Nodulation of legumes by members of the β-subclass of Proteobacteria

Abstract

Members of the Leguminosae form the largest plant family on Earth, with around 18,000 species. The success of legumes can largely be attributed to their ability to form a nitrogen-fixing symbiosis with specific bacteria known as rhizobia, manifested by the development of nodules on the plant roots in which the bacteria fix atmospheric nitrogen, a major contributor to the global nitrogen cycle. Rhizobia described so far belong exclusively to the alpha-subclass of Proteobacteria, where they are distributed in four distinct phylogenetic branches. Although nitrogen-fixing bacteria exist in other proteobacterial subclasses, for example Herbaspirillum and Azoarcus from the phylogenetically distant beta-subclass, none has been found to harbour the nod genes essential for establishing rhizobial symbiosis. Here we report the identification of proteobacteria from the beta-subclass that nodulate legumes. This finding shows that the ability to establish a symbiosis with legumes is more widespread in bacteria than anticipated to date.

Novel Burkholderia bacteria isolated from Lebeckia ambigua – A perennial suffrutescent legume of the fynbos

“…1 and S2), previously isolated from Aspalathus carnosus (Moulin et al, 2001;Vandamme et al, 2002) and shown to be effective on several Cyclopia species (Elliott et al, 2007a). All strains in group four, except WSM4205, originate from sites 10 and 11.…”

“…The Betaproteobacteria are a class of bacteria first reported to contain root nodule bacteria by Moulin et al (2001). These are mainly from the genus Burkholderia, which are the dominant nodule occupants of species of the large sub-tropical genus Mimosa found in the Cerrado and the Caatinga dos Reis et al, 2010).…”

Ectopic phytocystatin expression increases nodule numbers and influences the responses of soybean (Glycine max) to nitrogen deficiency

“…Like other legumes, soybean is able to form a mutually-beneficial symbiotic relationship with nitrogenfixing bacteria (Oldroyd et al, 2011). Symbiotic nitrogen fixation occurring in soybean root nodules that house the bacteria supports high crop productivity even in nitrogen-poor soils (Moulin et al, 2001).…”

A large diversity of non-rhizobial endophytes found in legume root nodules in Flanders (Belgium)

“…While traditionally, rhizobia belonged to the genera, Azorhizobium, Bradyrhizobium, Ensifer, Mesorhizobium and Rhizobium (Sawada et al, 2003), in recent years nitrogen fixing root nodule bacteria have also been described in other Alphaproteobacterial genera, including Ochrobactrum (Trujillo et al, 2005), Methylobacterium (Sy et al, 2001), Microvirga (Ardley et al, 2012;Radl et al, 2014), Devosia (Rivas et al, 2003) and Phyllobacterium . Furthermore, so-called Betarhizobia have in the last ten years been described in the Betaproteobacterial genera Burkholderia and Cupriavidus (Chen et al, 2001;Moulin et al, 2001;De Meyer et al, 2013a;De Meyer et al, 2013b;De Meyer et al, 2014). In addition to strains that can elicit nodules and belong to documented rhizobial species, several other bacterial species have been reported from legume nodules without a clear indication of their role within the host.…”