IN BACILLUS-SUBTILIS DEGU-P IS A POSITIVE REGULATOR OF THE OSMOTIC RESPONSE

The osmosensitivity presented by spo0A and degU null mutant strains of Bacillus subtilis pointed to their protein products as essential regu lators for the osmotic response. This was further investigated by anal yzing their transcription activity. The results showed that both spo0A -lacZ and degSU-lacZ were induced by the hypertonic medium. The actual phosphorylation state of these proteins was also analyzed by the bias of two reporter gene promoters activity (degQ-lacZ and degQ-lacZ). Th e absence of repression of abrB in hypertonic conditions suggested tha t Spo0A was not phosphorylated while the derepression of degQ promoter suggested that DegU-P was formed. These results were in accordance wi th the observed absence of sporulation in hyperosmotic media and semi- constitutive osmotolerance of degU(h) mutant strains known to retain p hosphorylated DegU. The failure to secrete proteases and to sporulate in hypertonic media suggested that Spo0A acts through abrB regulation in the prevention of alternate responses. The role of DegU-P as positi ve regulator of the osmotic response seems to be settled and is discus sed.