Molecular insights into bacteroid development duringRhizobium–legume symbiosis

Abstract

Rhizobial soil bacteria can form a symbiosis with legumes in which the bacteria fix atmospheric nitrogen into ammonia that can be utilized by the host. The plant, in turn, supplies the rhizobia with a carbon source. After infecting the host cell, the bacteria differentiate into a distinct bacteroid form, which is able to fix nitrogen. The bacterial BacA protein is essential for bacteroid differentiation in legumes producing nodule-specific cysteine-rich peptides (NCRs), which induce the terminal differentiation of the bacteria into bacteroids. NCRs are antimicrobial peptides similar to mammalian defensins, which are important for the eukaryotic response to invading pathogens. The BacA protein is essential for rhizobia to survive the NCR peptide challenge. Similarities in the lifestyle of intracellular pathogenic bacteria suggest that host factors might also be important for inducing chronic infections associated with Brucella abortus and Mycobacterium tuberculosis. Moreover, rhizobial lipopolysaccharide is modified with an unusual fatty acid, which plays an important role in protecting the bacteria from environmental stresses. Mutants defective in the biosynthesis of this fatty acid display bacteroid development defects within the nodule. In this review, we will focus on these key components, which affect rhizobial bacteroid development and survival.

Comparative genomics of Bradyrhizobium japonicum CPAC 15 and Bradyrhizobium diazoefficiens CPAC 7: elite model strains for understanding symbiotic performance with soybean

“…Recently, it was demonstrated that Bradyrhizobium strains have (ω-1)-hydroxylated very long chain fatty acids (VLCFAs), accompanied by 3-hydroxydodecanoic and 3-hydroxytetradecanoic acids; this pattern is unique to the slow-growing rhizobia [74]. Rhizobial VLCFAs are worthy of attention because of their importance to the intracellular lifestyle [75]. According to Choma & Komaniecka [4], genes related to the biosynthesis of VLCFAs in USDA 110 T probably correspond to bll3807–bll3811.…”

Genomic studies of nitrogen-fixing rhizobial strains from Phaseolus vulgaris seeds and nodules

“…The establishment of these symbioses by rhizobia, a collective term for strains from genera such as Rhizobium , Sinorhizobium , Mesorhizobium and Bradyrhizobium , involves the formation of organ-like structures on the legume roots (for recent reviews see references [1] and [2]). The rhizobia in the nodules are present in a metabolically differentiated form called bacteroids, which perform the reduction of atmospheric dinitrogen into ammonium.…”

Phenotypic characterization of Astragalus glycyphyllos symbionts and their phylogeny based on the 16S rDNA sequences and RFLP of 16S rRNA gene

“…Most of these plants exhibit a unique ability to induce the root and/or stem nodules and establish symbiotic interaction with the soil bacteria called rhizobia. Inside nodules, rhizobia convert nitrogen from atmosphere into ammonium which is assimilated by plant (Haag et al 2013; Perret et al 2000). Due to agricultural and ecological importance of N 2 fixing nodule bacteria, their diversity and taxonomy have been investigated extensively and, in a consequence, the Rhizobium systematics has been greatly improved in the last three decades.…”