microalgae has been applied for the synthesis of recombinant proteins and vaccines, the production of bio hydrogen, and bioremediation of contaminated soil.Moreover, most microalgae are unable to grow on exogenous glucose in the absence of light. They have been genetically modified for expression of glucose transporters (glut1 or hup1) to live in the dark along with glucose. In addition,the metabolic engineering of microalgae for production of hydrogen has also been developed. Under sulphur deficient conditions, the rate of O2 production drops below that of the respiratory O2 consumption, cultures become anaerobic and H2 gas is generated.