Accurate Quantification of Laminarin in Marine Organic Matter with Enzymes from Marine Microbes

Molecular insights into the hydrolysis and transglycosylation of a deep-sea Planctomycetota-derived GH16 family laminarinase

The biochemical and structural characteristics of PtLam, a laminarinase from deep-sea Planctomycetota, have been extensively elucidated, unveiling the fundamental molecular mechanisms governing substrate recognition and enzymatic catalysis. PtLam functions as an exo-laminarinase with the ability to sequentially hydrolyze laminarin, cleaving glucose units individually. Notably, PtLam exhibits proficient transglycosylation capabilities, utilizing various sugar alcohols as acceptors, with lyxose, in particular, yielding exclusively transglycosylated products. Structural analysis of both apo-PtLam and its laminarin oligosaccharide-bound complex revealed significant conformational alterations in active residues upon substrate binding. Moreover, pivotal residues involved in substrate recognition were identified, with subsequent mutation assays indicating the contribution of positive subsites in modulating exo-hydrolysis and transglycosidic activities. These results enhance our comprehension of laminarin cycling mechanisms by marine Planctomycetota, while also providing essential enzyme components for laminarin hetero-oligosaccharide synthesis.IMPORTANCEThe ubiquitous Planctomycetota, with distinctive physiological traits, exert a significant influence on global carbon and nitrogen fluxes. Their intimate association with algae suggests a propensity for efficient polysaccharide degradation; however, research on glycoside hydrolases derived from Planctomycetota remains scarce. Herein, we unveil the GH16 family laminarinase PtLam from deep-sea Planctomycetota, shedding light on its catalytic mechanisms underlying hydrolysis and transglycosylation. Our findings elucidate the enzymatic pathways governing the marine laminarin cycle orchestrated by Planctomycetota, thereby fostering the exploration of novel polysaccharide hydrolases with promising practical implications.

Photoperiod and temperature interactions drive the latitudinal distribution of Laminaria hyperborea (Laminariales, Phaeophyceae) under climate change

Due to global rises in temperature, recent studies predict marine species shifting toward higher latitudes. We investigated the impact of interacting abiotic drivers on the distribution potential of the temperate kelp Laminaria hyperborea. The ecosystem engineering species is widespread along European coasts but has not yet been observed in the High Arctic, although it can survive several months of low temperatures and darkness. To investigate its ability to extend northward in future, we conducted a long-term multifactorial experiment with sporophytes from Porsangerfjorden, Norway-close to the species' documented northernmost distribution margin. The samples were exposed to three different photoperiods (PolarDay, LongDay, and PolarNight) at 0°C, 5°C, and 10°C for 3 months. Optimum quantum yield of photosynthesis (Fv/Fm), dry weight, pigments, phlorotannins, and storage carbohydrates were monitored. Both physiological and biochemical parameters revealed that L. hyperborea was strongly influenced by the different photoperiods and their interaction with temperature, while temperature alone exerted only minor effects. The Fv/Fm data were integrated into a species distribution model to project a possible northward expansion of L. hyperborea. The combination of extended day lengths and low temperatures appeared to be the limiting reason for northward spread of L. hyperborea until recently. However, with water temperatures reaching 10°C in summer, this kelp will be able to thrive also in the High Arctic. Moreover, no evidence of stress to Arctic winter warming was observed. Consequently, L. hyperborea has a high potential for spreading northward with further warming which may significantly affect the structure and function of Arctic ecosystems.

Genes for laminarin degradation are dispersed in the genomes of particle-associated Maribacter species

Laminarin is a cytosolic storage polysaccharide of phytoplankton and macroalgae and accounts for over 10% of the world's annually fixed carbon dioxide. Algal disruption, for example, by viral lysis releases laminarin. The soluble sugar is rapidly utilized by free-living planktonic bacteria, in which sugar transporters and the degrading enzymes are frequently encoded in polysaccharide utilization loci. The annotation of flavobacterial genomes failed to identify canonical laminarin utilization loci in several particle-associated bacteria, in particular in strains of Maribacter. In this study, we report in vivo utilization of laminarin by Maribacter forsetii accompanied by additional cell growth and proliferation. Laminarin utilization coincided with the induction of an extracellular endo-laminarinase, SusC/D outer membrane oligosaccharide transporters, and a periplasmic glycosyl hydrolase family 3 protein. An ABC transport system and sugar kinases were expressed. Endo-laminarinase activity was also observed in Maribacter sp. MAR_2009_72, Maribacter sp. Hel_I_7, and Maribacter dokdonensis MAR_2009_60. Maribacter dokdonensis MAR_2009_71 lacked the large endo-laminarinase gene in the genome and had no endo-laminarinase activity. In all genomes, genes of induced proteins were scattered across the genome rather than clustered in a laminarin utilization locus. These observations revealed that the Maribacter strains investigated in this study participate in laminarin utilization, but in contrast to many free-living bacteria, there is no co-localization of genes encoding the enzymatic machinery for laminarin utilization.

Automated Synthesis of Algal Fucoidan Oligosaccharides

Fucoidan, a sulfated polysaccharide found in algae, plays a central role in marine carbon sequestration and exhibits a wide array of bioactivities. However, the molecular diversity and structural complexity of fucoidan hinder precise structure-function studies. To address this, we present an automated method for generating well-defined linear and branched α-fucan oligosaccharides. Our syntheses include oligosaccharides with up to 20 cis-glycosidic linkages, diverse branching patterns, and 11 sulfate monoesters. In this study, we demonstrate the utility of these oligosaccharides by (i) characterizing two endo-acting fucoidan glycoside hydrolases (GH107), (ii) utilizing them as standards for NMR studies to confirm suggested structures of algal fucoidans, and (iii) developing a fucoidan microarray. This microarray enabled the screening of the molecular specificity of four monoclonal antibodies (mAb) targeting fucoidan. It was found that mAb BAM4 has cross-reactivity to β-glucans, while mAb BAM2 has reactivity to fucoidans with 4-O-sulfate esters. Knowledge of the mAb BAM2 epitope specificity provided evidence that a globally abundant marine diatom, Thalassiosira weissflogii, synthesizes a fucoidan with structural homology to those found in brown algae. Automated glycan assembly provides access to fucoidan oligosaccharides. These oligosaccharides provide the basis for molecular level investigations into fucoidan's roles in medicine and carbon sequestration.

Essential bioactive competence of laminarin (β-glucan)/ laminaran extracted from Padina tetrastromatica and Sargassum cinereum biomass

Marine algae-based drug discovery has recently received a lot of attention. This study was conducted to extract laminarin-enriched solvent extracts from Padina tetrastromatica and Sargassum cinereum and to evaluate their anticancer activity against the HeLa cell line in vitro (MTT assay). Furthermore, their toxicity was determined through a zebra fish model study. P. tetrastromatica and S. cinereum biomasses have a higher concentration of essential biomolecules such as carbohydrates, protein, and crude fiber, as well as essential minerals (Na, Mg, K, Ca, and Fe) and secondary metabolites. Methanol extracts, in particular, contain a higher concentration of vital phytochemicals than other solvent extracts. The laminarin quantification assay states that methanol extracts of P. tetrastromatica and S. cinereum are rich in laminarin, which is primarily confirmed by FTIR analysis. In an anticancer study, laminarin-MeE from P. tetrastromatica and S. cinereum at concentrations of 750 and 1000 μg mL-1 demonstrated 100% activity against HeLa cells. The Zebra fish model-based toxicity study revealed that the laminarin-enriched MeE of P. tetrastromatica and S. cinereum is non-toxic. These findings revealed that the laminarin-enriched MeE of P. tetrastromatica and S. cinereum has significant anticancer activity without causing toxicity.

