The accumulation of genetic information and the development in molecular biologic techniques enable us to design and construct the artificial gene regulatory networks. Since there is a tight relationship between the regulation of gene expression and cell population heterogeneity, analysis of cell population heterogeneity of well-designed artificial gene regulatory networks can provide insights into the underlying mechanisms of gene regulation mechanisms. In the current work we are interested in examining the role of gene network structure of modified lacP/O systems on gene expression patterns, particularly the degree of heterogeneity within a population as indicated by a reporter protein. We are designing and constructing negative feedback gene regulatory systems by placing the gene encoding the green fluorescent protein (gfp), which serves as a reporter, and the gene encoding the LacI repressor protein under the control of the same or different lac promoter systems in Escherichia coli. We are also investigating the difference of cell population heterogeneity between the systems with one or two lac operators by monitoring the GFP expression at the single cell level using a flow cytometer. Results from chemostat experiments of strains carrying various genetic constructs will be presented and discussed.