Two proteolytic thermophilic aerobic bacterial strains, PA-9 and PA-5, were isolated from Buranga hot springs in western Uganda. The cells were rods, approximately 10-12 microm in length and 3 microm in width. Isolate PA-9 grew at between 38 degrees C and 68 degrees C (optimum, 62 degrees C), and PA-5 grew at between 37 degrees C and 72 degrees C (optimum, 60 degrees C). Both isolates grew optimally at pH 7.5-8.5. Their 16S rRNA gene sequences indicated that they belong to the newly described genus Geobacillus. Zymogram analysis of the crude enzyme extracts revealed the presence of two extracellular proteases for isolate PA-5, and at least eight for isolate PA-9. The optimum temperature and pH for casein-degrading activity were 70 degrees C, pH 6.5 for isolate PA-9, but caseinolytic activity could also be observed at 2 degrees C. In the case of isolate PA-5, optimal activity was observed over a temperature and pH range of 50-70 degrees C and pH 5-10, respectively.