Fig 3.

Response of STEC ure gene cluster to different environmental conditions. (A) Cultures were incubated in buffered NiCl₂-supplemented DMEM for 18 h. The medium was also supplemented with NH₄Cl, NaCl, (NH₄)₂SO₄, or urea or adjusted to pH 5.5 as indicated, and the quantitative urease assay was performed for STEC 88-0643. (B) Comparison between STEC strains 88-0643, 537/89, and Mo28. (C) Aliquots of the STEC 88-0643 cultures grown for use in the quantitative urease assay were taken for RNA extraction followed by qRT-PCR using ureD as the target gene. Relative mRNA expressions were calculated for cultures containing NH₄Cl compared to no added NH₄Cl. For all experiments, the results include means and standard errors based on at least three biological replicates. The results for each of the different sets of growth conditions were compared to the result for growth in medium buffered at pH 7.5 and containing no added chemicals, and P values were calculated using the Student t test and are indicated as follows: *, P < 0.01; **, P < 0.001; ***; P < 0.0001; and ****, P > 0.2.