Figure 2.

(a) Survival of spores of B. subtilis strains. The initial counts of spores were determined following heating for 10 min at 80 °C (gray bars). Survival of spores after 60 min at 100 °C is indicated by black bars. A downward arrow means that counts were below the detection limit, i.e., 1.7 log units. Heating was applied to spores of the following strains: 168, 168ΔyitF, 168HR (which is 168 including the Tn1546 transposon encompassing five operons), 168HR without Tn1546 (168HRΔTn1546), 168HR without tnpA (168HRΔtnpA), 168HR without operon 1 (168HRΔop1), 168HR without operon 2 (168HRΔop2), 168HR without spoVA^2mob (168HRΔspoVA^2mob), 168HR without gene 4 (168HRΔgene 4), 168HR without gene 5 (168HRΔgene 5), strain 168 amyE::spoVA^2mob, in which spoVA^2mob was inserted on the amyE locus, and strain B4067, a food isolate producing high-level heat-resistant spores. (b and c) Representative pictures of transmisison electron microscopy cross sections of spores of B. subtilis strain 168 and 168HR, respectively.