Bacteria on the foundational kelp in kelp forest ecosystems: Insights from culturing, whole genome sequencing and metabolic assays.

In coastal marine ecosystems, kelp forests serve as a vital habitat for numerous species and significantly influence local nutrient cycles. Bull kelp, or Nereocystis luetkeana, is a foundational species in the iconic kelp forests of the northeast Pacific Ocean and harbours a complex microbial community with potential implications for kelp health. Here, we report the isolation and functional characterisation of 16 Nereocystis-associated bacterial species, comprising 13 Gammaproteobacteria, 2 Flavobacteriia and 1 Actinomycetia. Genome analyses of these isolates highlight metabolisms potentially beneficial to the host, such as B vitamin synthesis and nitrogen retention. Assays revealed that kelp-associated bacteria thrive on amino acids found in high concentrations in the ocean and in the kelp (glutamine and asparagine), generating ammonium that may facilitate host nitrogen acquisition. Multiple isolates have genes indicative of interactions with key elemental cycles in the ocean, including carbon, nitrogen and sulphur. We thus report a collection of kelp-associated microbial isolates that provide functional insight for the future study of kelp-microbe interactions.

Direct Degradation of Fresh and Dried Macroalgae by Agarivorans albus B2Z047.

Marine macroalgae are increasingly recognized for their significant biological and economic potential. The key to unlocking this potential lies in the efficient degradation of all carbohydrates from the macroalgae biomass. However, a variety of polysaccharides (alginate, cellulose, fucoidan, and laminarin), are difficult to degrade simultaneously in a short time. In this study, the brown alga Saccharina japonica was found to be rapidly and thoroughly degraded by the marine bacterium Agarivorans albus B2Z047. This strain harbors a broad spectrum of carbohydrate-active enzymes capable of degrading various polysaccharides, making it uniquely equipped to efficiently break down both fresh and dried kelp, achieving a hydrolysis rate of up to 52%. A transcriptomic analysis elucidated the presence of pivotal enzyme genes implicated in the degradation pathways of alginate, cellulose, fucoidan, and laminarin. This discovery highlights the bacterium's capability for the efficient and comprehensive conversion of kelp biomass, indicating its significant potential in biotechnological applications for macroalgae resource utilization.

Seaweeds as a major source of dietary microplastics exposure in East Asia.

Microplastics (MPs) occurrence in marine ecosystems is well known, but their accumulation in seaweeds and subsequent human exposure remain understudied. This research quantifies MPs presence in two commonly consumed seaweeds, kelp (Saccharina japonica) and nori (Pyropia yezoensis), in East Asia, revealing widespread contamination dominated by microfibers (<500 µm). Based on dietary patterns, human uptake through seaweed consumption was estimated and quantified. Notably, Chinese people consume an estimated 17,034 MPs/person/year through seaweed consumption, representing 13.1% of their total annual MPs intake. This seaweeds-derived exposure surpasses all other dietary sources, contributing up to 45.5% of overall MPs intake. The highest intake was in South Korea, followed by North Korea, China, and Japan. This research identifies seaweeds as a major, previously overlooked route of dietary MPs exposure. These findings are crucial for comprehensive risk assessments of seaweed consumption and the development of mitigation strategies, particularly for populations in East Asian countries.

Ammonification by kelp associated microbes increases ammonium availability.

Microbes contribute biologically available nitrogen to the ocean by fixing nitrogen gas from the atmosphere and by mineralizing organic nitrogen into bioavailable dissolved inorganic nitrogen (DIN). Although the large concentration of plants and algae in marine coastal environments provides ample habitat and reliable resources for microbial communities, the role of the microbiome in host-microbe nitrogen cycling remains poorly understood. We tested whether ammonification by epiphytic microbes increased water column ammonium and improved host access to nitrogen resources by converting organic nitrogen into inorganic nitrogen that is available for assimilation by hosts. When bull kelp (Nereocystis luetkeana) in the northeast Pacific was incubated with 15N labelled amino acid tracers, there was accumulation of 15N in kelp tissue, as well as accumulation of 15NH4 in seawater, all consistent with the conversion of dissolved organic nitrogen to ammonium. Metagenomic analysis of surface microbes from two populations of Nereocystis indicated relative similarity in the percentage of genes related to ammonification between the two locations, though the stressed kelp population that had lower tissue nitrogen and a sparser microbiome had greater ammonification rates. Microbial communities on coastal macrophytes may contribute to the nitrogen requirements of their hosts through metabolisms that make ammonium available.

