Proposal of Carbonactinosporaceae fam. nov. within the class Actinomycetia. Reclassification of Streptomyces thermoautotrophicus as Carbonactinospora thermoautotrophica gen. nov., comb. nov.

Streptomyces thermoautotrophicus UBT1 has been suggested to merit generic status due to its phylogenetic placement and distinctive phenotypes among Actinomycetia. To evaluate whether 'S. thermoautotrophicus' represents a higher taxonomic rank, 'S. thermoautotrophicus' strains UBT1 and H1 were compared to Actinomycetia using 16S rRNA gene sequences and comparative genome analyses. The UBT1 and H1 genomes each contain at least two different 16S rRNA sequences, which are closely related to those of Acidothermus cellulolyticus (order Acidothermales). In multigene-based phylogenomic trees, UBT1 and H1 typically formed a sister group to the Streptosporangiales-Acidothermales clade. The Average Amino Acid Identity, Percentage of Conserved Proteins, and whole-genome Average Nucleotide Identity (Alignment Fraction) values were ≤58.5%, ≤48%, ≤75.5% (0.3) between 'S. thermoautotrophicus' and Streptosporangiales members, all below the respective thresholds for delineating genera. The values for genomics comparisons between strains UBT1 and H1 with Acidothermales, as well as members of the genus Streptomyces, were even lower. A review of the 'S. thermoautotrophicus' proteomic profiles and KEGG orthology demonstrated that UBT1 and H1 present pronounced differences, both tested and predicted, in phenotypic and chemotaxonomic characteristics compared to its sister clades and Streptomyces. The distinct phylogenetic position and the combination of genotypic and phenotypic characteristics justify the proposal of Carbonactinospora gen. nov., with the type species Carbonactinospora thermoautotrophica comb. nov. (type strain UBT1, = DSM 100163 = KCTC 49540) belonging to Carbonactinosporaceae fam. nov. within Actinomycetia.

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