Fig 7.

Detection of T3SS-dependent secretion of YopE– and YopM–β-lactamase but not YitA– or YipA–β-lactamase in culture supernatants. Y. pestis(pCR-XL-TOPO::yitR) strains with (KIM5) or without (KIM6) the pCD1 virulence plasmid encoding the T3SS and engineered to express YitA–, YipA–, YopM– (pMM83), or YopE–β-lactamase (pMM85) were grown in TMH overnight at 21°C, normalized, and then subcultured in TMH (without CaCl₂) and incubated at 21°C (gray columns) or 37°C (black columns) for an additional 4 h. Bacterial lysates (A) and culture supernatants (B) were incubated with fluorocillin for 4 h, and the fluorescence of each sample was measured. The means and standard errors for three experiments are indicated. Y. pestis KIM5 lacking β-lactamase fusion proteins and sterile TMH medium were used as background controls.