Lithium-sensing riboswitch classes regulate expression of bacterial cation transporter genes.

Lithium is rare in Earth's crust compared to the biologically relevant alkali metal cations sodium and potassium but can accumulate to toxic levels in some environments. We report the experimental validation of two distinct bacterial riboswitch classes that selectively activate gene expression in response to elevated Li concentrations. These RNAs commonly regulate the expression of nhaA genes coding for ion transporters that weakly discriminate between Na and Li. Our findings demonstrated that the primary function of Li riboswitches and associated NhaA transporters is to prevent Li toxicity, particularly when bacteria are living at high pH. Additional riboswitch-associated genes revealed how some cells defend against the deleterious effects of Li in the biosphere, which might become more problematic as its industrial applications increase.