High resolution analysis of proteome dynamics during Bacillus subtilis sporulation

Bacillus subtilis vegetative cells switch to sporulation upon nutrient limitation. To investigate the proteome dynamics during sporulation, high resolution time-lapse proteomics was performed in a cell population that was induced to sporulate synchronously. Here, we are the first to comprehensively investigate the changeover of sporulation regulatory proteins, coat proteins and other proteins involved in sporulation and spore biogenesis. Protein co-expression analysis revealed four co-expressed modules (blue, brown, green and yellow). Modules brown and green are upregulated during sporulation and contain proteins associated with sporulation. Module blue, is negatively correlated with modules brown and green, and contained ribosomal and metabolic proteins. Finally, module yellow shows co-expression with the three other modules. Notably, several proteins not belonging to any of the known transcription regulons were identified as co-expressed with modules brown and green. We speculate that they may also play roles during sporulation. Finally, levels of some coat proteins, for example morphogenetic coat proteins, decreased late in sporulation. We speculate on their possible role in guiding or helping assembly of other coat proteins, after which they can be disposed of, but such a hypothesis remains to be experimentally addressed.