Journal of Applied Phycology最新文献

This study deals with the optimization of sequential ultrasound-microwave extraction of carrageenan from Kappaphycus alvarezii and its comparison with aqueous and alkali extraction. Optimization of extraction parameters was carried out using Response Surface Methodology. For the evaluation of the parameters Central Composite Rotatable Design with three independent parameters (temperature, extraction time and liquid/solid ratio) at five different levels was studied with yield as a response. ANOVA was performed to find the significance of the model. The highest extraction yield of 61.25 ± 0.70% with 10 min of ultrasound pre-treatment at 400 W followed by 15 min of microwave extraction at 93 °C was obtained using sequential UMAE. The structural characterization of extracted polysaccharide confirmed the presence of kappa-carrageenan. The physicochemical properties such as 3,6-anhydrogalactose, sulfate, protein content, rheology, and gel strength of carrageenan were measured. The carrageenan extracted using MAE and sequential UMAE showed high 3,6-anhydrogalactose content (41.12 ± 0.91%) and low sulfate content compared to aqueous extracted carrageenan. The rheological curves showed shear-thinning behaviour and higher apparent viscosity values for UMAE extracted carrageenan. In addition, sequential UMAE showed the highest values for gel strength (588.03 ± 4.81 g) and antioxidant activity (DPPH method: 28.80 ± 0.43; ABTS method: 32.35 ± 0.35) due to high 3,6-anhydrogalactose content, which was formed on removal of the sulfate group from precursor carrageenan.

Crop protection from algal grazers is a key area of concern, as grazing zooplankton and flagellates can decimate microalgae crops and impede economic viability of cultivation for biofuels and bioproducts. Inhibition of grazing by chemical and physical interference is one promising solution; however, there have been few empirical tests of this approach that use defense traits innate to algal crop species. Botryococcus braunii is of particular interest because a) it excretes high levels of hydrocarbons and exopolysaccharides and b) forms colonies and possesses chemical defenses. Here we conduct a controlled laboratory experiment to test whether B. braunii can mitigate losses to grazing by two distinct grazers, Daphnia magna and Poterioochromonas malhamensis, due to both chemical inhibition and physical interference linked to large/inedible colonies. We show that chemical and physical defenses interactively reduce the total effect of grazing, thus significantly increasing the biomass and growth rates of cultures of B. braunii and Nannochloropsis limnetica when either grazer is present. We also find that B. braunii medium enhances the growth of N. limnetica. Our study demonstrates how community engineering can identify synergies arising from algal co-cultivation (e.g., by using industrially relevant strains for crop protection). While our lab study serves as a proof-of-concept, future research should test this strategy at pilot scale; if successful, such ecological discoveries may help to reduce the costs of large-scale deployment of algal cultivation for sustainable foods, fuels, bioproducts (e.g., bioplastics), and carbon capture.

The red alga Betaphycus gelatinus showed little monthly variation in carrageenan yields, 3,6-anhydrogalactose and sulfate contents for the native carrageenans (68.2 – 73.1%, 23.1—24.8% and 17.9 – 20.3%, respectively) and for alkali-modified carrageenans (23.7 – 31.5%, 41.6 – 43.9% and 8.6 – 8.8%, respectively). The gelling and melting temperatures and 1.5% gel strength of alkali-modified carrageenans from April to June showed no change, with the recorded values of 40.8 °C, 74.5 °C and 310 g cm⁻², respectively. The molecular weight of the native carrageenan was evaluated as 876 kDa by GPC. ¹H and ¹³C NMR spectra proved that the carrageenan is composed predominantly of a hybrid of beta-carrageenan and kappa-carrageenan. The relative peak areas of the α-anomeric proton signals in ¹H NMR spectra and the signal intensities of the anomeric carbons in ¹³C NMR spectra indicated that the native carrageenan showed little variation in the relative proportions of beta-carrageenan and kappa-carrageenan (52:48), but after alkali-modified carrageenan, the beta-carrageenan component increased significantly compared to the kappa-carrageenan component (69:31). These results will contribute more information on hybrid carrageenan from the red alga B. gelatinus in Vietnam.

