Team:Peking/Overview

Background

“……over their pools, and over all their ponds of water, that they may become blood; and there shall be blood throughout all the land of Egypt, both in vessels of wood and in vessels of stone....... all the waters that were in the river were turned to blood!” said Exodus 7 Hebrew. Algal blooms have existed since long time ago and were recorded in books including the Holy Bible.

Algal bloom in aquatic ecosystems could be caused by several reasons like eutrophication, high temperature, strong light and so on. Considering rapid developments in industry and agriculture, and dramatic climate change within decades, algal bloom has become widespread among water areas from the Five Great Lakes in North America to small fishing ponds in East Europe. Treating algal bloom is often time-consuming and costly, for example, that the Japanese government had paid 30 years and 18.5 billion dollars eliminating annual burst of cyanobacteria in Lake Biwa.

The most remarkable characteristic of algal bloom is its colossal biomass. They can not only shade submerged vegetation, but also deplete oxygen and cause anoxia, thus being harmful to the organisms living in the water fields. Although several existing methods have been implemented to counteract algal bloom, these methods have noticeable weaknesses or expensive for cost. Furthermore, many species of cyanobacteria secret toxins into water, tens of them are more toxic than cardio-toxin. In 1996, a water contaminated affair of microcystin (a kind of cyanobacteria toxin) in Brazil claimed 76 human lives in total.

Project

This year, in order to improve the method of annihilating algal bloom, Peking iGEM engineered E.coli to kill the cyanobacteria and degrade the toxins existing in the aquatic ecosystem.

First, we innovatively introduced a bactericidal enzyme, lysozyme to annihilate the algal bloom. Besides, we found that the killing efficiency would be enhanced if the average distances between E.coli and cyanobacteria were reduced. Therefore, we introduced two improvement methods, Binding and Gas vesicle, to curtail this distance. The binding was accomplished by anchoring a protein that binds to Microcystis.aeruginosa specifically. Gas vesicle, kindly given by the OUC-China iGEM team, consists of a low-density protein complex that can make our E.coli float up to the water surface.

Then, except for treating the remarkable biomass of cyanobacteria, the toxins secreted by cyanobacteria contribute to other serious environmental problems. Thus we targeted to degrade the microcystin, one of the algal secreted peptide having hepatotoxic effect. We implemented a protein MlrA that can decrease its toxicity significantly.

Finally, our transgenic E.coli should be cleared away after completion of killing and degradation work because of biosafety concerns. Therefore, we used holin, a hole-forming membrane protein, and endolysin, a muralytic enzyme, to construct a suicide system which will be triggered when M. aeruginosa are killed and the concentration of specific inducer molecules decreases.