An engineered microbial platform for direct biofuel production from brown macroalgae

Investigation of mannitol as a potential substrate for production of 2'-fucosyllactose in Yarrowia lipolytica

Mannitol, boasting abundant availability in marine biomass resource, represents a promising feedstock for biomanufacturing. Herein, Yarrowia lipolytica was found to synthesize 2'-fucosyllactose (2'-FL) more efficiently when using mannitol and lactose as substrate, compared to glucose and lactose. Notably, the strain maintained robust growth and 2'-FL production even when cultivated in brown algae processing wastewater. Transcriptome analysis of Y. lipolytica grown on mannitol revealed that two endogenous hexose transporters (Yht1 and Yht3) potentially modulated mannitol uptake. By optimizing the mannitol transporter and the GDP-d-mannose synthesis pathway, a 2'-FL producing strain was constructed with a titer of 9 g/L. Fed-batch fermentation in an inorganic salt medium supplemented with mannitol and lactose elevated the 2'-FL titer to 27.6 g/L. Collectively, this study demonstrates the efficacy of mannitol for 2'-FL biosynthesis and advances the sustainable utilization of algal resources.

Alpha-ketoacid decarboxylases: Diversity, structures, reaction mechanisms, and applications for biomanufacturing of platform chemicals and fuels

In living cells, alpha-ketoacid decarboxylases (KDCs, EC 4.1.1.-) are a class of enzymes that convert alpha-ketoacids into aldehydes through decarboxylation. These aldehydes serve as either drop-in chemicals or precursors for the biosynthesis of alcohols, carboxylic acids, esters, and alkanes. These compounds play crucial roles in cellular metabolism and fitness and the bioeconomy, facilitating the sustainable and renewable biomanufacturing of platform chemicals and fuels. This review explores the diversity and classification of KDCs, detailing their structures, mechanisms, and functions. We highlight recent advancements in repurposing KDCs to enhance their efficiency and robustness for biomanufacturing. Additionally, we present modular KDC-dependent metabolic pathways for the microbial biosynthesis of aldehydes, alcohols, carboxylic acids, esters, and alkanes. Finally, we discuss recent developments in the modular cell engineering technology that can potentially be applied to harness the diversity of KDC-dependent pathways for biomanufacturing platform chemicals and fuels.

Value-added biotransformation of agricultural byproducts by cellulolytic fungi: a review

Agricultural byproducts generally contain abundant bioactive compounds (e.g., cellulose/hemicellulose, phenolic compounds (PCs), and dietary fibers (DFs)), but most of them are neglected and underutilized. Owing to the complicated and rigid structures of agricultural byproducts, a considerable amount of bioactive compounds are entrapped in the polymer matrix, impeding their further development and utilization. In recent years, the prominent performance of cellulolytic fungi to grow and degrade agricultural byproducts has been applied to achieve efficient biotransformation of byproducts to high-value compounds, which is a green and sustainable strategy for the reutilization of agricultural byproducts. This review comprehensively summarizes recent progress in the value-added biotransformation of agricultural byproducts by cellulolytic fungi, including (1) direct utilization of agricultural byproducts for biochemicals and bioethanol production via a consolidated bioprocessing, (2) recovery and biotransformation of bounded PCs from agricultural byproducts for higher bioactive properties, as well as (3) modification and conversion of insoluble DF from agricultural byproducts to produce functional soluble DF. The functional enzymes, potential mechanisms, and metabolic pathways involved are emphasized. Moreover, promising advantages and current bottlenecks using cellulolytic fungi have also been elucidated, shedding further perspectives for sustainable and efficient reutilization of agricultural byproducts by cellulolytic fungi.

Recent Advances in Alginate Lyase Engineering for Efficient Conversion of Alginate to Value-Added Products

Alginate lyases depolymerize alginate and generate alginate oligosaccharides (AOS) and eventually 4-deoxy-L-erythro-5-hexoseulose uronate (DEH), a monosaccharide. Recently, alginate lyases have garnered significant attention due to the increasing demand for AOS, which exhibit bioactivities beneficial to human health, livestock productivity, and agricultural efficiency. Additionally, these enzymes play a crucial role in producing DEH, essential in alginate catabolism in bacteria. This review explains the industrial value of AOS and DEH, which contribute broadly to industries ranging from the food industry to biorefinery processes. This review also highlights recent advances in alginate lyase applications and engineering, including domain truncation, chimeric enzyme design, rational mutagenesis, and directed evolution. These approaches have enhanced enzyme performance for efficient AOS and DEH production. We also discuss current challenges and future directions toward industrial-scale bioconversion of alginate-rich biomass.

Bioprospecting of cellulases from marine fungi for macro-algal biomass degradation for biofuel application

The marine ecosystem, the largest on Earth, supports around 80 % of plant and animal species. Marine macroalgae, rich in polysaccharides like cellulose, remain underutilized despite their potential in a circular bioeconomy. Efficient valorization can promote sustainability, whereas mismanagement raises ecological concerns. Unlike lignocellulosic biomass, macroalgae lack lignin, making their processing unique. Global interest in macroalgae for biofuel applications is growing, particularly through polysaccharide-degrading biocatalysts like cellulases. Fungi, known for secreting extracellular cellulases and other enzymes, play a key role in biomass degradation. Marine fungi associated with macroalgae may possess enhanced enzymatic capabilities, enabling efficient algal polysaccharide breakdown. These fungi have immense potential in macroalgal biorefineries, facilitating the conversion of complex polysaccharides into oligosaccharides and monosaccharides for biofuels, pharmaceuticals, nutraceuticals, and cosmetics. Developing advanced bioprocessing technologies for marine fungi could provide robust cellulases that withstand industrial conditions, optimizing macroalgal biomass conversion. This review comprehensively examines cellulase production from marine fungi, their bioprocessing strategies, and their role in degrading macroalgal biomass. Additionally, other fungal enzymes and their industrial applications are briefly discussed. This study highlights the potential of marine fungi-derived cellulases in biofuel production, aligning with sustainable development goals and supporting global bioeconomic advancements.

Characterization of alginate-degrading bacteria isolated from seaweed-producing areas of South Korean territory and verification of the bacteria as plant growth-promoting biofertilizer

Alginate, a carbohydrate polymer produced by seaweed and some bacteria, is widely used in the food and medicine industries. Alginate oligosaccharides, produced by depolymerizing alginate, exhibit diverse biological functions, such as plant protection and growth promotion, enhancement of microbial metabolic activity, and potential applications in biofuel production. This study isolated 13 alginate-degrading bacterial strains from over a thousand seaside soil bacteria in South Korea and investigated their alginate-degrading characteristics. Through 16S rDNA sequencing, Marinomonas sp., Zobellella sp., and Pseudomonas sp. were newly identified at the subspecies level. Notably, this study is the first to report the alginate-degrading capability of Zobellella sp. The substrate specificity of each bacterial strain was analyzed toward poly-α-L-guluronate and poly-β-D-mannuronate, the two major alginate polymeric components. Furthermore, 3 of the 13 isolated strains were demonstrated to synthesize auxin, and their application to Arabidopsis thaliana confirmed enhanced vegetative growth. These findings advance our understanding of alginate degradation and highlight the potential of these bacteria and their alginate lyases as valuable resources in biotechnology applications. In addition, the potential of these bacteria as biofertilizers for promoting plant growth and the production of functional alginate oligosaccharides underscores the need for further exploration and development in this field.IMPORTANCEThis study aimed to isolate alginate-degrading bacteria from the soil samples collected in South Korea's major seaweed production areas and evaluate their potential as biofertilizers. Alginate, a primary component of brown algae, breaks down into alginate oligosaccharides, which are known to enhance plant growth. In this study, 13 strains of alginate-degrading bacteria were isolated, and some of them showed the potential for plant growth promotion and stress defense through strong biofilm formation and auxin production. Importantly, these bacterial strains exhibited plant growth-promoting potential, demonstrating their applicability in combination with seaweed-based fertilizers. These findings provide valuable insights that could broaden the industrial utilization of seaweed-derived fertilizers, contributing to enhanced agricultural productivity and sustainability.