Metagenomic insights into the dynamic degradation of brown algal polysaccharides by kelp-associated microbiota.

Marine bacteria play important roles in the degradation and cycling of algal polysaccharides. However, the dynamics of epiphytic bacterial communities and their roles in algal polysaccharide degradation during kelp decay are still unclear. Here, we performed metagenomic analyses to investigate the identities and predicted metabolic abilities of epiphytic bacterial communities during the early and late decay stages of the kelp Saccharina japonica. During kelp decay, the dominant epiphytic bacterial communities shifted from Gammaproteobacteria to Verrucomicrobia and Bacteroidetes. In the early decay stage of S. japonica, epiphytic bacteria primarily targeted kelp-derived labile alginate for degradation, among which the gammaproteobacterial Vibrionaceae (particularly Vibrio) and Psychromonadaceae (particularly Psychromonas), abundant in alginate lyases belonging to the polysaccharide lyase (PL) families PL6, PL7, and PL17, were key alginate degraders. More complex fucoidan was preferred to be degraded in the late decay stage of S. japonica by epiphytic bacteria, predominantly from Verrucomicrobia (particularly Lentimonas), Pirellulaceae of Planctomycetes (particularly Rhodopirellula), Pontiellaceae of Kiritimatiellota, and Flavobacteriaceae of Bacteroidetes, which depended on using glycoside hydrolases (GHs) from the GH29, GH95, and GH141 families and sulfatases from the S1_15, S1_16, S1_17, and S1_25 families to depolymerize fucoidan. The pathways for algal polysaccharide degradation in dominant epiphytic bacterial groups were reconstructed based on analyses of metagenome-assembled genomes. This study sheds light on the roles of different epiphytic bacteria in the degradation of brown algal polysaccharides.IMPORTANCEKelps are important primary producers in coastal marine ecosystems. Polysaccharides, as major components of brown algal biomass, constitute a large fraction of organic carbon in the ocean. However, knowledge of the identities and pathways of epiphytic bacteria involved in the degradation process of brown algal polysaccharides during kelp decay is still elusive. Here, based on metagenomic analyses, the succession of epiphytic bacterial communities and their metabolic potential were investigated during the early and late decay stages of Saccharina japonica. Our study revealed a transition in algal polysaccharide-degrading bacteria during kelp decay, shifting from alginate-degrading Gammaproteobacteria to fucoidan-degrading Verrucomicrobia, Planctomycetes, Kiritimatiellota, and Bacteroidetes. A model for the dynamic degradation of algal cell wall polysaccharides, a complex organic carbon, by epiphytic microbiota during kelp decay was proposed. This study deepens our understanding of the role of epiphytic bacteria in marine algal carbon cycling as well as pathogen control in algal culture.

Synchrotron X-rays reveal the modes of Fe binding and trace metal storage in the brown algae Laminaria digitata and Ectocarpus siliculosus.

Iron is accumulated symplastically in kelp in a non-ferritin core that seems to be a general feature of brown algae. Microprobe studies show that Fe binding depends on tissue type. The sea is generally an iron-poor environment and brown algae were recognized in recent years for having a unique, ferritin-free iron storage system. Kelp (Laminaria digitata) and the filamentous brown alga Ectocarpus siliculosus were investigated using X-ray microprobe imaging and nanoprobe X-ray fluorescence tomography to explore the localization of iron, arsenic, strontium, and zinc, and micro-X-ray absorption near-edge structure (µXANES) to study Fe binding. Fe distribution in frozen hydrated environmental samples of both algae shows higher accumulation in the cortex with symplastic subcellular localization. This should be seen in the context of recent ultrastructural insight by cryofixation-freeze substitution that found a new type of cisternae that may have a storage function but differs from the apoplastic Fe accumulation found by conventional chemical fixation. Zn distribution co-localizes with Fe in E. siliculosus, whereas it is chiefly located in the L. digitata medulla, which is similar to As and Sr. Both As and Sr are mostly found at the cell wall of both algae. XANES spectra indicate that Fe in L. digitata is stored in a mineral non-ferritin core, due to the lack of ferritin-encoding genes. We show that the L. digitata cortex contains mostly a ferritin-like mineral, while the meristoderm may include an additional component.

