Fig. 7.

Constitutive expression of the S. marcescens Db10 type VI secretion system. (A to C) β-Galactosidase activity of a chromosomal T6SS-lacZ reporter in strain SLM8 (a nondisruptive insertion of lacZ between SMA2274 and SMA2275) under different growth conditions. Expression of T6SS-lacZ was monitored through growth in liquid LB medium (A) or minimal medium (B) at 37°C, 30°C, or 22°C as indicated. In panel C, cells at an OD₆₀₀ of 0.5 were either grown in liquid culture (Liquid) or inoculated as a 25-μl spot and grown on solid medium (Plate) for a further 4, 8, 16, or 24 h at 30°C before measurement of β-galactosidase activity. In all cases, β-galactosidase activity is expressed per cell (see Materials and Methods) and bars show means ± SEM (n=3). (D) Immunoblot detection of Hcp (SMA2263) levels in the cellular and secreted fractions of wild-type Db10 (WT) and SJC3 (ΔclpV) throughout growth in LB medium at 37°C. The amount of material loaded in each lane corresponded to the same number of cells (i.e., was normalized for OD₆₀₀). Hcp is indicated by a black arrow.