Response of Streptococcus thermophilus CNRZ368 and its colonial variants to oxidative stress: Evidence for an inducible defence system

Abstract

The aerotolerance of Streptococcus thermophilus raises the question of the existence of a defence system against oxidative stress. This work, focused on the strain CNRZ368, provides evidence that such a system actually exists and characterises its inducible and adaptative character. Besides, it shows that survival depends on the physiological state of the culture. Moreover, CNRZ368 is subject to a conditional colonial instability, relying on oxygen conditions: grown under anaerobic conditions, CNRZ368 does not show any polymorphism, whereas under aerobic conditions, four colonial phenotypes can be distinguished. The diffuse phenotype is the predominant one. Ring, edged and opaque phenotypes, constituting almost 1% of the population, are considered as variant phenotypes. A statistical analysis shows the existence of an enrichment of resistant isolates to oxidative stress among colonial variants.