Journal of Applied Phycology最新文献

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.

Mixotrophic cultivation of Haematococcus lacustris is one of the most promising strategies to produce natural astaxanthin. During mixotrophic growth, microalgae assimilate and metabolize organic carbon in addition to photosynthetic growth, resulting in increased biomass productivity. Several studies have evaluated the effect of different organic carbon sources on mixotrophic growth in various microalgae species. However, knowledge of detailed growth kinetics as a function of substrate concentration and light intensity is lacking. In this study, the growth kinetics of H. lacustris using four different carbon sources and the effect of light under mixotrophic and photoautotrophic conditions are described. Mixotrophic cultivation showed significant differences in respect to applied substrate and achieved maximum specific growth rates of 0.91 ± 0.13, 0.19 ± 0.05, 0.36 ± 0.05, and 0.23 ± 0.05 day⁻¹, for acetate, methanol, glucose, and glycerol, respectively. Optimal growth at mixotrophic conditions using acetate was 1.8 times higher than the sum of hetero- and photoautotrophic growth. Furthermore, the optimum light intensity was 1.3 times higher for mixotrophic than for autotrophic growth. Thus, mixotrophy increases light intensity tolerance. These results indicate a strong interconnection between carbon metabolism and photosynthetic activity and lay the foundation for more detailed mathematical models describing the mixotrophic growth of H. lacustris.

Graphical Abstract

The oleaginous genera Nannochloropsis and Microchloropsis are recognized for their lipid accumulation capacity. Microalgal lipid accumulation is triggered by nitrogen starvation, negatively affecting photosynthesis and growth. Moreover, light and temperature play pivotal roles in microalgal physiology, lipid accumulation and composition. This study focuses on comparing the responses of eight microalgal strains from Nannochloropsis (N. oceanica Necton, N. oceanica IMET1, Nannochloropsis. sp. CCAP211/78, N. oculata, and N. limnetica) and Microchloropsis (M. gaditana CCFM01, M. gaditana CCMP526, and M. salina) to light, temperature, and nitrogen availability. Biomass, lipid content and productivities were monitored under different light intensities (150 (LL) and 600 μmol photons m⁻² s⁻¹ (HL)) and temperatures (15, 25, 30℃) under nitrogen (N-) starvation and replete conditions. Under N-starvation and HL, N. sp. exhibited the highest lipid content (59%) and productivity (0.069 g L^-1 day^-1), while N. oculata had the lowest lipid content (37.5%) and productivity (0.037 g L^-1 day^-1) among the eight strains. Notably, M. gaditana CCFM01 achieved the highest EPA content (4.7%), contrasting with N. oceanica IMET1 lowest EPA content (2.9%) under 150 μmol photons m⁻² s⁻¹ and N-repletion. The response to temperature fluctuations under LL was strain-dependent. Microchloropsis salina and M. gaditana CCFM01 demonstrated the highest and lowest lipid productivities (0.069 g L^-1 day^-1 and 0.022 g L^-1 day^-1, respectively) at 15℃ under N-starvation. Moreover, significant EPA accumulation across various strains was observed in N. oculata (5.7%) under N-repletion at 15°C, surpassing M. gaditana CCFM01 by 40%. Ultimately, the physiological responses to cultivation conditions vary markedly among microalgal strains, even within the same genus or species. This knowledge is essential for selecting suitable strains for the efficient microalgal lipid production industry.

Graphical Abstract

Optimi zing cultivation conditions for the maximal lipid production in Nannochloropsis andMicrochloropsis

