In recent decades, harmful algal blooms (HABs) – commonly known as red tides – have increasingly impacted human health, caused significant economic losses to fisheries and damaged coastal environments and ecosystems. Here, we demonstrate a method to control and suppress HABs through selective algal lysis. The approach harnesses the algicidal effects of aminoclays, which are comprised of a high density of primary amine groups covalently bonded by metal cation backbones. Positively charged colloidals of aminoclays induce cell lysis in HABs within several minutes exposure but have negligible impact on non-harmful phytoplankton, zooplankton and farmed fish. This selective lysis is due to the ammonium characteristics of the aminoclay and the electrostatic attraction between the clay nanoparticles and the algal cells. In contrast, yellow loess clay, a recognized treatment for HABs, causes algal flocs with little cell lysis. Thus, the aminoclay loading can be effective for the mitigation of HABs.

To date, Chlorella vulgaris is the most used species of microalgae in the food and feed additive industries, and also considered as a feasible cell factory for bioproducts. However, the lack of an efficient genetic engineering tool makes it difficult to improve the physiological characteristics of this species. Therefore, the development of new strategic approaches such as genome editing is trying to overcome this hurdle in many research groups. In this study, the possibility of editing the genome of C. vulgaris UTEX395 using clustered regularly interspaced short palindromic repeats (CRISPR)-associated protein 9 (Cas9) has been proven to target nitrate reductase (NR) and adenine phosphoribosyltransferase (APT). Genome-edited mutants, nr and apt, were generated by a DNA-mediated and/or ribonucleoprotein (RNP)-mediated CRISPR-Cas9 system, and isolated based on the negative selection against potassium chlorate or 2-fluoroadenine in place of antibiotics. The null mutation of edited genes was demonstrated by the expression level of the correspondent proteins or the mutation of transcripts, and through growth analysis under specific nutrient conditions. In conclusion, this study offers relevant empirical evidence of the possibility of genome editing in C. vulgaris UTEX395 by CRISPR-Cas9 and the practical methods. Additionally, among the generated mutants, nr can provide an easier screening strategy during DNA transformation than the use of antibiotics owing to their auxotrophic characteristics. These results will be a cornerstone for further advancement of the genetics of C. vulgaris.

Background: The development of microalgal strains for enhanced biomass and biofuel production has received increased attention. Moreover, strain development via metabolic engineering for commercial production is being considered as the most efficient strategy. Pyruvate is an essential metabolite in the cells and plays an essential role in amino acid biosynthesis and de novo fatty acid biosynthesis in plastids. Although pyruvate can be a valuable target for metabolic engineering, its transporters have rarely been studied in microalgae. In this study, we aimed to identify the plastidial pyruvate transporter of Phaeodactylum tricornutum and utilize it for strain development. Results: We identified putative pyruvate transporter localized in the plastid membrane of Phaeodactylum tricornutum. Transformants overexpressing the pyruvate transporter were generated to increase the influx of pyruvate into plastids. Overexpression of a plastidial pyruvate transporter in P. tricornutum resulted in enhanced biomass (13.6% to 21.9%), lipid contents (11% to 30%), and growth (3.3% to 8.0%) compared to those of wild type during one-stage cultivation. Conclusion: To regulate the pyruvate influx and its metabolism in plastids, we generated transformants overexpressing the putative plastidial pyruvate transporter in P. tricornutum. They showed that its overexpression for compartmentalizing pyruvate in plastids could be an attractive strategy for the effective production of biomass and lipids with better growth, via enhanced pyruvate metabolism in plastids.