Synergistic effects of starch and carrageenan from Kappaphycus alvarezii in composite film formation: Physicochemical and degradable properties.

Rising concerns around plastic pollution from single-use plastic (SUPs), especially food packaging, have driven interest in sustainable alternatives. As such, algae biomass has gained attention for bioplastic production due to algae's rapid growth and abundant polysaccharides. This research focuses on extracting carrageenan from Kappaphycus alvarezii, extensively cultivated in Sabah, Malaysia, and utilizing it in combination with starch and glycerol to develop algae-based films. The physicochemical properties and degradation rate of these films were evaluated, revealing that the addition of carrageenan enhanced overall thermal stability meanwhile increasing water solubility, water content but reducing the degradation rate and swelling degree. This is primarily due to the crystalline structures of carrageenan, which provide a more rigid arrangement compared to the network of starch polymers. However, the incorporation of starch into the blends has enhanced the elongation and surface morphology, resulting in more balanced properties. Overall, these carrageenan films displayed impressive thermal, mechanical, and biodegradability characteristics, establishing their viability as substitutes for conventional plastics.

L-Lactate dehydrogenase from Cyanidioschyzon merolae shows high catalytic efficiency for pyruvate reduction and is inhibited by ATP.

L-Lactate is a commodity chemical used in various fields. Microorganisms have produced L-lactate via lactic fermentation using saccharides derived from crops as carbon sources. Recently, L-lactate production using microalgae, whose carbon source is carbon dioxide, has been spotlighted because the prices of the crops have increased. A red alga Cyanidioschyzon merolae produce L-lactate via lactic fermentation under dark anaerobic conditions. The L-lactate titer of C. merolae is higher than those of other microalgae but lower than those of heterotrophic bacteria. Therefore, an increase in the L-lactate titer is required in C. merolae. L-Lactate dehydrogenase (L-LDH) catalyzes the reduction of pyruvate to L-lactate during lactic fermentation. C. merolae possesses five isozymes of L-LDH. The results of previous transcriptome analysis suggested that L-LDHs are the key enzymes in the lactic fermentation of C. merolae. However, their biochemical characteristics, such as catalytic efficiency and tolerance for metabolites, have not been revealed. We compared the amino acid sequences of C. merolae L-LDHs (CmLDHs) and characterized one of the isozymes, CmLDH1. BLAST analysis revealed that the sequence similarities of CmLDH1 and the other isozymes were above 99%. The catalytic efficiency of CmLDH1 under its optimum conditions was higher than those of L-LDHs of other organisms. ATP decreased the affinity and turnover number of CmLDH1 for NADH. These findings contribute to understanding the characteristics of L-LDHs of microalgae and the regulatory mechanisms of lactic fermentation in C. merolae.

Towards sustainable water management for Galdieria sulphuraria cultivation.

The red microalga Galdieria sulphuraria has emerged as a promising biotechnological platform for large-scale cultivation and production of high-value compounds, such as the blue pigment phycocyanin. However, a large amount of freshwater and a substantial supply of nutrients challenge both the environmental and the economic sustainability of algal cultivation. Additionally, the extremophilic nature of Galdieria sulphuraria requires cultivation in an acidic culture medium that directly leads to strongly acidic wastewater, which in turn generally exceeds legal limits for industrial wastewater discharge. This research aims to address these challenges, by investigating cultivation water reuse as a strategy to reduce the impacts of Galdieria sulphuraria management. The results indicated that a 25 % water reuse may be easily implemented and showed to be effective at the pilot scale, providing no significant changes in microalgae growth (biomass productivity ~0.21 g L-1 d-1) or in phycocyanin accumulation (~ 10.8 % w/w) after three consecutive cultivation cycles in reused water. Moreover, a single cultivation cycle with water reuse percentages of 71 and 98 %, achieved with membrane filtration and with centrifugation, respectively, was also successful (biomass productivity ~0.24 g L-1 d-1). These findings encourage freshwater reuse implementations in the microalgae sector and support further investigations focusing on coupling cultivation and harvesting in continuous, real-scale configurations. Centrifugation and membrane filtration required substantially different specific electrical energy consumption for water reuse and biomass concentration: in real applications, the former technique would roughly span from 1 to 10 kWh m-3 while the latter is expected to fall within the ample range 0.1-100 kWh m-3, strongly dependent on system size. For this reason, the most suitable separation train should be chosen on a case-by-case basis, considering the prevailing flow rate and the target biomass concentration factor targeted by the separation process.

