Growth temperatures of archaeal communities can be estimated from the guanine-plus-cytosine contents of 16S rRNA gene fragments

Prokaryote growth temperatures in environmental samples are difficult to measure because it is hard to culture viable prokaryotes in natural environments. We comprehensively surveyed growth temperatures and 16S rRNA sequences of prokaryotes to estimate their growth temperatures based on guanine-plus-cytosine contents (P_GC) of their 16S rRNA sequences. We focused on archaea because of the wide range of growth temperatures within this group. Their minimum (T_min), optimum (T_opt) and maximum (T_max) growth temperatures correlated strongly with P_GC of their 16S rRNA genes. Linear regression equations were established to approximate T_min, T_opt and T_max from P_GC. We also established a linear regression equation for calculating P_GC of 16S rRNA genes based on the melting temperatures (T_m) of PCR fragments, without using a clone library or sequencing. Environmental samples were obtained from a wide variety of microbial natural habitats. T_m of archaeal 16S rRNA genes amplified by real-time PCR were determined by melting curve analysis. Based on those values, P_GC of 16S rRNA genes and mean T_min, T_opt and T_max were calculated using the linear regression equations. These temperatures correlated strongly with the in situ temperatures. T_max agreed particularly well with these temperatures, suggesting many archaea live at their maximum growth temperatures.