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The critical first step to achieve the successful cultivation of Ecklonia radiata is the on-demand production of viable zoospores to seed culture ropes. However, the availability of zoospores from fertile field sporophytes is restricted to a narrow seasonal window. Therefore, the objective of this study was to develop a method to artificially induce the formation of sori to obtain viable zoospores. Firstly, we developed a method for the formation of sori under hatchery conditions and maintained individuals in different size groups under short- (8 h L:16 h D) and standard (12 h L: 12 h D) daylength. After 4 weeks, mature sori were present in all treatments and successfully released viable zoospores, which formed gametophytes and sporophytes with transition rates of up to 100%. Secondly, sori formation under hatchery conditions was compared to the natural population to ensure that the formation was genuinely driven by hatchery conditions. Individuals of E. radiata were maintained as whole individuals and isolated lateral fronds under short- and standard daylength for 4 weeks and their reproductive state was compared to sporophytes collected from the field at the beginning and end of the trial. Sori were formed faster and in significantly higher quantities on isolated fronds than whole individuals and more than 70% of all isolated fronds developed sori after 4 weeks. Crucially, all artificially induced sori released viable zoospores, while none were released from naturally formed sori. The developed method can be used to enable the year-round production of high quality sporelings of E. radiata.

This study aimed to evaluate the effects of twenty species of tropical macroalgae on in vitro fermentation parameters, total gas production (TGP) and methane (CH4) production when incubated in rumen fluid from cattle fed a low quality roughage diet. Primary biochemical parameters of macroalgae were characterized and included proximate, elemental, and fatty acid (FAME) analysis. Macroalgae and the control, decorticated cottonseed meal (DCS), were incubated in vitro for 72 h, where gas production was continuously monitored. Post-fermentation parameters, including CH4 production, pH, ammonia, apparent organic matter degradability (OMd), and volatile fatty acid (VFA) concentrations were measured. All species of macroalgae had lower TGP and CH4 production than DCS. Dictyota and Asparagopsis had the strongest effects, inhibiting TGP by 53.2% and 61.8%, and CH4 production by 92.2% and 98.9% after 72 h, respectively. Both species also resulted in the lowest total VFA concentration, and the highest molar concentration of propionate among all species analysed, indicating that anaerobic fermentation was affected. Overall, there were no strong relationships between TGP or CH4 production and the >70 biochemical parameters analysed. However, zinc concentrations >0.10 g x kg(-1) may potentially interact with other biochemical components to influence TGP and CH4 production. The lack of relationship between the primary biochemistry of species and gas parameters suggests that significant decreases in TGP and CH4 production are associated with secondary metabolites produced by effective macroalgae. The most effective species, Asparagopsis, offers the most promising alternative for mitigation of enteric CH4 emissions.

The green seaweeds Derbesia tenuissima and Ulva ohnoi were assessed comparatively for yields of biomass and bioproducts (fatty acids, soluble fibres and amino acids) under controlled land-based culture over 6 months. The intensive cultivation of these seaweeds yielded an average biomass productivity of 15 g dry weight (dw) m⁻² day⁻¹ (56 t dw ha⁻¹ year⁻¹) for D. tenuissima and 38 g dw m⁻² day⁻¹ (138 t dw ha⁻¹ year⁻¹) for U. ohnoi. The production of D. tenuissima was comparatively consistent, ranging between 8 and 20 g dw m⁻² day⁻¹, while that of U. ohnoi was highly variable and stochastic, ranging between 16 and 77 g dw m⁻² day⁻¹. The major bioproducts were lipids (13 % dw) and fatty acids (5 % dw) for D. tenuissima and soluble fibres (ulvan, 12 % dw) for U. ohnoi. These concentrations were consistent over time, irrespective of the variation in environmental conditions and biomass productivity. In addition, D. tenuissima and U. ohnoi are potential bioresources for the extraction of proteins (amino acids). The amino acid content of D. tenuissima (24 % dw) was higher than that of U. ohnoi (13 % dw). However, the annual amino acid productivity of U. ohnoi (18 t ha⁻¹ year⁻¹) was higher than that of D. tenuissima (14 t ha⁻¹ year⁻¹) due to the higher annual productivity of biomass. Notably, both species offer niche opportunities to deliver multiple products through a biorefinery process.

