Analysis of Curtobacterium Genomic Sequences Reveals the Basis for Further Taxonomic Refinements

Genus Curtobacterium includes phytopathogenic Gram-positive actinomycetes that pose a significant threat to agriculture. Infections of legumes, sugar or table beet, and some other plants, caused by bacteria of the genus Curtobacterium, lead to significant economic losses and demands careful research of the pathogen taxonomy and biology. Recently, the polyphasic approach has identified new taxonomic groups within this genus, but an increasing amount of genomic data encourages a more thorough genomic analysis. In this study, all available by July 2023 NCBI GenBank draft and complete genomic sequences, including sequences derived from metagenomic data, were used for comprehensive genomic analysis. The analysis included both intergenomic comparisons and complex phylogenetic studies. High similarity of 16S rRNA genes and, thus, very low bootstrap support of branches are other obstacles for successful use of this method. To obtain more reliable results, phylogenetic analysis employing concatenated alignments of conserved single-copy genes was conducted. Clustering of Curtobacterium genomic sequences compared by average nucleotide identity has supported our phylogenetic conclusions, indicating delineation of new taxonomic groups: one or two new genera and several new species. In addition, analysis of the pangenome involving all known complete genomes showed a significant difference between different groups of Curtobacterium bacteria, supporting the taxonomic changes within this genus.