Unraveling the lipid and pigment biosynthesis in Coelastrella sp. M-60: Genomics-enabled transcript profiling

Metabolic engineering and synthetic biology strategies for producing high-value natural pigments in Microalgae

Microalgae are microorganisms capable of producing bioactive compounds using photosynthesis. Microalgae contain a variety of high value-added natural pigments such as carotenoids, phycobilins, and chlorophylls. These pigments play an important role in many areas such as food, pharmaceuticals, and cosmetics. Natural pigments have a health value that is unmatched by synthetic pigments. However, the current commercial production of natural pigments from microalgae is not able to meet the growing market demand. The use of metabolic engineering and synthetic biological strategies to improve the production performance of microalgal cell factories is essential to promote the large-scale production of high-value pigments from microalgae. This paper reviews the health and economic values, the applications, and the synthesis pathways of microalgal pigments. Overall, this review aims to highlight the latest research progress in metabolic engineering and synthetic biology in constructing engineered strains of microalgae with high-value pigments and the application of CRISPR technology and multi-omics in this context. Finally, we conclude with a discussion on the bottlenecks and challenges of microalgal pigment production and their future development prospects.

A cheap two-step cultivation of Phaeodactylum tricornutum for increased TAG production and differential expression of TAG biosynthesis associated genes

A cheap cultivation of microalgae greatly reduces the biodiesel production cost. Subsequently in this study, citric acid and effluents from sugar and tannery industries were used as the nutritional supplements for the improvement of biomass and TAG production in Phaeodactylum tricornutum using two-step cultivation. When compared to control (media without supplementation), a considerable increase in biomass and chlorophyll a was obtained with citric acid (CA) and sugar industry effluent (SIE) supplemented media. In the two-step cultivation method, biomass raised from CA (100mg·L^-1) and SIE (1.5mL·L^-1) supplementations in the first step, viz. biomass production (BP) step was allowed for lipid accumulation in the second step, viz. lipid production (LP) step, and thus yielded enhanced lipids of 11.5 ± 0.7mg·L^-1·day^-1 and 13.5 ± 1.9mg·L^-1·day^-1 respectively, with improved TAG synthesis. Further, differential expression analysis of TAG biosynthetic genes of P. tricornutum under single-step and two-step cultivation modes were performed, and the gene expression patterns were studied.

Biomass utilization and production of biofuels from carbon neutral materials

The availability of organic matters in vast quantities from the agricultural/industrial practices has long been a significant environmental challenge. These wastes have created global issues in increasing the levels of BOD or COD in water as well as in soil or air segments. Such wastes can be converted into bioenergy using a specific conversion platform in conjunction with the appropriate utilization of the methods such as anaerobic digestion, secondary waste treatment, or efficient hydrolytic breakdown as these can promote bioenergy production to mitigate the environmental issues. By the proper utilization of waste organics and by adopting innovative approaches, one can develop bioenergy processes to meet the energy needs of the society. Waste organic matters from plant origins or other agro-sources, biopolymers, or complex organic matters (cellulose, hemicelluloses, non-consumable starches or proteins) can be used as cheap raw carbon resources to produce biofuels or biogases to fulfill the ever increasing energy demands. Attempts have been made for bioenergy production by biosynthesizing, methanol, n-butanol, ethanol, algal biodiesel, and biohydrogen using different types of organic matters via biotechnological/chemical routes to meet the world's energy need by producing least amount of toxic gases (reduction up to 20-70% in concentration) in order to promote sustainable green environmental growth. This review emphasizes on the nature of available wastes, different strategies for its breakdown or hydrolysis, efficient microbial systems. Some representative examples of biomasses source that are used for bioenergy production by providing critical information are discussed. Furthermore, bioenergy production from the plant-based organic matters and environmental issues are also discussed. Advanced biofuels from the organic matters are discussed with efficient microbial and chemical processes for the promotion of biofuel production from the utilization of plant biomasses.

