Bacterial RuBisCO Is Required for Efficient Bradyrhizobium/Aeschynomene Symbiosis

Abstract

Rhizobia and legume plants establish symbiotic associations resulting in the formation of organs specialized in nitrogen fixation. In such organs, termed nodules, bacteria differentiate into bacteroids which convert atmospheric nitrogen and supply the plant with organic nitrogen. As a counterpart, bacteroids receive carbon substrates from the plant. This rather simple model of metabolite exchange underlies symbiosis but does not describe the complexity of bacteroids' central metabolism. A previous study using the tropical symbiotic model Aeschynomene indica/photosynthetic Bradyrhizobium sp. ORS278 suggested a role of the bacterial Calvin cycle during the symbiotic process. Herein we investigated the role of two RuBisCO gene clusters of Bradyrhizobium sp. ORS278 during symbiosis. Using gene reporter fusion strains, we showed that cbbL1 but not the paralogous cbbL2 is expressed during symbiosis. Congruently, CbbL1 was detected in bacteroids by proteome analysis. The importance of CbbL1 for symbiotic nitrogen fixation was proven by a reverse genetic approach. Interestingly, despite its symbiotic nitrogen fixation defect, the cbbL1 mutant was not affected in nitrogen fixation activity under free living state. This study demonstrates a critical role for bacterial RuBisCO during a rhizobia/legume symbiotic interaction.

Genetic Diversity, Symbiotic Evolution, and Proposed Infection Process of Bradyrhizobium Strains Isolated from Root Nodules of Aeschynomene americana L. in Thailand

“…4). The grouping based on nifH similarity was well correlated with the grouping based on types of nodulation genes (Table 3), Also, this finding correlated with the ability to fix nitrogen in the free-living state detected from the most of divergent nod-containing strains, which was reported to be restricted among rhizobia to photosynthetic bradyrhizobia (14). Moreover, we found that the A. americana strain SUTN9-2 could nodulate all CI group representatives of Aeschynomene, but ORS285 could nodulate only CI groups 2 and 3.…”

Diversity and distribution of autotrophic microbial community along environmental gradients in grassland soils on the Tibetan Plateau

“…Numerous species of Actinomycetales were reported to be cold adapted and could grow at or below 0°C and were observed in Antarctic soils (Babalola et al 2009). Rhizobiales consisted of Bradyrhizobium, Starkeya, Rhizobium, and Mesorhizobium which were reported to degrade diverse organic matters and are typical symbiotic rhizobia that establish an N 2 -fixing symbiosis with its legume host soybean (Borodina et al 2005;Gourion et al 2011;Singh and Tabita 2010). Burkholderiales consisted of Variovorax paradoxus and Rubrivivax gelatinosus are capable of degrading diverse organic carbons including starch, cellulose, gelatin, chitin, and humic acids (Han et al 2011;Nagashima et al 2012;Satola et al 2013).…”

Preferential Association of Endophytic Bradyrhizobia with Different Rice Cultivars and Its Implications for Rice Endophyte Evolution

“…Perhaps the ability to form nodules without Nod factor, rather than being driven solely by the plants, has also been dependent on a specific single bacterial evolution/mutation (41). The CalvinBenson-Bassham (CBB) cycle from Bradyrhizobium species plays an important role in chemoautotrophic growth (42), and it is important for efficient symbiosis with A. indica (43) by controlling the oxygen tension of the early stage of symbiosis (44). In addition, the ancestors of B. japonicum and A. indica symbionts were photosynthetic free-living bacteria (37).…”