Work horse strain Clostridioides difficile 630Δerm is oblivious to its anaerobic lifestyle

The laboratory reference strain 630Δerm of the anaerobic human pathogen Clostridioides difficile is characterized by a remarkable high oxygen tolerance. We show that an amino acid exchange in the DNA binding domain of the hydrogen peroxide sensor PerR results in a constitutive derepression of PerR-controlled genes and thus in an oxidative stress response even under anaerobic conditions. This questions the model status, strain 630Δerm claims in C. difficile research.