## 1 Introduction  
The world's ever-growing population is anticipated to reach over 9.7 billion by 2050. Therefore, demands on our limited natural resources will also increase to meet the energy and non-instrument requirements for such high population [1; 2]. Currently, the world's food production capacity is highly influenced by many challenges including the growing competition for land, clean water and energy, as well as the overexploitation of fisheries. Climate change due to the use of fossil fuels poses another threat and with it comes a requirement for food and energy production with less impact on the environment [2; 3]. Microalgae, microscopic photosynthetic organisms, are essential for life on Earth. Their photoautotrophic growth mechanism consumes the atmospheric carbon dioxide and produces almost half of the atmospheric oxygen and constitutes the base of the food chain for aquaculture species [4]. With enormous biodiversity, microalgae can synthesise, accumulate, and secrete a wide range of primary and secondary metabolites [5]. Many of which are valuable substances with potential applications in various industries such as food, feed, cosmetics, pharmaceutical and nutraceuticalals. Yet, microalgae are considered as under-exploited \"food crops\" [6]. Studies suggest that most microalgae species can synthesise high-quality protein characterised by favourable amino acid profiles, which competes well with the quality of conventional protein sources [7]. Large-scale microalgae production as a potential solution for the predicted shortage of protein supply in the world has been proposed, and the National Aeronautics and Space Administration (NASA) has agreed that microalgae make great, compact food for astronauts, while the WHO recognised microalgae as a \"Super Food\" [8]. The lipid content and fatty acids profile of microalgae are of key interest. In the biofuel field, an optimal balance between saturated and unsaturated fatty acids is sought to be achieved. In contrast, essential polyunsaturated fatty acids (PUFA) which mammals are unable to synthesise are the target for food and feed purposes [6]. It is well agreed that for the algal biotechnology to achieve its potential, it is necessary to investigate more species and characterise their chemical and physical properties as well as culturing conditions and downstream processing [6]. Microalgae produce relatively high amounts of lipids and, therefore, they are regarded as the third-generation feedstock for biofuels with the potential to override the 1 st generation (crop-based) and second-generation (lignocellulosic-based) biofuels. Due to their high lipid content and ability to grow all year round, microalgae can be considered one of the best sources for biodiesel production. They can produce 58,700-136,900 L/ha/year of oil compared with 172-5950 L/ha/year of oil from the terrestrial oilseed crops [9]. Hence, producing biodiesel from microalgae may be the only way to produce a sufficient amount of fuel to replace current petro-diesel usage in the transportation sector. Cultivating microalgae for food and bioenergy does not compete with the terrestrial food crops for resources and/or space as marginal and non-arable land is adequate to set up a large scale open or closed system for production [10]. Reducing land use and carbon and water footprints is an essential element for sustainable biofuel production [11; 12]. _C. reinhardtii_ is the most researched unicellular green microalgae with sophisticated genetic tools and has become the model organism to study a variety of cellular functions [13]. The chloroplasts of _C. reinhardtii_ have been engineered to produce recombinant proteins intended for therapeutically use in either humans or animals [14]. For this purpose, _C. reinhardtii_ has been proved to be an inexpensive and easy to scale up the system. _C. reinhardtii_ is generally regarded as safe (GRAS) [15]. Oral vaccines engineered from the chloroplast of this microalgae could be available with reduced cost and improved easiness to use and handle [16].