Current perspectives on integrated approaches to enhance lipid accumulation in microalgae

Advances of microalgae-based enhancement strategies in industrial flue gas treatment: From carbon sequestration to lipid production

The acceleration of industrial development and urban expansion has led to a significant increase in flue gas emissions, posing a significant risk to human health and ecosystems. Recent studies have elucidated the significant potential of microalgae in the domain of sustainable industrial flue gas treatment. However, the inherent multifaceted factors within flue gas exert inhibitory effects on microalgal growth, thereby diminishing the overall system efficacy. Therefore, it is necessary to systematically analyze the flue gas components and propose complete intermediate treatment steps to alleviate their stressful effects on microalgae. Concurrently, to address the intrinsic limitations of the systemic functionality and enhance the applicability of microalgal biotechnology in industrial flue gas treatment, this review proposes a series of innovative solutions and strategies aimed at improving carbon fixation efficiency and lipid productivity of microalgae during flue gas treatment. In addition, the feasibility and potential limitations of these strategies in industrial applications are also discussed. Furthermore, through systematic comparative analysis, the optimal scheme and development trend of industrial flue gas emission reduction technology are explored. This comprehensive review not only establishes a theoretical foundation for the application of microalgae in industrial flue gas treatment, but also offers valuable insights for future research directions in related fields.

Potential of oleaginous microbes for lipid accumulation and renewable energy generation

Biocomponents (such as lipids) accumulate in oleaginous microorganisms and could be used for renewable energy production. Oleaginous microbes are characterized by their ability to accumulate high levels of lipids, which can be converted into biodiesel. The oleaginous microbes (including microalgae, bacteria, yeast, and fungi) can utilize diverse substrates. Thus, in this study, commercially viable oleaginous microorganisms are comparatively summarized for their growth conditions, substrate utilization, and applications in biotechnological processes. Lipid content is species-dependent, as are culture conditions (such as temperature, pH, nutrients, and culture time) and substrates. Lipid production can be increased by selecting suitable microorganisms and substrates, optimizing environmental conditions, and using genetic engineering techniques. In addition, the emphasis on downstream processes (including harvesting, cell disruption, lipid extraction, and transesterification) highlights their critical role in enhancing cost-effectiveness. Oleaginous microorganisms are potential candidates for lipid biosynthesis and could play a key role in meeting the energy needs of the world in the future.

Abiotic factors improving fatty acid profiling of freshwater indigenous microalgae isolated from Kumaun region of Uttarakhand, India

Microalgae have grabbed huge attention as a potential feedstock for biofuel production in response to the rise in energy consumption and the energy crisis. In the present study, indigenous microalgal strains were isolated from four freshwater lakes in the Kumaun region, Uttarakhand, India. Based on growth and lipid profiles, the four best-performing isolates were selected for further experiments. Initial identification of isolates was done by morphological observations, which were further validated by molecular identification using ITS sequencing. The screened cultures were subjected to abiotic stress conditions (varying concentrations of nitrogen and different temperatures) to monitor the biomass, lipid accumulation, and biochemical compositions (chlorophyll and carotenoids). The quantification of fatty acids was checked via gas chromatographic analysis. The strains were identified as KU_MA3 Chlamydopodium starrii, KU_MA4 Tetradesmus nygaardii, KU_MA5 Desmodesmus intermedius, and KU_MA6 Tetradesmus nygaardii. KU_MA3 Chlamydopodium starrii showed the best results in terms of growth and lipid production at 21 °C and 0.37 g/L NaNO2 concentration. The percentage of fatty acid methyl esters (FAMEs) attained >80% and met the standard for biodiesel properties. The strain has the potential to attain higher biomass and accumulate higher lipid content, and after some more studies, it can be used for upscaling processes and large-scale biodiesel production.

Phycoremediation of heavy metals and production of biofuel from generated algal biomass: a review

Due to human activity and natural processes, heavy metal contamination frequently affects the earth's water resources. The pollution can be categorized as resistant and persistent since it poses a significant risk to terrestrial and marine biological systems and human health. Because of this, several appeals and demands have been made worldwide to try and clean up these contaminants. Through bioremediation, algal cells are frequently employed to adsorb and eliminate heavy metals from the environment. Bioremediation is seen as a desirable strategy with few adverse effects and low cost. Activities and procedures for bioremediation involving algal cells depend on various environmental factors, including salinity, pH, temperature, the concentration of heavy metals, the amount of alga biomass, and food availability. Additionally, the effectiveness of removing heavy metals from the environment by assessing how environmental circumstances affect algal activities. The main issues discussed are (1) heavy metal pollution of water bodies, the role of algal cells in heavy metal removal, the methods by which algae cells take up and store heavy metals, and the process of turning the algae biomass produced into biofuel. (2) To overcome the environmental factors and improve heavy metals bioremediation, many strategies are applied, such as immobilizing the cells, consortium culture, and using dry mass rather than living cells. (3) The processes for converting produced algal biomass into biofuels like biodiesel and biomethanol. The present study discusses the life cycle assessment and the limitations of biofuel products from algae biomass.

Temperature, phosphorus and species composition will all influence phytoplankton production and content of polyunsaturated fatty acids

Temperature increases driven by climate change are expected to decrease the availability of polyunsaturated fatty acids in lakes worldwide. Nevertheless, a comprehensive understanding of the joint effects of lake trophic status, nutrient dynamics and warming on the availability of these biomolecules is lacking. Here, we conducted a laboratory experiment to study how warming (18-23°C) interacts with phosphorus (0.65-2.58 μM) to affect phytoplankton growth and their production of polyunsaturated fatty acids. We included 10 species belonging to the groups diatoms, golden algae, cyanobacteria, green algae, cryptophytes and dinoflagellates. Our results show that both temperature and phosphorus will boost phytoplankton growth, especially stimulating certain cyanobacteria species (Microcystis sp.). Temperature and phosphorus had opposing effects on polyunsaturated fatty acid proportion, but responses are largely dependent on species. Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) synthesizing species did not clearly support the idea that warming decreases the production or content of these essential polyunsaturated fatty acids. Our results suggest that warming may have different effects on the polyunsaturated fatty acid availability in lakes with different nutrient levels, and that different species within the same phytoplankton group can have contrasting responses to warming. Therefore, we conclude that future production of EPA and DHA is mainly determined by species composition.

