Phylogenetic relationships within the order Halobacteriales inferred from 16S rRNA gene sequences

Abstract

Phylogenetic relationships within the halophilic archaea were inferred from comparisons of the 16S rRNA gene sequences from 61 strains, representing 18 genera with validly published names within the orderHalobacteriales. Trees produced using distance-matrix (least-squares and neighbour-joining) methods affirm with strong bootstrap support that the members of the orderHalobacterialesare a monophyletic group. Ten genera were supported as monophyletic groups [Haloarcula,Halobiforma,Halococcus,Haloferax,Halorubrum,Halosimplex(multiple sequences from a single strain),Natrialba,Natrinema,NatronococcusandNatronorubrum] and eight genera were represented by a single strain (Halobacterium,Halobaculum,Halogeometricum,Halomicrobium,Halorhabdus,Halosimplex,NatronobacteriumandNatronomonas). The genusHaloterrigenawas always paraphyletic, and the phylogenetic placement of and sister groups toHalobacteriumandNatronomonascould not be resolved. Both treeing methods failed to resolve the deep branching patterns within the orderHalobacterialesand the relationships between the major clades. Additional representation from the currently monospecific genera and/or the use of other macromolecules may be required to resolve the relationships within the orderHalobacteriales.