Enhancing tomato plant immune responses to Fusarium wilt disease by red seaweed Jania sp.

The novelty of this study lies in demonstrating a new approach to control wilt diseases using Jania ethyl acetate extract. In the current investigation, the potential impacts of Jania sp. ethyl acetate extract (JE) on Tomato Fusarium oxysporum wilt (FOW) have been studied. The in vitro antifungal potential of JE against F. oxysporum (FO) was examined. GC-MS investigation of the JE revealed that, the compounds possessing fungicidal action were Phenol,2-methoxy-4-(2-propenyl)-,acetate, Eugenol, Caryophyllene oxide, Isoespintanol, Cadinene, Caryophylla-4(12),8(13)-dien-5à-ol and Copaen. Jania sp. ethyl acetate extract exhibited strong antifungal potential against FO, achieving a 20 mmzone of inhibition. In the experiment, two different methods were applied: soil irrigation (SI) and foliar application (FS) of JE. The results showed that both treatments reduced disease index present DIP by 20.83% and 33.33% respectively. The findings indicated that during FOW, proline, phenolics, and the antioxidant enzymes activity increased, while growth and photosynthetic pigments decreased. The morphological features, photosynthetic pigments, total phenol content, and antioxidant enzyme activity of infected plants improved when JE was applied through soil or foliar methods. It is interesting to note that the application of JE had a substantially less negative effect on the isozymes peroxidase and polyphenol oxidase in tomato plants, compared to FOW. These reactions differed depending on whether JE was applied foliarly or via the soil. Finally, the use of Jania sp. could be utilized commercially as an ecologically acceptable method to protect tomato plants against FOW.

Evaluation of Antioxidant Activity of Residue from Bioethanol Production Using Seaweed Biomass.

This study explores the potential of producing bioethanol from seaweed biomass and reusing the residues as antioxidant compounds. Various types of seaweed, including red (Gelidium amansii, Gloiopeltis furcata, Pyropia tenera), brown (Saccharina japonica, Undaria pinnatifida, Ascophyllum nodosum), and green species (Ulva intestinalis, Ulva prolifera, Codium fragile), were pretreated with dilute acid and enzymes and subsequently processed to produce bioethanol with Saccharomyces cerevisiae BY4741. Ethanol production followed the utilization of sugars, resulting in the highest yields from red algae > brown algae > green algae due to their high carbohydrate content. The residual biomass was extracted with water, ethanol, or methanol to evaluate its antioxidant activity. Among the nine seaweeds, the A. nodosum bioethanol residue extract (BRE) showed the highest antioxidant activity regarding the 2,2-diphenyl-1-picrylhydrazyl (DPPH) activity, ferric reducing antioxidant power (FRAP), and reactive oxygen species (ROS) inhibition of H2O2-treated RAW 264.7 cells. These by-products can be valorized, contributing to a more sustainable and economically viable biorefinery process. This dual approach not only enhances the utilization of marine resources but also supports the development of high-value bioproducts.

Insights into the physiology, biochemistry and ecological significance of the red seaweed Tricleocarpa fragilis in the Andaman Sea.

The present study focused on the physiological and biochemical aspects of Tricleocarpa fragilis, red seaweed belonging to the phylum Rhodophyta, along the South Andaman coast, with particular attention given to its symbiotic relationships with associated flora and fauna. The physicochemical parameters of the seawater at the sampling station, such as its temperature, pH, and salinity, were meticulously analyzed to determine the optimal harvesting period for T. fragilis. Seaweeds attach to rocks, dead corals, and shells in shallow areas exposed to moderate wave action because of its habitat preferences. Temporal variations in biomass production were estimated, revealing the highest peak in March, which was correlated with optimal seawater conditions, including a temperature of 34 ± 1.1 °C, a pH of 8 ± 0.1, and a salinity of 32 ± 0.8 psu. GC‒MS analysis revealed n-hexadecanoic acid as the dominant compound among the 36 peaks, with major bioactive compounds identified as fatty acids, diterpenes, phenolic compounds, and hydrocarbons. This research not only enhances our understanding of ecological dynamics but also provides valuable insights into the intricate biochemical processes of T. fragilis. The established antimicrobial potential and characterization of bioactive compounds from T. fragilis lay a foundation for possible applications in the pharmaceutical industry and other industries.