A single enzyme becomes a Swiss Army knife

An alga that abandoned photosynthesis? This Primer explores a PLOS Biology study showing that a single horizontal gene transfer event allowed the diatom Nitzschia sing1 to evolve a complete enzymatic machinery to break down alginate from brown algae, unlocking a new ecological niche.

Renewable Energy from Beach-Cast Seaweed: Calorific Power Heating Studies with Macroalgae

Some stretches of the Brazilian coast are regularly subject to a natural process of macroalgae deposition. In urban beach areas, public institutions responsible for cleaning collect this biomass and dispose of it in landfills. When this biomass is exposed to the sun for a long time in the littoral area, a decomposition process begins and causes greenhouse gas emission into the atmosphere. Macroalgae biomass is a natural resource that could be used for renewable energy, contributing to meeting the growing demand for low environmental impacts of energy, indicating the possibility of participating in sustainable development. The objective of this research was to evaluate the energetic potential of macroalgae biomass deposited on the Maceió coast; specifically, the combustion capacity of aggregate biomass and pellet biofuel produced with macroalgae. The research, which analysed 13 species, proceeded using a calorimetric pump methodology to determine the power heating value and a mass spectrophotometer to determine the available energetic chemical elements. The result of 8.82 MJ/Kg was similar to the main biomass used in Brazil, the sugarcane bagasse, evaluated at 8.91 MJ/Kg. Aggregated macroalgae biomass in condensed pellets with energetic composites obtained a value of 4823 Kcal/Kg, 1.2% more than the average of terrestrial biomass pellets. Therefore, these results show possibilities to produce biofuel using thermal energy from marine macroalgae biomass.

Genomic analysis of Vreelandella sp. F11 reveals its role in alginate utilization

Alginate, mainly produced by brown algae, is an important polysaccharide that supports the growth of marine bacteria. Vreelandella sp. F11 is a Gram-negative and aerobic marine bacterium, which was isolated from the brown algae sample collected from the Weihai coast, the Yellow Sea, China. Here, we present the complete genome of strain F11 and its genomic characteristics to utilize alginate. The genome of strain F11 comprises one circular chromosome with 4,840,724 bp and a GC content of 55.04 %. Strain F11 could grow with alginate as the sole carbon source. Genomic analysis revealed that strain F11 contains a gene cluster, encoding the enzymes, transporters and a regulator protein involved in utilizing alginate. Gene annotations suggested that the alginate utilization system of strain F11 is similar to those in Vibrio strains. However, strain F11 does not contain homologs of known KdgF (a key enzyme involved in the metabolism of alginate monomer) and inner membrane transporters of alginate oligomer uptake. The result indicated that strain F11 contains novel KdgF and inner membrane transporter system, which warrants further investigation. These data suggested that Vreelandella strains play a role in alginate utilization in the ocean and lay a foundation for the application of Vreelandella in the conversion of brown algae.

Alginate catabolic systems in marine bacteria

Brown algae, constituting the second largest group of marine macroalgae, fix significant amounts of inorganic carbon into alginate, the most abundant polysaccharide found in their cell walls. Alginate serves as an important macromolecular carbon source for marine bacteria. The catabolism of alginate by bacteria is an important step in the marine carbon cycle, and this area of research has attracted growing interests over the past decade. Here, we provide an overview of the recent advances in our understanding of marine bacterial alginate catabolic systems, both in individual organisms and within bacterial consortia, discuss the possibility of additional alginate metabolic pathways in light of the present findings, and highlight the future research foci.

A review on multifunctional calcium alginate fibers for full-time and multipurposed wound treatment: From fundamentals to advanced applications

Recent progress in wound healing has highlighted the need for more effective treatment strategies capable of addressing the complex biological and physiological challenges of wound repair. Traditional wound dressings often fail to address the complex and evolving needs of chronic, acute, and burn wounds, particularly in terms of promoting healing, preventing infection, and supporting tissue regeneration. In response to these challenges, calcium alginate fibers (CAFs) have emerged as promising materials, characterized by their exceptional structural properties and diverse biological functions, offering significant commercial potential for the development of advanced wound dressings and therapeutic solutions. Here, a brief review of the CAFs for promoting wound healing is presented, with specific discussions of the fundamental characteristics of CAFs and its feasibility to be applied for adjusting physiological and pathological processes involved in wound healing. Then, a comprehensive and in-depth depiction of emerging representative fabrication techniques for generating CAFs is categorized and reviewed. Moreover, emerging applications benefits from the CAFs are reviewed, highlighting the multifunctional roles and benefits of CAFs in facilitating wound repair. Finally, the challenges and perspectives for further advancing CAFs toward a more powerful and versatile therapeutic strategy are discussed, particularly regarding new opportunities in biomedical research and clinical applications.

Complete xylan utilization pathway and regulation mechanisms involved in marine algae degradation by cosmopolitan marine and human gut microbiota

β-1,3-xylan, typically found in marine algae as a major cell wall polysaccharide, represents an overlooked pool of organic carbon in global oceans. Whilst our understanding of microbial catabolism of xylans has improved significantly, particularly from biotransformations of terrestrial plant biomass that are typically composed of β-1,4-xylans, knowledge on how microbes utilize β-1,3-xylan remains limited. Here, we describe the discovery of a complete pathway for β-1,3-xylan catabolism and its regulation in a marine bacterium, Vibrio sp. EA2. The pathway starts with the extracellular decomposition of β-1,3-xylan by two β-1,3-xylanases into β-1,3-xylooligomers, which are mainly internalized by an ATP-binding cassette transporter. The substrate binding protein of this transporter has an L-shaped substrate binding pocket to preferentially bind β-1,3-xylooligomers. Subsequently, two intracellular β-1,3-xylosidases degrade β-1,3-xylooligomers into fermentable xylose. The pathway is activated by a unique regulator with xylose being the effector. This β-1,3-xylan catabolic pathway differs from that of β-1,4-xylan catabolism in enzymes, transporters, and regulators. Bioinformatic analysis suggests that the β-1,3-xylan catabolism pathway is not only prevalent in diverse marine bacteria and cosmopolitan human gut microbiota, such as Bacteroides, but also likely transferred horizontally from algae-degrading marine bacteria to the human gut.

A bifunctional endolytic alginate lyase with two different lyase catalytic domains from Vibrio sp. H204

Alginate lyases can fully degrade alginate into various size-defined unsaturated oligosaccharide products by β-elimination. Here, we identified the bifunctional endolytic alginate lyase Aly35 from the marine bacterium Vibrio sp. Strain H204. The enzyme Aly35 is classified into the polysaccharide lyase 7 superfamily and contains two alginate lyase catalytic domains. The relationship and function of the two lyase domains are not well known. Thus, the full-length recombinant enzyme and its truncated proteins Aly35-CD1 (catalytic domain 1), Aly35-CD2 (catalytic domain 2 domain) were constructed. The three enzymes showed similar biochemical characteristics and exhibited temperature and pH stability. Further research showed that Aly35 and Aly35-CD2 can efficiently degrade alginate, polymannuronate (PM) and polyguluronate (PG) into a series of unsaturated oligosaccharides, while Aly35-CD1 exhibits greater PM-degrading activity than that of Aly35-CD2 but can not degraded PG efficiently. The results suggest that the domain (Trp295-His582) is critical for PG-degrading activity, the domain has (Leu53-Lys286) higher PM-degrading activity, both catalytic domains together confer increased alginate (including M-blocks and G blocks)-degrading activity. The enzyme Aly35 and its truncations Aly35-CD1 and Aly35-CD2 will be useful tools for structural analyses and for preparing bioactive oligosaccharides, especially Aly35-CD1 can be used to prepare G unit-rich oligosaccharides from alginate.

