T. maritima and B. subtilis are bacteria that inhabit significantly different thermal environments, ∼80 vs ∼40 °C, yet employ similar lysine riboswitches to aid in the transcriptional regulation of the genes involved in the synthesis and transport of amino acids. Despite notable differences in G-C base pair frequency and primary sequence, the aptamer moieties of each riboswitch have striking similarities in tertiary structure, with several conserved motifs and long-range interactions. In order to explore genetic adaptation in extreme thermal environments, we compare the kinetic and thermodynamic behaviors in T. maritima and B. subtilis lysine riboswitches via single molecule fluorescence resonance energy transfer (smFRET) analysis. Kinetic studies reveal that riboswitch folding rates increase with lysine concentration while the unfolding rates are independent of lysine. This indicates that both riboswitches bind lysine through an induced-fit (“bind-then-fold”) mechanism, with lysine binding necessarily preceding conformational changes. Temperature-dependent van’t Hoff studies reveal qualitative similarities in the thermodynamic landscapes for both riboswitches in which progression from the open, lysine-unbound state to both transition states (‡) and closed, lysine-bound conformations is enthalpically favored yet entropically penalized, with comparisons of enthalpic and entropic contributions extrapolated to a common [K+] = 100 mM in quantitative agreement. Finally, temperature dependent Eyring analysis reveals the TMA and BSU riboswitches to have remarkably similar folding/unfolding rate constants when extrapolated to their respective (40 °C and 80 °C) environmental temperatures. Such behavior suggests a shared strategy for ligand binding and aptamer conformational change in the two riboswitches, based on thermodynamic adaptations in number of G-C base pairs and/or modifications in tertiary structure that stabilize the ligand-unbound conformation to achieve biocompetence under both hyperthermophilic and mesothermophilic conditions.