Phylogenetic study of thermophilic genera Anoxybacillus, Geobacillus, Parageobacillus, and proposal of a new classification Quasigeobacillus gen. nov.

Abstract

A phylogenetic study of Anoxybacillus, Geobacillus and Parageobacillus was performed using publicly available whole genome sequences. A total of 113 genomes were selected for phylogenomic metrics including calculation of Average Nucleotide Identity (ANI) and Average Amino acid Identity (AAI), and a maximum likelihood tree was built from alignment of a set of 662 orthologous core genes. The combined results from the core gene tree and ANI and AAI dendrograms show that the genomes split into two main clades, clade I containing all Geobacillus, all Parageobacillus and some species of Anoxybacillus, and clade II, containing the majority of Anoxybacillus species. Clade I is further partitioned into three clades, consisting separately of Geobacillus, Parageobacillus, and a third clade which we suggest should be elevated to a new genus Quasigeobacillus gen. nov. Two species of Anoxybacillus showed inconsistent positioning among the trees produced by differing methods and could not be clearly resolved into any of the three existing genera or the new genus. This research shows the importance of considering closely related genera together when studying phylogeny or assigning genomic affinities.