Value-added utilization technologies for seaweed processing waste in a circular economy: Developing a sustainable modern seaweed industry

The global seaweed industry annually consumes approximately 600,000 tons of dried algal biomass to produce algal hydrocolloids, yet only 15-30% of this biomass is utilized, with the remaining 70-85% discarded or released as scum or wastewater during the hydrocolloid extraction process. This residual biomass is often treated as waste and not considered for further commercial use, which contradicts the principles of sustainable development. In reality, the residual algal biomass could be employed to extract additional biochemical components, such as pigments, proteins, and cellulose, and these ingredients have important application prospects in the food sector. According to the biorefinery concept, recycling various products alongside the principal product enhances overall biomass utilization. Transitioning from traditional single-product processes to multi-product biorefineries, however, raises operating costs, presenting a significant challenge. Alternatively, developing value-added utilization technologies that target seaweed waste without altering existing processes is gaining traction among industry practitioners. Current advancements include methods such as separation and extraction of residual biomass, anaerobic digestion, thermochemical conversion, enzymatic treatment, functionalized modification of algal scum, and efficient utilization through metabolic engineering. These technologies hold promise for converting seaweed waste into alternative proteins, dietary supplements, and bioplastics for food packaging. Combining multiple technologies may offer the most effective strategy for future seaweed waste treatment. Nonetheless, most research on value-added waste utilization remains at the laboratory scale, necessitating further investigation at pilot and commercial scales.

Polysaccharide breakdown products drive degradation-dispersal cycles of foraging bacteria through changes in metabolism and motility

Most of Earth's biomass is composed of polysaccharides. During biomass decomposition, polysaccharides are degraded by heterotrophic bacteria as a nutrient and energy source and are thereby partly remineralized into CO2. As polysaccharides are heterogeneously distributed in nature, following the colonization and degradation of a polysaccharide hotspot the cells need to reach new polysaccharide hotspots. Even though many studies indicate that these degradation-dispersal cycles contribute to the carbon flow in marine systems, we know little about how cells alternate between polysaccharide degradation and motility, and which environmental factors trigger this behavioral switch. Here, we studied the growth of the marine bacterium Vibrio cyclitrophicus ZF270 on the abundant marine polysaccharide alginate, both in its soluble polymeric form as well as on its breakdown products. We used microfluidics coupled to time-lapse microscopy to analyze motility and growth of individual cells, and RNA sequencing to study associated changes in gene expression. We found that single cells grow at reduced rate on alginate until they form large groups that cooperatively break down the polymer. Exposing cell groups to digested alginate accelerates cell growth and changes the expression of genes involved in alginate degradation and catabolism, central metabolism, ribosomal biosynthesis, and transport. However, exposure to digested alginate also triggers cells to become motile and disperse from cell groups, proportionally increasing with the group size before the nutrient switch, and this is accompanied by high expression of genes involved in flagellar assembly, chemotaxis, and quorum sensing. The motile cells chemotax toward polymeric but not digested alginate, likely enabling them to find new polysaccharide hotspots. Overall, our findings reveal cellular mechanisms that might also underlie bacterial degradation-dispersal cycles, which influence the remineralization of biomass in marine environments.

Enhanced algin oligosaccharide production through selective breeding and optimization of growth and degradation conditions in Cobetia sp. cqz5-12-M1

Algin oligosaccharides have been applied in diverse industries and could be innovative synthesized by alginate-degrading bacteria. For enhance the alginate degradation efficiency to produce more algin oligosaccharides, a mutant strain (Cobetia sp. cqz5-12-M1) was obtained through the complex mutagenesis using UV and the alkylating agent 1-methyl-3-nitro-1-nitrosoguanidine. The enzyme activity of the fermentation supernatant of mutant exhibited a significant 38.09% (53.98 ± 0.69 U/mL) increase, and its optimal growth conditions were determined as: 5 g/L sodium alginate, 5 g/L yeast powder, 30 g/L NaCl, 2 g/L K2HPO4, 2 g/L KH2PO4, 1 g/L MgSO4•7H2O, 0.01 g/L FeSO4•7H2O, pH 6.5, and 34 ℃. Moreover, its optimal degradation conditions were identified as: 5 g/L sodium alginate, 5 g/L yeast powder, 30 g/L NaCl, 2 g/L K2HPO4, 2 g/L KH2PO4, 1 g/L MgSO4•7H2O, 0.01 g/L FeSO4•7H2O, pH 6.5, 31 ℃ and 72 h, yielding an enzyme activity of 120.98 ± 1.40 U/mL in the fermentation supernatant. Conclusive experiments on reagent tolerance revealed the growth of the mutant strain was significantly inhibited by 3% hydrogen peroxide, 5% carbolic acid, and 10 mg/mL gatifloxacin. Additionally, the alginate degradation capacity of mutant strain was highly significantly inhibited by 75% ethanol and all tested antibiotics.

Natural transformation of Vibrio natriegens with large genetic cluster enables alginate assimilation for isopentenol production

Alginate is a major component of brown macroalgae, and its efficient utilization is critical for developing sustainable technologies. Vibrio natriegens is a fast-growing marine bacterium that has gained massive attention due to its potential as an alternative industrial chassis. However, V. natriegens cannot naturally metabolize alginate, limiting its usage in marine biomass conversion. In this study, V. natriegens was engineered to utilize marine biomass, kelp, as a carbon source. A total of 33.8 kb of the genetic cluster for alginate assimilation from Vibrio sp. dhg was integrated into V. natriegens by natural transformation. Engineered V. natriegens was further modified to produce 1.8 mg/L of isopentenol from 16 g/L of crude kelp powder. This study not only presents the very first case in which V. natriegens can be naturally transformed with large DNA fragments but also highlights the potential of this strain for converting marine biomass into valuable products.

Systematic review on carrageenolytic enzymes: From metabolic pathways to applications in biotechnology

Carrageenan, the major carbohydrate component of some red algae, is an important renewable bioresource with very large annual outputs. Different types of carrageenolytic enzymes in the carrageenan metabolic pathway are potentially valuable for the production of carrageenan oligosaccharides, biofuel, and other chemicals obtained from carrageenan. However, these enzymes are not well-developed for oligosaccharide or biofuel production. For further application, comprehensive knowledge of carrageenolytic enzymes is essential. Therefore, in this review, we first summarize various carrageenolytic enzymes, including the recently discovered β-carrageenase, carrageenan-specific sulfatase, exo-α-3,6-anhydro-D-galactosidase (D-ADAGase), and exo-β-galactosidase (BGase), and describe their enzymatic characteristics. Subsequently, the carrageenan metabolic pathways are systematically presented and applications of carrageenases and carrageenan oligosaccharides are illustrated with examples. Finally, this paper discusses critical aspects that can aid researchers in constructing cascade catalytic systems and engineered microorganisms to efficiently produce carrageenan oligosaccharides or other value-added chemicals through the degradation of carrageenan. Overall, this paper offers a comprehensive overview of carrageenolytic enzymes, providing valuable insights for further exploration and application of these enzymes.

