Microalgal biomass represents a sustainable bioresource for various applications, such as food, nutraceuticals, pharmaceuticals, feed, and other bio-based products. For decades, its mass production has attracted widespread attention and interest. The process of microalgal biomass production involves several techniques, mainly cultivation, harvesting, drying, and pollution control. These techniques are often designed and optimized to meet optimal growth conditions for microalgae and to produce high-quality biomass at acceptable cost. Importantly, mass production techniques are important for producing a commercial product in sufficient amounts. However, it should not be overlooked that microalgal biotechnology still faces challenges, in particular the high cost of production, the lack of knowledge about biological contaminants and the challenge of loss of active ingredients during biomass production. These issues involve the research and development of low-cost, standardized, industrial-scale production equipment and the optimization of production processes, as well as the urgent need to increase the research on biological contaminants and microalgal active ingredients. This review systematically examines the global development of microalgal biotechnology for biomass production, with emphasis on the techniques of cultivation, harvesting, drying and control of biological contaminants, and discusses the challenges and strategies to further improve quality and reduce costs. Moreover, the current status of biomass production of some biotechnologically important species has been summarized, and the importance of improving microalgae-related standards for their commercial applications is noted.

Obesity is a global chronic disease epidemic that is attributed to the abnormal accumulation of lipids in adipose tissue. Astaxanthin (AST) from Haematococcus pluvialis, a natural carotenoid, exhibits antioxidant, anti-lipogenic, anti-diabetic and other potent effects. Herein, we evaluated the effect of AST to illuminate its efficacy and mechanisms in high-fat diet-fed mice. AST supplementation not only significantly decreased body weight and lipid droplet accumulation in the liver but also modulated liver function and serum lipid levels. Lipidomic analysis revealed that 13 lipids might be potential biomarkers responsible for the effects of AST in lipid reduction, such as total free fatty acids (FFAs), triacylglycerols (TGs) and cholesterol esters (CEs). The gut microbiota sequencing results indicated that AST alleviated HFD-induced gut microbiota dysbiosis by optimizing the ratio of Firmicutes to Bacteroides and inhibiting the abundance of obesity-related pathogenic microbiota while promoting the abundance of probiotics related to glucose and lipid metabolism. In addition, qRT-PCR demonstrated that AST could regulate the gene expressions of the AMPK/SREBP1c pathway by downregulating lipogenesis correlated-genes and upregulating the lipid oxidant related-gene. The present study revealed the new function of AST in regulating lipid metabolism, which provided a theoretical basis for the development of high-quality AST functional food and the application of diet active substances in obesity, as demonstrated in mice.

The aim of this study is to probe a new function of astaxanthin (AST) from Haematococcus pluvialis on chemotherapeutic drug induced liver injury in mice. Doxorubicin-induced liver injury was treated with different doses of AST, and the body weight, food intake, urinalysis, liver function, and oxidative stress indexes were examined. The hepatocyte apoptosis level, pathological sections of liver tissue and the expression of antioxidant related genes were also determined. This study found that DOX could induce serious liver injury through cytotoxicity. AST treatment could decrease the level of liver function indexes (ALT, GOT, ALP and TBil), reduce the concentration of MDA and ROS, and increase the activities of SOD, CAT and GPX in the liver. AST could also repair the damaged hepatocyte in mice with liver injury and reduce the degree of the cellular apoptosis. In addition, AST could interfere with the expression of some related genes in the Keap1/Nrf2 signaling pathway by downregulating the expression of Keap1 and activating the transcription factor Nrf2 via enhancing the level of ERK, which upregulates downstream peroxiredoxins. The present research found and illustrated a new food function of AST, indicating that AST could be used in the therapy of chemotherapy induced side effects.

The basic leucine-region zipper (bZIP) transcription factors (TFs) act as crucial regulators in various biological processes and stress responses in plants. Currently, bZIP family members and their functions remain elusive in the green unicellular algae Chlamydomonas reinhardtii, an important model organism for molecular investigation with genetic engineering aimed at increasing lipid yields for better biodiesel production. In this study, a total of 17 C. reinhardtii bZIP (CrebZIP) TFs containing typical bZIP structure were identified by a genome-wide analysis. Analysis of the CrebZIP protein physicochemical properties, phylogenetic tree, conserved domain, and secondary structure were conducted. CrebZIP gene structures and their chromosomal assignment were also analyzed. Physiological and photosynthetic characteristics of C. reinhardtii under salt stress were exhibited as lower cell growth and weaker photosynthesis, but increased lipid accumulation. Meanwhile, the expression profiles of six CrebZIP genes were induced to change significantly during salt stress, indicating that certain CrebZIPs may play important roles in mediating photosynthesis and lipid accumulation of microalgae in response to stresses. The present work provided a valuable foundation for functional dissection of CrebZIPs, benefiting the development of better strategies to engineer the regulatory network in microalgae for enhancing biofuel and biomass production.