With the rapid development of synthetic biology, genetic engineering, and molecular manipulation methods in recent years, microalgae, as representatives of microbial cell factories, have been widely used as hosts in the production of high-value bioproducts, such as oils, pigments, proteins, and biofuels, demonstrating promising prospects of application in biochemical energy, food and drugs, and environmental protection. Despite these advancements, the low production efficiency of microalgae limits their industrial application. In addition to strain improvement and culture condition optimization, the regulation by exogenous chemical additives serves as a promising optimization strategy. This method relies on straightforward phenotypic screening and circumvents the necessity for intricate understanding of molecular targets in the metabolic and catabolic pathways involved in the synthesis of bioproducts. It enables rapid yield increasing of high-value bioproducts from microalgae and obtaining the required phenotypes. Although studies have reported the use of alternatives means such as exogenous additives to improve the growth of microalgae and the yield of high-value bioproducts, the classification and summarization of the types, applications, targeted strains, and molecular mechanisms of these additives are not comprehensive. Here, we review the studies using chemical inducers or enhancers to improve cell growth and high-value bioproduct accumulation in microalgae in recent years. This paper focuses on the types of exogenous additives, the effects of exogenous additives and their combinations on microalgae growth and high-value bioproduct accumulation, and the molecular mechanisms of related effects. We aim to provide information for researchers to use methods of synthetic biology to develop suitable cell chassis and harness microalgae for industrial production.
Microalgae/drug effects* ; Biofuels

Formate is an important solar fuel, with large application potential in bioconversion. Especially, the win-win collaboration is achieved when formate is applied to the cultivation of microalgae, which combines the advantages from both artificial and natural photosynthesis. However, the inhibition of formate on the photosynthetic electron transport hinders the application of formate at high concentrations. The engineering or directed evolution of the regulation pathway is a case-by-case and time-consuming strategy. Here, we developed a new strategy by introducing a Stenotrophomonas sp. strain which was isolated and identified from the long-term self-evolution process of Chlamydomonas reinhardtii for adapting to high concentrations of formate. The co-culture with the strain or the fermentation broth relieved the inhibition of formate (50 mmol/L) on C. reinhardtii and promoted the growth of the microalga. Especially, the protein content increased significantly to nearly 50% of the dried weight. In addition, the co-culture also benefited the growth of both Chlorella pyrenoidesa and Synechocystis sp. PCC 6803 exposed to formate, which indicated broader applicability of this strategy. This strategy provides the opportunity to overcome the bottleneck in the formate-mediated artificial-natural hybrid photosynthesis and to aid the development of technologies for solar energy-driven production of bulk biomass, including proteins, by carbon dioxide reduction.
Photosynthesis/physiology* ; Formates/pharmacology* ; Stenotrophomonas/growth & development* ; Microalgae/metabolism* ; Chlamydomonas reinhardtii/growth & development*

The aim of this study was to construct Chlorella mutants deficient in chlorophyll synthesis by atmospheric pressure room temperature plasma (ARTP) mutagenesis, and screen novel algal species with very low chlorophyll content which is suitable for protein production by fermentation. Firstly, the lethal rate curve of mixotrophic wild type cells was established by optimizing the mutagenesis treatment time. The mixotrophic cells in early exponential phase were treated by the condition of over 95% lethal rate, and 4 mutants with the visual change of colony color were isolated. Subsequently, the mutants were cultured in shaking flasks heterotrophically for evaluation of their protein production performance. P. ks 4 mutant showed the best performance in Basal medium containing 30 g/L glucose and 5 g/L NaNO₃. The protein content and productivity reached 39.25% dry weight and 1.15 g/(L·d), with an amino acid score of 101.34. The chlorophyll a content decreased 98.78%, whereas chlorophyll b was not detected, and 0.62 mg/g of lutein content made the algal biomass appear golden yellow. This work provides a novel germplasm, the mutant P. ks 4 with high yield and high quality, for alternative protein production by microalgal fermentation.
Chlorella/metabolism* ; Chlorophyll A/metabolism* ; Plant Breeding ; Mutagenesis ; Chlorophyll/metabolism* ; Biomass ; Microalgae

Intense utilization and mining of fossil fuels for energy production have resulted in environmental pollution and climate change. Compared to fossil fuels, microalgae is considered as a promising candidate for biodiesel production due to its fast growth rate, high lipid content and no occupying arable land. However, monocultural microalgae bear high cost of harvesting, and are prone to contamination, making them incompetent compared with traditional renewable energy sources. Co-culture system induces self-flocculation, which may reduce the cost of microalgae harvesting and the possibility of contamination. In addition, the productivity of lipid and high-value by-products are higher in co-culture system. Therefore, co-culture system represents an economic, energy saving, and efficient technology. This review aims to highlight the advances in the co-culture system, including the mechanisms of interactions between microalgae and other microorganisms, the factors affecting the lipid production of co-culture, and the potential applications of co-culture system. Finally, the prospects and challenges to algal co-culture systems were also discussed.
Biofuels ; Biomass ; Coculture Techniques ; Flocculation ; Microalgae

Microalgae are a group of photosynthetic microorganisms, which have the general characteristics of plants such as photosynthesis, and some species have the ability of movement which resembles animals. Recently, it was reported that microalgae cells can be engineered to precisely deliver medicine-particles and other goods in microfluidic chips. These studies showed great application potential in biomedical treatment and pharmacodynamic analysis, which have become one of the current research hotspots. However, these developments have been rarely reviewed. Here, we summarized the advances in manageable movement exemplified by a model microalgae Chlamydomonas reinhardtii based on its characteristics of chemotaxis, phototaxis, and magnetotaxis. The bottlenecks and prospects in the application of microalgae-based tactic movement were also discussed. This review might be useful for rational design and modification of microalgal manageable movement to achieve targeted transport in medical and other fields.
Chlamydomonas reinhardtii ; Microalgae ; Microfluidics ; Photosynthesis