Quantitative Analysis of The High-Yield Hydrolysis of Kelp by Laminarinase and Alginate Lyase.

Kelp is an abundant, farmable biomass-containing laminarin and alginate as major polysaccharides, providing an excellent model substrate to study their deconstruction by simple enzyme mixtures. Our previous study showed strong reactivity of the glycoside hydrolase family 55 during hydrolysis of purified laminarin, raising the question of its reactivity with intact kelp. In this study, we determined that a combination of a single glycoside hydrolase family 55 ß-1,3-exoglucanase with a broad-specificity alginate lyase from the polysaccharide lyase family 18 gives efficient hydrolysis of untreated kelp to a mixture of simple sugars, that is, glucose, gentiobiose, mannitol-end glucose, and mannuronic and guluronic acids and their soluble oligomers. Quantitative assignments from nanostructure initiator mass spectrometry (NIMS) and 2D HSQC NMR spectroscopy and analysis of the reaction time-course are provided. The data suggest that binary combinations of enzymes targeted to the unique polysaccharide composition of marine biomass are sufficient to deconstruct kelp into soluble sugars for microbial fermentation.

A novel and high-throughput approach to assess photosynthetic thermal tolerance of kelp using chlorophyll α fluorometry.

Foundation seaweed species are experiencing widespread declines and localized extinctions due to increased instability of sea surface temperature. Characterizing temperature thresholds are useful for predicting patterns of change and identifying species most vulnerable to extremes. Existing methods for characterizing seaweed thermal tolerance produce diverse metrics and are often time-consuming, making comparisons between species and techniques difficult, hindering insight into global patterns of change. Using three kelp species, we adapted a high-throughput method - previously used in terrestrial plant thermal biology - for use on kelps. This method employs temperature-dependent fluorescence (T-F0 ) curves under heating or cooling regimes to determine the critical temperature (Tcrit ) of photosystem II (PSII), i.e., the breakpoint between slow and fast rise fluorescence response to changing temperature, enabling rapid assays of photosynthetic thermal tolerance using a standardized metric. This method enables characterization of Tcrit for up to 48 samples per two-hour assay, demonstrating the capacity of T-F0 curves for high-throughput assays of thermal tolerance. Temperature-dependent fluorescence curves and their derived metric, Tcrit , may offer a timely and powerful new method for the field of phycology, enabling characterization and comparison of photosynthetic thermal tolerance of seaweeds across many populations, species, and biomes.

Carbon Sequestration in the Form of Recalcitrant Dissolved Organic Carbon in a Seaweed (Kelp) Farming Environment.

Under climate change scenarios, the contribution of macroalgae to carbon sequestration has attracted wide attention. As primary producers, macroalgae can release substantial amounts of dissolved organic carbon (DOC) in seawater. However, little is known about the molecular composition and chemical properties of DOC derived from macroalgae and which of them are recalcitrant DOC (RDOC) that can be sequestered for a long time in the ocean. In the most intensive seaweed (kelp) farming area (Sanggou Bay) in China, we found that kelp mariculture not only significantly increased DOC concentration, but also introduced a variety of new DOC molecular species, many of which were sulfur-containing molecules. A long-term DOC degradation experiment revealed that those DOC with strong resistance to microbial degradation, i.e., RDOC, account for approximately 58% of the DOC extracted from kelp mariculture area. About 85% (3587 out of 4224 with different chemical features) of the RDOC molecular species were steadily present throughout the long-term degradation process. 15% (637 out of 4224 with different chemical features) of the RDOC molecular species were likely newly generated by microorganisms after metabolizing macroalgae-derived labile DOC. All these stable RDOC should be included in the blue carbon budgets of seaweed.