A state of the art review on the co-cultivation of microalgae-fungi in wastewater for biofuel production

The microalgae have a great potential as the fourth generation biofuel feedstock to deal with energy crisis, but the cost of production and biomass harvest are the major hurdles in terms of large scale production and applications. Using filamentous fungi to culture targeted alga for biomass accumulation and eventually harvesting is a sustainable way to mitigate environmental impacts. Microalgal co-culture method could be an alternative to overcome limitations and increase biomass yield and lipid accumulation. It was found to be the high feasibility for the production of biofuels from fungi and microalgae using wastewater. This article aimed to state the synergistic approaches, their culture protocols, harvesting procedure and their potential biotechnological applications. Additionally, algal-fungal consortia could digest cellulosic biomass, potentially reducing operating costs as part of industrial need. As a result of co-cultivation, biofuel production could be economically feasible owing to its excellent ability to treat wastewater and be eco-friendly. The implications of the innovative co-cultivation technology have demonstrated the potential for further development based on the policies that have been supported and implemented.

Enhancing microalgal lipid accumulation for biofuel production

Microalgae have high lipid accumulation capacity, high growth rate and high photosynthetic efficiency which are considered as one of the most promising alternative sustainable feedstocks for producing lipid-based biofuels. However, commercialization feasibility of microalgal biofuel production is still conditioned to the high production cost. Enhancement of lipid accumulation in microalgae play a significant role in boosting the economics of biofuel production based on microalgal lipid. The major challenge of enhancing microalgal lipid accumulation lies in overcoming the trade-off between microalgal cell growth and lipid accumulation. Substantial approaches including genetic modifications of microalgal strains by metabolic engineering and process regulations of microalgae cultivation by integrating multiple optimization strategies widely applied in industrial microbiology have been investigated. In the present review, we critically discuss recent trends in the application of multiple molecular strategies to construct high performance microalgal strains by metabolic engineering and synergistic strategies of process optimization and stress operation to enhance microalgal lipid accumulation for biofuel production. Additionally, this review aims to emphasize the opportunities and challenges regarding scaled application of the strategic integration and its viability to make microalgal biofuel production a commercial reality in the near future.

Statistical optimization and formulation of microalga cultivation medium for improved omega 3 fatty acid production

Microalgae are considered a rich source of high-value metabolites with an array of nutraceutical and pharmaceutical applications. Different strategies have been developed for cultivating microalgae at large-scale photobioreactors but high cost and low productivity are the major hurdles. Optimizing the composition of media for the cultivation of microalgae to induce biomass production and high-value metabolite accumulation has been considered as an important factor for sustainable product development. In this study, the effect of plant growth regulators together with basal microalgal cultivation medium on biomass, total lipid, and EPA production was studied using the Plackett-Burman model and Response surface methodology. The traditional one-factor-at-a-time optimization approach is laborious, time-consuming, and requires more experiments which makes the process and analysis more difficult. The Designed PB model was found to be significant for biomass (396 mg/L), lipid (254 mg/L), and EPA (5.6%) production with a P value < 0.05. The major objective of this study is to formulate a medium for EPA production without compromising the growth properties. Further, we had formulated a new media using RSM to achieve the goal and the significant variables selected were NaNO3, NaH2PO4, and IAA and was found to be significant with 16.72% EPA production with a biomass production of 893 mg/L with a P value < 0.05. The formulated medium can be used in large-scale cultivation systems which can enhance biomass production as well as the omega 3 fatty acid production in marine microalgae Nannochloropsis oceanica.

Supplementary Information

The online version contains supplementary material available at 10.1007/s43393-021-00069-1.

Differential Zn and Mn sensitivity of microalgae species from genera Bracteacoccus and Lobosphaera

One of the most common pollutants in natural ecosystems is heavy metals. Algae are sensitive to the action of heavy metals. This allows to use algae to assess the toxicity of heavy metals, bioindication, and during phycoremediation. This study examines the effect of different Zn and Mn concentrations (1.0, 5.0, 25.0, 50.0, 500.0, 1000.0 mg L^-1) on green algae Bracteacoccus minor and Lobosphaera incisa in a chronic bioassay. The results of this study showed that the toxic effect of Zn and Mn on B. minor and L. incisa begins to manifest itself at the lowest of the studied metal concentrations-1 mg L^-1. The critical concentration of Zn, which leads to the complete death of B. minor and L. incisa, is 50.0 and 500.0 mg L^-1, and Mn is 1000.0 mg L^-1 and 500.0 mg L^-1, respectively. It was found that principal component (PC) 1 accounts for 60.47% of the total variance and reflects changes associated with low concentrations of heavy metals (up to 5.0 mg L^-1). PC2 accounts for 27.95% of the total variance. PC2 is mostly associated with high concentrations of ions of heavy metals. Thus, the effect of Zn and Mn concentrations up to 5 mg L^-1and above 50 mg L^-1on B. minor and L. incisa has a different character. At the same time, the response of the studied algae species to the action of Zn and Mn has individual differences. In general, B. minor is more resistant to Mn, while L. incisa is more resistant to Zn.