Unveiling the role of novel carbohydrate-binding modules in laminarin interaction of multimodular proteins from marine Bacteroidota during phytoplankton blooms

Laminarin, a β(1,3)-glucan, serves as a storage polysaccharide in marine microalgae such as diatoms. Its abundance, water solubility and simple structure make it an appealing substrate for marine bacteria. Consequently, many marine bacteria have evolved strategies to scavenge and decompose laminarin, employing carbohydrate-binding modules (CBMs) as crucial components. In this study, we characterized two previously unassigned domains as laminarin-binding CBMs in multimodular proteins from the marine bacterium Christiangramia forsetii KT0803T, thereby introducing the new laminarin-binding CBM families CBM102 and CBM103. We identified four CBM102s in a surface glycan-binding protein (SGBP) and a single CBM103 linked to a glycoside hydrolase module from family 16 (GH16_3). Our analysis revealed that both modular proteins have an elongated shape, with GH16_3 exhibiting greater flexibility than SGBP. This flexibility may aid in the recognition and/or degradation of laminarin, while the constraints in SGBP could facilitate the docking of laminarin onto the bacterial surface. Exploration of bacterial metagenome-assembled genomes (MAGs) from phytoplankton blooms in the North Sea showed that both laminarin-binding CBM families are widespread among marine Bacteroidota. The high protein abundance of CBM102- and CBM103-containing proteins during phytoplankton blooms further emphasizes their significance in marine laminarin utilization.

Structural and biochemical analysis of family 92 carbohydrate-binding modules uncovers multivalent binding to β-glucans

Carbohydrate-binding modules (CBMs) are non-catalytic proteins found appended to carbohydrate-active enzymes. Soil and marine bacteria secrete such enzymes to scavenge nutrition, and they often use CBMs to improve reaction rates and retention of released sugars. Here we present a structural and functional analysis of the recently established CBM family 92. All proteins analysed bind preferentially to β-1,6-glucans. This contrasts with the diversity of predicted substrates among the enzymes attached to CBM92 domains. We present crystal structures for two proteins, and confirm by mutagenesis that tryptophan residues permit ligand binding at three distinct functional binding sites on each protein. Multivalent CBM families are uncommon, so the establishment and structural characterisation of CBM92 enriches the classification database and will facilitate functional prediction in future projects. We propose that CBM92 proteins may cross-link polysaccharides in nature, and might have use in novel strategies for enzyme immobilisation.

Conversion of β-1,6-Glucans to Gentiobiose using an endo-β-1,6-Glucanase PsGly30A from Paenibacillus sp. GKG

A plethora of di- and oligosaccharides isolated from the natural sources are used in food and pharmaceutical industry. An enzymatic hydrolysis of fungal cell wall β-glucans is a good alternative to produce the desired oligosaccharides with different functionalities, such as the flavour enhancer gentiobiose. We have previously identified PsGly30A as a potential yeast cell wall degrading β-1,6-glycosidase. The aim of this study is to characterise the PsGly30A enzyme, a member of the GH30 family, and to evaluate its suitability for the production of gentiobiose from β-1,6-glucans. An endo-β-1,6-glucanase PsGly30A encoding gene from Paenibacillus sp. GKG has been cloned and overexpressed in Escherichia coli. The recombinant enzyme has been active towards pustulan and yeast β-glucan, but not on laminarin from the Laminaria digitata, confirming the endo-β-1,6-glucanase mode of action. The PsGly30A shows the highest activity at pH 5.5 and 50 °C. The specific activity of PsGly30A on pustulan (1262±82 U/mg) is among the highest reported for GH30 β-1,6-glycosidases. Moreover, gentiobiose is the major reaction product when pustulan, yeast β-glucan or yeast cell walls have been used as a substrate. Therefore, PsGly30A is a promising catalyst for valorisation of the yeast-related by-products.

Blue Biotechnology: Marine Bacteria Bioproducts

The ocean is the habitat of a great number of organisms with different characteristics. Compared to terrestrial microorganisms, marine microorganisms also represent a vast and largely unexplored reservoir of bioactive compounds with diverse industrial applications like terrestrial microorganisms. This review examines the properties and potential applications of products derived from marine microorganisms, including bacteriocins, enzymes, exopolysaccharides, and pigments, juxtaposing them in some cases against their terrestrial counterparts. We discuss the distinct characteristics that set marine-derived products apart, including enhanced stability and unique structural features such as the amount of uronic acid and sulfate groups in exopolysaccharides. Further, we explore the uses of these marine-derived compounds across various industries, ranging from food and pharmaceuticals to cosmetics and biotechnology. This review also presents a broad description of biotechnologically important compounds produced by bacteria isolated from marine environments, some of them with different qualities compared to their terrestrial counterparts.

Metabolisms and multiple functions of laminaran in marine algae under global change: A critical review

Laminaran is a major storage of carbohydrate in marine algae. Its high content and potential functions draw increasing attention. However, our understanding of its metabolisms and functions is still fragmented. After reviewing, marine algae exhibit a spectacular capacity of laminaran accumulation especially in the diatom Odontella aurita (65 % DW). Marine particulate organic carbon (POC) also has high contents of laminaran (42 ± 21 % DW). Laminaran shows a diel variation trend in marine algae, the content of which increases in the day but decreases at night. Laminaran also significantly accumulates in the stationary phase of algal growth. Furthermore, the metabolic pathway of laminaran and the remolding carbon mechanism in response to marine nitrogen limitation are proposed and comprehensively discussed. Laminaran production in marine phytoplankton is predicted to increase in future warmer and CO2-enriched oceans. Laminaran has diverse biological functions, including antioxidant, antimicrobial, anti-cancer, immunomodulatory, wound healing, and prebiotics. In addition, laminaran is also a major carbon storage compound in marine algae, suggesting its significant ecological function in marine carbon cycle. This study provides new insight into algal laminaran functions and its response mechanisms to environmental and climate changes.

An enzyme-pHBH method for specific quantification of porphyran

Porphyran, the major polysaccharide extracted from Porphyra, exhibits tremendous potential for development as functional food or pharmaceutical due to its multiple biological activities. The quantitative analysis of porphyran is important for the quality control in product development. However, the specific quantitative method of porphyran has not been established, and the lack of reference substance makes the quantification more challenging. Here, a common component of porphyran, with high purity, similar molecular weight distribution, sourced from different Porphyra producing areas in China was first prepared by a series of isolation and purification steps, and utilized as the reference substance for porphyran quantification. Subsequently, the porphyran was fully degraded into oligosaccharides by using a β-porphyranase, followed by employing para-hydroxybenzoic acid hydrazide (pHBH) method to detect the content of the generated reducing sugar. The enzyme-pHBH method for porphyran specific quantification was established. Results showed that this method was validated with good linearity, high accuracy and precision, and reliability. Addtionally, NaCl with a concentration below 0.5 %, alcohol under 8 % and other polysaccharide including chitosan, agarose, chondrotin sulfate, alginate, hyaluronic acid and κ-carrageenan did not interfere with this method. This approach is promising for quality control of the porphyran products and offers a feasible strategy for the specific quantification of other polysaccharides.

From algae to advancements: laminarin in biomedicine

Laminarin, a complicated polysaccharide originating from brown algae, has emerged as a compelling candidate in the domain of biomedical research. This enigmatic molecule, composed of glucose units associated with both β-1,3 and β-1,6 glycosidic bonds, possesses an array of remarkable characteristics that render it auspicious for multifaceted biomedical applications. This review investigates the comprehensive potential of laminarin in the biomedical domain, emphasizing its remarkable biocompatibility, low cytotoxicity, and cell proliferation support. Laminarin's immunomodulatory attributes position it as an encouraging contender in immunotherapy and the development of vaccines. Moreover, its anti-inflammatory and antioxidant characteristics provide a promising avenue for combatting conditions associated with oxidative stress. In particular, laminarin excels as a drug delivery vehicle owing to its exceptional encapsulation capabilities emerging from its porous framework. Integrating pH and redox responsiveness in laminarin-based drug delivery systems is poised to redefine targeted therapies. Laminarin substantially contributes to tissue engineering by improving adhesion, migration of cells, and deposition of extracellular matrix. This augmentation magnifies the regenerative capability of tissue-engineered constructs, substantiated by the advancement of laminarin-based wound dressings and tissue scaffolds, marking considerable progress in the domain of wound healing and tissue regeneration. While laminarin exhibits substantial potential in biomedical applications, it remains in the initial phases of exploration. Comprehensive preclinical and clinical research is warranted to verify its effectiveness and safety across various applications. In essence, laminarin, a marine marvel, has the capability to remodel biomedical research, offering inventive solutions to complex difficulties.

