Optimizing Bacillus subtilis spore isolation and quantifying spore harvest purity

► We optimize a method for Bacillus subtilis spore isolation. ► Spore separation produces approximately 40 mg of B. subtilis spores per liter of commercially available growth medium. ► We develop a semi-automated method to rapidly quantify the percent spores within a purified B. subtilis spore biomass. ► Average spore purity for twenty-two purified B. subtilis spore harvests was 88 ± 11% (error is 1σ) with a median of 93%.