Research on Chlorella Essay

Chlorella, also known as Chlorophyceae (green algae), is a single cell with small coccoid shape. Chlorella found to contains abundance of nutrients such as proteins, polysaccharides, minerals, vitamins and photosynthetic pigments (including carotenoids and chlorophyll a and b). They have been widely used as health food (32), live feed for aquaculture (33), for biodesel production (34), as well as bioremediation of waste water (35). Evidences have been reported that Chlorella contains immunostimulator (36), wound healing as well as antitumor and antioxidants properties (37). For decades, Chlorella has been used as model organism in plant studied and research due to its cosmopolitan occurrence (38). They can be found in everywhere such as in soil, marine, brackish water ponds, freshwater lakes and ponds as well as in extreme conditions environment such as in snows, hotspring, desert sand crusts (3943). For instance, Chlorella has been used in toxicity test such as the toxicity of oxide nanoparticles (44). It has the ability to survive even in their unfavourable conditions including in varying temperature and light intensities conditions as well as low availability of nutrients (45). Studies have showed that Chlorella was able to grow at low temperatures (20 oC) (39,45,46) Therefore, Chlorella is chosen for the present study.
Further emission of greenhouse gases into the atmosphere will continue and increase the severity of climate change, causing irreversible impacts on the population and ecosystems. In fact, global warming has driven changes in microalgae species in terms of growth rate (47,48), cell composition (14), chlorophyll concentration (47,49)nd lipid content (39). Different species of microalgae show different responses to the change in temperature. For instance, Renaud et al., 2002 showed different species of microalgae have different optimum temperature to achieve optimum growth (49).Table 1 summarise the effect of temperature on algae.
The problem of continuous depletion of stratosphere ozone layer is getting more serious, leading to an increase level of UVB reaching the earth's surface. As a consequences, high levels of UVB radiation affects a series of physiological process on microalgae, similar to the effect of temperature, such as photosynthesis and growth rate (52,53), saturated fatty acid concentration (52), photosynthetic pigments (54), carbon fixation and PS II activity (53). Table 2 summarise the effect of UVR on algae.
Global surface temperature change can influence the levels of UVR onto the earth's surface and vice versa. Significant evidence was shown in the polar region since polar ecosystems are sensitive to the climate change. In polar region, change in surface temperature can trigger change in circulation patterns which can affect the ozone depletion (30). Shindell et al. proposed that Artic ozone loss is associated with the increased stratospheric temperature induced by the increased level of greenhouse gases (57). Similar results showed in Antarctic regions, greenhouse gas induced the cooling of lower stratosphere, worsening the expansion of Antarctic ozone hole (57)(58). Wong et al., 2015 reported that with increasing temperature under UVR exposure, PS II activity of Antarctic Chlorella was significantly decreased, indicating photosynthesis stress exerted on microalgae (59).