Review on integrated biofuel production from microalgal biomass through the outset of transesterification route: a cascade approach for sustainable bioenergy

In recent years, microalgal feedstocks have gained immense potential for sustainable biofuel production. Thermochemical, biochemical conversions and transesterification processes are employed for biofuel production. Especially, the transesterification process of lipid molecules to fatty acid alkyl esters (FAAE) is being widely employed for biodiesel production. In the case of the extractive transesterification process, biodiesel is produced from the extracted microalgal oil. Whereas In-situ (reactive) transesterification allows the direct conversion of microalgae to biodiesel avoiding the sequential steps, which subsequently reduces the production cost. Though microalgae have the highest potential to be an alternate renewable feedstock, the minimization of biofuel production cost is still a challenge. The biorefinery approaches that rely on simple cascade processes involving cost-effective technologies are the need of an hour for sustainable bioenergy production using microalgae. At the same time, combining the biorefineries for both (i) high value-low volume (food and health supplements) and (ii) low value- high volume (waste remediation, bioenergy) from microalgae involves regulatory and technical problems. Waste-remediation and algal biorefinery were extensively reviewed in many previous reports. On the other hand, this review focuses on the cascade processes for efficient utilization of microalgae for integrated bioenergy production through the transesterification. Microalgal biomass remnants after the transesterification process, comprising carbohydrates as a major component (process flow A) or the carbohydrate fraction after bio-separation of pretreated microalgae (process flow B) can be utilized for bioethanol production. Therefore, this review concentrates on the cascade flow of integrated bioprocessing methods for biodiesel and bioethanol production through the transesterification and biochemical routes. The review also sheds light on the recent combinatorial approaches of transesterification of microalgae. The applicability of spent microalgal biomass residue for biogas and other applications to bring about zero-waste residue are discussed. Furthermore, techno-economic analysis (TEA), life cycle assessment (LCA) and challenges of microalgal biorefineries are discussed.

(Bio)Technological aspects of microalgae pigments for cosmetics

Photosynthetic microorganisms convert carbon dioxide and solar radiation into interesting bioactive compounds not yet entirely explored. Several species of microalgae are known to be rich in colored high-valuable components that, although remarkable, are poorly explored as natural sources of pigments for cosmetics. Pigments associated to photosynthetic activity include chlorophyll, β-carotene, astaxanthin, xanthophylls, and phycobiliproteins, many of which have shown high potential as cosmetic actives due to their antioxidant, immune-enhancing, and anti-inflammatory properties. In the last decade, concern with a young and beautiful appearance has emerged, encouraging many consumers to use anti-aging cosmetics daily. As a result, the cosmetic market has been growing and evolving rapidly to meet consumer expectations. However, due to regular use and the sensitive nature of facial skin, local adverse reactions may often occur, such as irritation, sensitization, or photoreactions, and safety evaluation is mandatory prior to marketing. It is, therefore, understandable that new actives from natural sources, such as microalgae, are perceived as attractive alternatives for consumers who seek ingredients without allergenic potential. Thus, the cosmetic industry has recently started to explore the inclusion of compounds extracted from microalgae and cyanobacteria in innovative formulations. Herein, we revised nontraditional microalgae species for pigment production with cosmetic applications, indicating those that could also be considered potential ingredients for innovative cosmetics. KEY POINTS: • Extraction methods for pigments from photosynthetic microorganisms were compiled. • Innovative cosmeceuticals could be developed with natural pigments. • Safety features of such natural pigments were also described.

Revision of Coelastrella (Scenedesmaceae, Chlorophyta) and first register of this green coccoid microalga for continental Norway

A terrestrial green microalga was isolated at Ås, in Akershus County, Norway. The strain corresponded to a coccoid chlorophyte. Morphological characteristics by light and electron microscopy, in conjunction with DNA amplification and sequencing of the 18 s rDNA gene and ITS sequences, were used to identify the microalgae. The characteristics agree with those of the genus Coelastrella defined by Chodat, and formed a sister group with the recently described C. thermophila var. globulina. Coelastrella is a relatively small numbered genus that has not been observed in continental Norway before; there are no previous cultures available in collections of Norwegian strains. Gas chromatography analyses of the FAME-derivatives showed a high percentage of polyunsaturated fatty acids (44–45%) especially linolenic acid (C18:3n3; 30–34%). After the stationary phase, the cultures were able to accumulate several carotenoids as neoxanthin, pheophytin a, astaxanthin, canthaxanthin, lutein, and violaxanthin. Due to the scarcity of visual characters suitable for diagnostic purposes and the lack of DNA sequence information, there is a high possibility that species of this genus have been neglected in local environmental studies, even though it showed interesting properties for algal biotechnology.