Competition between cocultured TM1040 (HmuR+) and LH02 (HmuR−) for different iron sources. Competition between cocultured TM1040 (HmuR+) and LH02 (HmuR−) for different iron sources. The abundance of each strain was determined by qPCR using primers targeting either the kanamycin resistance cassette for LH02 or the region of the hmuR gene deleted in LH02 and retained in TM1040. The vertical axis displays the absolute concentration of qPCR copies detected from each strain (×109 ml−1) with respect to time. FeCl3 and heme were added at 500 nM, hemoglobin was added at ~17 μg/ml, and algal lysate was added at a concentration providing ~11 nM heme equivalents. Shane L. Hogle et al. mSystems 2017; doi:10.1128/mSystems.00124-16