Photometric immersion refractometry of bacterial spores

Publisher Website
Google Scholar
Abstract
Photometric immersion refractometry was used to determine the average apparent refractive index (.hivin.n) of 5 types of dormant Bacillus spores representing a 600-fold range in moist-heat resistance determined as a D100 value. The .hivin.n of a spore type increased as the molecular size of various immersion solutes decreased. For comparison of the spore types, the .hivin.n of the entire spore and of the isolated integument was determined by use of bovine serum albumin, which is excluded from permeating into them. The .hivin.n of the sporoplast (the structures bounded by the outer pericortex membrane) was determined by use of glucose, permeated into the spore only as deeply as the pericortex membrane. Among the various spore types, an exponential increase in the heat resistance correlated with the .hivin.n of the entire spore and of the sporoplast, but not of the isolated perisporoplast integument. Correlation of the .hivin.n with the solids content of the entire spore provided a method of experimentally obtaining the refractive index increment (d.hivin.n/dc), which was constant for the various spore types and enables the calculation of solids and water content from an .hivin.n. The total water content is distributed unequally within the dormant spore, with less water in the sporoplast than in the perisporoplast integument. The sporoplast becomes more refractile and more dehydrated as the heat resistance becomes greater among the various spore types.