Update on the classification of higher ranks in the phylum Actinobacteria

Genome analysis is one of the main criteria for description of new taxa. Availability of genome sequences for all the actinobacteria with a valid nomenclature will, however, require another decade’s works of sequencing. This paper describes the rearrangement of the higher taxonomic ranks of the members of the phylum ‘ Actinobacteria ’, using the phylogeny of 16S rRNA gene sequences and supported by the phylogeny of the available genome sequences. Based on the refined phylogeny of the 16S rRNA gene sequences, we could arrange all the members of the 425 genera of the phylum ‘ Actinobacteria ’ with validly published names currently in use into six classes, 46 orders and 79 families, including 16 new orders and 10 new families. The order Micrococcales Prévot 1940 (Approved Lists 1980) emend. Nouioui et al . 2018 is now split into 11 monophyletic orders: the emended order Micrococcales and ten proposed new orders Aquipuribacterales , Beutenbergiales , Bogoriellales , Brevibacteriales , Cellulomonadales , Demequinales , Dermabacterales , Dermatophilales , Microbacteriales and Ruaniales . Further, the class ‘ Actinobacteria ’ Stackebrandt et al . 1997 emend. Nouioui et al . 2018 was described without any nomenclature type, and therefore the name ‘ Actinobacteria ’ is deemed illegitimate. In accordance to Rule 8 of the International Code of Nomenclature of Prokaryotes, Parker et al . 2019, we proposed the name Actinomycetia which is formed by using the stem of the name Actinomycetales Buchanan 1917 (Approved Lists 1980) emend. Zhi et al . 2009, to replace the name ‘ Actinobacteria ’. The nomenclature type of the proposed new class Actinomycetia is the order Actinomycetales Buchanan 1917 (Approved Lists 1980) emend. Zhi et al . 2009.