Heterogeneity and RpoS status of MC4100TF segregants. (A) Growth of MC4100TF colonies isolated from an LB-stab on TGP +X-P (minimal medium plate supplemented with X-P, a chromogenic substrate for alkaline phosphatase). Light-blue colonies are high-RpoS and the others with a more intense blue colour are low-RpoS segregants. Ten of these low-RpoS segregants were isolated and further analysed. Patches of overnight cultures of MC4100TF segregants (1-10), MC4100TF and MC4100BS were grown on (B) LB-agar and stained with iodine for the detection of glycogen accumulation and on (C) TGP+X-P plates. (D) Bacteria grown overnight in LB medium were assayed for RpoS by immunoblotting with monoclonal anti-RpoS antibodies. 1-10, MC4100TF segregants; BS, MC4100BS; TF, MC4100TF.