Taxonomic and functional stability overrules seasonality in polar benthic microbiomes

Coastal shelf sediments are hot spots of organic matter mineralization. They receive up to 50% of primary production, which, in higher latitudes, is strongly seasonal. Polar and temperate benthic bacterial communities, however, show a stable composition based on comparative 16S rRNA gene sequencing despite different microbial activity levels. Here, we aimed to resolve this contradiction by identifying seasonal changes at the functional level, in particular with respect to algal polysaccharide degradation genes, by combining metagenomics, metatranscriptomics, and glycan analysis in sandy surface sediments from Isfjorden, Svalbard. Gene expressions of diverse carbohydrate-active enzymes changed between winter and spring. For example, β-1,3-glucosidases (e.g. GH30, GH17, GH16) degrading laminarin, an energy storage molecule of algae, were elevated in spring, while enzymes related to α-glucan degradation were expressed in both seasons with maxima in winter (e.g. GH63, GH13_18, and GH15). Also, the expression of GH23 involved in peptidoglycan degradation was prevalent, which is in line with recycling of bacterial biomass. Sugar extractions from bulk sediments were low in concentrations during winter but higher in spring samples, with glucose constituting the largest fraction of measured monosaccharides (84% ± 14%). In porewater, glycan concentrations were ~18-fold higher than in overlying seawater (1107 ± 484 vs. 62 ± 101 μg C l-1) and were depleted in glucose. Our data indicate that microbial communities in sandy sediments digest and transform labile parts of photosynthesis-derived particulate organic matter and likely release more stable, glucose-depleted residual glycans of unknown structures, quantities, and residence times into the ocean, thus modulating the glycan composition of marine coastal waters.

Carbohydrates and carbohydrate degradation gene abundance and transcription in Atlantic waters of the Arctic

Carbohydrates are chemically and structurally diverse, represent a substantial fraction of marine organic matter and are key substrates for heterotrophic microbes. Studies on carbohydrate utilisation by marine microbes have been centred on phytoplankton blooms in temperate regions, while far less is known from high-latitude waters and during later seasonal stages. Here, we combine glycan microarrays and analytical chromatography with metagenomics and metatranscriptomics to show the spatial heterogeneity in glycan distribution and potential carbohydrate utilisation by microbes in Atlantic waters of the Arctic. The composition and abundance of monomers and glycan structures in POM varied with location and depth. Complex fucose-containing sulfated polysaccharides, known to accumulate in the ocean, were consistently detected, while the more labile β-1,3-glucan exhibited a patchy distribution. Through 'omics analysis, we identify variations in the abundance and transcription of carbohydrate degradation-related genes across samples at the community and population level. The populations contributing the most to transcription were taxonomically related to those known as primary responders and key carbohydrate degraders in temperate ecosystems, such as NS4 Marine Group and Formosa. The unique transcription profiles for these populations suggest distinct substrate utilisation potentials, with predicted glycan targets corresponding to those structurally identified in POM from the same sampling sites. By combining cutting-edge technologies and protocols, we provide insights into the carbohydrate component of the carbon cycle in the Arctic during late summer and present a high-quality dataset that will be of great value for future comparative analyses.

Advances in oligosaccharides production from brown seaweeds: extraction, characterization, antimetabolic syndrome, and other potential applications

Brown seaweeds are a promising source of bioactive substances, particularly oligosaccharides. This group has recently gained considerable attention due to its diverse cell wall composition, structure, and wide-spectrum bioactivities. This review article provides a comprehensive update on advances in oligosaccharides (OSs) production from brown seaweeds and their potential health applications. It focuses on advances in feedstock pretreatment, extraction, characterization, and purification prior to OS use for potential health applications. Brown seaweed oligosaccharides (BSOSs) are extracted using various methods. Among these, enzymatic hydrolysis is the most preferred, with high specificity, mild reaction conditions, and low energy consumption. However, the enzyme selection and hydrolysis conditions need to be optimized for desirable yield and oligosaccharides composition. Characterization of oligosaccharides is essential to determine their structure and properties related to bioactivities and to predict their most suitable application. This is well covered in this review. Analytical techniques such as high-performance liquid chromatography (HPLC), gas chromatography (GC), and nuclear magnetic resonance (NMR) spectroscopy are commonly applied to analyze oligosaccharides. BSOSs exhibit a range of biological properties, mainly antimicrobial, anti-inflammatory, and prebiotic properties among others. Importantly, BSOSs have been linked to possible health advantages, including metabolic syndrome management. Metabolic syndrome is a cluster of conditions, such as obesity, hypertension, and dyslipidemia, which increase the risk of cardiovascular disease and type 2 diabetes. Furthermore, oligosaccharides have potential applications in the food and pharmaceutical industries. Future research should focus on improving industrial-scale oligosaccharide extraction and purification, as well as researching their potential utility in the treatment of various health disorders.[Figure: see text].

Advances in oligosaccharides production from algal sources and potential applications

In recent years, algal-derived glycans and oligosaccharides have become increasingly important in health applications due to higher bioactivities than plant-derived oligosaccharides. The marine organisms have complex, and highly branched glycans and more reactive groups to elicit greater bioactivities. However, complex and large molecules have limited use in broad commercial applications due to dissolution limitations. In comparison to these, oligosaccharides show better solubility and retain their bioactivities, hence, offering better applications opportunity. Accordingly, efforts are being made to develop a cost-effective method for enzymatic extraction of oligosaccharides from algal polysaccharides and algal biomass. Yet detailed structural characterization of algal-derived glycans is required to produce and characterize the potential biomolecules for improved bioactivity and commercial applications. Some macroalgae and microalgae are being evaluated as in vivo biofactories for efficient clinical trials, which could be very helpful in understanding the therapeutic responses. This review discusses the recent advancements in the production of oligosaccharides from microalgae. It also discusses the bottlenecks of the oligosaccharides research, technological limitations, and probable solutions to these problems. Furthermore, it presents the emerging bioactivities of algal oligosaccharides and their promising potential for possible biotherapeutic application.

Phytoplankton Producer Species and Transformation of Released Compounds over Time Define Bacterial Communities following Phytoplankton Dissolved Organic Matter Pulses

Phytoplankton-bacterium interactions are mediated, in part, by phytoplankton-released dissolved organic matter (DOMp). Two factors that shape the bacterial community accompanying phytoplankton are (i) the phytoplankton producer species, defining the initial composition of released DOMp, and (ii) the DOMp transformation over time. We added phytoplankton DOMp from the diatom Skeletonema marinoi and the cyanobacterium Prochlorococcus marinus MIT9312 to natural bacterial communities from the eastern Mediterranean and determined the bacterial responses over a time course of 72 h in terms of cell numbers, bacterial production, alkaline phosphatase activity, and changes in active bacterial community composition based on rRNA amplicon sequencing. Both DOMp types were demonstrated to serve the bacterial community as carbon and, potentially, phosphorus sources. Bacterial communities in diatom-derived DOM treatments maintained higher Shannon diversities throughout the experiment and yielded higher bacterial production and lower alkaline phosphatase activity compared to cyanobacterium-derived DOM after 24 h of incubation (but not after 48 and 72 h), indicating greater bacterial usability of diatom-derived DOM. Bacterial communities significantly differed between DOMp types as well as between different incubation times, pointing to a certain bacterial specificity for the DOMp producer as well as a successive utilization of phytoplankton DOM by different bacterial taxa over time. The highest differences in bacterial community composition with DOMp types occurred shortly after DOMp additions, suggesting a high specificity toward highly bioavailable DOMp compounds. We conclude that phytoplankton-associated bacterial communities are strongly shaped by the phytoplankton producer as well as the transformation of its released DOMp over time. IMPORTANCE Phytoplankton-bacterium interactions influence biogeochemical cycles of global importance. Phytoplankton photosynthetically fix carbon dioxide and subsequently release the synthesized compounds as dissolved organic matter (DOMp), which becomes processed and recycled by heterotrophic bacteria. Yet the importance of phytoplankton producers in combination with the time-dependent transformation of DOMp compounds on the accompanying bacterial community has not been explored in detail. The diatom Skeletonema marinoi and the cyanobacterium Prochlorococcus marinus MIT9312 belong to globally important phytoplankton genera, and our study revealed that DOMp of both species was selectively incorporated by the bacterial community. The producer species had the highest impact shortly after DOMp appropriation, and its effect diminished over time. Our results improve the understanding of the dynamics of organic matter produced by phytoplankton in the oceans as it is utilized and modified by cooccurring bacteria.

