A culture of E. coli is grown on minimal medium plates supplemented with either tryptophan, histidine, or lysine. The resulting colonies are replica plated to three minimal medium plates containing no supplements. The next day, colonies grow on the minimal medium replica plated from the histidine and lysine plates, but colonies do not grow on the tryptophan replica plate. This indicates that the E. coli strain is a

histidine auxotroph.

tryptophan auxotroph.

histidine and lysine auxotroph.

prototroph.