Insight into the efficiency of microalgae' lipidic extracts as photosensitizers for Antimicrobial Photodynamic Therapy against Staphylococcus aureus.

Antibacterial resistance causes around 1.27 million deaths annually around the globe and has been recognized as a top 3 priority health threat. Antimicrobial photodynamic therapy (aPDT) is considered a promising alternative to conventional antibiotic treatments. Algal lipid extracts have shown antibacterial effects when used as photosensitizers (PSs) in aPDT. In this work we assessed the photodynamic efficiency of lipidic extracts of microalgae belonging to different phyla (Bacillariophyta, Chlorophyta, Cyanobacteria, Haptophyta, Ochrophyta and Rhodophyta). All the extracts (at 1 mg mL-1) demonstrated a reduction of Staphylococcus aureus >3 log10 (CFU mL-1), exhibiting bactericidal activity. Bacillariophyta and Haptophyta extracts were the top-performing phyla against S. aureus, achieving a reduction >6 log10 (CFU mL-1) with light doses of 60 J cm-2 (Bacillariophyta) and 90 J cm-2 (Haptophyta). The photodynamic properties of the Bacillariophyta Phaeodactylum tricornutum and the Haptophyta Tisochrysis lutea, the best effective microalgae lipid extracts, were also assessed at lower concentrations (75 µg mL-1, 7.5 µg mL-1, and 3.75 µg mL-1), reaching, in general, inactivation rates higher than those obtained with the widely used PSs, such as Methylene Blue and Chlorine e6, at lower concentration and light dose. The presence of chlorophyll c, which can absorb a greater amount of energy than chlorophylls a and b; rich content of polyunsaturated fatty acids (PUFAs) and fucoxanthin, which can also produce ROS, e.g. singlet oxygen (1O2), when photo-energized; a lack of photoprotective carotenoids such as ß-carotene, and low content of tocopherol, were associated with the algal extracts with higher antimicrobial activity against S. aureus. The bactericidal activity exhibited by the extracts seems to result from the photooxidation of microalgae PUFAs by the 1O2 and/or other ROS produced by irradiated chlorophylls/carotenoids, which eventually led to bacterial lipid peroxidation and cell death, but further studies are needed to confirm this hypothesis. These results revealed the potential of an unexplored source of natural photosensitizers (microalgae lipid extracts) that can be used as PSs in aPDT as an alternative to conventional antibiotic treatments, and even to conventional PSs, to combat antibacterial resistance.

Ultrasound Depolymerization and Characterization of Poly- and Oligosaccharides from the Red Alga Solieria chordalis (C. Agardh) J. Agardh 1842.

Red seaweed carrageenans are frequently used in industry for its texturizing properties and have demonstrated antiviral activities that can be used in human medicine. However, their high viscosity, high molecular weight, and low skin penetration limit their use. Low-weight carrageenans have a reduced viscosity and molecular weight, enhancing their biological properties. In this study, ι-carrageenan from Solieria chordalis, extracted using hot water and dialyzed, was depolymerized using hydrogen peroxide and ultrasound. Ultrasonic depolymerization yielded fractions of average molecular weight (50 kDa) that were rich in sulfate groups (16% and 33%) compared to those from the hydrogen peroxide treatment (7 kDa, 6% and 9%). The potential bioactivity of the polysaccharides and low-molecular-weight (LMW) fractions were assessed using WST-1 and LDH assays for human fibroblast viability, proliferation, and cytotoxicity. The depolymerized fractions did not affect cell proliferation and were not cytotoxic. This research highlights the diversity in the biochemical composition and lack of cytotoxicity of Solieria chordalis polysaccharides and LMW fractions produced by a green (ultrasound) depolymerization method.

Effect of the dietary supplementation with sunflower oil-enriched bromoform from Asparagopsis taxiformis on lambs' growth, health, and ruminal methane production.