Structural basis for the minimal bifunctional alginate epimerase AlgE3 from Azotobacter chroococcum

Among the epimerases specific to alginate, some of them in Azotobacter genera convert β-d-mannuronic acid to α-l-guluronic acid but also have lyase activity to degrade alginate. The remarkable characteristics of these epimerases make it a promising enzyme for tailoring alginates to meet specific demands. Here, we determined the structure of the bifunctional mannuronan C-5 epimerase AlgE3 from Azotobacter chroococcum (AcAlgE3) in complex with several mannuronic acid oligomers as well as in apo form, which allowed us to elucidate the binding manner of each mannuronic acid oligomer, and the structural plasticity, which is dependent on calcium ions. Moreover, a comprehensive analysis of the lyase activity profiles of AcAlgE3 combined with structural characteristics explained the preference for different chain length oligomers.

Micro/nanoengineered agricultural by-products for biomedical and environmental applications

Agriculturally derived by-products generated during the growth cycles of living organisms as secondary products have attracted increasing interest due to their wide range of biomedical and environmental applications. These by-products are considered promising candidates because of their unique characteristics including chemical stability, profound biocompatibility and offering a green approach by producing the least impact on the environment. Recently, micro/nanoengineering based techniques play a significant role in upgrading their utility, by controlling their structural integrity and promoting their functions at a micro and nano scale. Specifically, they can be used for biomedical applications such as tissue regeneration, drug delivery, disease diagnosis, as well as environmental applications such as filtration, bioenergy production, and the detection of environmental pollutants. This review highlights the diverse role of micro/nano-engineering techniques when applied on agricultural by-products with intriguing properties and upscaling their wide range of applications across the biomedical and environmental fields. Finally, we outline the future prospects and remarkable potential that these agricultural by-products hold in establishing a new era in the realms of biomedical science and environmental research.

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.

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.

Direct and robust citramalate production from brown macroalgae using fast-growing Vibrio sp. dhg

Brown macroalgae is a promising feedstock for biorefinery owing to its high biomass productivity and contents of carbohydrates such as alginate and mannitol. However, the limited availability of microbial platforms efficiently catabolizing the brown macroalgae sugars has restricted its utilization. In this study, the direct production of citramalate, an important industrial compound, was demonstrated from brown macroalgae by utilizing Vibrio sp. dhg, which has a remarkably efficient catabolism of alginate and mannitol. Specifically, citramalate synthase from Methanocaldococcus jannaschii was synthetically expressed, and competing pathways were removed to maximally redirect the carbon flux toward citramalate production. Notably, a resulting strain, VXHC, produced citramalate up to 9.8 g/L from a 20 g/L mixture of alginate and mannitol regardless of their ratios. Citramalate was robustly produced even when diverse brown macroalgae were provided directly. Collectively, this study showcased the high potential of brown macroalgae biorefinery using Vibrio sp. dhg.

Characterization and Mechanism Study of a Novel PL7 Family Exolytic Alginate Lyase from Marine Bacteria Vibrio sp. W13

Alginate lyase can degrade alginate into oligosaccharides through β-elimination for various biological, biorefinery, and agricultural purposes. Here, we report a novel PL7 family exolytic alginate lyase VwAlg7A from marine bacteria Vibrio sp. W13 and achieve the heterologous expression in E. coli BL21 (DE3). VwAlg7A is 348aa with a calculated molecular weight of 36 kDa, containing an alginate lyase 2 domain. VwAlg7A exhibits specificity towards poly-guluronate. The optimal temperature and pH of VwAlg7A are 30 °C and 7.0, respectively. The activity of VwAlg7A can be significantly inhibited by the Ni2+, Zn2+, and NaCl. The Km and Vmax of VwAlg7A are 36.9 mg/ml and 395.6 μM/min, respectively. The ESI and HPAEC-PAD results indicate that VwAlg7A cleaves the sugar bond in an exolytic mode. Based on the molecular docking and mutagenesis results, we further confirmed that R98, H169, and Y303 are important catalytic residues.

Biochemical characterization and key catalytic residue identification of a novel alpha-agarase with CBM2 domain

Agarooligosaccharides have great potential in food industry because of their various bio-activities, while the limited availability and diversity of α-agarases hinder agarooligosaccharides' broader application. To overcome this limitation, a computer-assisted method was used to screen and identify novel agarases. Firstly, one novel α-agarase, AgaB, with an N-terminal CBM2 domain (the first report of this domain in agarases), was discovered. Purified agarases only exhibited activity against agarose, with optimum activity at 40℃ and pH 8.0. Analysis of hydrolysis products indicated that AgaB is an endo-type α-agarase, producing agarotetraose and agarohexaose. Secondly, AgaB truncated CBM2 showed increased Km values, suggesting that CBM2 aids in substrate binding. Thirdly, E468 and D333 are possibly catalytic amino acids, which was supported by molecular docking results and mutants. Biochemical characterization of first reported CBM2-containing agarase and catalytic mechanism study lay the foundation for the exploration and development of α-agarases in the future.

Life Cycle Assessment of a large commercial kelp farm in Shandong, China

The environmental benefits of seaweed cultivation have gained a lot of attention, both in policy strategies and by private companies. Sustainability evaluations of seaweed farming have however focused on a very small part of global production of seaweed - on European cultivations at research and pilot-scales although Asia stands for 99 % of global production with China alone producing 60 %. In this study, we use Life Cycle Assessment (LCA) to evaluate the environmental performance of a 400-hectare Chinese kelp farm with a yearly harvest of 60,000 tons. Primary data from the farm was used to assess impacts up until harvest for the functional unit of 1 ton of fresh-weight kelp. Included in the LCA were impact on climate change, acidification terrestrial and marine eutrophication, and use of land water and energy. In addition, we calculated nutrient uptake. Further, we extracted inventory data of four published LCA studies of farmed kelp and recalculated environmental impacts, applying the same background data and method choices with the aim to compare the effects of scale and cultivation system. The results of the hotspot analysis showed that the plastic ropes and buoys dominated impacts on climate change, freshwater and marine eutrophication, and energy consumption. Consequently, the most effective improvement action was recycling after use. The yearly harvest of the Chinese farm was 1000-4000 times larger than previously evaluated farms compared. Results suggest that streamlined and mature production in the large-scale Chinese kelp farm led to lower electricity and fuel consumption compared to small-scale production, thus placing the Chinese farm with a climate impact of 57.5 kg CO2 eq. per ton fresh-weight kelp on the lower end when comparing the carbon footprint. There was a large variation in carbon footprints, which implies that the kelp cultivation sector has considerable room for optimization.

Ecological function and interaction of different bacterial groups during alginate processing in coastal seawater community

The degradation of high molecular weight organic matter (HMWOM) is a core process of oceanic carbon cycle, which is determined by the activity of microbial communities harboring hundreds of different species. Illustrating the active microbes and their interactions during HMWOM processing can provide key information for revealing the relationship between community composition and its ecological functions. In this study, the genomic and transcriptional responses of microbial communities to the availability of alginate, an abundant HMWOM in coastal ecosystem, were elucidated. The main degraders transcribing alginate lyase (Aly) genes came from genera Alteromonas, Psychrosphaera and Colwellia. Meanwhile, some strains, mainly from the Rhodobacteraceae family, did not transcribe Aly gene but could utilize monosaccharides to grow. The co-culture experiment showed that the activity of Aly-producing strain could promote the growth of Aly-non-producing strain when alginate was the sole carbon source. Interestingly, this interaction did not reduce the alginate degradation rate, possibly due to the easily degradable nature of alginate. This study can improve our understanding of the relationship between microbial community activity and alginate metabolism function as well as further manipulation of microbial community structure for alginate processing.

