Expression and Characterization of a Novel Thermostable and pH-Stable β-Agarase from Deep-Sea Bacterium Flammeovirga Sp. OC4

Directed preparation of algal oligosaccharides with specific structures by algal polysaccharide degrading enzymes

Seaweed polysaccharides have a wide range of sources and rich content, with various biological activities such as anti-inflammatory, anti-tumor, anticoagulant, and blood pressure lowering. They can be applied in fields such as food, agriculture, and medicine. However, the poor solubility of macromolecular seaweed polysaccharides limits their further application. Reports have shown that some biological activities of seaweed oligosaccharides are more extensive and superior to that of seaweed polysaccharides. Therefore, reducing the degree of polymerization of polysaccharides will be the key to the high value utilization of seaweed polysaccharide resources. There are three main methods for degrading algal polysaccharides into algal oligosaccharides, physical, chemical and enzymatic degradation. Among them, enzymatic degradation has been a hot research topic in recent years. Various types of algal polysaccharide hydrolases and related glycosidases are powerful tools for the preparation of algal oligosaccharides, including α-agarases, β-agaroses, α-neoagarose hydrolases and β-galactosidases that are related to agar, κ-carrageenases, ι-carrageenases and λ-carrageenases that are related to carrageenan, β-porphyranases that are related to porphyran, funoran hydrolases that are related to funoran, alginate lyases that are related to alginate and ulvan lyases related to ulvan. This paper describes the bioactivities of agar oligosaccharide, carrageenan oligosaccharide, porphyran oligosaccharide, funoran oligosaccharide, alginate oligosaccharide and ulvan oligosaccharide and provides a detailed review of the progress of research on the enzymatic preparation of these six oligosaccharides. At the same time, the problems and challenges faced are presented to guide and improve the preparation and application of algal oligosaccharides in the future.

Agarose biodegradation by deep-sea bacterium Vibrio natriegens WPAGA4 with the agarases through horizontal gene transfer

This study aimed to reveal the importance of horizontal gene transfer (HGT) for the agarose-degrading ability and the related degradation pathway of a deep-sea bacterium Vibrio natriegens WPAGA4, which was rarely reported in former works. A total of four agarases belonged to the GH50 family, including Aga3418, Aga3419, Aga3420, and Aga3472, were annotated and expressed in Escherichia coli cells. The agarose degradation products of Aga3418, Aga3420, and Aga3472 were neoagarobiose, while those of Aga3419 were neoagarobiose and neoagarotetraose. The RT-qPCR analysis showed that the expression level ratio of Aga3418, Aga3419, Aga3420, and Aga3472 was stable at about 1:1:1.5:2.5 during the degradation, which indicated the optimal expression level ratio of the agarases for agarose degradation by V. natriegens WPAGA4. Based on the genomic information, three of four agarases and other agarose-degrading related genes were in a genome island with a G + C content that was obviously lower than that of the whole genome of V. natriegens WPAGA4, indicating that these agarose-degrading genes were required through HGT. Our results demonstrated that the expression level ratio instead of the expression level itself of agarase genes was crucial for agarose degradation by V. natriegens WPAGA4, and HGT occurred in the deep-sea environment, thereby promoting the deep-sea carbon cycle and providing a reference for studying the evolution and transfer pathways of agar-related genes.

Statistical optimization of process variables for agarase production using Microbacterium sp. SS5 strain from non-marine sources

Agar oligosaccharides are thought to be valuable biomolecules with high bioactivity potential, along with a wide range of applications and advantages. The current study aimed to optimize the culture parameters required to produce agarase enzyme and agar oligosaccharides from industrial waste agar. Microbacterium spp. strain SS5 was isolated from a non-marine source and could synthesize oligo derivatives for use in a variety of industries ranging from food to pharmaceuticals. In addition, the strain and culture conditions were optimized to maximize extracellular agarase production. The bacterium grew best at pH 5.0 - 9.0, with an optimal pH of 7.5 - 8.0; temperatures ranging from 25 to 45 °C, with an optimal of 35 °C; and carbon and nitrogen concentrations of 0.5% each. Plackett-Burman experimental design and response surface methods were used to optimize various process parameters for agarase production by Microbacterium spp. strain SS5. Using the Plackett-Burman experimental design, eleven process factors were screened, and agar, beef extract, CaCl2, and beginning pH were found as the most significant independent variables affecting agarase production with confidence levels above 90%. To determine the optimal concentrations of the identified process factors on agarase production, the Box- Behnken design was used. Agarase production by Microbacterium spp. strain SS5 after optimization was 0.272 U/mL, which was determined to be greater than the result obtained from the basal medium (0.132 U/mL) before screening using Plackett-Burman and BBD with a fold increase of 2.06.

Marine enzymes: Classification and application in various industries

Oceans are regarded as a plentiful and sustainable source of biological compounds. Enzymes are a group of marine biomaterials that have recently drawn more attention because they are produced in harsh environmental conditions such as high salinity, extensive pH, a wide temperature range, and high pressure. Hence, marine-derived enzymes are capable of exhibiting remarkable properties due to their unique composition. In this review, we overviewed and discussed characteristics of marine enzymes as well as the sources of marine enzymes, ranging from primitive organisms to vertebrates, and presented the importance, advantages, and challenges of using marine enzymes with a summary of their applications in a variety of industries. Current biotechnological advancements need the study of novel marine enzymes that could be applied in a variety of ways. Resources of marine enzyme can benefit greatly for biotechnological applications duo to their biocompatible, ecofriendly and high effectiveness. It is beneficial to use the unique characteristics offered by marine enzymes to either develop new processes and products or improve existing ones. As a result, marine-derived enzymes have promising potential and are an excellent candidate for a variety of biotechnology applications and a future rise in the use of marine enzymes is to be anticipated.