The red seaweed Asparagopsis taxiformis has a potent antimethanogenic effect, which has been proven both in vitro and in vivo. Vegetable oil immersions of this seaweed (hereafter Bromoil) help stabilise the bromoform (CHBr3) responsible for its antimethanogenic effect. We evaluate the effects of increasing the levels of CHBr3 in lamb diets on growth performance, methane (CH4) production, animal health and meat quality. Twenty-four Merino Branco ram lambs were fed a ground complete compound feed, supplemented with 50 mL/kg DM of sunflower oil with different CHBr3 content. The treatments were defined by the CHBr3 doses in the oil: 0 mg (control - B0), 15 mg (B15), 30 mg (B30) and 45 mg (B45) of CHBr3 per kg of feed DM. The feed was prepared daily by mixing Bromoil with the compound feed. At the end of the experiment, the lambs were sacrificed, the ruminal content was collected for in vitro fermentation to evaluate CH4 production and organic matter (OM) degradability, and the rumen mucosa was sampled for histological examination. Meat samples were collected for chemical composition and CHBr3 analysis. The half-life of CHBr3 in the air-exposed feed was 3.98 h making it very difficult to establish the practiced level of CHBr3 supplementation. Lambs-fed treatments B30 and B45 decreased DM intake by up to 28%. Average daily gain was also reduced due to CHBr3 supplementation, with B45 showing results 40% lower than B0. DM feed conversion ratio was similar for all treatments. The degradability of OM, the volume of total gas and of gas without CH4 were unaffected by the experimental treatments, evaluated by the in vitro method. However, the volume of CH4 decreased by up to 75% for treatments above 30 mg/kg DM, while the yield of CH4/g OM degraded was reduced by up to 78% with treatments above 30 mg/kg DM. Meat chemical composition was not affected by Bromoil supplementation and no traces of CHBr3 were found in meat samples. During this experiment, the animals presented normal health and behaviour. However, postslaughter examination of the rumen showed distinct lesions on the ventral region of the rumen mucosa of animals supplemented with Bromoil. These lesions were more severe in the animals receiving treatments B30 and B45. This research determined that although concentrations of CHBr3 in the diet above 30 mg/kg DM helped to reduce CH4 emissions, it negatively affected the performance and rumen wall.

Iodine identification in major edible seaweed Kappaphycus alvarezii and establishment of an iodine reduction method for its protein extract for utilization as a protein source.

Kappaphycus alvarezii is the most widely cultivated seaweed globally. The use of the protein contained in K. alvarezii as an alternative protein source seems to be an effective countermeasure against the protein crisis. Here, we identified the iodine chemical species in K. alvarezii and developed an iodine reduction method. We used various fractionation methods and showed that almost all the iodine in the K. alvarezii alkali extract is present as an iodinated protein, and reducing the amount of iodine per protein was difficult. Subsequently, an iodine reduction method was established to cleave the covalent bonds between the protein and iodine, and we could successfully reduce the amount of iodine per protein by approximately half.

The photosynthetic performance and photoprotective role of carotenoids response to light stress in intertidal red algae Neoporphyra haitanensis.

Neoporphyra haitanensis, a red alga harvested for food, thrives in the intertidal zone amid dynamic and harsh environments. High irradiance represents a major stressor in this habitat, posing a threat to the alga's photosynthetic apparatus. Interestingly, N. haitanensis has adapted to excessive light despite the absence of a crucial xanthophyll cycle-dependent photoprotection pathway. Thus, it is valuable to investigate the mechanisms by which N. haitanensis copes with excessive light and to understand the photoprotective roles of carotenoids. Under high light intensities and prolonged irradiation time, N. haitanensis displayed reduction in photosynthetic efficiency and phycobiliproteins levels, as well as different responses in carotenoids. The decreased carotene contents suggested their involvement in the synthesis of xanthophylls, as evidenced by the up-regulation of lycopene-ß-cyclase (lcyb) and zeaxanthin epoxidase (zep) genes. Downstream xanthophylls such as lutein, zeaxanthin, and antheraxanthin increased proportionally to light stress, potentially participating in scavenging reactive oxygen species (ROS). When accompanied by the enhanced activity of ascorbate peroxidase (APX), these factors resulted in a reduction in ROS production. The responses of intermediates α-cryptoxanthin and ß-cryptoxanthin were felt somewhere between carotenes and zeaxanthin/lutein. Furthermore, these changes were ameliorated when the organism was placed in darkness. In summary, down-regulation of the organism's photosynthetic capacity, coupled with heightened xanthophylls and APX activity, activates photoinhibition quenching (qI) and antioxidant activity, helping N. haitanensis to protect the organism from the damaging effects of excessive light exposure. These findings provide insights into how red algae adapt to intertidal lifestyles.

