A Pangenomic Analysis of the Diversity and Biological Functioning of the Genus Azotobacter

Azotobacter is a diverse genus of free-living soil bacteria that fix atmospheric nitrogen and act as biocontrol agents for different phytopathogens. This study utilized the genomic sequences from four different Azotobacter species, comprising 30 strains, to construct the genus pangenome. Through comparative genomics and pangenomic analysis, we elucidated the genomic diversity and functional relationship between and within the species of the Azotobacter genus. The selected Azotobacter strains exhibited an average nucleotide identity of ≥85%, with core genes constituting up to 9% and a large proportion of 55% of unique genes. This indicated the sharing of a highly open pangenome of the Azotobacter genus. The Clusters of Orthologous Groups analysis revealed that core, unique, and accessory genes play a significant role in Azotobacter’s metabolic and information storage processes. The Kyoto Encyclopedia of Genes and Genomes enrichment evaluation showed general functioning, amino acid transport, and metabolism as the major biological processes of the Azotobacter’s genomic content. Furthermore, the predominant biosynthetic gene clusters present in the genomic structure of the Azotobacter genus exhibited 27% participation in the production of nonribosomal peptide (NRP)-metallophores, 17% for the nonribosomal peptide synthetase-independent (NI)-siderophores, and 17% for type III polyketide synthase. The genomic content analysis of the core genome revealed various genes that encoded for acid and universal stress proteins, playing a role in Azotobacter adaptation. For the biological functioning attributes, it was found that alginate production, riboflavin transporters, nitrogen-responsive regulatory flavoprotein, nitrogen-related phosphotransferase, and molybdenum cofactor genes were involved in its core genome for the major functioning of its nitrogen fixation.