Channels modestly impact compartment‐specific ATP levels during Bacillus subtilis sporulation and a rise in the mother cell ATP level is not necessary for Pro‐σK cleavage

• Published in: Molecular microbiology 2020-10, Vol.114 (4), p.563-581
• Main Authors: Parrell, Daniel, Kroos, Lee
• Format: Article
• Language: English
• Subjects: adenosine triphosphate; ATP; Bacillus subtilis; Channels; Cleavage; Compartments; Cytoplasm; Gene expression; gene expression regulation; Mutants; Protein turnover; Proteins; sigma factor; signal transduction; spores; Sporulation
• ISSN: 0950-382X; 1365-2958
• DOI: 10.1111/mmi.14560

Starvation of Bacillus subtilis initiates endosporulation involving formation of mother cell (MC) and forespore (FS) compartments. During engulfment, the MC membrane migrates around the FS and protein channels connect the two compartments. The channels are necessary for postengulfment FS gene expression, which relieves inhibition of SpoIVFB, an intramembrane protease that cleaves Pro‐σK, releasing σK into the MC. SpoIVFB has an ATP‐binding domain exposed to the MC cytoplasm, but the role of ATP in regulating Pro‐σK cleavage has been unclear, as has the impact of the channels on MC and FS ATP levels. Using luciferase produced separately in each compartment to measure relative ATP concentrations during sporulation, we found that the MC ATP concentration rises about twofold coincident with increasing cleavage of Pro‐σK, and the FS ATP concentration does not decline. Mutants lacking a channel protein or defective in channel protein turnover exhibited modest and varied effects on ATP levels, which suggested that low ATP concentration does not explain the lack of postengulfment FS gene expression in channel mutants. Furthermore, a rise in the MC ATP level was not necessary for Pro‐σK cleavage by SpoIVFB, based on analysis of mutants that bypass the need for relief of SpoIVFB inhibition. During Bacillus subtilis endosporulation, the mother cell membrane engulfs the forespore and channel complexes form that may impact ATP concentrations in the compartments. Upon engulfment completion, channel destruction occurs and the Pro‐σK cleavage complex is activated. The mother cell ATP concentration was found to increase twofold coincident with channel protein loss, but this was not required to activate Pro‐σK cleavage.