characteristics of the plant (Tan et al, 1999;Gao et al, 2002;Yan et al, 2007).…”

Different Mesorhizobium species associated with Caragana carry similar symbiotic genes and have common host ranges

“…Caragana species are deciduous shrubs or small trees mainly growing in the arid and semi-arid regions of Asia and Eastern Europe. Belonging to the tribe Galegae, most species of Caragana, Astragalus, Glycyrrhiza, Colutea, Sphaerophysa, Halimodendron, Oxytropis, Gueldenstaedtia, Tibetia, Alhagi and Galega form nitrogen-fixing nodules on their roots with species of the genera Mesorhizobium, Rhizobium and Bradyrhizobium (Chen et al, 1995;Lindström & Lehtomäk, 1988;Gao et al, 2001Gao et al, , 2002Tan et al, 2001;Fernando et al, 2005;Yan et al, 2007).…”