Cell Density

Efficient sporulation requires high cell density, as when cell density is low, the Rap (response regulator aspartyl phosphatase) proteins RapA, RapB, and RapE dephosphorylate Spo0F-PO4, prevents Spo0A activation. The rapA and rapE genes are cotranscribed with a downstream open reading frame encoding the signaling peptide precursors PhrA and PhrE, respectively, which are processed and exported out of the cell. As cell density increases, the processed peptides are imported by the oligopeptide permease (Opp) and inhibit the activity of RapA and RapE; similarly, the processed product of PhrC (CSF [competence- and sporulation-stimulating factor])inhibits RapB. Inhibition of the Rap proteins prevents dephosphorylation of Spo0F-PO4 and allows phosphorylation of Spo0A and the initiation of sporulation when cell density is high.^[1]

References

[1] Hilbert, D.W., Piggot, P.J., (June 2004) Compartmentalization of Gene Expression during Bacillus subtilis Spore Formation. Microbiology and Molecular Biology Reviews. Vol. 68, No. 2. Pp 234-262

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Cell Density

References