Microalgae is an easy-to-obtain natural biological material with many varieties and abundant natural reserves. Microalgae are rich in natural fluorescein, which can be used as a contrast agent for fluorescence imaging and photoacoustic imaging for medical imaging. With its active surface, microalgae can effectively adsorb functional molecules, metal elements, etc., and have good application prospects in the field of drug delivery. Microalgae can generate oxygen through photosynthesis to increase local oxygen concentration, reverse local hypoxia to enhance the efficacy of hypoxic tumors and promote wound healing. In addition, microalgae have good biocompatibility, and different administration methods have no obvious toxicity. This paper reviews the research progress on the biomedical application of microalgae in bioimaging, drug delivery, hypoxic tumor treatment, wound healing.
Drug Delivery Systems ; Humans ; Hypoxia ; Microalgae ; Oxygen ; Wound Healing

Filamentous microalga Tribonema sp. has the advantages of highly resistance to zooplankton-predation, easy harvesting, and high cellular lipid content, in particular large amounts of palmitoleic acid (PA) and eicosapentaenoic acid (EPA). Therefore, Tribonema sp. is considered as a promising biomass feedstock to produce biodiesel and high-value products. In this work, we studied the effect of different concentrations of nitrogen (NaNO₃: 255-3 060 mg/L), phosphorus (K₂HPO₄: 4-240 mg/L), iron ((NH₄)₃FeC₁₂H₁₀O₁₄: 0.6-12 mg/L) and magnesium (MgSO₄: 7.5-450 mg/L) on the biomass, lipid content, and fatty acid composition of Tribonema sp. FACHB-1786, aiming at enhancing cell lipid productivity. The growth of Tribonema sp. had a positive correlation with the concentration of magnesium, and the maximum biomass of Tribonema sp. (under the condition of 450 mg/L MgSO₄) was 8.09 g/L, much greater than those reported in previous studies using the same and other Tribonema species under autotrophic conditions. Different nitrogen concentrations exerted no significant effect on algal growth (P > 0.05), but a higher nitrogen concentration resulted in a greater amount of lipid in the cells. The maximum volumetric productivities of total lipids (319. 6 mg/(L·d)), palmitoleic acid (135.7 mg/(L·d)), and eicosapentaenoic acid (24.2 mg/(L·d)) of Tribonema sp. were obtained when the concentrations of NaNO₃, K₂HPO₄, (NH₄)₃FeC₁₂H₁₀O₁₄, and MgSO₄ were 765 mg/L, 80 mg/L, 6 mg/L, and 75 mg/L, respectively. This study will provide a reference for substrate optimization for Tribonema sp. growth and lipid production.
Biofuels ; Biomass ; Lipids ; Microalgae ; Nitrogen ; Stramenopiles

Astaxanthin is widely applied as a nutraceutical, pharmaceutical, and aquaculture feed additive because of its high antioxidant activity. Haematococcus pluvialis is a microalgal species that can largely accumulate astaxanthin under adverse environmental conditions. Here we review the research progress of astaxanthin biosynthesis in H. pluvialis, including the induction and regulation of massive astaxanthin, the relationship between astaxanthin synthesis, photosynthesis and lipid metabolism.
Chlorophyceae ; Chlorophyta ; Microalgae ; Xanthophylls

A rapid and accurate determination method of lipids in microalgae plays a significant role in an efficient breeding process for high-lipid production of microalgae. Using low field nuclear magnetic resonance (LF-NMR), we developed a direct quantitative method for cellular lipids in Chlorella protothecoides cells. The LF-NMR signal had a linear relationship with the lipid content in the microalgae cells for both dry cell samples and algal broth samples (R2 > 0.99). These results indicated that we could use this method for accurate determination of microalgal lipids. Although LF-NMR is a rapid and easy lipid determination method in comparison to conventional methods, low efficiency would limit its application in high throughput screening. Therefore, we developed a novel combined high throughput screening method for high-lipid content mutants of C. protothecoides. Namely, we initially applied Nile red staining method for semi-quantification of lipid in the pre-screening process, and following with LF-NMR method for accurate lipid determination in re-screening process. Finally, we adopted this novel screening method in the breeding process of high-lipid content heterotrophic cells of C. protothecoides. From 3 098 mutated strains 108 high-lipid content strains were selected through pre-screening process, and then 9 mutants with high-lipid production were obtained in the re-screening process. In a consequence, with heterotrophical cultivation of 168 h, the lipid concentration could reach 5 g/L, and the highest lipid content exceeded 20% (W/W), which was almost two-fold to that of the wild strain. All these results demonstrated that the novel breeding process was reliable and feasible for improving the screening efficiency.
Chlorophyta ; chemistry ; Heterotrophic Processes ; High-Throughput Screening Assays ; Lipids ; analysis ; Magnetic Resonance Spectroscopy ; Microalgae ; chemistry ; Staining and Labeling

Microalgae is a single-cell organism with the characteristics of high light energy utilization rate, fast growth rate, high-value bioactive components and high energy material content. Therefore, microalgae has broad application prospects in food, feed, bioenergy, carbon sequestration, wastewater treatment and other fields. In this article, the microalgae biotechnology development in recent years were fully consulted, through analysis from the literature and patent. The progress of microalgal biotechnology at home and abroad is compared and discussed. Furthermore, the project layout, important achievements and development bottlenecks of microalgae biotechnology in our country were also summarized. At last, future development directions of microalgae biotechnology were discussed.
Bibliometrics ; Biofuels ; Biomass ; Biotechnology ; trends ; Microalgae ; metabolism ; Waste Water