Exploring the Prospects of Fermenting/Co-Fermenting Marine Biomass for Enhanced Bioethanol Production

With the rising demands for renewable fuels, there is growing interest in utilizing abundant and sustainable non-edible biomass as a feedstock for bioethanol production. Macroalgal biomass contains a high content of carbohydrates in the form of special polysaccharides like alginate, agar, and carrageenan that can be converted to fermentable sugars. In addition, using seagrass as a feedstock for bioethanol production can provide a sustainable and renewable energy source while addressing environmental concerns. It is a resource-rich plant that offers several advantages for bioethanol production, including its high cellulose content, rapid growth rates, and abundance in coastal regions. To reduce sugar content and support efficient microbial fermentation, co-fermentation of macroalgae with seagrass (marine biomass) can provide complementary sugars and nutrients to improve process yields and economics. This review comprehensively covers the current status and future potential of fermenting macroalgal biomass and seagrass, as well as possible combinations for maximizing bioethanol production from non-edible energy crops. An overview is provided on the biochemical composition of macroalgae and seagrass, pretreatment methods, hydrolysis, and fermentation processes. Key technical challenges and strategies to achieve balanced co-substrate fermentation are discussed. The feasibility of consolidated bioprocessing to directly convert mixed feedstocks to ethanol is also evaluated. Based on current research, macroalgae-seagrass co-fermentation shows good potential to improve the bioethanol yields, lower the cost, and enable more optimal utilization of diverse marine biomass resources compared to individual substrates.

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 β-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 Cold-Adapted and High-Alkaline Alginate Lyase with Potential for Alginate Oligosaccharides Preparation

Alginate oligosaccharides (AOs) prepared through enzymatic reaction by diverse alginate lyases under relatively controllable and moderate conditions possess versatile biological activities. But widely used commercial alginate lyases are still rather rare due to their poor properties (e.g., lower activity, worse thermostability, ion tolerance, etc.). In this work, the alginate lyase Alyw208, derived from Vibrio sp. W2, was expressed in Yarrowia lipolytica of food grade and characterized in order to obtain an enzyme with excellent properties adapted to industrial requirements. Alyw208 classified into the polysaccharide lyase (PL) 7 family showed maximum activity at 35 °C and pH 10.0, indicating its cold-adapted and high-alkaline properties. Furthermore, Alyw208 preserved over 70% of the relative activity within the range of 10-55 °C, with a broader temperature range for the activity compared to other alginate-degrading enzymes with cold adaptation. Recombinant Alyw208 was significantly activated with 1.5 M NaCl to around 2.1 times relative activity. In addition, the endolytic Alyw208 was polyG-preferred, but identified as a bifunctional alginate lyase that could degrade both polyM and polyG effectively, releasing AOs with degrees of polymerization (DPs) of 2-6 and alginate monomers as the final products (that is, DPs 1-6). Alyw208 has been suggested with favorable properties to be a potent candidate for biotechnological and industrial applications.

Utilization of Macroalgae for the Production of Bioactive Compounds and Bioprocesses Using Microbial Biotechnology

To achieve sustainable development, alternative resources should replace conventional resources such as fossil fuels. In marine ecosystems, many macroalgae grow faster than terrestrial plants. Macroalgae are roughly classified as green, red, or brown algae based on their photosynthetic pigments. Brown algae are considered to be a source of physiologically active substances such as polyphenols. Furthermore, some macroalgae can capture approximately 10 times more carbon dioxide from the atmosphere than terrestrial plants. Therefore, they have immense potential for use in the environment. Recently, macroalgae have emerged as a biomass feedstock for bioethanol production owing to their low lignin content and applicability to biorefinery processes. Herein, we provided an overview of the bioconversion of macroalgae into bioactive substances and biofuels using microbial biotechnology, including engineered yeast designed using molecular display technology.

Blood-Glucose-Powered Metabolic Fuel Cell for Self-Sufficient Bioelectronics

Currently available bioelectronic devices consume too much power to be continuously operated on rechargeable batteries, and are often powered wirelessly, with attendant issues regarding reliability, convenience, and mobility. Thus, the availability of a robust, self-sufficient, implantable electrical power generator that works under physiological conditions would be transformative for many applications, from driving bioelectronic implants and prostheses to programing cellular behavior and patients' metabolism. Here, capitalizing on a new copper-containing, conductively tuned 3D carbon nanotube composite, an implantable blood-glucose-powered metabolic fuel cell is designed that continuously monitors blood-glucose levels, converts excess glucose into electrical power during hyperglycemia, and produces sufficient energy (0.7 mW cm^-2 , 0.9 V, 50 mm glucose) to drive opto- and electro-genetic regulation of vesicular insulin release from engineered beta cells. It is shown that this integration of blood-glucose monitoring with elimination of excessive blood glucose by combined electro-metabolic conversion and insulin-release-mediated cellular consumption enables the metabolic fuel cell to restore blood-glucose homeostasis in an automatic, self-sufficient, and closed-loop manner in an experimental model of type-1 diabetes.

Design of a stable ethanologenic bacterial strain without heterologous plasmids and antibiotic resistance genes for efficient ethanol production from concentrated dairy waste

Engineering sustainable bioprocesses that convert abundant waste into fuels is pivotal for efficient production of renewable energy. We previously engineered an Escherichia coli strain for optimized bioethanol production from lactose-rich wastewater like concentrated whey permeate (CWP), a dairy effluent obtained from whey valorization processes. Although attractive fermentation performances were reached, significant improvements are required to eliminate recombinant plasmids, antibiotic resistances and inducible promoters, and increase ethanol tolerance. Here, we report a new strain with chromosomally integrated ethanologenic pathway under the control of a constitutive promoter, without recombinant plasmids and resistance genes. The strain showed extreme stability in 1-month subculturing, with CWP fermentation performances similar to the ethanologenic plasmid-bearing strain. We then investigated conditions enabling efficient ethanol production and sugar consumption by changing inoculum size and CWP concentration, revealing toxicity- and nutritional-related bottlenecks. The joint increase of ethanol tolerance, via adaptive evolution, and supplementation of small ammonium sulphate amounts (0.05% w/v) enabled a fermentation boost with 6.6% v/v ethanol titer, 1.2 g/L/h rate, 82.5% yield, and cell viability increased by three orders of magnitude. Our strain has attractive features for industrial settings and represents a relevant improvement in the existing ethanol production biotechnologies.

The arabinose transporter MtLat-1 is involved in hemicellulase repression as a pentose transceptor in Myceliophthora thermophila

BACKGROUND

Filamentous fungi possess an array of secreted enzymes to depolymerize the structural polysaccharide components of plant biomass. Sugar transporters play an essential role in nutrient uptake and sensing of extracellular signal molecules to inhibit or trigger the induction of lignocellulolytic enzymes. However, the identities and functions of transceptors associated with the induction of hemicellulase genes remain elusive.

