FIG. 2.

Blue halo formation restricted to specific lysogen-antibiotic combinations. Top agar supplemented with AB734 λφ[ibp::lacZ] (A through D), AB734 λφ[P3rpoH::lacZ] (E), or AB734 λφ[cspA::lacZ] (F) cells was poured over LB agar plates spread with X-Gal. Antibiotic disks (Difco) impregnated with 30 μg of chloramphenicol (A), 30 μg of tetracycline (B and F), 300 U of polymyxin B (C and E), or 10 μg of streptomycin (D) were placed on the surfaces of the plates. The plates were incubated overnight at 30°C (A through E) or 37°C (F).