Exploring the bioactive potential of algae residue extract via subcritical water extraction: Insights into chemical composition and biological activity.

Gelidium sesquipedale is valued in the Spanish agar industry, but its production generates substantial waste, often discarded despite its nutritional and bioactive content. Subcritical water extraction (SWE) at 175 °C and 50 bar for 130 min was performed on this waste after agar extraction, comparing it to conventional ethanol extraction. The SWE extract exhibited superior nutritional profile, including proteins (170.6 ± 1.0 mg/gfreeze-dried-extract), essential amino acids (18.1%), carbohydrates (148.1 ± 0.3 mg/gfreeze-dried-extract), total phenolic content (57 ± 7 mg-EqGA/gfreeze-dried-extract), and also containing Maillard reaction compounds, such as 5-hydroxymethylfurfural, furfural, 2-furanmethanol, 1-(2-furanyl)-ethanone, and 5-methyl-2-furfural, influencing color, aroma and flavor. This extract showed better antioxidant and anti-inflammatory properties than the conventional extract, and higher xanthine oxidase, tyrosinase, and acetylcholinesterase inhibition activities. Toxicological assessment on human cells indicated the safety of the SWE extract. Therefore, SWE technology offers a promising method to valorize G. sesquipedale residue, yielding a bioactive and nutrient-rich extract suitable for food and nutraceutical applications.

Traditional and new trend strategies to enhance pigment contents in microalgae.

Microalgae are a source of a wide variety of commodities, including particularly valuable pigments. The typical pigments present in microalgae are the chlorophylls, carotenoids, and phycobiliproteins. However, other types of pigments, of the family of water-soluble polyphenols, usually encountered in terrestrial plants, have been recently reported in microalgae. Among such microalgal polyphenols, many flavonoids have a yellowish hue, and are used as natural textile dyes. Besides being used as natural colorants, for example in the food or cosmetic industry, microalgal pigments also possess many bioactive properties, making them functional as nutraceutical or pharmaceutical agents. Each type of pigment, with its own chemical structure, fulfills particular biological functions. Considering both eukaryotes and prokaryotes, some species within the four most promising microalgae groups (Cyanobacteria, Rhodophyta, Chlorophyta and Heterokontophyta) are distinguished by their high contents of specific added-value pigments. To further enhance microalgae pigment contents during autotrophic cultivation, a review is made of the main related strategies adopted during the last decade, including light adjustments (quantity and quality, and the duration of the photoperiod cycle), and regard to mineral medium characteristics (salinity, nutrients concentrations, presence of inductive chemicals). In contrast to what is usually observed for growth-related pigments, accumulation of non-photosynthetic pigments (polyphenols and secondary carotenoids) requires particularly stressful conditions. Finally, pigment enrichment is also made possible with two new cutting-edge technologies, via the application of metallic nanoparticles or magnetic fields.

Penicianstinoids F-K, six undescribed meroterpenoids from the marine algicolous fungus Penicillium sp. RR-DL-1-7.

Six previously undescribed meroterpenoids, penicianstinoids F-K (1-6), together with four known analogues, dehydroaustinol (7), dehydroaustin (8), penicianstinoid A (9), and furanoaustinol (10), were isolated from the cultures of the algicolous fungus Penicillium sp. RR-DL-1-7, derived from the red alga Rhodomela confervoides. Their structures and relative configuration were established by detailed spectroscopic analysis of NMR and HR-MS experiments, and the absolute configurations were assigned by X-ray diffraction and ECD spectral analysis. None of the isolates showed obvious growth inhibitory effects against five plankton and four bacteria species tested.

A multiscale analysis of coralline algae Lithophylloideae (Corallinophycidae, Rhodophyta) shedding new light on understanding cryptic diversity.

