FIG 1.

Stx2a levels are amplified by culture supernatants from Mcc1229-producing strains. Cell-free supernatants of E. coli 0.1229ΔB17::FRT grown in various media were used to culture E. coli O157:H7 strain PA2. Stx2a levels were measured by an R-ELISA and normalized to the OD₆₂₀ of each culture; the means and standard errors of the means (SEM) are reported (minimum n = 3). M9 medium was supplemented with 0.1% Casamino Acids, 0.005% thiamine, and 0.4% of the indicated carbon source. Cultures grown in the spent supernatants of 0.1229ΔB17::FRT are indicated by solid bars. Cultures grown in the spent supernatants of the double microcin mutant 0.1229ΔB17::FRTΔmctAB::cat are given as crosshatched bars. For comparison, PA2 was grown in fresh medium of the same composition, as indicated by empty bars. All such “broth control” cultures yielded less than 5 μg/ml/OD Stx2a.