Long-term changes in kelp forests in an inner basin of the Salish Sea.

Kelp forests form an important biogenic habitat that responds to natural and human drivers. Global concerns exist about threats to kelp forests, yet long-term information is limited and research suggests that trends are geographically distinct. We examined distribution of the bull kelp Nereocystis luetkeana over 145 years in South Puget Sound (SPS), a semi-protected inner basin in a fjord estuary complex in the northeast Pacific Ocean. We synthesized 48 historical and modern Nereocystis surveys and examined presence/absence within 1-km segments along 452 km of shoreline. Compared to the earliest baseline in 1878, Nereocystis extent in 2017 decreased 63%, with individual sub-basins showing up to 96% loss. Losses have persisted for decades, across a range of climate conditions. In recent decades, Nereocystis predominantly occurred along shorelines with intense currents and mixing, where temperature and nutrient concentrations did not reach thresholds for impacts to Nereocystis performance, and high current speeds likely excluded grazers. Losses predominated in areas with elevated temperature, lower nutrient concentrations, and relatively low current velocities. The pattern of long-term losses in SPS contrasts with stability in floating kelp abundance during the last century in an area of the Salish Sea with greater wave exposure and proximity to oceanic conditions. These findings support the hypothesis that kelp beds along wave-sheltered shorelines exhibit greater sensitivity to environmental stressors. Additionally, shorelines with strong currents and deep-water mixing may provide refugia within sheltered systems.

Remnant kelp bed refugia and future phase-shifts under ocean acidification.

Ocean warming, ocean acidification and overfishing are major threats to the structure and function of marine ecosystems. Driven by increasing anthropogenic emissions of CO2, ocean warming is leading to global redistribution of marine biota and altered ecosystem dynamics, while ocean acidification threatens the ability of calcifying marine organisms to form skeletons due to decline in saturation state of carbonate Ω and pH. In Tasmania, the interaction between overfishing of sea urchin predators and rapid ocean warming has caused a phase-shift from productive kelp beds to overgrazed sea urchin barren grounds, however potential impacts of ocean acidification on this system have not been considered despite this threat for marine ecosystems globally. Here we use automated loggers and point measures of pH, spanning kelp beds and barren grounds, to reveal that kelp beds have the capacity to locally ameliorate effects of ocean acidification, via photosynthetic drawdown of CO2, compared to unvegetated barren grounds. Based on meta-analysis of anticipated declines in physiological performance of grazing urchins to decreasing pH and assumptions of nil adaptation, future projection of OA across kelp-barrens transition zones reveals that kelp beds could act as important pH refugia, with urchins potentially becoming increasingly challenged at distances >40 m from kelp beds. Using spatially explicit simulation of physicochemical feedbacks between grazing urchins and their kelp prey, we show a stable mosaicked expression of kelp patches to emerge on barren grounds. Depending on the adaptative capacity of sea urchins, future declines in pH appear poised to further alter phase-shift dynamics for reef communities; thus, assessing change in spatial-patterning of reef-scapes may indicate cascading ecological impacts of ocean acidification.

Socioeconomic prospects of a seaweed bioeconomy in Sweden.

Seaweed cultivation is a large industry worldwide, but production in Europe is small compared to production in Asian countries. In the EU, the motivations for seaweed farming may be seen from two perspectives; one being economic growth through biomass production and the other being the provisioning of ecosystem services such as mitigating eutrophication. In this paper, we assess the economic potential of large-scale cultivation of kelp, Saccharina latissima, along the Swedish west coast, including the value of externalities. The findings suggest that seaweed farming has the potential of becoming a profitable industry in Sweden. Furthermore, large-scale seaweed farming can sequester a significant share of annual anthropogenic nitrogen and phosphorus inflows to the basins of the Swedish west coast (8% of N and 60% of P). Concerning the valuation of externalities, positive values generated from sequestration of nitrogen and phosphorus are potentially counteracted by negative values from interference with recreational values. Despite the large N and P uptake, the socioeconomic value of this sequestration is only a minor share of the potential financial value from biomass production. This suggests that e.g. payment schemes for nutrient uptake based on the socioeconomic values generated is not likely to be a tipping point for the industry. Additionally, seaweed cultivation is not a cost-efficient measure in itself to remove nutrients. Policy should thus be oriented towards industry development, as the market potential of the biomass will be the driver that may unlock these bioremediation opportunities.

