Journal of Applied Phycology最新文献

Benthic phototrophic communities play a crucial role in the functioning of shallow lake ecosystems. The complexity of benthic algal communities poses challenges for exploring their fine structures using traditional methods such as light microscopy. However, confocal laser scanning microscopy (CLSM) offers the potential for microscale-level structural investigation of phototrophic biofilms, thereby contributing to a deeper understanding of the structural and compositional changes within these communities. The primary objective of this study was to develop a relatively rapid, semi-automated, and freely available image processing method to facilitate the tracking of spatio-temporal alterations in intact biofilms. To evaluate our image processing method, we conducted an eight-week long outdoor mesocosm experiment, manipulating temperatures based on two global warming scenarios (assuming intermediate- and high degree of greenhouse gas emission), with increases of 3°C and 5°C, respectively, compared to the reference/unheated mesocosms. Eight limestone cubes were placed on the bottom of each mesocosm to provide 'natural' surfaces for phytobenthos colonization, which was subsequently analysed by confocal microscopy. We hypothesized that increasing water temperature might have a significant impact on the taxonomic composition of algal biofilms, particularly on the abundance of phototrophic prokaryotes and eukaryotes. The designed 'FIJI macro' efficiently analysed the recorded images, including single images, series of Z-stack images, and projection images. Our image processing method effectively discriminated photosynthetic prokaryotes and eukaryotes based on their pigment composition and proved suitable for the high-throughput analysis of structural and compositional changes in algal biofilms. Moreover, this study confirmed that climate-induced warming can lead to an increasing dominance of cyanobacteria in benthic phototrophic communities at the expense of eukaryotic algae.

The human population is steadily increasing and new alternative protein sources are necessary to secure food safety. There is a growing interest in macroalgae, or seaweed, as an alternative food source as they are rich in nutrients, minerals and carbohydrates. Among the diverse species of macroalga, Palmaria palmata, a red seaweed of growing interest due to its high protein content, represents a potential candidate for contributing to food security and animal feed. Novel methods are being investigated for extracting valuable components from seaweed, including protein. In this study, pulsed electric field (PEF) and enzymatic assisted extraction (EAE) were tested to investigate whether the methods, alone or in combination, were sufficient for protein extraction from P. palmata. The results show high extraction yields of dry matter consisting mostly of carbohydrates and ash when using EAE. The results point to a concentration of protein, including essential amino acids, in the pellet after extraction with a combination of PEF and EAE, or EAE alone. There is potential for the protein-rich pellet in animal feed. For the supernatant, there are potential uses within biostimulants.

In this study two types of marine algae: red algae (Callithamnion corymbosum – CC-RAB) and green algae (Ulva lactuca – UL-GAB), were used for the retention of Cu²⁺, Zn²⁺ and Co²⁺ ions from aqueous media, by biosorption. Both types of marine algae are abundant on the Romanian coast of the Black Sea and, since they have no uses, they represent a serious problem for the beach area. Therefore, their use as biosorbents for the recovery of some metal ions of strategic industrial importance (such as Cu²⁺, Zn²⁺ and Co²⁺ ions) may represent a way to valorise this biomass resource. In order to evaluate the biosorptive performances of the red algae biomass (CC-RAB) and green algae biomass (UL-GAB), batch experimental studies were carried out at different initial solution pH, biosorbent dose, initial metal ions concentration contact time and temperature. The optimal conditions (pH = 5.0; 2.0 g biosorbent L^-1, 3 h, 25 ±1 °C) were then used to obtain kinetic curves and biosorption isotherms, which were modelled. The pseudo-second order kinetic model best fits the kinetic data, while the biosorption isotherms are described by the Langmuir model, for all studied metal ions on both biosorbents. The maximum biosorption capacity depends on the nature of algae biosorbent, and follows the order: Cu²⁺ (81.25 mg g^-1) > Zn²⁺ (73.69 mg g^-1) > Co²⁺ (27.89 mg g^-1) in the case of CC-RAB, and Zn²⁺ (69.29 mg g^-1) > Cu²⁺ (43.47 mg g^-1) > Co²⁺ (26.15 mg g^-1) in the case of UL-GAB. The thermodynamic parameters (∆G⁰, ∆H⁰ and ∆S⁰) were also evaluated, and the obtained values indicate that all biosorption processes are spontaneous and endothermic. In addition, desorption of metal ions is quantitative in acid media, but the biosorption capacities decrease significantly after the first cycle of use. All these aspects have important environmental implications, and may provide benchmarks in the design of a strategy for the valorisation of this biomass resource.

Gracilaria cornea was exposed to different irradiance intensities (low, moderate, and high) and light qualities (white and white + blue) in experimental cultures. Photosynthetic physiology was measured through daily growth rate, maximum photosynthesis, maximum photochemical efficiency, pigment content (chlorophyll a, phycobiliproteins, carotenoids), and elemental content of carbon and nitrogen. Gracilaria cornea effectively acclimated to low irradiance conditions and displayed tolerance to moderate irradiance, whereas high irradiance resulted in the deterioration of thalli. A decrease in maximum photochemical efficiency and maximum photosynthesis rate under high irradiance conditions was observed. Pigment content decreased during the acclimation period at high irradiance levels but increased when blue light was added under moderate irradiance conditions. The antioxidant capacity decreased in thalli exposed to high irradiance conditions, whereas the addition of blue light increased antioxidant capacity. Overall, the combination of white and blue light stimulated the accumulation of all evaluated compounds in G. cornea. Interestingly, higher values for photosynthesis, pigments, and certain antioxidants were observed under low irradiance conditions. These findings enhance our understanding of the adaptation strategies employed by G. cornea, potentially leading to improvements in indoor cultivation and the control of chemical compound production for nutraceutical applications.

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.

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.

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.

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.