RESULTS

In this study, we reveal that the L-arabinose transporter MtLat-1 is associated with repression of hemicellulase gene expression in the filamentous fungus Myceliophthora thermophila. The absence of Mtlat-1 caused a decrease in L-arabinose uptake and consumption rates. However, mycelium growth, protein production, and hemicellulolytic activities were markedly increased in a ΔMtlat-1 mutant compared with the wild-type (WT) when grown on arabinan. Comparative transcriptomic analysis showed a different expression profile in the ΔMtlat-1 strain from that in the WT in response to arabinan, and demonstrated that MtLat-1 was involved in the repression of the main hemicellulase-encoding genes. A point mutation that abolished the L-arabinose transport activity of MtLat-1 did not impact the repression of hemicellulase gene expression when the mutant protein was expressed in the ΔMtlat-1 strain. Thus, the involvement of MtLat-1 in the expression of hemicellulase genes is independent of its transport activity. The data suggested that MtLat-1 is a transceptor that senses and transduces the molecular signal, resulting in downstream repression of hemicellulolytic gene expression. MtAra-1 protein directly regulated the expression of Mtlat-1 by binding to its promoter region. Transcriptomic profiling indicated that the transcription factor MtAra-1 also plays an important role in expression of arabinanolytic enzyme genes and L-arabinose catabolism.

CONCLUSIONS

M. thermophila MtLat-1 functions as a transceptor that is involved in L-arabinose transport and signal transduction associated with suppression of the expression of hemicellulolytic enzyme-encoding genes. The data presented in this study add to the models of the regulation of hemicellulases in filamentous fungi.

A First Marine Vibrio Biocatalyst to Produce Ethanol from Alginate, which is a Rich Polysaccharide in Brown Macroalgal Biomass

The use of un-utilized feedstock and seawater for material and/or energy production using marine microbial catalysts is one potential option toward contributing to the development of a more sustainable society. Ethanol production from alginate, which is an oxidized polysaccharide present in brown seaweed, is extremely difficult due to the imbalance of reducing power in the microbial cells. Production of ethanol by such means has so far been unsuccessful using marine microbial biocatalysts. To produce ethanol from alginate, an alternative pathway consisting of a pyruvate decarboxylase gene (pdc) and an alcohol dehydrogenase II gene (adhII) derived from Zymomonas mobilis strain ZM4 was implemented into a metabolically engineered bacterium, Vibrio halioticoli, which is a representative marine alginate decomposer. No ethanol from alginate was produced in the wild-type V. halioticoli; however, the engineered V. halioticoli harboring the pdc and adhII operon (Pet operon), designated to the V. halioticoli (Pet), was able to produce 880 mg/L ethanol in maximum from 1.5% alginate for 72 h. The Pet operon also worked on the other marine alginolytic vibrios for ethanol production from alginate. This is the first case of ethanol production from alginate using marine bacterial biocatalysts under seawater-based media.

A Review of Biohydrogen Production from Saccharina japonica

Saccharina japonica (known as Laminaria japonica or Phaeophyta japonica), one of the largest macroalgae, has been recognized as food and medicine for a long time in some Asian countries, such as China, South Korea, Japan, etc. In recent years, S. japonica has also been considered the most promising third-generation biofuel feedstock to replace fossil fuels, contributing to solving the challenges people face regarding energy and the environment. In particular, S. japonica-derived biohydrogen (H2) is expected to be a major fuel source in the future because of its clean, high-yield, and sustainable properties. Therefore, this review focuses on recent advances in bio-H2 production from S. japonica. The cutting-edge biological technologies with suitable operating parameters to enhance S. japonica’s bio-H2 production efficiency are reviewed based on the Scopus database. In addition, guidelines for future developments in this field are discussed.

Challenges and opportunities for third-generation ethanol production: A critical review

In recent decades, third-generation (3G) biofuels have become a more attractive method of fuel production, as algae cultivation does not infringe on resources needed for food production. Additionally, algae can adapt to different environments, has high photosynthetic efficiency (CO2 fixation), and has a high potential for carbohydrate accumulation. The prevalence of algae worldwide demonstrates its ability to adapt to different environments and climates, proving its biodiversity and versatility. Algae can be grown in wastewater, seawater, and even sewage, thus ensuring a lower water footprint and greater energy efficiency during algal biomass production. Because of this, the optimization of 3G ethanol production appears to be an excellent alternative to mitigate environmental impacts and increase energy and food security. This critical review presents (i) the stages of cultivation and processing of micro and macroalgae; (ii) the selection of yeasts (through engineering and/or bioprospecting) to produce ethanol from these biomasses; (iii) the potential of seawater-based facilities to reduce water footprint; and (iv) the mass and energy balances of 3G ethanol production in the world energy matrix. This article is, above all, a brainstorm on the environmental viability of algae bioethanol.

A novel alginate lyase and its domain functions for the preparation of unsaturated monosaccharides

Brown algae are considered promising crops for the production of sustainable biofuels. However, the commercial application has been limited by lack of efficient methods for converting alginate into fermentable sugars. Herein, we cloned and characterized a novel alginate lyase AlyPL17 from Pedobacter hainanensis NJ-02. It possessed outstanding catalytic efficiency toward polymannuronic acid (polyM), polyguluronic acid (polyG), and alginate sodium, with k_cat of 39.42 ± 1.9 s^-1, 32.53 ± 0.88 s^-1, and 38.30 ± 2.12 s^-1, respectively. AlyPL17 showed maximum activity at 45 °C and pH 9.0. The domain truncation did not change the optimal temperature and optimal pH, but greatly reduced the activity. In addition, AlyPL17 degrades alginate through the cooperative action of two structural domains in an exolytic mode. The minimal degradation substrate of AlyPL17 is a disaccharide. Furthermore, AlyPL17 and AlyPL6 can synergistically degrade alginate to prepare unsaturated monosaccharides that can be converted to 4-deoxy-L-erythron-5-hexoseuloseuronate acid (DEH). DEH is reduced to KDG by DEH reductase (Sdr), which enters the Entner-Doudoroff (ED) pathway as a common metabolite and is converted to bioethanol. KEY POINTS: • Biochemical characterization of alginate lyase from Pedobacter hainanensis NJ-02 and its truncated form. • Degradation patterns of AlyPL17 and the role of its domains in product distribution and mode of action. • Potential of synergistic degradation system for efficient preparation of unsaturated monosaccharides.

Cell aggregation is associated with enzyme secretion strategies in marine polysaccharide-degrading bacteria

Polysaccharide breakdown by bacteria requires the activity of enzymes that degrade polymers either intra- or extra-cellularly. The latter mechanism generates a localized pool of breakdown products that are accessible to the enzyme producers themselves as well as to other organisms. Marine bacterial taxa often show marked differences in the production and secretion of degradative enzymes that break down polysaccharides. These differences can have profound effects on the pool of diffusible breakdown products and hence on the ecological dynamics. However, the consequences of differences in enzymatic secretions on cellular growth dynamics and interactions are unclear. Here we study growth dynamics of single cells within populations of marine Vibrionaceae strains that grow on the abundant marine polymer alginate, using microfluidics coupled to quantitative single-cell analysis and mathematical modelling. We find that strains that have low extracellular secretions of alginate lyases aggregate more strongly than strains that secrete high levels of enzymes. One plausible reason for this observation is that low secretors require a higher cellular density to achieve maximal growth rates in comparison with high secretors. Our findings indicate that increased aggregation increases intercellular synergy amongst cells of low-secreting strains. By mathematically modelling the impact of the level of degradative enzyme secretion on the rate of diffusive oligomer loss, we find that enzymatic secretion capability modulates the propensity of cells within clonal populations to cooperate or compete with each other. Our experiments and models demonstrate that enzymatic secretion capabilities can be linked with the propensity of cell aggregation in marine bacteria that extracellularly catabolize polysaccharides.

Marine macroalgae polysaccharides-based nanomaterials: an overview with respect to nanoscience applications

Background

Exploration of marine macroalgae poly-saccharide-based nanomaterials is emerging in the nanotechnology field, such as wound dressing, water treatment, environmental engineering, biosensor, and food technology.