Microalgae are ideal candidates for bioremediation and biotechnological applications. However, salinity and nutrient resource availability vary seasonally and between cultivation sites, potentially impacting on biomass productivity. The aim of this study was to screen pollutant-tolerant freshwater microalgae (Desmodesmus armatus, Mesotaenium sp., Scenedesmus quadricauda and Tetraedron sp.), isolated from Tarong power station ash-dam water, for their tolerance to cultivation at a range of salinities. To determine if biochemical composition could be manipulated, the effects of 4-day nutrient limitation were also determined. Microalgae were cultured at 2, 8, 11 and 18 ppt salinity, and nutrient uptake was monitored daily. Growth, total lipid, fatty acid (FA), and amino acid contents were quantified in biomass harvested while nutrient-replete and, after 4 days, nutrient-deplete. D. armatus showed the highest salinity tolerance actively growing in up to 18 ppt while Mesotaenium sp. was the least halotolerant with decreasing growth rates from 11 ppt. However, Mesotaenium sp. at 2 and 8 ppt had the highest biomass productivity and nutrient requirements of the four species, making it ideal for nutrient remediation of eutrophic freshwater effluents. Salinity and nutrient status had minimal influence on total lipid and FA contents in D. armatus and Mesotaenium sp., while nutrient depletion induced an increase of total lipid and FAs in S. quadricauda and Tetraedron sp., which was further increased with increasing salinity. As none of the growth conditions affected amino acid profiles of the species, these findings provide a basis for species selection based on site-specific salinity conditions and nutrient resource availability.

Microalgae are ideal candidates for waste-gas and -water remediation. However, salinity often varies between different sites. A cosmopolitan microalga with large salinity tolerance and consistent biochemical profiles would be ideal for standardised cultivation across various remediation sites. The aims of this study were to determine the effects of salinity on Picochlorum atomus growth, biomass productivity, nutrient uptake and biochemical profiles. To determine if target end-products could be manipulated, the effects of 4-day nutrient limitation were also determined. Culture salinity had no effect on growth, biomass productivity, phosphate, nitrate and total nitrogen uptake at 2, 8, 18, 28 and 36 ppt. 11 ppt, however, initiated a significantly higher total nitrogen uptake. While salinity had only minor effects on biochemical composition, nutrient depletion was a major driver for changes in biomass quality, leading to significant increases in total lipid, fatty acid and carbohydrate quantities. Fatty acid composition was also significantly affected by nutrient depletion, with an increased proportion of saturated and mono-unsaturated fatty acids. Having established that P. atomus is a euryhaline microalga, the effects of culture salinity on the development of the freshwater cyanobacterial contaminant Pseudanabaena limnetica were determined. Salinity at 28 and 36 ppt significantly inhibited establishment of P. limnetica in P. atomus cultures. In conclusion, P. atomus can be deployed for bioremediation at sites with highly variable salinities without effects on end-product potential. Nutrient status critically affected biochemical profiles--an important consideration for end-product development by microalgal industries. 28 and 36 ppt slow the establishment of the freshwater cyanobacterium P. limnetica, allowing for harvest of low contaminant containing biomass.

Physical and chemical properties of biodiesel are influenced by structural features of the fatty acids, such as chain length, degree of unsaturation and branching of the carbon chain. This study investigated if microalgal fatty acid profiles are suitable for biodiesel characterization and species selection through Preference Ranking Organisation Method for Enrichment Evaluation (PROMETHEE) and Graphical Analysis for Interactive Assistance (GAIA) analysis. Fatty acid methyl ester (FAME) profiles were used to calculate the likely key chemical and physical properties of the biodiesel [cetane number (CN), iodine value (IV), cold filter plugging point, density, kinematic viscosity, higher heating value] of nine microalgal species (this study) and twelve species from the literature, selected for their suitability for cultivation in subtropical climates. An equal-parameter weighted (PROMETHEE-GAIA) ranked Nannochloropsis oculata, Extubocellulus sp. and Biddulphia sp. highest; the only species meeting the EN14214 and ASTM D6751-02 biodiesel standards, except for the double bond limit in the EN14214. Chlorella vulgaris outranked N. oculata when the twelve microalgae were included. Culture growth phase (stationary) and, to a lesser extent, nutrient provision affected CN and IV values of N. oculata due to lower eicosapentaenoic acid (EPA) contents. Application of a polyunsaturated fatty acid (PUFA) weighting to saturation led to a lower ranking of species exceeding the double bond EN14214 thresholds. In summary, CN, IV, C18:3 and double bond limits were the strongest drivers in equal biodiesel parameter-weighted PROMETHEE analysis.

