Formation of unique T-shape budding and differential impacts of low surface water on Bacillus mycoides rhizoidal colony.

Bacillus mycoides Ko01 strain grows rapidly and forms extensive rhizoidal colonies on hard agar despite limited surface water availability. The agar concentrations affect the handedness of the colonies as well as other colony architectures. In this study, we found that the local curvature of cell chains in the developing colonies did not vary based on the agar concentration, while concentration does affect the handedness of chirality at the macroscale. This result suggests independence between the microscale filament curvature and macroscale colony chirality. In addition, we discovered a novel microscopic property of cells that has not been observed before: T-shaped budding under extremely low surface water availability conditions. We propose that this feature gives rise to chaotic colony morphology. Together with bundling of chains, cells form a unique set of spatial arrangements under different surface water availability. These properties appear to impact the structural features of thick tendrils, and thereby the overall morphology of colonies. Our study provides additional insights as to how bacteria proliferate, spread, and develop macroscale colony architecture under water-limited conditions.