Multiple enzymatic approaches to hydrolysis of fungal β-glucans by the soil bacterium Chitinophaga pinensis

The genome of the soil Bacteroidota Chitinophaga pinensis encodes a large number of glycoside hydrolases (GHs) with noteworthy features and potentially novel functions. Several are predicted to be active on polysaccharide components of fungal and oomycete cell walls, such as chitin, β-1,3-glucan and β-1,6-glucan. While several fungal β-1,6-glucanase enzymes are known, relatively few bacterial examples have been characterised to date. We have previously demonstrated that C. pinensis shows strong growth using β-1,6-glucan as the sole carbon source, with the efficient release of oligosaccharides from the polymer. We here characterise the capacity of the C. pinensis secretome to hydrolyse the β-1,6-glucan pustulan and describe three distinct enzymes encoded by its genome, all of which show different levels of β-1,6-glucanase activity and which are classified into different GH families. Our data show that C. pinensis has multiple tools to deconstruct pustulan, allowing the species' broad utility of this substrate, with potential implications for bacterial biocontrol of pathogens via cell wall disruption. Oligosaccharides derived from fungal β-1,6-glucans are valuable in biomedical research and drug synthesis, and these enzymes could be useful tools for releasing such molecules from microbial biomass, an underexploited source of complex carbohydrates.

Fucoid brown algae inject fucoidan carbon into the ocean

Brown algae annually convert gigatons of carbon dioxide into carbohydrates, including the complex extracellular matrix polysaccharide fucoidan. Due to its persistence in the environment, fucoidan is potentially a pathway for marine carbon sequestration. Rates of fucoidan secretion by brown algae remain unknown due to the challenge of identifying and quantifying complex polysaccharides in seawater. We adapted the techniques of anion exchange chromatography, enzyme-linked immunosorbent assay, and biocatalytic enzyme-based assay for detection and quantification of fucoidan. We found the brown alga Fucus vesiculosus at the Baltic Sea coast of south-west Finland to secrete 0.3% of their biomass as fucoidan per day. Dissolved fucoidan concentrations in seawater adjacent to algae reached up to 0.48 mg L-1. Fucoidan accumulated during incubations of F. vesiculosus, significantly more in light than in darkness. Maximum estimation by acid hydrolysis indicated fucoidan secretion at a rate of 28 to 40 mg C kg-1 h-1, accounting for 44 to 50% of all exuded dissolved organic carbon. Composed only of carbon, oxygen, hydrogen, and sulfur, fucoidan secretion does not consume nutrients enabling carbon sequestration independent of algal growth. Extrapolated over a year, the algae sequester more carbon into secreted fucoidan than their biomass. The global utility of fucoidan secretion is an alternative pathway for carbon dioxide removal by brown algae without the need to harvest or bury algal biomass.

Effective fucoxanthin production in the flagellate alga Poterioochromonas malhamensis by coupling heterotrophic high-cell-density fermentation with illumination

The unicellular flagellate algae Poterioochromonas malhamensis is a potential fucoxanthin-rich resource for sustainable and cost-effective fucoxanthin production. Light and nutrients are critical regulators for the accumulation of fucoxanthin in P. malhamensis. In this study, the maximum fucoxanthin yield of 50.5 mg L−1 and productivity of 6.31 mg L−1 d−1 were achieved by coupling high-cell-density fermentation with illumination. It was found that the combined use of organic and inorganic nitrogen (N) nutrition could improve the fucoxanthin yield as single inorganic or organic N had limitation to enhance cell growth and fucoxanthin accumulation. White light was the optimal light quality for fucoxanthin accumulation. Under white light and a moderate light intensity of 150 μmol m−2 s−1, the highest biomass concentration and fucoxanthin content reached 32.9 g L−1 and 1.56 mg g−1 of dry cell weight (DCW), respectively. This is the first study on effective fucoxanthin production in P. malhamensis by integrating illumination with high-cell-density fermentation, which paved the way for further development of P. malhamensis as a potential source for commercial fucoxanthin production.

Structures and functions of algal glycans shape their capacity to sequester carbon in the ocean

Algae synthesise structurally complex glycans to build a protective barrier, the extracellular matrix. One function of matrix glycans is to slow down microorganisms that try to enzymatically enter living algae and degrade and convert their organic carbon back to carbon dioxide. We propose that matrix glycans lock up carbon in the ocean by controlling degradation of organic carbon by bacteria and other microbes not only while algae are alive, but also after death. Data revised in this review shows accumulation of algal glycans in the ocean underscoring the challenge bacteria and other microbes face to breach the glycan barrier with carbohydrate active enzymes. Briefly we also update on methods required to certify the uncertain magnitude and unknown molecular causes of glycan-controlled carbon sequestration in a changing ocean.

Bacterial surface interactions with organic colloidal particles: Nanoscale hotspots of organic matter in the ocean

Colloidal particles constitute a substantial fraction of organic matter in the global ocean and an abundant component of the organic matter interacting with bacterial surfaces. Using E. coli ribosomes as model colloidal particles, we applied high-resolution atomic force microscopy to probe bacterial surface interactions with organic colloids to investigate particle attachment and relevant surface features. We observed the formation of ribosome films associating with marine bacteria isolates and natural seawater assemblages, and that bacteria readily utilized the added ribosomes as growth substrate. In exposure experiments ribosomes directly attached onto bacterial surfaces as 40–200 nm clusters and patches of individual particles. We found that certain bacterial cells expressed surface corrugations that range from 50–100 nm in size, and 20 nm deep. Furthermore, our AFM studies revealed surface pits in select bacteria that range between 50–300 nm in width, and 10–50 nm in depth. Our findings suggest novel adaptive strategies of pelagic marine bacteria for colloid capture and utilization as nutrients, as well as storage as nanoscale hotspots of DOM.

Fungi hijack a ubiquitous plant apoplastic endoglucanase to release a ROS scavenging β-glucan decasaccharide to subvert immune responses

Plant pathogenic and beneficial fungi have evolved several strategies to evade immunity and cope with host-derived hydrolytic enzymes and oxidative stress in the apoplast, the extracellular space of plant tissues. Fungal hyphae are surrounded by an inner insoluble cell wall layer and an outer soluble extracellular polysaccharide (EPS) matrix. Here, we show by proteomics and glycomics that these two layers have distinct protein and carbohydrate signatures, and hence likely have different biological functions. The barley (Hordeum vulgare) β-1,3-endoglucanase HvBGLUII, which belongs to the widely distributed apoplastic glycoside hydrolase 17 family (GH17), releases a conserved β-1,3;1,6-glucan decasaccharide (β-GD) from the EPS matrices of fungi with different lifestyles and taxonomic positions. This low molecular weight β-GD does not activate plant immunity, is resilient to further enzymatic hydrolysis by β-1,3-endoglucanases due to the presence of three β-1,6-linked glucose branches and can scavenge reactive oxygen species. Exogenous application of β-GD leads to enhanced fungal colonization in barley, confirming its role in the fungal counter-defensive strategy to subvert host immunity. Our data highlight the hitherto undescribed capacity of this often-overlooked EPS matrix from plant-associated fungi to act as an outer protective barrier important for fungal accommodation within the hostile environment at the apoplastic plant-microbe interface.

