Fig. 7.

Only PspB and PspC are necessary to prevent secretin-induced toxicity and cytoplasmic membrane permeability to ONPG.

A. Anti-PspA, -PspB, and -PspC immunoblot analysis of tacp-pspA strain derivatives with the indicated gene deletions. Samples were taken at the 4 h time point from the + YsaC cultures in panel B. Ponceau S staining of the PspC region of the nitrocellulose membrane is shown as a loading control.

B. Growth of tacp-pspA operon strain derivatives with the indicated gene deletions. Strains contained either pBAD33 (− YsaC) or pAJD935 (+ YsaC). All culture media contained 0.02% arabinose. 10 μM IPTG was also included in the medium as indicated above each graph. Optical density was measured hourly.

C. ONPG hydrolysis by tacp-pspA operon strain derivatives with a Φ(catp-lacZ) operon fusion on the chromosome. Strains contained pBAD33 (− YsaC) or pAJD935 (+ YsaC). All were grown with 0.02% arabinose and 10 μM IPTG. ONPG hydrolysis was monitored by increased absorbance at 420 nm. Readings were normalized so absorbance at 2 min was zero for all samples. Total β-galactosidase activities of cells permeabilized with SDS and chloroform were not significantly different, indicating no differences in β-galactosidase enzyme content (data not shown).