Algal blooms seriously threaten the ecological integrity and sustainability of aquatic ecosystems. They can deplete oxygen causing harmful effects to the phytoplankton, and also produce a variety of toxic secondary metabolites such as microcystins. Among many kinds of cyanobacteria potentially causing water bloom, Microcystis aeruginosa accounts for a significant proportion[1]. We developed a new approach to control the population of Microcystis aeruginosa in the water which can overcome the weakness of other methods. Our genetically engineered E. coli, which can express and secrete hen egg lysozyme and kill Microcystis aeruginosa efficiently, safely, and controllably, with the help of α- hemolysin type I secretion system in E. coli. Moreover, an immunity system is introduced into the E. coli in case that secreted lysozyme could potentially be harmful to our genetically engineered E. coli.