Diversity of rhizobia associated with Amorpha fruticosa isolated from Chinese soils and description of Mesorhizobium amorphae sp. nov.

Abstract

Fifty-five Chinese isolates from nodules of Amorpha fruticosa were characterized and compared with the type strains of the species and genera of bacteria which form nitrogen-f ixing symbioses with leguminous host plants. A polyphasic approach, which included RFLP of PCR-amplif ied 165 rRNA genes, multilocus enzyme electrophoresis (MLEE), DNA-DNA hybridization, 165 rRNA gene sequencing, electrophoretic plasmid profiles, cross-nodulation and a phenotypic study, was used in the comparative analysis. The isolates originated from several different sites in China and they varied in their phenotypic and genetic characteristics. The majority of the isolates had moderate to slow growth rates, produced acid on YMA and harboured a 930 kb symbiotic plasmid (pSym). Five different RFLP patterns were identified among the 16s rRNA genes of all the isolates. Isolates grouped by PCR-RFLP of the 165 rRNA genes were also separated into groups by variation in MLEE profiles and by DNA-DNA hybridization. A representative isolate from each of these DNA homology groups had a separate position in a phylogenetic tree as determined from sequencing analysis of the 165 rRNA genes. A new species, Mesorhizobium amorphae, is proposed for the majority of the isolates, which belonged to a moderately slow-to slow-growing, acid-producing group based upon their distinct phylogenetic position, their unique electrophoretic type, their low DNA homology with reference strains representing the species within the genus Mesorhizobium and their distinct phenotypic features. Strain ACCC 19665 was chosen as the type strain for M. amorphae sp. nov.

Mesorhizobium septentrionale sp. nov. and Mesorhizobium temperatum sp. nov., isolated from Astragalus adsurgens growing in the northern regions of China

“…Species identification is normally based upon both genetic or genomic comparison and phenotypic characterization. Genetic distance of 0?5 in multilocus enzyme electrophoresis (Martínez-Romero et al, 1991;Wang et al, 1999), 70 % DNA-DNA relatedness in DNA hybridization Wayne et al, 1987) and 80 % similarity in numerical taxonomy (Chen et al, 1991;Gao et al, 1994) have been used or suggested as reference borders for species differentiation. These values are used in relevant analyses in this work.…”

“…Colonies on YMA medium are circular, convex, translucent and have a diameter of 1 mm within 7-10 days at 28 u C. The generation times are 5-9 h in PY broth (Wang et al, 1999 The type strain is SDW018 T (=CCBAU 11018 T =HAMBI 2583 T ); it has the characteristics described for the species. The G+C content of the genomic DNA of the type strain is 65?1 %.…”

“…Colonies on YMA medium are circular, convex, translucent and have a diameter of 1 mm within 7-10 days at 28 u C. Generation times are 6-9 h in PY broth (Wang et al, 1999). Can use fructose, glucose, inositol, malate, maltose, D-mannose, melibiose, sodium succinate, D-sorbitol, sucrose, trehalose and turanose as sole carbon sources, and use hypoxanthine, L-isoleucine, L-phenylalanine and D-threonine as sole nitrogen sources.…”

Insights learned from pBTAi1, a 229-kb accessory plasmid from Bradyrhizobium sp. strain BTAi1 and prevalence of accessory plasmids in other Bradyrhizobium sp. strains

“…In the soybean symbiont Bradyrhizobium japonicum, symbiosisrelated and hydrogenase genes are localized to on a 611-kb chromosomal-borne symbiosis island that displays a distinct distribution of insertion sequence elements relative to the rest of the chromosome (Gottfert et al, 2001;Kaneko et al, 2002). Interestingly, while Mesorhizobium loti has a chromosomal-borne symbiosis island, the moderately slow-growing Mesorhizobium amorphae was found to carry a 930-kb pSym (Wang et al, 1999).…”

Mesorhizobium alhagi sp. nov., isolated from wild Alhagi sparsifolia in north-western China

“…Several novel rhizobial taxa have been described from this region: the genus Sinorhizobium (Chen et al, 1988) and species Mesorhizobium tianshanense (Chen et al, 1995), Mesorhizobium amorphae (Wang et al, 1999), Sinorhizobium xinjiangense (Chen et al, 1988;Peng et al, 2002), Sinorhizobium kummerowiae (Wei et al, 2003), Rhizobium yanglingense (Tan et al, 2001), Rhizobium indigoferae (Wei et al, 2002) and Rhizobium loessense (Wei et al, 2003). In this paper we describe some isolates from the legume Alhagi sparsifolia, which grows wild in this region.…”