The soil-dwelling nematode Steinernema feltiae is found across a wide range of environmental conditions. We asked if its only bacterial symbiont, Xenorhabdus bovienii, shows intraspecific variability in its thermal range, which may affect effectiveness of S. feltiae against host insects. We isolated X. bovienii from S. feltiae from six different natural locations with different mean annual temperatures and two laboratory cultures. We estimated X. bovienii thermal range and determined the specific growth rate based on optical density measurements and mathematical modeling using the Ratkowsky model. The minimal temperature (Tmin) of X. bovienii growth ranged from 0.9 ± 2.2 °C to 7.1 ± 1.4 °C. The optimal temperature (Topt) varied between 25.1 ± 0.2 °C and 30.5 ± 0.2 °C. The model showed that X. bovienii stops multiplying at around 36 °C. The calculated specific X. bovienii growth rate ranged from 2.0 ± 0.3 [h−1] to 3.6 ± 0.5 [h−1]. No differences in Tmin, Topt, and Tmax between the isolated bacteria were found. Additionally, X. bovieniiTopt did not correlate with the mean annual temperature of S. feltiae origin. However, the obtained growth curves suggested that the analyzed X. bovienii may show some variability when comparing the growth curves characteristics.