Expressing of Two Antibacterial Recombinant Protein in E. Coli Showed Different Effect on Host Growth

Background and aim: bacterial expression systems for heterologous protein production are attractive because of their ability to grow rapidly and at high density on inexpensive substrates. however, the rational choice of the adequate promoter system and host for a specific protein of interest remains difficult. a given gene product whether foreign or native can be toxic to the cell when expressed in large quantities. in this project, we observed the effect of two antibacterial recombinant proteins, on e. coli bl21 (de3) growing process in the auto-inducing medium. one of the recombinant proteins was phage native lysin and other one was engineered type of this enzyme. lysins are phage enzymes that can hydrolase peptidoglycan layer of bacterial membrane.methods: an auto-inducing medium have lactose as inducer sugar was used for preventing of basal expression and increasing the accuracy of investigation about the effect of external protein expression on bacterial host growth. for pre-culture, a non-inducing media have no inducer sugar and made entirely from purified ingredients was used to minimize contamination probability by inducing agents. auto-inducing cultures with 50 µg/ml kanamycin were inoculated with one- thousandth volume of saturated pre-culture medium. bacterial cultures were grown over 24 hours at 37ºc in a shaker incubator with shaking rate of 220 rpm. bacterial growth was monitored by measuring the optical density at 600 nm (od600nm) per hour. growth curves were plotted for all bacteria have heterologous recombinant protein.results: the results showed that the presence of heterologous recombinant engineered lysin was prevented the bacterial growth significantly and just continued until an od600 ~6 comparing with od600 ~16 for native lysin.conclusion: the engineered lysin could destroy e.coli from inside of the cell. therefore, the antibacterial effect of an engineered enzyme is absolutely noticeable in comparison to intact native protein also in this stage.