DescriptionThe Genus Bacillus contains Gram-positive, aerobic spore-forming bacteria. Some Bacillus species are a big concern for the food industry due to financial losses from spoilage. Relatively little is known about how their spore structures contribute to their physiological characteristics. As an important interface between the cytoplasm and the outer environment, membranes play vital roles in maintaining cell survival and growth. This study was undertaken to determine the membrane rigidity of vegetative cells and spores among Bacillus species. B. subtilis, B. cereus, B. anthracis Sterne, B. mycoides, B. thuringiensis that were grown and harvested under the same conditions. 1, 6-diphenyl-1, 3, 5-hexatriene (DPH) was used as a fluorescent probe in the measurement of cell membrane rigidity. There were significant differences in the vegetative cell membrane rigidity among these five Bacillus species when they were grown on three different media (Luria Broth, Nutrient Broth and Luria Broth Noble Agar). There were also significant differences in the spore membrane rigidity among the three Bacillus Species. Significant differences also existed in the membrane rigidity between the vegetative cell membrane and the spore membrane for Bacillus subtilis and Bacillus anthracis Sterne. This represents the first report regarding spore membrane rigidity and its relationship to the rigidity of vegetative cell membranes among Bacillus species.