Slp expression maps according to inducing conditions of the L9(34) orthogonal design. A, B, C are three independent experiments. M: Protein marker; 1: Uninducing strain; 2-4 represent OD600 of 0.5, and inducing temperature of 28, 32, 37℃; 5-7 represent OD600 of 0.8, and inducing temperature of 37, 28, 32℃; 8-10 represent OD600 of 1.0, and inducing temperature of 32, 37, 28℃.