After incubation for 24 h at 37 C, sporulation was
confirmed by phase-contrast microscopy. Spore preparations were
cleaned by repeated centrifugation and washings with sterile
distilled water until the spores were >99% free of sporulating cells,
cell debris and germinated spores. After suspension in distilled
water at a final OD600 of w6, they were stored at 20 C until used