There is global interest in cultivating the red alga Asparagopsis taxiformis due to its efficacy as a potent anti-methanogenic feed supplement and as a biofilter for the bioremediation of nutrient-enriched waters. However, the development of A. taxiformis cultivation is currently hindered by a lack of information about the conditions required to maximise tetraspore release and thus secure a reliable source of germlings for out-planting. In this study, we examined the effects of temperature, irradiance, and standard nutrient supplementation (F/8, potassium iodide (KI) and arsenic trioxide (As₂O₃)) on the number of germlings produced per tetrasporophyte, using a strain of A. taxiformis widespread within the Great Barrier Reef, Australia. Temperature, irradiance and nutrient supplementation played a pivotal role in germling numbers, which was optimised at 22 °C under 7 µmol photons m⁻² s⁻¹ and with supplementation of F/8 nutrient media, arsenic trioxide (As₂O₃; 98 µg L⁻¹) and potassium iodide (KI; 166 µg L⁻¹). Once tetrasporophytes were removed from these inducing conditions, tetrasporogenesis ceased within 12 days. In a further five-week experiment investigating the effect of separate supplementation of As₂O₃ and KI, germling numbers were maximised under supplementation with either As₂O₃ or As₂O₃ + KI, with the relative growth rate of tetrasporophytes maximised under supplementation with F/8 + As₂O₃ + KI. Under optimum conditions, an average of 3,261 ± 826 (SD) germlings were produced per tetrasporophyte over a five-week period. Our results provide a strong starting point for developing hatchery protocols for generating a reliable supply of germlings for nursery cultivation in tropical settings.

Eucheumatoid cultivation is an important alternative livelihood for small-scale farmers in coastal areas in east Malaysia. Over the last 50 years, the same clones of the red eucheumatoid Kappaphycus alvarezii and Kappaphycus striatus have been vegetatively propagated for cultivation resulting in low genetic diversity. This has made the cultivars more vulnerable to pests and diseases, which has been further exacerbated by climate change. There is an urgent need, therefore, to develop new cultivars that are resilient to pests and diseases, as well as environmental change. In this study, wild eucheumatoids were collected from four regions in Semporna, East Malaysia: Kerindingan, Sibuhun, Sebangkat and Omadal. These eucheumatoids were then grown at a commercial seaweed farm in Silungun, Semporna using two methods: i) tie-tie and ii) basket net for 60 days and their performance was evaluated based on growth and survival rates. A higher mean specific growth rate (SGR) was recorded by wild-collected Kappaphycus spp. (2.15 ± 1.90% day⁻¹) and Eucheuma denticulatum (2.83 ± 3.27% day⁻¹) when tie-tie was used. However, survival of the wild-collected eucheumatoids was better with the basket net, which led to a reduction in grazing and prevented detachment from culture lines. Of 212 original individuals, 72 survived throughout the study, despite the prevalence of pests and ice-ice disease. Of these, 46.15% Kappaphycus spp. and 50.75% E. denticulatum survived when cultivated using the basket net and 17.20% Kappaphycus spp. and 30.77% E. denticulatum survived when cultivated using tie-tie. The mean SGR and survival rate were significantly correlated with temperature, salinity, pH, current velocity and rainfall (p < 0.05). The surviving wild-collected Kappaphycus spp. and E. denticulatum have the potential to be developed into new cultivars for possible commercial use.

The increased demand for sustainable and ecological agricultural tools to decrease the dependency on chemical fertilizers has surged throughout the last years. Cyanobacteria and microalgae-based biostimulants offer an innovative solution and ecofriendly platform for plant biostimulant production, due to their metabolic diversity and valuable value-added products. Focuses were directed especially towards marine and freshwaters microalgae whereas indigenous soil microalgae were rarely prospected for their biostimulant potential. The aim of this study was to assess the biostimulant activity of the soil microalga Chlorella vulgaris on seed germination performance. The effects of extraction method and plant choice on the biostimulant activity of C. vulgaris were investigated via the comparison of the composition and activity of four extraction techniques (aqueous extraction, acid hydrolysis extraction, organic solvent extraction, microwave-assisted aqueous extraction) on two different plant seed models (wheat and tomato). Seeds were soaked with four different concentrations (from 0.1 g L⁻¹ to 2 g L⁻¹) to determine dose-dependent effects. Results demonstrated significant differences in extracts biochemical composition and biostimulant effects on seed germination enhancement. Extract composition in terms of biomolecules concentrations revealed significant dissimilarities. Seed germination indices and biometric parameters were significantly improved by lower doses (0.1 g L⁻¹ and 1 g L⁻¹), while higher doses (2 g L⁻¹) usually revealed negative effects. The best increases in wheat and tomato seed germination parameters were reached by using acid hydrolysis, aqueous and microwave-assisted aqueous extracts at lower doses. Thus, our results highlight that aqueous extract-based methods were as effective as other techniques. These findings shed light on the advantages of eco-extraction processes and microalgae-based aqueous extracts as eco-friendly biostimulants eligible for sustainable agriculture.

