Quantitative Characterisation of Morphological and Phenotypic Changes During Microbial Cell Differentiation and Multicellular Behaviour

  • Michael Porter

Student thesis: Doctoral ThesisDoctor of Philosophy


Bacteria inhabit almost every conceivable niche on the planet and have evolved adaptations that confer fitness to one or a number of environments. Because of these adaptations, some species of bacteria are successful living in such different environments as the root of a plant and in the gut of a human. One such species is Bacillus subtilis and, as it is non-pathogenic, makes it an ideal organism to use in the study of bacterial environmental adaptation. It is a motile, Gram-positive, endospore-forming bacterium that can live swimming in liquid or can form communities of cells – termed biofilms - in a self-produced extracellular matrix either floating on top of a liquid or sitting on a solid surface. In this work I will detail publications, to which I contributed, covering the differentiation and regulation of B. subtilis, looking at molecules governing gene activation and silencing during the transition from one growth environment to another, and the effect this has on the production of excreted molecules that modify the cells’ local environment to aid in community, rather than planktonic, growth. I will also describe my latest research using microscopical methods to examine and quantify multicellular behaviours of B. subtilis in three distinct phases of the development of colony biofilms. These methods include monitoring expression of a fluorescent reporter for an operon whose gene products produce the polysaccharide component of the extracellular matrix, and doing so with strains deficient in the major matrix component genes results in establishing that regulation of this gene network is inter-dependant on the matrix as a whole. Furthermore, following the types of motion displayed by the cells of matrix mutant strains by time-lapse microscopy, and employing still-image quantitation, reveals some physical properties of the matrix components and goes some way to explain the common macro-scale morphologies of these structures described previously.
Date of Award2020
Original languageEnglish
SupervisorNicola Stanley-Wall (Supervisor) & Jason Swedlow (Supervisor)


  • Bacterial differentiation
  • bacterial multicellularity
  • biofilms
  • microscopy

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