PERIODIC GROWTH OF BACILLUS-SUBTILIS COLONIES ON AGAR PLATES

Bacillus subtilis colonies show periodic growth on agar plates. The organism has been observed to show several colony morphologies including diffusion-limited aggregation (DLA) type, dense branching morphology (DBM), Eden type, and spreading without producing openings. The agar concentration for the periodic growth is higher than that of DBM and lower than that of DLA or Eden type. The nutrient (peptone) concentration for the periodic growth is higher than that of DLA and DBM and lower than that of Eden type. The colony grows towards a place with higher peptone concentration. These findings suggest that the diffusion of nutrient particles, i.e. the concentration gradient of peptone particles at the growing perimeter of a colony, would be essentially involved in the periodic growth. The distance between concentric rings of a colony is constant and intervention between two colonies is not observed, unlike the Liesegang ring.