Developmental switch of S-layer protein synthesis in Bacillus anthracis

Adjustment of the synthesis of abundant protein to the requirements of the cell involves processes critical to the minimization of energy expenditure. The regulation of S-layer genes might be a good model for such processes because expression must be controlled, such that the encoded proteins exactly cover the surface of the bacterium. Bacillus anthracis has two S-layer genes, sap and eag, encoding the S-layer proteins Sap and EA1 respectively. We report that the production and surface localization of Sap and EA1 are under developmental control, suggesting that an exponential phase 'Sap layer' is subsequently replaced by a stationary phase 'EA1 layer'. This switch is controlled at the transcriptional level: sap is most certainly transcribed by RNA polymerase containing sigma(A), whereas eag expression depends on sigma(H). More importantly, Sap is required for the temporal control of eag, and EA1 is involved in strict feedback regulation of eag. This control may be direct because both S-layer proteins bind, in vitro, the eag promoter, specifically suggesting that they might act as transcriptional repressors.