Enhanced production of Shiga toxin 1 in enterohaemorrhagic Escherichia coli by oxygen

Enterohaemorrhagic (EHEC) produces Shiga toxin 1 (Stx1) and Shiga toxin 2 (Stx2). Although and were found within the late operons of the Stx-encoding phages (Stx-phages), could mainly be transcribed from the promoter ( ), which represents the functional operator-binding site (Fur box) for the transcriptional regulator Fur (ferric uptake regulator), upstream of . In this study, we found that the production of Stx1 by EHEC was affected by oxygen concentration. Increased Stx1 production in the presence of oxygen is dependent on Fur, which is an Fe -responsive transcription factor. The intracellular Fe pool was lower under microaerobic conditions than under anaerobic conditions, suggesting that lower Fe availability drove the formation of less Fe -Fur, less DNA binding to the region, and an increase in Stx1 production.