Main body

In this article, the current innovation and encroachments of marine macroalgae polysaccharide-based nanoparticles (NPs), and their promising opportunities, for future prospect in different industries are briefly reviewed. The extraction and advancement of various natural sources from marine polysaccharides, including carrageenan, agarose, fucoidan, and ulvan, are highlighted in order to provide a wide range of impacts on the nanofood technology. Further, seaweed or marine macroalgae is an unexploited natural source of polysaccharides, which involves numerous different phytonutrients in the outermost layer of the cell and is rich in sulphated polysaccharides (SP), SP-based nanomaterial which has an enhanced potential value in the nanotechnology field.

Conclusion

At the end of this article, the promising prospect of SP-based NPs and their applications in the food sector is briefly addressed.

Characterization of Multiple Alginate Lyases in a Highly Efficient Alginate-Degrading Vibrio Strain and Its Degradation Strategy

Alginate is an important polysaccharide in the ocean that supports the growth of marine microorganisms. Many widespread Vibrio species possess alginate lyases and can utilize alginate as a carbon source, but the detailed alginate degradation mechanism in Vibrio remains to be further explored. In this study, we obtained a highly efficient alginate-degrading strain, Vibrio pelagius WXL662, with 11 alginate lyases (VpAly-I to -XI) and further elucidated its molecular mechanism of alginate degradation. Three alginate utilization loci (AUL) were identified in different parts of WXL662's genome, comprising six alginate lyases (VpAly-I, -II, -VIII, -IX, -X, and -XI) and other genes related to alginate degradation. Most of the alginate-degrading genes are strongly induced when alginate is provided as the sole carbon source. Ten alginate lyases (VpAly-I to -X) had been purified and characterized, including six from polysaccharide lyase family 7 (PL7), three from PL17, and one from PL6. These recombinant alginate lyases existing in different cellular locations were active at a wide temperature (10 to 50°C) and pH (4.0 to 9.0) range, with different substrate preferences and diverse degradation products, enabling WXL662 to efficiently utilize alginate in a changing marine environment. Importantly, outer membrane vesicles (OMVs) can act as vectors for alginate lyases (VpAly-II, -V, and -VI) in WXL662. Further investigations of public Vibrio genomes revealed that most alginate-degrading vibrios possess one AUL instead of previously reported "scattered" system. These results emphasize the specific alginate degradation strategy in Vibrio pelagius WXL662, which can be used as a model strain to study the ecological importance of effective alginate-degrading vibrios in the ocean. IMPORTANCE Alginate is an important carbon source in the marine environment, and vibrios are major alginate utilizers. Previous studies focused only on the characteristics of individual alginate lyases in vibrios, but few of them discussed the comprehensive alginate-degrading strategy. Here, we depicted the alginate utilization mechanism and its ecological implications of a highly efficient alginate-degrading Vibrio strain, WXL662, which contained 11 alginate lyases with distinct enzymatic characteristics. Importantly, unlike other vibrios with only one alginate utilization locus (AUL) or the previously reported "scattered" system, three AUL were identified in WXL662. Additionally, the involvement of outer membrane vesicles (OMVs) in the secretion of alginate lyases is proposed for the first time.

Synergy of the Two Alginate Lyase Domains of a Novel Alginate Lyase from Vibrio sp. NC2 in Alginate Degradation

Alginate lyases play a vital role in the degradation of alginate, an important marine carbon source. Alginate is a complex macromolecular substrate, and the synergy of alginate lyases is important for the alginate utilization by microbes and the application of alginate lyases in biotechnology. Although many studies have focused on the synergy between different alginate lyases, the synergy between two alginate lyase domains of one alginate lyase has not been reported. Here, we report the synergism between the two catalytic domains of a novel alginate lyase, AlyC6', from the marine alginate-degrading bacterium Vibrio sp. NC2. AlyC6' contains two PL7 catalytic domains (CD1 and CD2) that have no sequence similarity. While both CD1 and CD2 are endo-lyases with the highest activity at 30°C, pH 8.0, and 1.0 M NaCl, they also displayed some different properties. CD1 was PM-specific, but CD2 was PG-specific. Compared with CD2, CD1 had higher catalytic efficiency, but lower substrate affinity. In addition, CD1 had a smaller minimal substrate than CD2, and the products from CD2 could be further degraded by CD1. These distinctions between the two domains enable them to synergize intramolecularly in alginate degradation, resulting in efficient and complete degradation of various alginate substrates. The bioinformatics analysis revealed that diverse alginate lyases have multiple catalytic domains, which are widespread, especially abundant in Flavobacteriaceae and Alteromonadales, which may secret multimodular alginate lyases for alginate degradation. This study provides new insight into bacterial alginate lyases and alginate degradation and is helpful for designing multimodular enzymes for efficient alginate depolymerization. IMPORTANCE Alginate is a major component in the cell walls of brown algae. Alginate degradation is carried out by alginate lyases. Until now, while most characterized alginate lyases contain one single catalytic domain, only a few have been shown to contain two catalytic domains. Furthermore, the synergy of alginate lyases has attracted increasing attention since it plays important roles in microbial alginate utilization and biotechnological applications. Although many studies have focused on the synergy between different alginate lyases, the synergy between two catalytic domains of one alginate lyase has not been reported. Here, a novel alginate lyase, AlyC6', with two functional alginate lyase domains was biochemically characterized. Moreover, the synergism between the two domains of AlyC6' was revealed. Additionally, the distribution of the alginate lyases with multiple alginate lyase domains was investigated based on the bioinformatics analysis. This study provides new insight into bacterial alginate lyases and alginate degradation.

The characterisation of Wickerhamomyces anomalus M15, a highly tolerant yeast for bioethanol production using seaweed derived medium

Advanced generation biofuels have potential for replacing fossil fuels as society moves forward into a net-zero carbon future. Marine biomass is a promising source of fermentable sugars for fermentative bioethanol production; however the medium derived from seaweed hydrolysis contains various inhibitors, such as salts that affected ethanol fermentation efficiency. In this study the stress tolerance of a marine yeast, Wickerhamomyces anomalus M15 was characterised. Specific growth rate analysis results showed that Wickerhamomyces anomalus M15 could tolerate up to 600 g/L glucose, 150 g/L xylose and 250 g/L ethanol, respectively. Using simulated concentrated seaweed hydrolysates, W. anomalus M15’s bioethanol production potential using macroalgae derived feedstocks was assessed, in which 5.8, 45.0, and 19.9 g/L ethanol was produced from brown (Laminaria digitata), green (Ulva linza) and red seaweed (Porphyra umbilicalis) based media. The fermentation of actual Ulva spp. hydrolysate harvested from United Kingdom shores resulted in a relatively low ethanol concentration (15.5 g/L) due to challenges that arose from concentrating the seaweed hydrolysate. However, fed-batch fermentation using simulated concentrated green seaweed hydrolysate achieved a concentration of 73 g/L ethanol in fermentations using both seawater and reverse osmosis water. Further fermentations conducted with an adaptive strain W. anomalus M15-500A showed improved bioethanol production of 92.7 g/L ethanol from 200 g/L glucose and reduced lag time from 93 h to 24 h in fermentation with an initial glucose concentration of 500 g/L. The results indicated that strains W. anomalus M15 and W. anomalus M15-500A have great potential for industrial bioethanol production using marine biomass derived feedstocks. It also suggested that if a concentrated high sugar content seaweed hydrolysate could be obtained, the bioethanol concentration could achieve 90 g/L or above, exceeding the minimum industrial production threshold.

