The biochemical composition of microalgae is significantly altered by growth conditions, thereby necessitating cultivation in precise culture conditions to synthesize biomass as feedstock for production of high-value compounds and biofuels. Nonetheless, culture conditions which promote rapid microalgal growth yields biomass with low concentrations of target metabolites (carotenoids, lipids, carbohydrates, etc.). Conversely, stress conditions introduced to trigger the induction of desired compounds in microalgal cells have an inhibitory effect on growth. Due to the contrasting conditions required for biomass production and accumulation of target compounds, a trade-off is often necessitated to increase the overall product yields. Two-stage microalgae cultivation, wherein biomass growth and product accumulation are separated into two discrete steps, has been identified as a viable approach to enhance the productivity of target compounds. In the first stage, optimal growth conditions are provided to achieve high biomass productivities, followed by exposure of cells to stress conditions for accumulation of target metabolites in the second stage. Microalgae cultivation systems constitute of open or closed reactors operated in batch, fed-batch, continuous or semi-continuous modes; under photoautotrophic, heterotrophic or mixotrophic metabolisms. In two-stage cultivation, two such configurations are integrated sequentially to exploit the inherent advantages of distinct cultivation systems. Nonetheless, the design of two-stage systems should be application specific as optimal culture conditions of each stage are reliant on the microalgal strain and the desired output. The present review provides an in-depth analysis on engineering approaches used for two-stage microalgae cultivation from an application-specific perspective, inclusive of discussion on techno-economic assessment and life cycle analysis of systems used for the biosynthesis of valuable compounds, generation of biofuel feedstock and wastewater bioremediation.
Digital library
-
-
Ulva lactuca is a green macro alga involved in devastating green tides observed worldwide. These green tides or blooms are a consequence of human activities. Ulva blooms occur mainly in shallow waters and the decomposition of this alga can produce dangerous vapors. Ulva lactuca is a species usually resembling lettuce, but genetic analyses demonstrated that other green algae with tubular phenotypes were U. lactuca clades although previously described as different species or even genera. The capacity for U. lactuca to adopt different phenotypes can be due to environment parameters, such as the degree of water salinity or symbiosis with bacteria. No efficient ways have been discovered to control these green tides, but the Mediterranean seas appear to be protected from blooms, which disappear rapidly in springtime. Ulva contains commercially valuable components, such as bioactive compounds, food or biofuel. The biomass due to this alga collected on beaches every year is beginning to be valorized to produce valuable compounds. This review describes different processes and strategies developed to extract these different valuable components.
-
Macroalgae (seaweed) can be cultured effectively for the production of useful algal biomass and removal of nutrients from fishpond effluents. A land-based, tide/gravity-driven flow-through, fish-macroalgae integrated system was studied at Makoba Bay, Zanzibar, Tanzania, during May–October, 2000. Rectangular cages made of 1-inch mesh netting were constructed in channels that received the outflows of the fishponds. Four species of macroalgae were planted in the cages and compared for their usefulness as biofilters. Gracilaria crassa and Ulva reticulata grew at average rates of 1.5 and 1.2 %, respectively. Both species removed nitrogen as seaweed protein at rates of up to 0.4 g N/m2 /d. The algal biomass produced was of good quality with protein dry weight contents of 13% for G. crassa and 26 % for U. reticulata. The biofilters also raised the pH values of the fishpond effluents and oxygenated the water. In contrast to Ulva and Gracilaria, species of Eucheuma and Chaetomorpha performed poorly in the fishpond effluents.
-
Species of the green macroalgae genus Ulva often exhibit rapid growth, are generally cosmopolitan, and are rich in amino acids, vitamins, proteins, and minerals and have high potential for commercial uses. Ulva aquaculture was established and experimentally integrated into fish and shrimp farming in Brazil as Integrated Multi-Trophic Aquaculture projects. Decreases in fish farm production are often due to deaths caused by stress – with consequent increases in production costs. Essential amino acids, such as tryptophan and phenylalanine, have been used in fish farms as anxiolytic agents. In that context, a bibliographic survey was carried out to investigate advances during the last 17 years in the use of tryptophan and phenylalanine produced by Ulva species in fish farming. The biosynthesis patterns of tryptophan and phenylalanine were also examined in the research data. References to the presence of tryptophan and phenylalanine in Ulva spp. were encountered in 32 articles, with Ulva lactuca being the species most cited. References to the use of essential amino acids as anxiolytics in fish farming were encountered in 23 articles, with tryptophan being the most cited; none of the articles, however, mentioned the use of Ulva spp. as sources of anxiolytics. Temperature and pH were the factors that most influenced phenylalanine production. In conclusion, there is a potential role for the use of selected species of Ulva in fish farming as sources of tryptophan and phenylalanine for anxiolytic purposes.
