Developmentally regulated proteolysis by MdfA and ClpCP mediates metabolic differentiation during <i>Bacillus subtilis</i> sporulation

<i>Bacillus subtilis</i> sporulation entails a dramatic transformation of the two cells required to assemble a dormant spore, with the larger mother cell engulfing the smaller forespore to produce the "cell within a cell" structure that is a hallmark of endospore formation. Sporulation also entails metabolic differentiation, whereby key metabolic enzymes are depleted from the forespore but maintained in the mother cell. This reduces the metabolic potential of the forespore, which becomes dependent on mother cell metabolism and the SpoIIQ-SpoIIIA channel to obtain metabolic building blocks necessary for development. We demonstrate that metabolic differentiation depends on the ClpCP protease and a forespore-produced protein encoded by the <i>yjbA</i> gene, which we have renamed MdfA (metabolic differentiation factor A). MdfA is conserved in aerobic endospore formers and required for spore resistance to hypochlorite. Using mass spectrometry and quantitative fluorescence microscopy, we show that MdfA mediates the depletion of dozens of metabolic enzymes and key transcription factors from the forespore. An accompanying study by Massoni and colleagues demonstrates that MdfA is a ClpC adaptor protein that directly interacts with and stimulates ClpCP activity. Together, these results document a developmentally regulated proteolytic pathway that reshapes forespore metabolism, reinforces differentiation, and enhances spore resistance to the oxidant hypochlorite.