Rivalry in Sibling Bacillus subtilis Colonies: Enemy or Family?

• Author / Creator

  Paul, Rajorshi

• A bacterial colony constitutes a complex microcosm which is equipped with a wide range of defensive adaptations that allow the colony to survive adverse environmental conditions and predation. The extreme resilience of bacteria in colonies has been a subject of continued research for nearly two centuries. Although many aspects of bacterial dynamics have been well studied, several features of bacterial growth and dispersion inside colonies still remain unexplored. In this thesis, I present my research on the interaction between two bacterial colonies. When two bacterial colonies interact with each other the interaction may be mutually beneficial or inhibitory in nature. It has been found that two Bacillus subtilis colonies growing adjacent to each other on a nutrient rich agar plate exhibit two distinct types of interactions: they either coalesce as they grow or form a distinct interface at the colony fronts without complete coalescence. The nature of interaction depends on the agar concentration in the growth medium and the initial separation between the colonies. When the agar concentration was lower than 1%, two sibling colonies were found to coalesce. At 1% or higher concentrations, colonies formed an interface when the separation between the colonies was 20 mm or higher. Interactions of a colony with solid structures and liquid drops have indicated that biochemical rather than presence of physical barriers are responsible for the interface formation. Based on the experimental findings, a reaction diffusion model has been formulated to numerically simulate the two interaction patterns. The model predicts if two sibling colonies will form an interface under the given combination of agar concentration and separation between the colonies. The model prediction agrees well with experimental findings and generates a dimensionless phase diagram containing coalescence and separation domains. The dimensionless critical separation d which demarcates the two interaction regimes was found to follow a simple power law in terms of the ratio of the diffusion coefficients D of the colony to the nutrients .

• Subjects / Keywords

  • Bacteria
  • Colony
  • Sibling Colonies
  • Bacillus subtilis
  • Interface
  • Coalescence
  • Interactions

• Graduation date

  Spring 2019

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/r3-vw8k-xh95

• License

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