Phylogenetic relationships among haloalkaliphilic archaea of the family Natrialbaceae

The family Natrialbaceae is a member of the class Halobacteria of the archaeal phylum Euryarchaeota. Seventeen genera with validly or effectively published names are currently included within this family. In this study, using pairwise average nucleotide identity and average amino acid identity comparisons in conjunction with phylogenetic analysis, it has been shown that the family Natrialbaceae is highly diverse and contains several potentially novel species and genera that are yet to be fully characterized. The deduced proteome sequence-based phylogenetic tree, constructed using the alignment- and parameter-free method CVTree3, contained six major clades, with Salinarchaeum sp. Harcht-Bsk1 being the only representative within clade 1. Furthermore, Haloterrigena daqingensis was found to be closely related to Natronorubrum sediminis, and it is proposed that these archaea together represent a novel genus. Interestingly, Haloterrigena jeotgali, Haloterrigena thermotolerans, and Natrinema pellirubrum were found to be very closely related to each other, and it is proposed that they be merged into a single species. Notably, the type genus Natrialba itself appeared to be heterogenous and contains species that could be broadly classified among two genera. Likewise, the genus Natrinema is also heterogenous and contains species that could be classified among six genera. Altogether, 19 novel genera have been proposed to be created, and four haloalkaliphilic archaea hitherto recognized only using genus names are confirmed to represent novel species.