Mis-regulation of Zn and Mn homeostasis is a key phenotype of Cu stress inStreptococcus pyogenes

Abstract

All bacteria possess homeostastic mechanisms that control the availability of micronutrient metals within the cell. Regulatory cross-talks between different metal homeostasis pathways within the same bacterial organism have been reported widely. In addition, there have been previous suggestions that some metal uptake transporters can promote adventitious uptake of the wrong metal. This work describes the cross-talk between the Cu homeostasis pathway and the Zn, Mn, and Fe pathways in Group A Streptococcus (GAS). Using a ∆copA mutant strain that lacks the primary Cu efflux pump and thus traps excess Cu in the cytoplasm, we show that Cu stress leads to strong downregulation of Zn and Mn uptake genes, and mild downregulation of Fe uptake genes. This effect is associated with depletion of cellular Zn levels, but not those of Mn or Fe. Co-supplementation of the culture medium with Zn and, to a lesser extent, Mn, but not Fe alleviates key Cu stress phenotypes, namely bacterial growth and production of the fermentation end-product lactate. However, neither Zn nor Mn treatment influences cellular Cu levels or Cu availability in Cu-stressed cells. In addition, we show that the Zn and Mn uptake transporters in GAS do not promote Cu uptake. Taken together, the results strengthen and extend our previous proposal that mis-repression of Zn uptake genes and cellular Zn depletion are key mechanisms of Cu stress in GAS. By comparison, although Mn homeostasis in GAS is perturbed during Cu stress, the relationship between the two metals is yet to be defined.