In recent years, numerous investigations have highlighted the importance of bioaerosols in the atmosphere as effective cloud condensation nuclei (CCN) or ice nuclei (IN) during atmospheric physics and chemistry processes. Culturable strains of the ice nuclei active (INA) bacteria Pseudomonas syringae have been isolated from cloud water samples. This has led to an increase in research on bioaerosols associated with climatic effects. Such research is important because of the impacts that bacteria have in certain atmospheric cloud physical processes, especially in precipitation processes. This paper reports freezing temperatures, measured via Valis even drops freezing method, of water droplets containing representative strains of three commonly recognized INA bacterial genera. These strains are Pseudomonas fluorescens , Erwinia uredovora , Xanthomonas campestris , Pseudomonas syringae pv. panici and Pseudomonas syringae pv. lachrymans. Results show that the first four bacteria strains do not have expected IN activity - freezing temperatures were -20.3±2.3℃, -21.8±2.3℃, -20.8±3.4℃, -19.9±3.3℃, respectively, when the concentration of the bacterial suspension was 108cells/mL (OD600=0.25). These are not significantly different from the freezing temperature of ultrapure water droplets, -20.8±2.7℃. However, a higher freezing temperature of -5.0±0.8℃ was observed from measurement of P. syringae pv. lachrymans (ps1-10) contained in water droplets with the same bacterial suspension concentration. Additionally, average freezing temperatures of the water droplets are correlated with bacterial concentration. With a concentration lower than 105 cells/mL, droplet freezing temperature decreased significantly, and was even close to that of ultrapure water when the concentration was less than 104cells/mL. This seems to indicate there was no IN activity for bacteria at such a low concentration. Based on the results, a question is raised that should be verified in the real atmosphere with lower bacterial concentrations. That is, can impacts of P. syringae on heterogeneous nucleation be attributed to their IN activity, or to some other unverified mechanisms?