Cryptic diversity abounds in many biological species, posing challenges to our understanding of biological diversity, conservation and management. Taking the common coralline algae, the subfamily Lithophylloideae as an illustration, this study delved into the implications of cryptic diversity through global-level phylogenetic and geographical analysis based upon Lithophylloideae molecular data worldwide, as well as a multi-locus time-calibrated phylogeny to elucidate their possible evolutionary process. The multiscale analysis revealed the polyphyly in current concept of the genus Lithophyllum. Geographic isolation resulting from the Tethys terminal event (TTE) has led to two distinct distribution regions for this so-called cosmopolitan genus: one regionally distributed along European coasts/Mediterranean that should include the taxonomical Lithophyllum; others widely distributed, particularly among pan-tropic waters, suggesting at least five groups to be rediscovered within the subfamily Lithophylloideae. Meanwhile, the cryptic genus Titanoderma, lacking morphological identification features with Lithophyllum, exhibited differences in distribution and evolutionary patterns consistent with their ecological habits, thus supporting their separation. This study provided useful hints for cryptic diversity, which advocated an integrative thinking to investigating global cryptic diversity and exploring the broad linkages between phylogenetic relationships and evolutionary origin, biogeography, morphological and ecological traits to achieve a more comprehensive understanding of biodiversity.

Dilute acid-assisted microbubbles-mediated ozonolysis of Eucheuma denticulatum phycocolloid for biobased L-lactic acid production.

Biobased L-lactic acid (L-LA) appeals to industries; however, existing technologies are plagued by limited productivity and high energy consumption. This study established an integrated process for producing macroalgae-based L-LA from Eucheuma denticulatum phycocolloid (EDP). Dilute acid-assisted microbubbles-mediated ozonolysis (DAMMO) was selected for the ozonolysis of EDP to optimize D-galactose recovery. Through single-factor optimization of DAMMO treatment, a maximum D-galactose recovery efficiency (59.10 %) was achieved using 0.15 M H2SO4 at 80 °C for 75 min. Fermentation with 3 % (w/v) mixed microbial cells (Bacillus coagulans ATCC 7050 and Lactobacillus acidophilus-14) and fermented residues achieved a 97.67 % L-LA yield. Additionally, this culture approach was further evaluated in repeated-batch fermentation and showed an average L-LA yield of 93.30 %, providing a feasible concept for macroalgae-based L-LA production.

The role of species thermal plasticity for alien species invasibility in a changing climate: A case study of Lophocladia trichoclados.

The Mediterranean Sea provides fertile ground for understanding the complex interplay between invasive species and native habitats, particularly within the context of climate change. This thermal tolerance study reveals the remarkable ability of Lophocladia trichoclados, a red algae species that has proven highly invasive, to adapt to varying temperatures, particularly thriving in colder Mediterranean waters, where it can withstand temperatures as low as 14 °C, a trait not observed in its native habitat. This rapid acclimation, occurring in less than a century, might entail a trade-off with high temperature resistance. Additionally, all sampled populations in the Mediterranean share the same haplotype, suggesting a common origin and the possibility that we might be facing an exceptionally acclimatable and invasive strain. This high degree of acclimatability could determine the future spread capacity in a changing scenario, highlighting the importance of considering both acclimation and adaptation in understanding the expansion of invasive species' ranges.

Microbiome-informed study of the mechanistic basis of methane inhibition by Asparagopsis taxiformis in dairy cattle.

