Abstract
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 (termed 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, containing 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, and might also play roles during sporulation. Finally, levels of some coat proteins, for example morphogenetic coat proteins, decreased late in sporulation.
Highlights
In response to unfavorable conditions, vegetative cells of Bacillus subtilis can enter the process of sporulation, to form resistant and metabolically dormant spores
As a result of sporulation genes’ transcription and mRNA translation, the vegetative cells undergo a series of morphological changes until the release of spores into the environment
This system allows more synchronous initiation of sporulation and leads to a significantly more homogeneous sporulating cell population. This in turn allows us to interrogate the sporulation process with a far greater sensitivity than is possible in the more heterogeneous populations created by traditional sporulation protocols. Using this newly established system we set out to characterize in great detail the sporulation process on the level of the proteome from the initiation of sporulation to the release of spores, in order to generate a highly time-resolved proteome map of B. subtilis sporulation
Summary
In response to unfavorable conditions, vegetative cells of Bacillus subtilis can enter the process of sporulation, to form resistant and metabolically dormant spores. To facilitate the investigation of protein changeover throughout the sporulation process, and directly interrogate the spore proteome, a kinA-inducible sporulation system has been set up [9,13] This system allows more synchronous initiation of sporulation and leads to a significantly more homogeneous sporulating cell population. Using this newly established system we set out to characterize in great detail the sporulation process on the level of the proteome from the initiation of sporulation to the release of spores, in order to generate a highly time-resolved proteome map of B. subtilis sporulation To this end we used metabolic labeling and mass spectrometry to monitor the proteome changeover during sporulation. This study shows for the first time a highly time-resolved view of protein expression changes during sporulation and reveals distinct modules of co-expressed proteins that are activated or repressed during the specific stages of sporulation
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