FIGURE 4.

Transcription of relV gene is highly induced during anaerobic TMAO respiration, and a V. cholerae mutant defective in relV gene exhibited a severe defect in CT production. A, promoter activity of relA and relV genes in N16961 grown anaerobically for 8 h in LB, LBT, or LBF was measured. N16961 reporter strains harboring each chromosomal lacZ reporter fusion were assayed in triplicate for β-galactosidase activity. Values of means ± S.D. (error bars) are presented. *, p < 0.05 versus β-galactosidase activity in LB-grown cultures. B, the levels of CT produced in N16961, ΔrelA, and ΔrelV mutants. Strains were grown anaerobically in LBT for 16 h, and culture supernatants were assayed for CT ELISA. Experimental conditions were identical to those described in the legend to Fig. 1. *, p < 0.05 versus CT produced in N16961; **, p < 0.001 versus CT produced in N16961.