The changing paradigm of rhizobial taxonomy and its systematic growth upto postgenomic technologies

• Published in: World journal of microbiology & biotechnology 2022-11, Vol.38 (11), p.206-206, Article 206
• Main Authors: Rajkumari, Jina, Katiyar, Prashant, Dheeman, Shrivardhan, Pandey, Piyush, Maheshwari, Dinesh Kumar
• Format: Article
• Language: English
• Subjects: Applied Microbiology; Biochemistry; Biomedical and Life Sciences; Biotechnology; Classification; Deoxyribonucleic acid; DNA; Environmental Engineering/Biotechnology; Genera; Genes; Genetic analysis; Genomes; Host plants; Leguminous plants; Life Sciences; Microbiology; Nodulation; Nodules; Nucleotide sequence; Nucleotides; Phylogeny; Review; rRNA 16S; Sequence analysis; Species; Taxonomy
• ISSN: 0959-3993; 1573-0972
• DOI: 10.1007/s11274-022-03370-w

Rhizobia are a diazotrophic group of bacteria that are usually isolated form the nodules in roots, stem of leguminous plants and are able to form nodules in the host plant owing to the presence of symbiotic genes. The rhizobial community is highly diverse, and therefore, the taxonomy and genera-wise classification of rhizobia has been constantly changing since the last three decades. This is mainly due to technical advancements, and shifts in definitions, resulting in a changing paradigm of rhizobia taxonomy. Initially, the taxonomic definitions at the species and sub species level were based on phylogenetic analysis of 16S rRNA sequence, followed by polyphasic approach to have phenotypic, biochemical, and genetic analysis including multilocus sequence analysis. Rhizobia mainly belonging to α- and β-proteobacteria, and recently new additions from γ -proteobacteria had been classified. Nowadays rhizobial taxonomy has been replaced by genome-based taxonomy that allows gaining more insights of genomic characteristics. These omics—technologies provide genome specific information that considers nodulation and symbiotic genes, along with molecular markers as taxonomic traits. Taxonomy based on complete genome sequence (genotaxonomy), average nucleotide identity, is now being considered as primary approach, resulting in an ongoing paradigm shift in rhizobial taxonomy. Also, pairwise whole-genome comparisons, phylogenomic analyses offer correlations between DNA and DNA re-association values that have delineated biologically important species. This review elaborates the present classification and taxonomy of rhizobia, vis-a-vis development of technical advancements, parameters and controversies associated with it, and describe the updated information on evolutionary lineages of rhizobia.