Microbial thermal adaptation will lead to a weakening of the positive feedback between climate warming and soil respiration. The thermal adaptations of microbial communities and fungal species has been widely proven. However, studies on the thermal adaptation of bacterial species, the most important decomposers in the soil, are still lacking. Here, we isolated six species of widely distributed dominant bacteria and studied the effects of constant warming and temperature fluctuations on those species. The results showed that both scenarios caused a downregulation of respiratory temperature sensitivity (Q10) of the bacterial species, accompanied by an elevation of the minimum temperature (Tmin) required for growth, suggesting that both scenarios caused thermal adaptation in bacterial species. Fluctuating and increasing temperatures are considered an important component of future warming. Therefore, the inclusion of physiological responses of bacteria to these changes is essential the prediction of global soil-atmosphere C feedbacks.