Metabolic engineering enables Bacillus licheniformis to grow on the marine polysaccharide ulvan

Background

Marine algae are responsible for half of the global primary production, converting carbon dioxide into organic compounds like carbohydrates. Particularly in eutrophic waters, they can grow into massive algal blooms. This polysaccharide rich biomass represents a cheap and abundant renewable carbon source. In nature, the diverse group of polysaccharides is decomposed by highly specialized microbial catabolic systems. We elucidated the complete degradation pathway of the green algae-specific polysaccharide ulvan in previous studies using a toolbox of enzymes discovered in the marine flavobacterium Formosa agariphila and recombinantly expressed in Escherichia coli.

Results

In this study we show that ulvan from algal biomass can be used as feedstock for a biotechnological production strain using recombinantly expressed carbohydrate-active enzymes. We demonstrate that Bacillus licheniformis is able to grow on ulvan-derived xylose-containing oligosaccharides. Comparative growth experiments with different ulvan hydrolysates and physiological proteogenomic analyses indicated that analogues of the F. agariphila ulvan lyase and an unsaturated β-glucuronylhydrolase are missing in B. licheniformis. We reveal that the heterologous expression of these two marine enzymes in B. licheniformis enables an efficient conversion of the algal polysaccharide ulvan as carbon and energy source.

Conclusion

Our data demonstrate the physiological capability of the industrially relevant bacterium B. licheniformis to grow on ulvan. We present a metabolic engineering strategy to enable ulvan-based biorefinery processes using this bacterial cell factory. With this study, we provide a stepping stone for the development of future bioprocesses with Bacillus using the abundant marine renewable carbon source ulvan.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12934-022-01931-0.

Enzymatic depolymerization of alginate by two novel thermostable alginate lyases from Rhodothermus marinus

Alginate (alginic acid) is a linear polysaccharide, wherein (1→4)-linked β-D-mannuronic acid and its C5 epimer, α-L-guluronic acid, are arranged in varying sequences. Alginate lyases catalyze the depolymerization of alginate, thereby cleaving the (1→4) glycosidic linkages between the monomers by a β-elimination mechanism, to yield unsaturated 4-deoxy-L-erythro-hex-4-enopyranosyluronic acid (Δ) at the non-reducing end of resulting oligosaccharides (α-L-erythro configuration) or, depending on the enzyme, the unsaturated monosaccharide itself. In solution, the released free unsaturated monomer product is further hydrated in a spontaneous (keto-enol tautomerization) process to form two cyclic stereoisomers. In this study, two alginate lyase genes, designated alyRm3 and alyRm4, from the marine thermophilic bacterium Rhodothermus marinus (strain MAT378), were cloned and expressed in Escherichia coli. The recombinant enzymes were characterized, and their substrate specificity and product structures determined. AlyRm3 (PL39) and AlyRm4 (PL17) are among the most thermophilic and thermostable alginate lyases described to date with temperature optimum of activity at ∼75 and 81°C, respectively. The pH optimum of activity of AlyRm3 is ∼5.5 and AlyRm4 at pH 6.5. Detailed NMR analysis of the incubation products demonstrated that AlyRm3 is an endolytic lyase, while AlyRm4 is an exolytic lyase, cleaving monomers from the non-reducing end of oligo/poly-alginates.

Sustainable alginate lyases catalyzed degradation of bio-based carbohydrates

Alginate is a water-soluble and acidic polysaccharide derived from the cell wall and intercellular substance of brown algae. It is widely distributed in brown algae, such as Laminaria, Sargassum, and Macrocystis, etc. Alginate lyase can catalytically degrade alginate in a β-eliminating manner, and its degradation product-alginate oligosaccharide (AOS) has been widely used in agriculture, medicine, cosmetics and other fields due to its wide range of biological activities. This article is mainly to make a brief introduction to the classification, source and application of alginate lyase. We hope this minireview can provide some inspirations for its development and utilization.

Cloning, expression, and characterization of a novel endo-type alginate lyase from Microbulbifer sp. BY17

BACKGROUND

Alginate oligosaccharides (AOS), with various physiological effects, have been widely used in the food, agricultural, and pharmaceutical industries. The biological enzymatic method of preparing AOS, using alginate lyase, has more advantages compared with physical and chemical methods. Cloning and heterologously expressing alginate lyase are therefore very important.

RESULTS

A novel alginate lyase, BY17PV7, from Microbulbifer sp. BY17, isolated from Gracilaria, was cloned and expressed in Escherichia coli BL21(DE3). BY17PV7 was about 27 KDa. BY17PV7 showed the greatest activity (150.42 ± 3.32 U/mg) at 43 °C and pH 8.9. It could be activated by Ca²⁺ , Mn²⁺ , Co²⁺ , Fe³⁺ , Na⁺ , and inhibited by Mg²⁺ , Zn²⁺ , Ba²⁺ , Cu²⁺ , sodium dodecyl sulfate (SDS), ethylene diamine tetraacetic acid (EDTA). BY17PV7 had a wide range of substrate specificity and good degradation effects for poly β-D-mannuronate (polyM) and poly α-L-guluronate (polyG), demonstrating that it is a bifunctional alginate lyase. The kinetic parameters showed that BY17PV7 had a greater affinity for polyG. BY17PV7 released AOS with a degree of polymerization (DP) of 3-4 in an endolytic manner from sodium alginate. Alginate oligosaccharides showed strong antioxidant ability of reducing Fe³⁺ and scavenging radicals such as hydroxyl, 2,2-azion-bia (3-ethylbenzo-thiazoline-6-sulfonic acid diammonium salt) (ABTS) and 2,2-diphenyl-1-picrylhydrazyl (DPPH).

CONCLUSION

A novel bifunctional alginate lyase, BY17PV7, was expressed and characterized in Escherichia coli BL21(DE3). The results were helpful for the analysis of the molecular mechanisms of degrading patterns in the polysaccharide lyase (PL) family. © 2022 Society of Chemical Industry.

Skinny kelp (Saccharina angustissima) provides valuable genetics for the biomass improvement of farmed sugar kelp (Saccharina latissima)

Saccharina latissima (sugar kelp) is one of the most widely cultivated brown marine macroalgae species in the North Atlantic and the eastern North Pacific Oceans. To meet the expanding demands of the sugar kelp mariculture industry, selecting and breeding sugar kelp that is best suited to offshore farm environments is becoming necessary. To that end, a multi-year, multi-institutional breeding program was established by the U.S. Department of Energy's (DOE) Advanced Research Projects Agency-Energy (ARPA-E) Macroalgae Research Inspiring Novel Energy Resources (MARINER) program. Hybrid sporophytes were generated using 203 unique gametophyte cultures derived from wild-collected Saccharina spp. for two seasons of farm trials (2019-2020 and 2020-2021). The wild sporophytes were collected from 10 different locations within the Gulf of Maine (USA) region, including both sugar kelp (Saccharina latissima) and the skinny kelp species (Saccharina angustissima). We harvested 232 common farm plots during these two seasons with available data. We found that farmed kelp plots with skinny kelp as parents had an average increased yield over the mean (wet weight 2.48 ± 0.90 kg m^-1 and dry weight 0.32 ± 0.10 kg m^-1) in both growing seasons. We also found that blade length positively correlated with biomass in skinny kelp x sugar kelp crosses or pure sugar kelp crosses. The skinny x sugar progenies had significantly longer and narrower blades than the pure sugar kelp progenies in both seasons. Overall, these findings suggest that sugar x skinny kelp crosses provide improved yield compared to pure sugar kelp crosses.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s10811-022-02811-1.