Biomass and lipid induction strategies in microalgae for biofuel production and other applications

Abstract

The use of fossil fuels has been strongly related to critical problems currently affecting society, such as: global warming, global greenhouse effects and pollution. These problems have affected the homeostasis of living organisms worldwide at an alarming rate. Due to this, it is imperative to look for alternatives to the use of fossil fuels and one of the relevant substitutes are biofuels. There are different types of biofuels (categories and generations) that have been previously explored, but recently, the use of microalgae has been strongly considered for the production of biofuels since they present a series of advantages over other biofuel production sources: (a) they don’t need arable land to grow and therefore do not compete with food crops (like biofuels produced from corn, sugar cane and other plants) and; (b) they exhibit rapid biomass production containing high oil contents, at least 15 to 20 times higher than land based oleaginous crops. Hence, these unicellular photosynthetic microorganisms have received great attention from researches to use them in the large-scale production of biofuels. However, one disadvantage of using microalgae is the high economic cost due to the low-yields of lipid content in the microalgae biomass. Thus, development of different methods to enhance microalgae biomass, as well as lipid content in the microalgae cells, would lead to the development of a sustainable low-cost process to produce biofuels. Within the last 10 years, many studies have reported different methods and strategies to induce lipid production to obtain higher lipid accumulation in the biomass of microalgae cells; however, there is not a comprehensive review in the literature that highlights, compares and discusses these strategies. Here, we review these strategies which include modulating light intensity in cultures, controlling and varying CO2 levels and temperature, inducing nutrient starvation in the culture, the implementation of stress by incorporating heavy metal or inducing a high salinity condition, and the use of metabolic and genetic engineering techniques coupled with nanotechnology.

Assessment of biomass potentials of microalgal communities in open pond raceways using mass cultivation

“…Although other microalgal strains have been successfully transformed, these are usually one-time cases with low reproducibility ( Siddiqui et al, 2019 ). In addition, native isolates are well adapted to local conditions and exhibit better performance and robustness ( Alishah Aratboni et al, 2019 ). Therefore, for large-scale industrial uses of microalgae, it is necessary to establish a microalgal mass cultivation system, such as the open pond raceway (OPR), using indigenous microalgal species instead of engineered strains.…”

Exploring the Role of a Cytokinin-Activating Enzyme LONELY GUY in Unicellular Microalga Chlorella variabilis

“…Therefore, for application in biofuel, instead of downregulating starch synthesis that may be disadvantageous for growth, it may be better to direct the flow of photosynthetic carbon to lipid biosynthesis rather than starch in these high biomass-producing strains ( Griffiths and Harrison, 2009 ; Hempel et al, 2012 ; Tan and Lee, 2016 ). Another reason for this may be due to prolonged incubation in the same medium that may have affected essential culture conditions like CO 2 levels, pH, and nutrient availability ( Alishah Aratboni et al, 2019 ). These factors, which were not altered in this study, play a significant role in increasing lipid levels ( Alishah Aratboni et al, 2019 ).…”

“…Another reason for this may be due to prolonged incubation in the same medium that may have affected essential culture conditions like CO 2 levels, pH, and nutrient availability ( Alishah Aratboni et al, 2019 ). These factors, which were not altered in this study, play a significant role in increasing lipid levels ( Alishah Aratboni et al, 2019 ). In the future, a permutation of the conditions mentioned above, along with the impact of nutrient limitation, can be studied to enhance the lipid levels of LOG OX1 for use in developing biofuel.…”

Comprehensive Utilization of Marine Microalgae for Enhanced Co-Production of Multiple Compounds

“…In addition, some marine microalgae can synthesize omega-3 polyunsaturated fatty acids (ω-3PUFAs), such as EPA and DHA, which can be used in the pharmaceutical industry [43]. For lipid biosynthesis, acetyl-CoA, derived from pyruvate (a product of G3P), is catalyzed into malonyl-CoA by acetyl-CoA carboxylase (ACC), which is the first committed step of fatty acid synthesis [44,45]. Fatty acids are derived from the fatty acid synthesis (FAS) pathway, followed by the desaturase/elongase pathway or polyketide synthase (PKS) pathway to produce polyunsaturated fatty acids (PUFAs) [42].…”