Ocean acidification increases iodine accumulation in kelp-based coastal food webs.

Kelp are main iodine accumulators in the ocean, and their growth and photosynthesis are likely to benefit from elevated seawater CO2 levels due to ocean acidification. However, there are currently no data on the effects of ocean acidification on iodine metabolism in kelp. As key primary producers in coastal ecosystems worldwide, any change in their iodine metabolism caused by climate change will potentially have important consequences for global geochemical cycles of iodine, including iodine levels of coastal food webs that underpin the nutrition of billions of humans around the world. Here, we found that elevated pCO2 enhanced growth and increased iodine accumulation not only in the model kelp Saccharina japonica using both short-term laboratory experiment and long-term in situ mesocosms, but also in several other edible and ecologically significant seaweeds using long-term in situ mesocosms. Transcriptomic and proteomic analysis of S. japonica revealed that most vanadium-dependent haloperoxidase genes involved in iodine efflux during oxidative stress are down-regulated under increasing pCO2 , suggesting that ocean acidification alleviates oxidative stress in kelp, which might contribute to their enhanced growth. When consumed by abalone (Haliotis discus), elevated iodine concentrations in S. japonica caused increased iodine accumulation in abalone, accompanied by reduced synthesis of thyroid hormones. Thus, our results suggest that kelp will benefit from ocean acidification by a reduction in environmental stress however; iodine levels, in kelp-based coastal food webs will increase, with potential impacts on biogeochemical cycles of iodine in coastal ecosystems.

Some aspects of the iodine metabolism of the giant kelp Macrocystis pyrifera (phaeophyceae).

Despite its paramount role in the functioning of coastal ecosystems, relatively little is known about halogen metabolism in giant kelp (Macrocystis pyrifera). This is an important shortcoming given the potential implications for marine and atmospheric chemical processes in the wide distribution range of Macrocystis. The work presented here constitutes the first in depth investigation of the uptake, efflux, and of the physiological function of iodide in this important kelp species. Iodide uptake and efflux rates were measured in adult sporophytes of Macrocystis under normal and stressed (exogenous hydrogen peroxide and an elicitor-triggered oxidative burst) conditions. Kelp tissue took up iodide according to Michaelis-Menten type kinetics when incubated in seawater enriched with various concentrations of iodide. Upon the addition of exogenous hydrogen peroxide, simulating oxidative stress, a marked efflux of iodide occurred. In situ generation of hydrogen peroxide was elicited in Macrocystis upon the addition of oligomeric degradation products of alginate as well as arachidonic acid and methyl jasmonate constituting a defensive oxidative burst that could be linked to iodine accumulation. H2O2 was detected at the single cell level using dichlorohydrofluorescein diacetate, a fluorogenic probe capable of detecting intracellular H2O2. When assayed for vanadium haloperoxidase activity, several bromoperoxidase isoforms were detected as well as a single iodoperoxidase. Altogether, the results of this study show that Macrocystis has an elaborate iodine metabolism, which is likely significant for impacting iodine speciation in seawater around kelp beds and for volatile halogen emissions into the coastal atmosphere.

Abiotic influences on bicarbonate use in the giant kelp, Macrocystis pyrifera, in the Monterey Bay.

