Helene Luisa Caroline Ferraz, Delamuta Jakeline Renata Marçon, Ribeiro Renan Augusto, Hungria Mariangela
Coordenação de Aperfeiçoamento de Pessoal de Nível Superior, SBN, Quadra 2, Bloco L, Lote 06, Edifício Capes, 70.040-020 Brasília, Distrito Federal, Brazil.
Department of Microbiology, Universidade Estadual de Londrina, C.P. 10011, 86057-970 Londrina, Paraná, Brazil.
Int J Syst Evol Microbiol. 2017 Jun;67(6):1827-1834. doi: 10.1099/ijsem.0.001870. Epub 2017 Jun 22.
Some bacteria collectively known as rhizobia can establish symbiotic relationships and the N2-fixation process with several legumes used as green manure, in pastures and for wood production. Symbionts belonging to the genus Bradyrhizobium are predominant in the tropics, and an increasing number of studies report high genetic diversity within the genus. We performed a polyphasic study with two strains belonging to the genus Bradyrhizobium- SEMIA 6399T and SEMIA 6404-isolated from root nodules of Deguelia costata (syn. Lonchocarpus costatus), an important legume native to eastern Brazil. In general, sequences of the 16S rRNA gene were highly conserved in members of the genus Bradyrhizobium, and the two strains were positioned in the Bradyrhizobiumelkanii superclade, sharing 100 % nucleotide identity with Bradyrhizobiumembrapense, Bradyrhizobiumerythrophlei and Bradyrhizobiumviridifuturi. However, multilocus sequence analysis with four housekeeping genes (dnaK, glnII, gyrB and recA) confirmed that the two strains belong to a distinct clade, sharing from 87.7 to 96.1 % nucleotide identity with related species of the genus Bradyrhizobium, being most closely related to B. viridifuturi. Average nucleotide identity of genome sequences between SEMIA 6399T and related species was lower than 92 %, below the threshold of species circumscription. nifH phylogeny clustered the SEMIA strains in a clade separated from other species of the genus Bradyrhizobium, and the nodD phylogeny revealed that SEMIA 6399T presents a more divergent sequence. Other phenotypic and genotypic traits were determined for the new group, and our data support the description of the SEMIA strains as representatives of Bradyrhizobium mercantei sp. nov.; SEMIA 6399T (=CNPSo 1165T=BR 6010T=U675T=LMG 30031T) was chosen as the type strain.
一些统称为根瘤菌的细菌能够与用作绿肥、牧场牧草及木材生产的几种豆科植物建立共生关系并进行固氮过程。缓生根瘤菌属的共生体在热带地区占主导地位，并且越来越多的研究报道该属内具有高度的遗传多样性。我们对从巴西东部本土重要豆科植物——科斯塔塔迪圭利亚（异名：科斯塔图斯刺槐）根瘤中分离得到的两株缓生根瘤菌——SEMIA 6399T和SEMIA 6404进行了多相研究。一般而言，16S rRNA基因序列在缓生根瘤菌属成员中高度保守，这两株菌位于慢生根瘤菌埃尔坎亚种进化枝中，与巴西固氮根瘤菌、赤褐固氮根瘤菌和绿色未来固氮根瘤菌的核苷酸同一性为100%。然而，利用四个管家基因（dnaK、glnII、gyrB和recA）进行的多位点序列分析证实这两株菌属于一个独特的进化枝，与缓生根瘤菌属相关物种的核苷酸同一性为87.7%至96.1%，与绿色未来固氮根瘤菌关系最为密切。SEMIA 6399T与相关物种之间基因组序列的平均核苷酸同一性低于92%，低于物种界定阈值。nifH系统发育分析将SEMIA菌株聚类到一个与缓生根瘤菌属其他物种分离的进化枝中，nodD系统发育分析表明SEMIA 6399T呈现出更为 divergent的序列。我们还确定了这个新类群的其他表型和基因型特征，我们的数据支持将SEMIA菌株描述为新种——默氏缓生根瘤菌的代表；选择SEMIA 6399T（=CNPSo 1165T=BR 6010T=U675T=LMG 30031T）作为模式菌株。