Glycoside hydrolase from the GH76 family indicates that marine Salegentibacter sp. Hel_I_6 consumes alpha-mannan from fungi

Microbial glycan degradation is essential to global carbon cycling. The marine bacterium Salegentibacter sp. Hel_I_6 (Bacteroidota) isolated from seawater off Helgoland island (North Sea) contains an α-mannan inducible gene cluster with a GH76 family endo-α-1,6-mannanase (ShGH76). This cluster is related to genetic loci employed by human gut bacteria to digest fungal α-mannan. Metagenomes from the Hel_I_6 isolation site revealed increasing GH76 gene frequencies in free-living bacteria during microalgae blooms, suggesting degradation of α-1,6-mannans from fungi. Recombinant ShGH76 protein activity assays with yeast α-mannan and synthetic oligomannans showed endo-α-1,6-mannanase activity. Resolved structures of apo-ShGH76 (2.0 Å) and of mutants co-crystalized with fungal mannan-mimicking α-1,6-mannotetrose (1.90 Å) and α-1,6-mannotriose (1.47 Å) retained the canonical (α/α)6 fold, despite low identities with sequences of known GH76 structures (GH76s from gut bacteria: <27%). The apo-form active site differed from those known from gut bacteria, and co-crystallizations revealed a kinked oligomannan conformation. Co-crystallizations also revealed precise molecular-scale interactions of ShGH76 with fungal mannan-mimicking oligomannans, indicating adaptation to this particular type of substrate. Our data hence suggest presence of yet unknown fungal α-1,6-mannans in marine ecosystems, in particular during microalgal blooms.

Biocatalytic quantification of α-glucan in marine particulate organic matter

Marine algae drive the marine carbon cycle, converting carbon dioxide into organic material. A major component of this produced biomass is a variety of glycans. Marine α-glucans include a range of storage glycans from red and green algae, bacteria, fungi, and animals. Although these compounds are likely to account for a high amount of the carbon stored in the oceans they have not been quantified in marine samples so far. Here we present a method to extract and quantify α-glucans (and compare it with the β-glucan laminarin) in particulate organic matter from algal cultures and environmental samples using sequential physicochemical extraction and enzymes as α-glucan-specific probes. This enzymatic assay is more specific and less susceptible to side reactions than chemical hydrolysis. Using HPAEC-PAD to detect the hydrolysis products allows for a glycan quantification in particulate marine samples down to a concentration of ≈2 µg/L. We measured glucans in three cultured microalgae as well as in marine particulate organic matter from the North Sea and western North Atlantic Ocean. While the β-glucan laminarin from diatoms and brown algae is an essential component of marine carbon turnover, our results further indicate the significant contribution of starch-like α-glucans to marine particulate organic matter. Henceforth, the combination of glycan-linkage-specific enzymes and chromatographic hydrolysis product detection can provide a powerful tool in the exploration of marine glycans and their role in the global carbon cycle.

Insights into Algal Polysaccharides: A Review of Their Structure, Depolymerases, and Metabolic Pathways

In recent years, marine macroalgae with extensive biomass have attracted the attention of researchers worldwide. Furthermore, algal polysaccharides have been widely studied in the food, pharmaceutical, and cosmetic fields because of their various kinds of bioactivities. However, there are immense barriers to their application as a result of their high molecular size, poor solubility, hydrocolloid nature, and low physiological activities. Unique polysaccharides, such as laminarin, alginate, fucoidan, agar, carrageenan, porphyran, ulvan, and other complex structural polysaccharides, can be digested by marine bacteria with many carbohydrate-active enzymes (CAZymes) by breaking down the limitation of glycosidic bonds. However, structural elucidation of algal polysaccharides, metabolic pathways, and identification of potential polysaccharide hydrolases that participate in different metabolic pathways remain major obstacles restricting the efficient utilization of algal oligosaccharides. This review focuses on the structure, hydrolase families, metabolic pathways, and potential applications of seven macroalgae polysaccharides. These results will contribute to progressing our understanding of the structure of algal polysaccharides and their metabolic pathways and will be valuable for clearing the way for the compelling utilization of bioactive oligosaccharides.

Metabolic engineering for valorization of macroalgae biomass

Marine macroalgae have huge potential as feedstocks for production of a wide spectrum of chemicals used in biofuels, biomaterials, and bioactive compounds. Harnessing macroalgae in these ways could promote wellbeing for people while mitigating climate change and environmental destruction linked to use of fossil fuels. Microorganisms play pivotal roles in converting macroalgae into valuable products, and metabolic engineering technologies have been developed to extend their native capabilities. This review showcases current achievements in engineering the metabolisms of various microbial chassis to convert red, green, and brown macroalgae into bioproducts. Unique features of macroalgae, such as seasonal variation in carbohydrate content and salinity, provide the next challenges to advancing macroalgae-based biorefineries. Three emerging engineering strategies are discussed here: (1) designing dynamic control of metabolic pathways, (2) engineering strains of halophilic (salt-tolerant) microbes, and (3) developing microbial consortia for conversion. This review illuminates opportunities for future research communities by elucidating current approaches to engineering microbes so they can become cell factories for the utilization of macroalgae feedstocks.

Marine microbial enzymes for the production of algal oligosaccharides and its bioactive potential for application as nutritional supplements

Marine macroalgae have a very high carbohydrate content due to complex algal polysaccharides (APS) like agar, alginate, and ulvan in their cell wall. Despite numerous reports on their biomedical properties, their hydrocolloid nature limits their applications. Algal oligosaccharides (AOS), which are hydrolyzed forms of complex APS, are gaining importance due to their low molecular weight, biocompatibility, bioactivities, safety, and solubility in water that makes it a lucrative alternative. The AOS produced through enzymatic hydrolysis using microbial enzymes have far-reaching applications because of its stereospecific nature. Identification and characterization of novel microorganisms producing APS hydrolyzing enzymes are the major bottlenecks for the efficient production of AOS. This review will discuss the marine microbial enzymes identified for AOS production and the bioactive potential of enzymatically produced AOS. This can improve our understanding of the biotechnological potential of microbial enzymes for the production of AOS and facilitate the sustainable utilization of algal biomass. Enzymatically produced AOS are shown to have bioactivities such as antioxidant, antiglycemic, prebiotic, immunomodulation, antiobesity or antihypercholesterolemia, anti-inflammatory, anticancer, and antimicrobial activity. The myriad of health benefits provided by the AOS is the need of the hour as there is an alarming increase in physiological disorders among a wide range of the global population.

Configured for the Human Gut Microbiota: Molecular Mechanisms of Dietary β-Glucan Utilization

The β-glucans are a disparate group of structurally diverse polysaccharides, whose members are widespread in human diets as components of the cell walls of plants, algae, and fungi (including yeasts), and as bacterial exopolysaccharides. Individual β-glucans from these sources have long been associated with positive effects on human health through metabolic and immunological effects. Remarkably, the β-configured glucosidic linkages that define these polysaccharides render them inaccessible to the limited repertoire of digestive enzymes encoded by the human genome. As a result, the various β-glucans become fodder for the human gut microbiota (HGM) in the lower gastrointestinal tract, where they influence community composition and metabolic output, including fermentation to short chain fatty acids (SCFAs). Only recently, however, have the specific molecular systems that enable the utilization of β-glucans by select members of the HGM been fully elucidated by combined genetic, biochemical, and structural biological approaches. In the context of β-glucan structures and their effects on human nutrition and health, we summarize here the functional characterization of individual polysaccharide utilization loci (PULs) responsible for the saccharification of mixed-linkage β(1→3)/β(1→4)-glucans, β(1→6)-glucans, β(1→3)-glucans, β(1→2)-glucans, and xyloglucans in symbiotic human gut bacteria. These exemplar PULs serve as well-defined biomarkers for the prediction of β-glucan metabolic capability in individual bacterial taxa and across the global human population.