-
Ulvan, a sulphated polysaccharide located in the cell walls of green algae that possesses unique structural properties albeit its repeating unit shares chemical affinity with glycosoaminoglycans, such as hyaluronan and chondroitin sulphate, has been increasingly studied over the years for applications in the pharmaceutical field. The increasing knowledge on ulvan’s chemical properties and biological activities has triggered its utilization in hybrid materials, given its potential efficacy in biomedical applications. In the present review, the use of ulvan in the design of different biomaterials, including membranes, particles, hydrogels, 3D porous structures and nanofibers, is presented. The applications of these structures may vary from drug delivery to wound dressing or bone tissue engineering. In this context, general information regarding the structure and chemical variability, extraction processes, physicochemical properties, and biological activities of ulvan is reported.
-
Species of green macroalgae (Chlorophyta) of the genus Ulva are edible seaweeds with a range of health promoting bioactive components. Ulva is high in dietary fibre which promotes gastrointestinal health and is linked to a reduction in the incidence of chronic diseases. The fundamental active constituent of Ulva is the soluble fibre ulvan, a gelling sulfated polysaccharide with biological activities including immunomodulating, antiviral, antioxidant, antihyperlipidemic and anticancer. Ulvan also has the capacity to modulate cellular signalling processes in both plant and animal systems leading to beneficial effects on productivity and health. Consequently, ulvan is of significant interest as a constituent in human health, agricultural, and biomaterial products. This comprehensive systematic review investigates and recommends acid extraction, ultrafiltration, sugar constituent and molecular weight analysis for the extraction, purification, and characterisation of ulvan, respectively. The biological activities of ulvans are then critically reviewed.
-
Microalgae have gained significant importance in biotechnology development, providing valuable goods and services in multiple applications. Although there is a rising market for most of these applications, the incorporation and introduction of microalgae into new venues will extend in the near future. These advances are due to the vast biodiversity of microalgal species, recent genetic engineering tools, and culture techniques. There are three main possible approaches for novel algal compounds from: (1) recently isolated yet less known microalgae; (2) selectively stressed conditions; and (3) enzymatically adjusted compounds from conventional molecules. All these approaches can be combined in a specific manner. This review discusses the opportunities, potential and limitations of introducing novel microalgae-based products, and how the recent technologies can be deployed to make these products financially viable. To give an outlook to the future, an analysis of the developments and predicted future market that further enlarge the promise of cultivating microalgae for commercial purposes are considered.
-
The Asian invasive brown seaweed Undaria pinnatifida was found for the first time in the Republic of Ireland in Kilmore Quay in Co. Wexford in July 2016. As this brown kelp is of considerable economic importance and is cultivated in Asia as well as in Europe, it opens up the discussion if this invasive species is socially acceptable to be cultivated in the Republic of Ireland for food and other purposes. This paper briefly examines the global economic importance, cultivation aspects compared to the European native equivalents such as Alaria esculenta and Saccharina latissima, cultivation yield, economic considerations and the ecological impact of the spread of Undaria into non-native areas. Based on the information and facts presented, it is concluded that Undaria from a physical, social and economic point of view can be cultivated in Ireland.
-
FAO fisheries fact sheet on Undaria pinnatifida (Harvey) Suringar, 187), also called wakame.
-
Farmers are one of the most important components of any plant-based cultivation industry. The Philippines is one of the world’s major producers of red carrageenophyte algae and has tens of thousands of farmers involved in this industry. The production of algae such as Kappaphycus and Eucheuma increased significantly from the early 1970s, when the industry was established, before declining from the mid-2000s, due to a number of reasons, including disease and epiphyte outbreaks. The introduction of biosecurity measures has been one approach used to tackle this decline. Biosecurity-related knowledge, attitude and practices (KAP) of the seaweed farmers were assessed in the four highest seaweed producing regions in the Philippines: (1) Tawi-Tawi, (2) Palawan, (3) Zamboanga and (4) Bohol. Analyses showed that seaweed farmers from Tawi-Tawi had relatively higher KAP mean scores than the other three sites. Palawan and Bohol farmers, however, scored lower on their knowledge, higher on their attitude and highest on their practices compared with the other areas. Farmers from Zamboanga scored the lowest in both their attitude and practice mean scores, although their knowledge score was one of the highest. This is the first KAP assessment applied to the seaweed farming industry globally and the results, in which the farmers’ biosecurity-related knowledge and practices, which scored “Fair” (50–75%) across all the regions, and their attitudes, which scored predominantly “Good” (> 75%) suggest that there is potential to raise the score for biosecurity practices. This assessment highlights how biosecurity challenges are currently addressed by seaweed farmers in the Philippines and suggests how the KAP survey could be used as a tool by policymakers and scientists to address gaps in biosecurity management practices.
Pages
Marine Agronomy Group, CAFNRM, UH-Hilo
200 W. Kawili st., HI 96720, USA
Contact: Marine.Agronomy.Group@gmail.com
Funding for this web portal is provided by the World Wildlife Fund and the University of Hawaii-Hilo.