Agricultural Research Council-Plant Health and Protection (ARC-PHP), P. Bag X134, Queenswood, Pretoria, 0121, South Africa.
ARC-PHP, P. Bag X5017, Vredenberg, Stellenbosch, South Africa.
World J Microbiol Biotechnol. 2020 Feb 24;36(3):40. doi: 10.1007/s11274-020-2811-x.
Recent developments in the legume rhizobium symbiotic interaction particularly those related to the emergence of novel strains of bacteria that nodulate and fix nitrogen in legumes is gaining momentum. These novel strains of bacteria were mostly isolated from the root nodules of indigenous and invasive legumes belonging to the sub families Papilionoideae and Mimosoideae in South Africa, South America and South East China. These rhizobia are phylogenetically and taxonomically different from the traditional 'alpha rhizobia' and are termed 'β-rhizobia' as they belong to the β-sub class of Proteobacteria. There are also new reports of novel species of root nodulating bacteria from the α-Proteobacteria, not known for several decades since the discovery of rhizobia. However, in this review focus is given to the emerging β-rhizobia isolated from the indigenous Papilionoid legumes in the Cape Floristic regions in South Africa and the indigenous and invasive Mimosoid legumes in South America and South East Asia respectively. The nodulation of the indigenous South African Papilionoid legumes including that of Aspalathus linearis (rooibos) is discussed in a bit detail. Previous reports indicated that A. linearis is very specific in its rhizobium requirement and was reported to be nodulated by the slow growing Bradyrhizobium spp. This review however summarizes that the bacteria associated with the root nodules of A. linearis belong to members of both the alpha (α) Proteobacteria that include Mesorhizobium, Rhizobium and Bradyrhizobium spp. and the beta (β) Proteobacteria represented by the genus Burkholderia (now reclassified as Paraburkholderia). In addition, the occurrence of Paraburkholderia as the newly emerging root nodule symbionts of various other legumes has been discussed. In doing so, the review highlights that nodulation is no longer restricted to the traditional 'rhizobia' group following the emergence of the new beta rhizobia as potential nodulators of various indigenous legumes. It thus provides some insights on the status of the legume-rhizobium host specificity concept and the loss of this specificity in several symbiotic associations that puts the long held dogma of host specificity of the legume rhizobium symbiosis in a dilemma.
豆科植物根瘤菌共生相互作用的最新进展，特别是与新型细菌菌株的出现有关，这些细菌菌株能够在豆科植物中结瘤和固氮，这一趋势正在增强。这些新型细菌菌株主要是从南非、南美洲和东南亚的豆科植物根瘤中分离出来的，这些豆科植物属于 Papilionoideae 和 Mimosoideae 亚科。这些根瘤菌在系统发育和分类上与传统的“α根瘤菌”不同，被称为“β根瘤菌”，因为它们属于β-变形菌亚类。也有新的报道称，来自α-变形菌的新型根瘤菌能够结瘤，这是自发现根瘤菌以来几十年都未曾有过的发现。然而，在本次综述中，重点关注了从南非开普植物区系中的本土豆科植物中分离出来的新兴β根瘤菌，以及分别从南美洲和东南亚的本土和入侵性含羞草科植物中分离出来的β根瘤菌。南非本土豆科植物（包括 Aspalathus linearis（罗布斯塔））的结瘤情况被详细讨论。先前的报告表明，A. linearis 在根瘤菌的需求方面非常特殊，仅被生长缓慢的 Bradyrhizobium spp. 结瘤。然而，本次综述总结了与 A. linearis 根瘤相关的细菌属于α（α）变形菌，包括 Mesorhizobium、Rhizobium 和 Bradyrhizobium spp.，以及β（β）变形菌，代表属 Burkholderia（现重新分类为 Paraburkholderia）。此外，还讨论了 Paraburkholderia 作为各种其他豆科植物新出现的根瘤共生体的出现。通过这样做，该综述强调了随着新型β根瘤菌的出现，结瘤不再仅限于传统的“根瘤菌”群体，因为新型β根瘤菌可能成为各种本土豆科植物的潜在结瘤菌。因此，这为豆科植物-根瘤菌宿主特异性概念的现状以及在几种共生关系中失去这种特异性提供了一些见解，这使得豆科植物-根瘤菌共生关系的长期以来的宿主特异性教条陷入了困境。