Polysaccharide-Bacteria Interactions From the Lens of Evolutionary Ecology

Microbes have the unique ability to break down the complex polysaccharides that make up the bulk of organic matter, initiating a cascade of events that leads to their recycling. Traditionally, the rate of organic matter degradation is perceived to be limited by the chemical and physical structure of polymers. Recent advances in microbial ecology, however, suggest that polysaccharide persistence can result from non-linear growth dynamics created by the coexistence of alternate degradation strategies, metabolic roles as well as by ecological interactions between microbes. This complex "landscape" of degradation strategies and interspecific interactions present in natural microbial communities appears to be far from evolutionarily stable, as frequent gene gain and loss reshape enzymatic repertoires and metabolic roles. In this perspective, we discuss six challenges at the heart of this problem, ranging from the evolution of genetic repertoires, phenotypic heterogeneity in clonal populations, the development of a trait-based ecology, and the impact of metabolic interactions and microbial cooperation on degradation rates. We aim to reframe some of the key questions in the study of polysaccharide-bacteria interactions in the context of eco-evolutionary dynamics, highlighting possible research directions that, if pursued, would advance our understanding of polysaccharide degraders at the interface between biochemistry, ecology and evolution.

High-cell-density cultivation of the flagellate alga Poterioochromonas malhamensis for biomanufacturing the water-soluble β-1,3-glucan with multiple biological activities

The microalga Poterioochromonas malhamensis was found to be capable of accumulating the storage β-1,3-glucan in soluble form under heterotrophic conditions. In this study, the highest biomass yield of 32.8 g L^-1 was achieved by combining the utilization of ammonium chloride as the nitrogen source, simultaneous addition of vitamins B1 and B12 and maintenance of pH at 6.0. Sugar profiling and nuclear magnetic resonance analysis indicated that the P. malhamensis β-1,3-glucan was composed of glucose with the β-(1 → 3) main chain and the β-(1 → 6) side chain. Under the optimal cultivation conditions, the cellular β-1,3-glucan content was up to 55% of the cell dry weight. Moreover, the P. malhamensis β-1,3-glucan could significantly promote the fin regeneration and improve the in vivo antioxidative activity of zebrafish. This study underpins the feasibility of culturing P. malhamensis under heterotrophic conditions for producing the highly water-soluble bioactive β-1,3-glucans for food and pharmaceutical applications.

Polysaccharide degradation by the Bacteroidetes: mechanisms and nomenclature

The Bacteroidetes phylum is renowned for its ability to degrade a wide range of complex carbohydrates, a trait that has enabled its dominance in many diverse environments. The best studied species inhabit the human gut microbiome and use polysaccharide utilization loci (PULs), discrete genetic structures that encode proteins involved in the sensing, binding, deconstruction, and import of target glycans. In many environmental species, polysaccharide degradation is tightly coupled to the phylum-exclusive type IX secretion system (T9SS), which is used for the secretion of certain enzymes and is linked to gliding motility. In addition, within specific species these two adaptive systems (PULs and T9SS) are intertwined, with PUL-encoded enzymes being secreted by the T9SS. Here, we discuss the most noteworthy PUL and non-PUL mechanisms that confer specific and rapid polysaccharide degradation capabilities to the Bacteroidetes in a range of environments. We also acknowledge that the literature showcasing examples of PULs is rapidly expanding and developing a set of assumptions that can be hard to track back to original findings. Therefore, we present a simple universal description of conserved PUL functions and how they are determined, while proposing a common nomenclature describing PULs and their components, to simplify discussion and understanding of PUL systems.

Cultivable Winogradskyella species are genomically distinct from the sympatric abundant candidate species

Winogradskyella is a genus within the phylum Bacteroidetes with a clear marine origin. Most members of this genus have been found associated with marine animals and algae, but also with inorganic surfaces such as sand. In this study, we analyzed genomes of eleven species recently isolated from surface seawater samples from the North Sea during a single spring algae bloom. Corresponding metagenomes yielded a single Candidatus species for this genus. All species in culture, with the exception of W. ursingii, affiliated with a Winogradskyella lineage characterized by large genomes (~4.3 ± 0.4 Mb), with high complexity in their carbohydrate and protein degradation genes. Specifically, the polysaccharide utilization loci (PULs) were diverse within each individual strain, indicating large substrate versatility. Although present in the North Sea, the abundances of these strains were at, or below, the detection limit of the metagenomes. In contrast, the single species, classified as Candidatus W. atlantica, to which all North Sea MAGs belonged, affiliated with a lineage in which the cultivated representatives showed small genomes of ~3.0-3.5 Mb, with the MAGs having ~2.3 Mb. In Ca. W. atlantica, genome streamlining has apparently resulted in the loss of biosynthesis pathways for several amino acids including arginine, methionine, leucine and valine, and the PUL loci were reduced to a single one for utilizing laminarin. This as-yet uncultivated species seems to capitalize on sporadically abundant substrates that are released by algae blooms, mainly laminarin. We also suggest that this streamlined genome might be responsible for the lack of growth on plates for this Candidatus species, in contrast to growth of the less abundant but coexisting members of the genus.

Dynamic carbon flux network of a diverse marine microbial community

The functioning of microbial ecosystems has important consequences from global climate to human health, but quantitative mechanistic understanding remains elusive. The components of microbial ecosystems can now be observed at high resolution, but interactions still have to be inferred e.g., a time-series may show a bloom of bacteria X followed by virus Y suggesting they interact. Existing inference approaches are mostly empirical, like correlation networks, which are not mechanistically constrained and do not provide quantitative mass fluxes, and thus have limited utility. We developed an inference method, where a mechanistic model with hundreds of species and thousands of parameters is calibrated to time series data. The large scale, nonlinearity and feedbacks pose a challenging optimization problem, which is overcome using a novel procedure that mimics natural speciation or diversification e.g., stepwise increase of bacteria species. The method allows for curation using species-level information from e.g., physiological experiments or genome sequences. The product is a mass-balancing, mechanistically-constrained, quantitative representation of the ecosystem. We apply the method to characterize phytoplankton-heterotrophic bacteria interactions via dissolved organic matter in a marine system. The resulting model predicts quantitative fluxes for each interaction and time point (e.g., 0.16 µmolC/L/d of chrysolaminarin to Polaribacter on April 16, 2009). At the system level, the flux network shows a strong correlation between the abundance of bacteria species and their carbon flux during blooms, with copiotrophs being relatively more important than oligotrophs. However, oligotrophs, like SAR11, are unexpectedly high carbon processors for weeks into blooms, due to their higher biomass. The fraction of exudates (vs. grazing/death products) in the DOM pool decreases during blooms, and they are preferentially consumed by oligotrophs. In addition, functional similarity of phytoplankton i.e., what they produce, decouples their association with heterotrophs. The methodology is applicable to other microbial ecosystems, like human microbiome or wastewater treatment plants.

Polysaccharide utilization by a marine heterotrophic bacterium from the SAR92 clade

SAR92 is one of the few examples of a widely distributed, abundant oligotroph that can be cultivated to study pathways of carbon oxidation in ocean systems. Genomic evidence for SAR92 suggests that this gammaproteobacterium might be a primary consumer of polysaccharides in the epipelagic zone, its main habitat. Here, we investigated cell growth, polysaccharide utilization gene expression, and carbohydrate-active enzyme abundance of a culturable SAR92 strain, HTCC2207, grown with different polysaccharides. Xylan and laminarin, two polysaccharides mainly produced by phytoplankton, supported the growth of HTCC2207 better than other polysaccharides. HTCC2207 possessed polysaccharide utilization loci (PULs) consisting of TonB-dependent receptor (TBDR) and glycoside hydrolase (GH) family genes. GH genes such as GH17 and GH3 presented no substrate-specificity and were induced by different sugar substrates, while expressions of GH16, GH10 and GH30 were enhanced in the glucose-treatment but suppressed in the polysaccharide-treatment, indicating complex polysaccharide utilization by HTCC2207. Metabolic pathways for laminarin and xylan were re-constructed in HTCC2207 based on the PULs genes and other predicted carbohydrate-active enzymes. This study reveals features of the epipelagic niche of SAR92 and provide insight into the biogeochemical cycling of labile, high-molecular carbohydrate compounds in the surface ocean.

