Estimating Tmin, Topt, and Tmax Based on PGC of 16S rRNA Genes

Because thermophilic and hyperthermophilic archaea have greater P_GC values for 16S rRNA genes compared with psychrophilic and mesophilic archaea (Galtier and Lobry, 1997; Khachane et al., 2005; Kimura et al., 2006, 2007, 2010), Kimura et al. (2013) proposed linear regression equations to infer T_min, T_opt, and T_max of cultured and not-yet cultured archaea based on P_GC of 16S rRNA genes. We therefore used these equations to estimate growth temperatures of H. hispanica based on P_GC value of each 16S rRNA gene.

Kimura et al. (2013) used partial 16S rRNA gene sequences (ca. 800 bp) between the archaea-specific primers 109aF and 915aR in order to estimate their growth temperatures (Table ​Table11). Thus, we manually selected the internal sequences from the 16S rRNA gene sequences determined in this study. P_GC values for the internal sequences were calculated using Genetyx-Mac ver. 17.0.6 (Genetyx, Tokyo, Japan). T_min, T_opt, and T_max were calculated based on P_GC of the respective sequence using Kimura’s equations.