FIG. 3.

Growth and yield of B. subtilis strains in LB medium containing 8% ethanol. The A₄₂₀ of strains bearing a null mutation(s) in sigB (PB153; ▵), in sigH (PB384; ◊), or in both sigB and sigH (PB386; ○) was monitored by placing samples into 0.9% (vol/vol) formaldehyde and measuring A₄₂₀ in a Varian DMS100 spectrophotometer, essentially as described by Neidhardt et al. (30). Over the range shown, A₄₂₀ was found to be directly correlated with viable cell counts, with 1 U of A₄₂₀ equal to 10⁸ CFU/ml. Growth medium was phosphate-buffered LB lacking salt (11) and supplemented with 8% (wt/vol) ethanol. Controls included wild-type strain PB2 (▪) and spoIIA (sigF) null mutant PB513 (□).