Journal of Applied Phycology最新文献

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.

Pyropia kinositae, a cold-water red algal species found in East Asian marine environments, thrives on aquaculture rafts and adapts to continuous submersion. Its robust growth and suitability for offshore and northern regions make P. kinositae ideal for evolving mariculture practices in China, aligning with the industry's shift towards these areas. This study extensively investigated the optimal cultivation conditions (temperature, light, salinity, and nutrient levels) for the gametophyte generation of P. kinositae, focusing on conchospore germination, conchosporeling growth, and thallus growth. Conchospore germination and conchosporeling growth were optimal at 17 °C and salinity of 25–30, with light intensity optimal at 40–70 μmol photons m⁻² s⁻¹ for conchospore germination and 100 μmol photons m⁻² s⁻¹ for conchosporeling growth. The thalli showed best growth at 2 mg L⁻¹ nitrogen, particularly at 12 °C with light intensity between 30–90 μmol photons m⁻² s⁻¹, where the peak photosynthetic rate and F_v/F_m value were observed, indicating optimal photosynthetic efficiency. Biochemical analysis of the thalli revealed significant variations in pigments such as chlorophyll a and carotenoid, alongside soluble proteins, ATP, and enzymes involved in photosynthesis, respiration, antioxidation, and nitrogen assimilation. Notably, higher nitrogen concentrations led to increased contents of soluble proteins, ATP, chlorophyll a, and carotenoid, as well as elevated activities of phosphofructokinase (PFK), nitrate reductase (NR) and malate dehydrogenase (MDH), suggesting increased nutrient availability enhanced the metabolic activities of the thalli. At a lower nitrogen concentration (0.1 mg L⁻¹), the highest SOD activity and H₂O₂ contents were observed, indicating increased ROS generation and scavenging under stress of nutrient levels. Activities of antioxidant enzymes, such as SOD and CAT, increased with temperature, peaking at 13 °C, highlighting the enhanced defense against oxidative stress at this temperature. Additionally, RuBisCO activity was the highest at a light intensity of 70 μmol photons m⁻² s⁻¹. The optimal environmental conditions for the growth of P. kinositae gametophyte generation were obtained based on the physiological and biochemical performance, offering crucial information for optimizing cultivation practices for this economically valuable macroalga.

Volatile fatty acids (VFA) and reducing sugars (RS) are widely used as platform molecules in biorefineries, facilitating the production of valuable biofuels and chemicals. From an environmental, economic and social perspective, third generation biomass, including macroalgae beach-cast, represents an innovative and optimal solution for the production of these commodities. This study explores the impact of ultrasound pretreatment on the invasive macroalga Rugulopteryx okamurae, aiming to produce RS and VFA through enzymatic hydrolysis and dark fermentation. Several ultrasound conditions were tested: amplitudes (0, 70-100 %), suspension volumes (300, 600 mL), and algal concentrations (4-8 %). Optimal results emerged with 100 % amplitude, 300 mL volume, and 4 % (w/v) algal concentration, leading to the maximum COD solubilization of 61.5 mg COD g-biomass^-1. For enzymatic hydrolysis, the pretreated sample achieved maximum RS concentrations (0.124 g-RS g-biomass^-1) with half the enzyme dosage required by the non-pretreated alga (25 vs 50 FPU g-biomass^-1), implying significant economic benefits for large-scale processes. The kinetic model proposed by Romero-Vargas et al. aligned perfectly with the experimental data, obtaining higher values of all the kinetic parameters for the pretreated sample. Dark fermentation showed substantial increases in organic matter solubilization and VFA production (10.36 mg-HAc g-biomass^-1) post ultrasound pretreatment: 21.1 % higher solubilization and 9.4 % increased VFA compared to non-pretreated biomass. The resulting VFA composition comprised 73 % acetic acid, 13 % propionic acid, and 8 % butyric acid. Utilization of chemical agents during sonication may further enhance overall processing yields.

In South Africa, the green seaweed Ulva lacinulata is grown in land-based integrated multi-trophic aquaculture (IMTA) farms with the abalone Haliotis midae. The Ulva serves as a biofilter and the co-produced Ulva is often used as feed for the abalone. To better understand the potential benefits and risks associated with this practice, this study characterised the bacterial microbiome associated with the seawater and Ulva raceways receiving abalone effluent (IMTA system) and compared this to Ulva tanks supplied with fertilised seawater (non-IMTA; control). Ulva samples were collected from each Ulva system, and water samples were collected at the inlet and outlet of each system. Bacterial communities were assessed using a culture-based approach and next-generation sequencing (NGS) of the V3-V4 16S rDNA region. It was observed that Ulva has the potential to reduce the bacterial load of abalone effluent, with the total number of potential culturable Vibrio species declining from 150×10³ cells mL^-1 in the inlet to 37×10³ cells mL^-1 in the outlet of the Ulva system. The NGS dataset supported these findings, with a reduction observed in Vibrio and Pseudoalteromonas from the inlet to outlet samples. A lower number of genera (p < 0.05) were observed on Ulva when compared with water samples, indicating that Ulva has a beneficial, modulatory effect on bacteria. These findings contribute towards the growing body of evidence for the benefits of seaweeds in IMTA and addresses the biosecurity concerns of abalone farmers wishing to improve the circularity of their farming activities by incorporating seaweeds.

Crustose coralline algae (CCA) from the genus Titanoderma are reported to induce high levels of coral larval settlement across a wide diversity of species. Consequently, Titanoderma is a promising taxon to cultivate in aquaculture facilities for application in coral reef restoration projects. However, knowledge on the optimum conditions to promote growth and reproduction in Titanoderma is limited. To investigate this, we cultured adult fragments of Titanoderma sp. at two temperatures (27.5 or 30 °C) and two light levels (mean maximum midday irradiance of 10 or 40 µmol photons m⁻² s⁻¹) on three different tile materials (CaCO₃, concrete, or PVC). We found that the combination of 27.5 °C and 40 µmol photons m⁻² s⁻¹ were best for adult fragment growth. Greater number of conceptacles were formed under higher light intensities, while temperature did not have an influence. Sporeling settlement and subsequent growth into juveniles were only evident at 40 µmol photons m⁻² s⁻¹, with substantially higher recruitment on substrates made of concrete. These results provide important insights for developing optimal conditions to cultivate Titanoderma sp. in aquaculture facilities to support reef restoration projects using sexually produced corals.