More than a transcription factor: Spo0A mediates phenotypic heterogeneity and controls replication in Bacillus subtilis

PhD ceremony: Ms. I.G. de Jong, 11.00 uur, Aula Academiegebouw, Broerstraat 5, Groningen

Dissertation: More than a transcription factor: Spo0A mediates phenotypic heterogeneity and controls replication in Bacillus subtilis

Promotor(s): prof. O.P. Kuipers

Faculty: Mathematics and Natural Sciences

The soil bacterium Bacillus subtilis is widely used as a model organism for cellular differentiation. One of the key regulators for cellular differentiation is Spo0A. The thesis of Imke de Jong focuses on phenotypic heterogeneity (cell-to-cell differences) of stress pathways affected by Spo0A. She provides the first study in which motility, competence development, exoprotease production, predation, cannibalism, sporulation as well as the nutritional status can be compared at the population and the single cell level. Her data show that each stress pathway is subject to phenotypic heterogeneity and that the level of heterogeneity varies in time. Interestingly, it seems that it is not the pre-adapted cells that contribute most to survival of a bacterial population in fluctuating environments, but that it is rather the non-adapted, high-energy cells that ensure survival when challenged with a new stress. Time-lapse fluorescence microscopy experiments show that heterogeneity in sporulation is caused by differences in the timing of expression of genes required for the activation of Spo0A. Since time-lapse fluorescence microscopy is tricky and difficult to learn, De Jongs thesis also includes a step-by-step protocol in written format and as a movie recorded by a professional film team. Besides being a transcription factor, Spo0A was suggested to inhibit DNA replication by binding to the orgin of replication (oriC). De Jong investigated this hypothesis and shows that mothercells which lack Spo0A-binding sequences in the oriC region over-replicate. Spores isolated from these strains show increased heterogeneity in germination and outgrowth and produce less offspring compared to wild type spores.