Fig. 1

a: Schematic illustration of the heme biosensor-coupled screening system. When the heme concentration is high, HrtR relieves the inhibition of tcR, tcR effluxes tetracycline, and the cells grow well. When the heme content is low, HrtR inhibits tcR expression, and excessive tetracycline inhibits the growth of the cells; b: Specific growth rates of SPHT at different tetracycline concentrations on addition of 5-aminolevulinic acid (ALA); c: Specific growth rates of SPHT at different tetracycline concentrations on addition of heme; d: Growth differences of SPHT caused by heme addition in the presence of 140 μg/mL tetracycline. *0.01 < p < 0.05, **0.001 < p < 0.01, ***p < 0.001