In the Monterey Bay region of central California, the giant kelp Macrocystis pyrifera experiences broad fluctuations in wave forces, temperature, light availability, nutrient availability, and seawater carbonate chemistry, all of which may impact their productivity. In particular, current velocities and light intensity may strongly regulate the supply and demand of inorganic carbon (Ci) as substrates for photosynthesis. Macrocystis pyrifera can acquire and utilize both CO2 and bicarbonate (HCO3- ) as Ci substrates for photosynthesis and growth. Given the variability in carbon delivery (due to current velocities and varying [DIC]) and demand (in the form of saturating irradiance), we hypothesized that the proportion of CO2 and bicarbonate utilized is not constant for M. pyrifera, but a variable function of their fluctuating environment. We further hypothesized that populations acclimated to different wave exposure and irradiance habitats would display different patterns of bicarbonate uptake. To test these hypotheses, we carried out oxygen evolution trials in the laboratory to measure the proportion of bicarbonate utilized by M. pyrifera via external CA under an orthogonal cross of velocity, irradiance, and acclimation treatments. Our Monterey Bay populations of M. pyrifera exhibited proportionally higher external bicarbonate utilization in high irradiance and high flow velocity conditions than in sub-saturating irradiance or low flow velocity conditions. However, there was no significant difference in proportional bicarbonate use between deep blades and canopy blades, nor between individuals from wave-exposed versus wave-protected sites. This study contributes a new field-oriented perspective on the abiotic controls of carbon utilization physiology in macroalgae.

The gelatinous extracellular matrix facilitates transport studies in kelp: visualization of pressure-induced flow reversal across sieve plates.

BACKGROUND AND AIMS: In vascular plants, important questions regarding phloem function remain unanswered due to problems with invasive experimental procedures in this highly sensitive tissue. Certain brown algae (kelps; Laminariales) also possess sieve tubes for photoassimilate transport, but these are embedded in large volumes of a gelatinous extracellular matrix which isolates them from neighbouring cells. Therefore, we hypothesized that kelp sieve tubes might tolerate invasive experimentation better than their analogues in higher plants, and sought to establish Nereocystis luetkeana as an experimental system. METHODS: The predominant localization of cellulose and the gelatinous extracellular matrix in N. luetkeana was verified using specific fluorescent markers and confocal laser scanning microscopy. Sieve tubes in intact specimens were loaded with fluorescent dyes, either passively (carboxyfluorescein diacetate; CFDA) or by microinjection (rhodamine B), and the movement of the dyes was monitored by fluorescence microscopy. KEY RESULTS: Application of CFDA demonstrated source to sink bulk flow in N. luetkeana sieve tubes, and revealed the complexity of sieve tube structure, with branches, junctions and lateral connections. Microinjection into sieve elements proved comparatively easy. Pulsed rhodamine B injection enabled the determination of flow velocity in individual sieve elements, and the direct visualization of pressure-induced reversals of flow direction across sieve plates. CONCLUSIONS: The reversal of flow direction across sieve plates by pressurizing the downstream sieve element conclusively demonstrates that a critical requirement of the Münch theory is satisfied in kelp; no such evidence exists for tracheophytes. Because of the high tolerance of its sieve elements to experimental manipulation, N. luetkeana is a promising alternative to vascular plants for studying the fluid mechanics of sieve tube networks.

Photosynthetic use of inorganic carbon in deep-water kelps from the Strait of Gibraltar.