In-situ macroalgal bioremediation could help prevent and reduce estuarine eutrophication. However, estuaries are dynamic ecosystems characterized by fluctuating abiotic conditions. Therefore, target macroalgal species for in-situ estuarine bioremediation must be able to maintain productivity under a range of challenging abiotic conditions. The aim of this study was to assess the tolerance of the novel bioremediation target Gracilaria transtasmanica to ambient and extreme levels of salinity, air-exposure, and light limitation that occur in estuarine environments. Three separate experiments were conducted to assess tolerance to each factor and photosynthetic functioning and growth were used to quantify the tolerance range of G. transtasmanica in each experiment. Specific Growth Rate (SGR) was significantly affected by salinity, air-exposure, and light limitation. Gracilaria transtasmanica was able to grow in salinities of 5 to 35 ppt, but growth rates decreased with decreasing salinity. Air-exposure periods of up to 9 h were tolerated, but growth rates decreased as air-exposure period increased. Gracilaria transtasmanica was able to maintain growth with a loss of up to 75% of ambient light and was also able to tolerate short periods (48 h) of continuous darkness. Photosynthetic function was unaffected by salinity, air-exposure, or light limitation. These results demonstrate the high tolerance of G. transtasmanica to light limitation, air-exposure and a broad range of salinities. Consequently, this species could be cultivated in a range of habitat types within estuaries. However, the optimal habitats for cultivation will be submerged subtidal channels and lower intertidal mudflats where the impacts of freshwater inflows and air-exposure are reduced.

The aim of this study was to evaluate the impact of cyanobacteria as a soil inoculant for cultivation of the medicinal plant, Allium sativum. Cyanobacterial strains isolated from the medicinal plant field were cultured in BG11/BG11° medium. Three cyanobacterial isolates, Nostoc sp. HNBGU 006 (NS-TGS), Pseudanabaena biceps (PaS-TGiS), Chroococcus turgidus (CS-TTS), were selected for in-vitro assays. Seedling growth assays were performed with A. sativum and Raphanus sativus seeds primed with different concentration of aqueous extracts prepared from these isolates. Live cell suspension of the selected cyanobacterium, NS-TGS, was inoculated in pot soil to observe the effect of cyanobacterization on growth of A. sativum. Maximum enhancement in all the growth parameters was exhibited by 1% aqueous extract of NS-TGS in comparison to control. The result of NS-TGS inoculation in pot soil revealed an increase of 54.92 % in root length, 31.28 % in shoot length, 112 % in dry weight and 50.33 % in yield. An enhancement of 84.28% in the allicin content was also recorded in cloves grown in treated soil as compared to control. There was significant enhancement in soil and leaf chlorophyll as well as soil potassium content with the highest recorded in the treatment BSI (before sowing inoculation) + ASI (after sowing inoculation). This study provides an insight to the cyanobacterization of soil with NS-TGS for the cultivation of A. sativum herb and is consistent with the sustainable agriculture approach.

Epimicrobiota associated with seaweeds are crucial for the health and development of their hosts due to their ability to produce antibiotics, phytohormones and vitamins, etc. However, there is limited knowledge related to the microbiota of commercially cultivated seaweed Saccharina japonica. In this study, we investigated the dynamics of microbiota associated with S. japonica from mature sporophytes to sporelings (usually from September to November) using Illumina sequencing of the V3-V4 hypervariable region of 16S rRNA gene. The composition and structure of epimicrobiota showed significant differences from mature sporophytes to 6-week-old sporelings (pairwise comparison: p < 0.05) and were relatively stable from 7-week-old sporelings to 8-week-old sporelings (pairwise comparison: p > 0.05). Blastopirellula and Pseudoalteromonas were the dominant genera of the community of mature sporophytes and 6-week-old sporelings, respectively. Rubritalea was the most dominant genus for both 7 and 8-week-old sporelings. These three genera were also part of the core microbiota, suggesting that they may play an essential function within the S. japonica holobiont. In addition, members of the Planctomicrobium and Roseibacillus were identified as both drivers (driving the dynamics of adjacent bacterial communities) and keystone taxa (critical for the stability and function of bacterial communities), which might be responsible for the epimicrobiota shifts from 7-week-old sporelings to 8-week-old sporelings and were fundamental for the newly assembled epimicrobiota. This study not only enriches the baseline data related to the microbiota of the commercially farmed S. japonica, but also helps nursery farms to develop techniques for disease control by monitoring the shifts of dominant taxa, core species, indicator species or keystone taxa.