Copious amounts of methane, a major constituent of greenhouse gases currently driving climate change, are emitted by livestock, and efficient methods that curb such emissions are urgently needed to reduce global warming. When fed to cows, the red seaweed Asparagopsis taxiformis (AT) can reduce enteric methane emissions by up to 80%, but the achieved results can vary widely. Livestock produce methane as a byproduct of methanogenesis, which occurs during the breakdown of feed by microbes in the rumen. The ruminant microbiome is a diverse ecosystem comprising bacteria, protozoa, fungi, and archaea, and methanogenic archaea work synergistically with bacteria to produce methane. Here, we find that an effective reduction in methane emission by high-dose AT (0.5% dry matter intake) was associated with a reduction in methanol-utilizing Methanosphaera within the rumen, suggesting that they may play a greater role in methane formation than previously thought. However, a later spike in Methanosphaera suggested an acquired resistance, possibly via the reductive dehalogenation of bromoform. While we found that AT inhibition of methanogenesis indirectly impacted ruminal bacteria and fermentation pathways due to an increase in spared H2, we also found that an increase in butyrate synthesis was due to a direct effect of AT on butyrate-producing bacteria such as Butyrivibrio, Moryella, and Eubacterium. Together, our findings provide several novel insights into the impact of AT on both methane emissions and the microbiome, thereby elucidating additional pathways that may need to be targeted to maintain its inhibitory effects while preserving microbiome health and animal productivity. IMPORTANCE: Livestock emits copious quantities of methane, a major constituent of the greenhouse gases currently driving climate change. Methanogens within the bovine rumen produce methane during the breakdown of feed. While the red seaweed Asparagopsis taxiformis (AT) can significantly reduce methane emissions when fed to cows, its effects appear short-lived. This study revealed that the effective reduction of methane emissions by AT was accompanied by the near-total elimination of methane-generating Methanosphaera. However, Methanosphaera populations subsequently rebounded due to their ability to inactivate bromoform, a major inhibitor of methane formation found in AT. This study presents novel findings on the contribution of Methanosphaera to ruminal methanogenesis, the mode of action of AT, and the possibility for complementing different strategies to effectively curb methane emissions.

Assessing the impact of arsenite and arsenate on Sarcodia suae: a tale of two toxicities.

Inorganic arsenic (iAs), which predominantly occurs as arsenite (As3+) and arsenate (As5+) in natural water, is primarily accumulated by seaweed in marine environments. However, the detailed mechanisms through which As3+ and As5+ affect the physiological processes of these organisms remain largely unknown. This study focused on evaluating the toxicological effects of As3+ and As5+ on the seaweed Sarcodia suae. Exposure to As3+ and As5+ resulted in IC50 values of 401.5 ± 9.4 µg L-1 and 975.8 ± 13 µg L-1, respectively. Morphological alterations and a reduction in phycoerythrin content were observed, particularly under As3+ exposure, with increased lipid peroxidation as evidenced by higher malondialdehyde levels. Exposure to As3+ also elevated the production of superoxide radicals, while decreasing hydrogen peroxide levels specifically in the presence of As3+. The induction of antioxidative enzyme activities, namely superoxide dismutase, catalase, glutathione reductase, and ascorbate peroxidase was observed, signaling an adaptive response to iAs-induced oxidative stress. Moreover, levels of the antioxidants ascorbate and glutathione were elevated post-exposure, especially in response to As3+. Additionally, bioaccumulation of arsenic was significantly higher in the As3+ compared to As5+. Collectively, the data suggest that As3+ imposes greater adverse effects and oxidative stress to S. suae, which responds by adjusting its antioxidative defense mechanisms to mitigate oxidative stress.

Molecular Dynamics Simulation Reveal the Structure-Activity Relationships of Kainoid Synthases.

Kainoid synthases are key enzymes in the biosynthesis of kainoids. Kainoids, as represented by DA and KA, are a class of naturally occurring non-protein amino acids with strong neurotransmitter activity in the mammalian central nervous system. Marine algae kainoid synthases include PnDabC from diatoms, which synthesizes domoic acid (DA), and DsKabC and GfKabC from red algae, which synthesize kainic acid (KA). Elucidation of the catalytic mechanism of kainoid synthases is of great significance for the rational design of better biocatalysts to promote the industrial production of kainoids for use in new drugs. Through modeling, molecular docking, and molecular dynamics simulations, we investigated the conformational dynamics of kainoid synthases. We found that the kainoid synthase complexes showed different stability in the simulation, and the binding and catalytic processes showed significant conformational transformations of kainoid synthase. The residues involved in specific interactions with the substrate contributed to the binding energy throughout the simulation process. Binding energy, the relaxed active pocket, electrostatic potential energy of the active pocket, the number and rotation of aromatic residues interacting with substrates during catalysis, and the number and frequency of hydrogen bonds between the individual functional groups revealed the structure-activity relationships and affected the degree of promiscuity of kainoid synthases. Our research enriches the understanding of the conformational dynamics of kainoid synthases and has potential guiding significance for their rational design.