Gao Jun-Lian, Turner Sarah Lea, Kan Feng Ling, Wang En Tao, Tan Zhi Yuan, Qiu Yu Hui, Gu Jun, Terefework Zewdu, Young J Peter W, Lindström Kristina, Chen Wen Xin
Department of Biology, University of York, PO Box 373, York Y01 5YW, UK.
Department of Applied Chemistry and Microbiology, Biocenter 1, PO Box 56, FIN-00014, University of Helsinki, Finland.
Int J Syst Evol Microbiol. 2004 Nov;54(Pt 6):2003-2012. doi: 10.1099/ijs.0.02840-0.
Ninety-five rhizobial strains isolated from Astragalus adsurgens growing in the northern regions of China were classified into three main groups, candidate species I, II and III, based on a polyphasic approach. Comparative analysis of full-length 16S rRNA gene sequences of representative strains showed that candidate species I and II were Mesorhizobium, while candidate species III, which consisted of non-nodulating strains, was closely related to Agrobacterium tumefaciens. The phylogenetic relationships of the three candidate species and some related strains were also confirmed by the sequencing of glnA genes, which were used as an alternative chromosomal marker. The DNA-DNA relatedness was between 11.3 and 47.1 % among representative strains of candidate species I and II and the type strains of defined Mesorhizobium species. Candidate III had DNA relatedness of between 4.3 and 25.2 % with type strains of Agrobacterium tumefaciens and Agrobacterium rubi. Two novel species are proposed to accommodate candidate species I and II, Mesorhizobium septentrionale sp. nov. (type strain, SDW014(T)=CCBAU 11014(T)=HAMBI 2582(T)) and Mesorhizobium temperatum sp. nov. (type strain, SDW018(T)=CCBAU 11018(T)=HAMBI 2583(T)), respectively. At least two distinct nodA sequences were identified among the strains. The numerically dominant nodA sequence type was most similar to that from the Mesorhizobium tianshanense type strain and was identified in strains belonging to the two novel species as well as other, as yet, undefined genome types. Host range studies indicate that the different nodA sequences correlate with different host ranges. Further comparative studies with the defined Agrobacterium species are needed to clarify the taxonomic identity of candidate species III.
采用多相分类方法，将从中国北方生长的直立黄芪中分离出的95株根瘤菌菌株分为三个主要类群，即候选种I、II和III。对代表性菌株的全长16S rRNA基因序列进行比较分析表明，候选种I和II属于中慢生根瘤菌属，而由不结瘤菌株组成的候选种III与根癌土壤杆菌密切相关。通过对作为替代染色体标记的谷氨酰胺合成酶基因（glnA）进行测序，也证实了这三个候选种与一些相关菌株的系统发育关系。候选种I和II的代表性菌株与已确定的中慢生根瘤菌属模式菌株之间的DNA-DNA相关性在11.3%至47.1%之间。候选种III与根癌土壤杆菌和悬钩子土壤杆菌模式菌株的DNA相关性在4.3%至25.2%之间。提出了两个新物种来容纳候选种I和II，分别为北方中慢生根瘤菌（Mesorhizobium septentrionale sp. nov.）（模式菌株，SDW014(T)=CCBAU 11014(T)=HAMBI 2582(T)）和温带中慢生根瘤菌（Mesorhizobium temperatum sp. nov.）（模式菌株，SDW018(T)=CCBAU 11018(T)=HAMBI 2583(T)）。在这些菌株中至少鉴定出两种不同的结瘤基因（nodA）序列。数量上占优势的nodA序列类型与来自天山中慢生根瘤菌模式菌株的序列最为相似，并且在属于这两个新物种以及其他尚未确定基因组类型的菌株中也有发现。宿主范围研究表明，不同的nodA序列与不同的宿主范围相关。需要与已确定的土壤杆菌属物种进行进一步的比较研究，以阐明候选种III的分类地位。