Mechanisms of inorganic carbon assimilation were investigated in the four deep-water kelps inhabiting sea bottoms at the Strait of Gibraltar; these species are distributed at different depths (Saccorhiza polysiches at shallower waters, followed by Laminaria ochroleuca, then Phyllariopsis brevipes and, at the deepest bottoms, Phyllariopsis purpurascens). To elucidate the capacity to use HCO3(-) as a source of inorganic carbon for photosynthesis in the kelps, different experimental approaches were used. Specifically, we measured the irradiance-saturated gross photosynthetic rate versus pH at a constant dissolved inorganic carbon (DIC) concentration of 2 mM, the irradiance-saturated apparent photosynthesis (APS) rate versus DIC, the total and the extracellular carbonic anhydrase (CAext), the observed and the theoretical photosynthetic rates supported by the spontaneous dehydration of HCO3(-) to CO2, and the δ(13)C signature in tissues of the algae. While S. polyschides and L. ochroleuca showed photosynthetic activity at pH 9.5 (around 1.0 µmol O2 m(-2) s(-1)), the activity was close to zero in both species of Phyllariopsis. The APS versus DIC was almost saturated for the DIC values of natural seawater (2 mM) in S. polyschides and L. ochroleuca, but the relationship was linear in P. brevipes and P. purpurascens. The four species showed total and CAext activities but the inhibition of the CAext originated the observed photosynthetic rates at pH 8.0 to be similar to the theoretical rates that could be supported by the spontaneous dehydration of HCO3(-). The isotopic (13)C signatures ranged from -17.40 ± 1.81 to -21.11 ± 1.73 ‰ in the four species. Additionally, the δ(13)C signature was also measured in the deep-water Laminaria rodriguezii growing at 60-80 m, showing even a more negative value of -26.49 ± 1.25 ‰. All these results suggest that the four kelps can use HCO3(-) as external carbon source for photosynthesis mainly by the action of external CAext, but they also suggest that the species inhabiting shallower waters show a higher capacity than the smaller kelps living in deeper waters. In fact, the photosynthesis in the two Phyllariopsis species could be accomplished by the spontaneous dehydration of HCO3(-) to CO2. These differences in the capacity to use HCO3(-) in photosynthesis among species could be important considering the increasing levels of atmospheric CO2 predicted for the near future.

Escaping herbivory: ocean warming as a refuge for primary producers where consumer metabolism and consumption cannot pursue.

Ocean warming is anticipated to strengthen the persistence of turf-forming habitat, yet the concomitant elevation of grazer metabolic rates may accelerate per capita rates of consumption to counter turf predominance. Whilst this possibility of strong top-down control is supported by the metabolic theory of ecology (MTE), it assumes that consumer metabolism and consumption keep pace with increasing production. This assumption was tested by quantifying the metabolic rates of turfs and herbivorous gastropods under a series of elevated temperatures in which the ensuing production and consumption were observed. We discovered that as temperature increases towards near-future levels (year 2100), consumption rates of gastropods peak earlier than the rate of growth of producers. Hence, turfs have greater capacity to persist under near-future temperatures than the capacity for herbivores to counter their growth. These results suggest that whilst MTE predicts stronger top-down control, understanding whether consumer-producer responses are synchronous is key to assessing the future strength of top-down control.

Saccharina genomes provide novel insight into kelp biology.

Seaweeds are essential for marine ecosystems and have immense economic value. Here we present a comprehensive analysis of the draft genome of Saccharina japonica, one of the most economically important seaweeds. The 537-Mb assembled genomic sequence covered 98.5% of the estimated genome, and 18,733 protein-coding genes are predicted and annotated. Gene families related to cell wall synthesis, halogen concentration, development and defence systems were expanded. Functional diversification of the mannuronan C-5-epimerase and haloperoxidase gene families provides insight into the evolutionary adaptation of polysaccharide biosynthesis and iodine antioxidation. Additional sequencing of seven cultivars and nine wild individuals reveal that the genetic diversity within wild populations is greater than among cultivars. All of the cultivars are descendants of a wild S. japonica accession showing limited admixture with S. longissima. This study represents an important advance toward improving yields and economic traits in Saccharina and provides an invaluable resource for plant genome studies.

γ-Aminobutyric Acid (GABA) Production and Angiotensin-I Converting Enzyme (ACE) Inhibitory Activity of Fermented Soybean Containing Sea Tangle by the Co-Culture of Lactobacillus brevis with Aspergillus oryzae.

To enhance the γ-aminobutyric acid (GABA) content, the optimized fermentation of soybean with added sea tangle extract was evaluated at 30°C and pH 5.0. The medium was first inoculated with Aspergillus oryzae strain FMB S46471 and fermented for 3 days, followed by the subsequent inoculation with Lactobacillus brevis GABA 100. After fermentation for 7 days, the fermented soybean showed approximately 1.9 g/kg GABA and exhibited higher ACE inhibitory activity than the traditional soybean product. Furthermore, several peptides in the fraction containing the highest ACE inhibitory activity were identified. The novel fermented soybean enriched with GABA and ACE inhibitory components has great pharmaceutical and functional food values.