Maximum-likelihood trees of 16S rRNA gene and FTHFS amino acid sequences for comparison of tree topology. Bootstrap values of ≥75% are shown at nodes as closed circles for both tree construction methods or open circles for maximum-likelihood only. In the interest of space, Carboxydothermus has been abbreviated “Carbox.” Marked classifications are indicated by capital letters as follows: A, Ruminococcaceae; B, Blautia group; C, Lachnospiraceae; D, Clostridiaceae; E, Eubacteriaceae; F, Veillonellaceae; G, Peptococcaceae; H, Thermoanaerobacteraceae; I, Syntrophomonadaceae; J, Desulfobacteraceae; K, Desulfobulbaceae; L, Syntrophobacteraceae; M, Desulfohalobiaceae; N, Nitrospiraceae; O, unclassified Planctomycetales; P, methanogenic archaea. The scale bar represents 10% sequence divergence.