Seaweed extracts are rich in diverse bioactive compounds that can stimulate growth and metabolism of plants. Thus, this study aimed to chemicallly characterize Laminaria japonica (LLE) and Ulva prolifera (ULE) liquid extracts, two formulated commercial products, and to assay their impact on seed germination and seedling development of common bean (Phaseolus vulgaris). Ultra-high performance liquid chromatography-mass spectrometry (UPLC-MS) identified 10 and 17 chemical compounds in liquid extracts of L. japonica and U. prolifera, respectively. Soaking common bean seeds with LLE or ULE increased the germination and seedling vigour. Both seaweed treatments also resulted in increased rooting, fresh weight, and length of roots and shoots in common bean seedlings. Soaking common bean seeds with LLE or ULE modified the carbohydrate, protein and amino acid content of common bean roots and shoots, as well as the α-amylase activity in roots. Sugars (mannitol and sucrose), organic acids (malic acid), and amino acids found in both seaweed extracts may exert effects on common bean seeds and seedlings, particularly on root development. Additionally, gibberellin, which is also found in ULE, could play a role in these effects. These results accurately describe the biochemical compounds present in two seaweed biostimulants and their effects on common bean seeds and plants.

Treatment of nitrogenous flue gas or wastewater using microalgae caters to the strategic goal of sustainable development and environmental protection. However, the physiological responses and metabolic mechanisms of microalgae responding to nitrogenous compounds in flue gas or wastewater are still not well understood. In this study, different nitrogen sources, nitrate, nitrite, and ammonium, were set up to simulate the nitrogen type in nitrogen-containing flue gas or wastewater for cultivation of Chlamydomonas reinhardtii, and the physiological responses and metabolic mechanisms of C. reinhardtii responding to the different types of nitrogen sources were analyzed by biochemical techniques and transcriptome sequencing technology at the RNA level. It was shown that different nitrogen sources can increase biomass production and protein content of C. reinhardtii, but higher concentration of nitrogenous compounds can inhibit growth. The maximum protein content reached 569.05 mg g⁻¹ in N− TAP medium supplemented with 14 mM ammonium nitrogen and the transcriptome results showed that ammonium greatly enhanced the metabolic pathways of N metabolism and C metabolism, indicating that proper concentration of ammonium could be the most direct and readily available nitrogen source for C. reinhardtii. This study lays a theoretical foundation for microalgae to effectively utilize nitrogen sources in nitrogen-containing flue gas or nitrogen-containing wastewater.

The use of algicidal Bacillus species has been considered as an effective and environmental-friendly treatment strategy to control harmful algal blooms. However, little information is available on Bacillus species against harmful Spirogyra. In this study, an isolate (A4) was found to have a strong algicidal activity against S. gracilis, and was identified molecularly and phenotypically as B. subtilis. Its significant algicidal effects were obtained at 3.0 × 10⁶ to 3.0 × 10⁹ CFU mL⁻¹, 15 °C to 35 °C, and photoperiods of 14 h:10 h, 24 h:0 h and 0 h:24 h (light/dark). In addition, the cell-free filtrate of isolate A4 could cause cell wall rupture and increase MDA, POD, CAT and SOD levels in S. gracilis, indicating an algicidal mode of indirect attack. The comparative LC–MS/MS-based metabolomics analysis further revealed that the differential metabolites and relevant metabolic pathways, especially the increased algicidal metabolites and their biosynthesis pathways such as pyrocatechol and benzoate degradation, could probably contribute to the efficient algicidal activity of isolate A4. The findings of this study provide valuable insights into the biological control of harmful Spirogyra using B. subtilis.

Seaweed cultivation, including kelp species, is rapidly expanding in many regions. A widely assumed co-benefit of seaweed farming is increased local carbon sequestration rates (thereby contributing to climate change mitigation), although direct field-based measurements of carbon assimilation and release are largely lacking. We quantified growth, erosion and dislodgement rates of farmed Saccharina latissima in Porthallow Bay (Cornwall, UK) throughout a typical cultivation season to provide insights into the carbon sequestration potential of small-scale kelp farms. Blade elongation rates increased from ~ 1.3 cm day⁻¹ to ~ 2.3 cm day⁻¹ in March–April, before declining to 1.4 cm day⁻¹ by May. Meanwhile, erosion rates remained low, ranging from ~ 0.5 to ~ 0.8 cm day⁻¹. Dislodgement rates decreased from 20% of plants in January–February to 5% in April–May. Rates of carbon accumulation and loss increased from January to May, related to an increase in standing stock. Conservative first-order estimates suggest that the farm captures 0.14 t C ha⁻¹ y⁻¹, of which up to 70% is released into the environment as particulate organic carbon. Based on previous estimates of carbon burial and storage rates, the farm may sequester 0.05 t CO₂e ha⁻¹ y⁻¹. These values suggest that scaling-up European kelp farming should be motivated by other co-benefits, such as low-carbon product alternatives, job creation and potential biodiversity gains, and not be solely driven by a perceived meaningful increase in carbon sequestration. Importantly, further information needs to be obtained from a variety of cultivation sites to develop a better understanding of carbon dynamics associated with kelp farms.