pH-temperature effects on the swelling of Bacillus subtilis spores during germination

With the intention of making clear how the bacterial spores germinate under different pH and temperature conditions, the volumetric change of the cells during germination was investigated by the Coulter counter method.After heat-activation at 70°C for 10min, spores of Bacillus subtilis were inoculated into Demain's media at pH 3 to 9, and incubated at 30, 40, and 50°C with shaking.The increase in spore cell volume after 2h of incubation at 30°C at pH 7-9, 5-6, and 3-4 was 18, 12, and 30%, respectively. The dependence of volume change on pH appeared more clear at 40°C. The increase of the spore volume at pH 5-9 at 50°C was not so large than at pH 5-9 at 30 and 40°C, on the other hand, large increase in the spore volume was obtained at pH 3-4 at 30, 40 and 50°C.It was speculated that increase in spore volume at pH 3-4 was caused by physicochemical expansion of spore coat in the acidic environment.