Marine Polysaccharides: Occurrence, Enzymatic Degradation and Utilization

Macroalgae species are fast growing and their polysaccharides are already used as food ingredient due to their properties as hydrocolloids or they have potential high value bioactivity. The degradation of these valuable polysaccharides to access the sugar components has remained mostly unexplored so far. One reason is the high structural complexity of algal polysaccharides, but also the need for suitable enzyme cocktails to obtain oligo- and monosaccharides. Among them, there are several rare sugars with high value. Recently, considerable progress was made in the discovery of highly specific carbohydrate-active enzymes able to decompose complex marine carbohydrates such as carrageenan, laminarin, agar, porphyran and ulvan. This minireview summarizes these achievements and highlights potential applications of the now accessible abundant renewable resource of marine polysaccharides.

Prebiotic potential of mushroom d-glucans: implications of physicochemical properties and structural features

Mushroom d-glucans are recognized as dietary fibers and as biologically active natural polysaccharides, with the advantages of being quite inexpensive for production, tolerable, and having a range of possible structures and physicochemical properties. The prebiotic potential of mushroom d-glucans has been explored in recent years, but the relationship between their various structural features and activity is poorly understood. This review focuses on comprehensively evaluating the prebiotic potential of mushroom d-glucans in face of their structural variations. Overall, mushroom d-glucans provide a unique set of different structures and physicochemical properties with prebiotic potential, where linkage type and solubility degree seem to be associated with prebiotic activity outcomes. The understanding of the effects of distinct structures and physicochemical properties in mushroom d-glucans on the gut microbiota contributes to the design and selection of new prebiotics in a more predictable way.

A critical review on production of biopolymers from algae biomass and their applications

Algae is abundantly present in our ecosystems and can be easily extracted and used for production of biopolymers. Algae does not produce any anthropogenic, harmful effects, has a good growth rate, and cultivable in wastewater. This literature elucidates the potential of algae biomass by comparing various seaweed and microalgae strains. The routes for biopolymer production were portrayed and their novel methods of isolation such as microwave assisted, ultrasound assisted, and subcritical water assisted extraction are discussed in detail. These novel methods are observed to be highly efficient compared to conventional solvent extraction, with the microwave assisted and ultrasound assisted processes yielding 33% and 5% more biopolymer respectively than the conventional method. Biopolymers are used in variety of applications such as environmental remediation, adsorbent and antioxidant. Biopolymer is shown to be highly effective in the removal of potentially toxic elements and is seen to extract more than 40 mg PTE/g biopolymer.

Overview on Microbial Enzymatic Production of Algal Oligosaccharides for Nutraceutical Applications

Global requirement for algal foods is increasing, as they are progressively consumed for its nutrition and health. Macroalgae is a proven source of metabolites, proteins, pigments, bioactive compounds, and algal polysaccharides. The unique polysaccharides such as agar, carrageenan, porphyran, alginate, fucoidan, laminarin, and ulvan are known for its wide range of bioactivities and extensively used for applications from tissue engineering to drug delivery. However, there are few limitations due to its high molecular size, low compatibility, and hydrocolloid nature. Hence, the enzymatically produced algal oligosaccharides have drawn tremendous attention due to its green synthesis, solubility, and lower molecular size. They are reported to have bioactivities including antioxidant, antiglycemic, immunostimulatory, anti-inflammatory, and prebiotic activities, which can be used in the healthcare and nutraceutical industry for the manufacture of functional foods and dietary supplements. However, identification of potential microorganisms, producing polysaccharide hydrolyzing enzymes, remains a major bottle neck for efficient utilization of bioactive algal oligosaccharides. This review summarizes the recent developments in the identification and characterization of microbial enzymes for the production of bioactive algal oligosaccharides. This can improve our understanding of bioactive algal oligosaccharides and pave way for efficient utilization of macroalgae to prevent various chronic diseases.

Changing expression patterns of TonB-dependent transporters suggest shifts in polysaccharide consumption over the course of a spring phytoplankton bloom

Algal blooms produce large quantities of organic matter that is subsequently remineralised by bacterial heterotrophs. Polysaccharide is a primary component of algal biomass. It has been hypothesised that individual bacterial heterotrophic niches during algal blooms are in part determined by the available polysaccharide substrates present. Measurement of the expression of TonB-dependent transporters, often specific for polysaccharide uptake, might serve as a proxy for assessing bacterial polysaccharide consumption over time. To investigate this, we present here high-resolution metaproteomic and metagenomic datasets from bacterioplankton of the 2016 spring phytoplankton bloom at Helgoland island in the southern North Sea, and expression profiles of TonB-dependent transporters during the bloom, which demonstrate the importance of both the Gammaproteobacteria and the Bacteroidetes as degraders of algal polysaccharide. TonB-dependent transporters were the most highly expressed protein class, split approximately evenly between the Gammaproteobacteria and Bacteroidetes, and totalling on average 16.7% of all detected proteins during the bloom. About 93% of these were predicted to take up organic matter, and for about 12% of the TonB-dependent transporters, we predicted a specific target polysaccharide class. Most significantly, we observed a change in substrate specificities of the expressed transporters over time, which was not reflected in the corresponding metagenomic data. From this, we conclude that algal cell wall-related compounds containing fucose, mannose, and xylose were mostly utilised in later bloom stages, whereas glucose-based algal and bacterial storage molecules including laminarin, glycogen, and starch were used throughout. Quantification of transporters could therefore be key for understanding marine carbon cycling.

Diatom fucan polysaccharide precipitates carbon during algal blooms

The formation of sinking particles in the ocean, which promote carbon sequestration into deeper water and sediments, involves algal polysaccharides acting as an adhesive, binding together molecules, cells and minerals. These as yet unidentified adhesive polysaccharides must resist degradation by bacterial enzymes or else they dissolve and particles disassemble before exporting carbon. Here, using monoclonal antibodies as analytical tools, we trace the abundance of 27 polysaccharide epitopes in dissolved and particulate organic matter during a series of diatom blooms in the North Sea, and discover a fucose-containing sulphated polysaccharide (FCSP) that resists enzymatic degradation, accumulates and aggregates. Previously only known as a macroalgal polysaccharide, we find FCSP to be secreted by several globally abundant diatom species including the genera Chaetoceros and Thalassiosira. These findings provide evidence for a novel polysaccharide candidate to contribute to carbon sequestration in the ocean.

A set of simple methods for detection and extraction of laminarinase

A carefully designed ammonium sulfate precipitation will simplify extraction of proteins and is considered to be a gold standard among various precipitation methods. Therefore, optimization of ammonium sulfate precipitation can be an important functional step in protein purification. The presence of high amounts of ammonium sulphate precludes direct detection of many enzymatically active proteins including reducing sugar assays (e.g. Nelson-Somogyi, Reissig and 3,5-dinitrosalicylic acid methods) for assessing carbohydrases (e.g. laminarinase (β (1-3)-glucanohydrolase), cellulases and chitinases). In this study, a simple method was developed using laminarin infused agarose plate for the direct analysis of the ammonium sulphate precipitates from Streptomyces rimosus AFM-1. The developed method is simple and convenient that can give accurate results even in presence of ammonium sulfate in the crude precipitates. Laminarin is a translucent substrate requiring the use of a stain to visualize the zones of hydrolysis in a plate assay. A very low-cost and locally available fluorescent optical fabric brightener Tinopal CBS-X has been used as a stain to detect the zones of hydrolysis. We also report simple methods to prepare colloidal chitin and cell free supernatant in this manuscript.