Filamentous macroalgae show promise as an innovative treatment method to remove residual nutrients from municipal wastewater treatment plant (WWTP) effluents. Therefore, the objective of this study was to isolate and identify target cultivars of freshwater macroalgae for the bioremediation of municipal wastewater. We isolated naturally occurring cultivars of filamentous freshwater macroalgae and successfully scaled up Oedogonium calcareum, O. pringsheimii, and Klebsormidium sp. (two cultivars) into monocultures. We assessed the productivity and bioremediation performance of cultivars on-site in the effluents from two WWTP with differing levels of treatment and differing residual nutrient concentrations. Oedogonium calcareum had the highest biomass productivity (9.7 g DW m−2 day−1) and lowest ash content (6.9–4.2% DW). Oedogonium pringsheimii had the best bioremediation performance, reducing the concentration of dissolved inorganic nitrogen (DIN) in the effluent over a 4-day period in batch culture from 18.6 to 2.2 mg L−1 and the concentration of dissolved reactive phosphorus (DRP) from 4.7 to 2.3 mg L−1 at the WWTP with relatively higher residual nutrient concentrations. Similarly, at the WWTP with relatively lower residual nutrient concentrations, O. pringsheimii reduced the concentration of DIN from 1.8 to 0.01 mg L−1 and the concentration of DRP from 0.03 to 0.01 mg L−1. Our results demonstrate that both O. calcareum and O. pringsheimii would be ideal species to select for the bioremediation of municipal wastewater due to their high productivities, ability to maintain unfouled monocultures in outdoor systems, and superior bioremediation performance. As a next step, continuous cultivation on-site over multiple seasons is required to confirm the suitability of these species as targets for bioremediation applications.

We investigated the potential of seaweeds as feedstock for oil‐based products, and our results support macroalgae (seaweeds) as a biomass source for oil‐based bioproducts including biodiesel. Not only do several seaweeds have high total lipid content above 10% dry weight, but in the brown alga Spatoglossum macrodontum 50% of these lipids are in the form of extractable fatty acids. S. macrodontum had the highest fatty acid content (57.40 mg g−1 dw) and a fatty acid profile rich in saturated fatty acids with a high content of C18:1, which is suitable as a biofuel feedstock. Similarly, the green seaweed Derbesia tenuissima has high levels of fatty acids (39.58 mg g−1 dw), however, with a high proportion of PUFA (n‐3) (31% of total lipid) which are suitable as nutraceuticals or fish oil replacements. Across all species of algae the critical parameter of fatty acid content (measured as fatty acid methyl esters, FAME) was positively correlated (R2 = 0.67) with total lipid content. However, the proportion of fatty acids to total lipid decreased markedly with total lipid content, generally between 30% and 50%, making it an inaccurate measure of the potential to identify seaweeds suitable for oil‐based bioproducts. Finally, we quantified within species variation of fatty acids across locations and sampling periods supporting either environmental effects on quantitative fatty acid profiles, or genotypes with specific quantitative fatty acid profiles, thereby opening the possibility to optimize the fatty acid content and quality for oil production through specific culture conditions and selective breeding.

Increased seaweed consumption may be linked to the lower incidence of metabolic syndrome in eastern Asia. This study investigated the responses to two tropical green seaweeds, Ulva ohnoi (UO) and Derbesia tenuissima (DT), in a rat model of human metabolic syndrome. Male Wistar rats (330–340 g) were fed either a corn starch-rich diet or a high-carbohydrate, high-fat diet with 25% fructose in drinking water, for 16 weeks. High-carbohydrate, high-fat diet-fed rats showed the signs of metabolic syndrome leading to abdominal obesity, cardiovascular remodelling and non-alcoholic fatty liver disease. Food was supplemented with 5% dried UO or DT for the final 8 weeks only. UO lowered total final body fat mass by 24%, systolic blood pressure by 29 mmHg, and improved glucose utilisation and insulin sensitivity. In contrast, DT did not change total body fat mass but decreased plasma triglycerides by 38% and total cholesterol by 17%. UO contained 18.1% soluble fibre as part of 40.9% total fibre, and increased magnesium, while DT contained 23.4% total fibre, essentially as insoluble fibre. UO was more effective in reducing metabolic syndrome than DT, possibly due to the increased intake of soluble fibre and magnesium.

The intestinal microbial community (microbiota) is dynamic and variable amongst individuals and plays an essential part in gut health and homeostasis. Dietary components can modulate the structure of the gut microbiota. In recent years, substantial efforts have been made to find novel dietary components with positive effects on the gut microbial community structure. Natural algal polysaccharides and carotenoids have been reported to possess various functions of biological relevance and their impact on the gut microbiota is currently a topic of interest. This study, therefore, reports the effect of the sulfated polysaccharide ulvan and the carotenoid astaxanthin extracted and purified from the aquacultured marine green macroalgae Ulva ohnoi and freshwater green microalgae Haematococcus pluvialis, respectively, on the temporal development of the murine gut microbiota. Significant changes with the increase in the bacterial classes Bacteroidia, Bacilli, Clostridia, and Verrucomicrobia were observed after feeding the mice with ulvan and astaxanthin. Duration of the treatments had a more substantial effect on the bacterial community structure than the type of treatment. Our findings highlight the potential of ulvan and astaxanthin to mediate aspects of host-microbe symbiosis in the gut, and if incorporated into the diet, these could assist positively in improving disease conditions associated with gut health.