The Biogeochemistry of Marine Polysaccharides: Sources, Inventories, and Bacterial Drivers of the Carbohydrate Cycle

Polysaccharides are major components of macroalgal and phytoplankton biomass and constitute a large fraction of the organic matter produced and degraded in the ocean. Until recently, however, our knowledge of marine polysaccharides was limited due to their great structural complexity, the correspondingly complicated enzymatic machinery used by microbial communities to degrade them, and a lack of readily applied means to isolate andcharacterize polysaccharides in detail. Advances in carbohydrate chemistry, bioinformatics, molecular ecology, and microbiology have led to new insights into the structures of polysaccharides, the means by which they are degraded by bacteria, and the ecology of polysaccharide production and decomposition. Here, we survey current knowledge, discuss recent advances, and present a new conceptual model linking polysaccharide structural complexity and abundance to microbially driven mechanisms of polysaccharide processing. We conclude by highlighting specific future research foci that will shed light on this central but poorly characterized component of the marine carbon cycle.

Linear and branched β-Glucans degrading enzymes from versatile Bacteroides uniformis JCM 13288T and their roles in cooperation with gut bacteria

β-glucans are the dietary nutrients present in oats, barley, algae, and mushrooms. The macromolecules are well known for their immune-modulatory activity; however, how the human gut bacteria digest them is vaguely understood. In this study, Bacteroides uniformis JCM 13288 ^T was found to grow on laminarin, pustulan, and porphyran. We sequenced the genome of the strain, which was about 5.05 megabase pairs and contained 4868 protein-coding genes. On the basis of growth patterns of the bacterium, two putative polysaccharide utilization loci for β-glucans were identified from the genome, and associated four putative genes were cloned, expressed, purified, and characterized. Three glycoside hydrolases (GHs) that were endo-acting enzymes (BuGH16, BuGH30, and BuGH158), and one which was an exo-acting (BuGH3) enzyme. The BuGH3, BuGH16, and BuGH158 can cleave linear exo/endo- β- 1-3 linkages while BuGH30 can digest endo- β- 1-6 linkages. BuGH30 and BuGH158 were further explored for their roles in digesting β- glucans and generation of oligosaccharides, respectively. The BuGH30 predominately found to cleave long chain β- 1-6 linked glucans, and obtained final product was gentiobiose. The BuGH158 used for producing oligosaccharides varying from degree of polymerization 2 to 7 from soluble curdlan. We demonstrated that these oligosaccharides can be utilized by gut bacteria, which either did not grow or poorly grew on laminarin. Thus, B. uniformis JCM 13288 ^T is not only capable of utilizing β-glucans but also shares these glycans with human gut bacteria for potentially maintaining the gut microbial homeostasis.

Plant species-specific recognition of long and short β-1,3-linked glucans is mediated by different receptor systems

Plants survey their environment for the presence of potentially harmful or beneficial microbes. During colonization, cell surface receptors perceive microbe-derived or modified-self ligands and initiate appropriate responses. The recognition of fungal chitin oligomers and the subsequent activation of plant immunity are well described. In contrast, the mechanisms underlying β-glucan recognition and signaling activation remain largely unexplored. Here, we systematically tested immune responses towards different β-glucan structures and show that responses vary between plant species. While leaves of the monocots Hordeum vulgare and Brachypodium distachyon can recognize longer (laminarin) and shorter (laminarihexaose) β-1,3-glucans with responses of varying intensity, duration and timing, leaves of the dicot Nicotiana benthamiana activate immunity in response to long β-1,3-glucans, whereas Arabidopsis thaliana and Capsella rubella perceive short β-1,3-glucans. Hydrolysis of the β-1,6 side-branches of laminarin demonstrated that not the glycosidic decoration but rather the degree of polymerization plays a pivotal role in the recognition of long-chain β-glucans. Moreover, in contrast to the recognition of short β-1,3-glucans in A. thaliana, perception of long β-1,3-glucans in N. benthamiana and rice is independent of CERK1, indicating that β-glucan recognition may be mediated by multiple β-glucan receptor systems.

Synergy between Cell Surface Glycosidases and Glycan-Binding Proteins Dictates the Utilization of Specific Beta(1,3)-Glucans by Human Gut Bacteroides

The human gut microbiota (HGM) has far-reaching impacts on human health and nutrition, which are fueled primarily by the metabolism of otherwise indigestible complex carbohydrates commonly known as dietary fiber. However, the molecular basis of the ability of individual taxa of the HGM to address specific dietary glycan structures remains largely unclear. In particular, the utilization of β(1,3)-glucans, which are widespread in the human diet as yeast, seaweed, and plant cell walls, had not previously been resolved. Through a systems-based approach, here we show that the symbiont Bacteroides uniformis deploys a single, exemplar polysaccharide utilization locus (PUL) to access yeast β(1,3)-glucan, brown seaweed β(1,3)-glucan (laminarin), and cereal mixed-linkage β(1,3)/β(1,4)-glucan. Combined biochemical, enzymatic, and structural analysis of PUL-encoded glycoside hydrolases (GHs) and surface glycan-binding proteins (SGBPs) illuminates a concerted molecular system by which B. uniformis recognizes and saccharifies these distinct β-glucans. Strikingly, the functional characterization of homologous β(1,3)-glucan utilization loci (1,3GUL) in other Bacteroides further demonstrated that the ability of individual taxa to utilize β(1,3)-glucan variants and/or β(1,3)/β(1,4)-glucans arises combinatorially from the individual specificities of SGBPs and GHs at the cell surface, which feed corresponding signals to periplasmic hybrid two-component sensors (HTCSs) via TonB-dependent transporters (TBDTs). These data reveal the importance of cooperativity in the adaptive evolution of GH and SGBP cohorts to address individual polysaccharide structures. We anticipate that this fine-grained knowledge of PUL function will inform metabolic network analysis and proactive manipulation of the HGM. Indeed, a survey of 2,441 public human metagenomes revealed the international, yet individual-specific, distribution of each 1,3GUL.IMPORTANCEBacteroidetes are a dominant phylum of the human gut microbiota (HGM) that target otherwise indigestible dietary fiber with an arsenal of polysaccharide utilization loci (PULs), each of which is dedicated to the utilization of a specific complex carbohydrate. Here, we provide novel insight into this paradigm through functional characterization of homologous PULs from three autochthonous Bacteroides species, which target the family of dietary β(1,3)-glucans. Through detailed biochemical and protein structural analysis, we observed an unexpected diversity in the substrate specificity of PUL glycosidases and glycan-binding proteins with regard to β(1,3)-glucan linkage and branching patterns. In combination, these individual enzyme and protein specificities support taxon-specific growth on individual β(1,3)-glucans. This detailed metabolic insight, together with a comprehensive survey of individual 1,3GULs across human populations, further expands the fundamental roadmap of the HGM, with potential application to the future development of microbial intervention therapies.

Laminarin is a major molecule in the marine carbon cycle

Marine microalgae sequester as much CO2 into carbohydrates as terrestrial plants. Polymeric carbohydrates (i.e., glycans) provide carbon for heterotrophic organisms and constitute a carbon sink in the global oceans. The quantitative contributions of different algal glycans to cycling and sequestration of carbon remain unknown, partly because of the analytical challenge to quantify glycans in complex biological matrices. Here, we quantified a glycan structural type using a recently developed biocatalytic strategy, which involves laminarinase enzymes that specifically cleave the algal glycan laminarin into readily analyzable fragments. We measured laminarin along transects in the Arctic, Atlantic, and Pacific oceans and during three time series in the North Sea. These data revealed a median of 26 ± 17% laminarin within the particulate organic carbon pool. The observed correlation between chlorophyll and laminarin suggests an annual production of algal laminarin of 12 ± 8 gigatons: that is, approximately three times the annual atmospheric carbon dioxide increase by fossil fuel burning. Moreover, our data revealed that laminarin accounted for up to 50% of organic carbon in sinking diatom-containing particles, thus substantially contributing to carbon export from surface waters. Spatially and temporally variable laminarin concentrations in the sunlit ocean are driven by light availability. Collectively, these observations highlight the prominent ecological role and biogeochemical function of laminarin in oceanic carbon export and energy flow to higher trophic levels.