Agarose-Degrading Characteristics of a Deep-Sea Bacterium Vibrio Natriegens WPAGA4 and Its Cold-Adapted GH50 Agarase Aga3420

Up until now, the characterizations of GH50 agarases from Vibrio species have rarely been reported compared to GH16 agarases. In this study, a deep-sea strain, WPAGA4, was isolated and identified as Vibrio natriegens due to the maximum similarity of its 16S rRNA gene sequence, the values of its average nucleotide identity, and through digital DNA-DNA hybridization. Two circular chromosomes in V. natriegens WPAGA4 were assembled. A total of 4561 coding genes, 37 rRNA, 131 tRNA, and 59 other non-coding RNA genes were predicted in the genome of V. natriegens WPAGA4. An agarase gene belonging to the GH50 family was annotated in the genome sequence and expressed in E. coli cells. The optimum temperature and pH of the recombinant Aga3420 (rAga3420) were 40 °C and 7.0, respectively. Neoagarobiose (NA2) was the only product during the degradation process of agarose by rAga3420. rAga3420 had a favorable stability following incubation at 10-30 °C for 50 min. The Km, Vmax, and kcat values of rAga3420 were 2.8 mg/mL, 78.1 U/mg, and 376.9 s-1, respectively. rAga3420 displayed cold-adapted properties as 59.7% and 41.2% of the relative activity remained at 10 3 °C and 0 °C, respectively. This property ensured V. natriegens WPAGA4 could degrade and metabolize the agarose in cold deep-sea environments and enables rAga3420 to be an appropriate industrial enzyme for NA2 production, with industrial potential in medical and cosmetic fields.

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.

Expression and Characterization of a Novel Cold-Adapted and Stable β-Agarase Gene agaW1540 from the Deep-Sea Bacterium Shewanella sp. WPAGA9

The neoagaro-oligosaccharides, degraded from agarose by agarases, are important natural substances with many bioactivities. In this study, a novel agarase gene, agaW1540, from the genome of a deep-sea bacterium Shewanella sp. WPAGA9, was expressed, and the recombinant AgaW1540 (rAgaW1540) displayed the maximum activity under the optimal pH and temperature of 7.0 and 35 °C, respectively. rAgaW1540 retained 85.4% of its maximum activity at 0 °C and retained more than 92% of its maximum activity at the temperature range of 20-40 °C and the pH range of 4.0-9.0, respectively, indicating its extensive working temperature and pH values. The activity of rAgaW1540 was dramatically suppressed by Cu²⁺ and Zn²⁺, whereas Fe²⁺ displayed an intensification of enzymatic activity. The K_m and V_max of rAgaW1540 for agarose degradation were 15.7 mg/mL and 23.4 U/mg, respectively. rAgaW1540 retained 94.7%, 97.9%, and 42.4% of its maximum activity after incubation at 20 °C, 25 °C, and 30 °C for 60 min, respectively. Thin-layer chromatography and ion chromatography analyses verified that rAgaW1540 is an endo-acting β-agarase that degrades agarose into neoagarotetraose and neoagarohexaose as the main products. The wide variety of working conditions and stable activity at room temperatures make rAgaW1540an appropriate bio-tool for further industrial production of neoagaro-oligosaccharides.

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.

Expression and Characterization of a GH16 Family β-Agarase Derived from the Marine Bacterium Microbulbifer sp. BN3 and Its Efficient Hydrolysis of Agar Using Raw Agar-Producing Red Seaweeds Gracilaria sjoestedtii and Gelidium amansii as Substrates

Agarases catalyze the hydrolysis of agarose to oligosaccharides which display an array of biological and physiological functions with important industrial applications in health-related fields. In this study, the gene encoding agarase (Aga-ms-R) was cloned from Microbulbifer sp. BN3 strain. Sequence alignment indicated that Aga-ms-R belongs to the GH16 family and contains one active domain and two carbohydrate binding module (CBM) domains. The mature Aga-ms-R was expressed successfully by employing the Brevibacillus system. Purified rAga-ms-R was obtained with a specific activity of 100.75 U/mg. rAga-ms-R showed optimal activity at 50 °C and pH 7.0, and the enzyme activity was stable at 50 °C and also over the pH range of 5.0–9.0. After exposure of rAga-ms-R to 70 °C for 30 min, only partial enzyme activity remained. Thin layer chromatographic analysis of the enzymatic hydrolysate of agar obtained using rAga-ms-R disclosed that the hydrolysate comprised, in a long intermediate-stage of the hydrolysis reaction, mainly neoagarotetraose (NA4) and neoagarohexaose (NA6) but ultimately, predominantly neoagarotetraose and trace amounts of neoagarobiose (NA2). Hydrolysates of the raw red seaweeds Gracilaria sjoestedtii and Gelidium amansii, produced by incubation with rAga-ms-R, were mainly composed of neoagarotetraose. The results demonstrate the high efficiency of rAga-ms-R in producing neoagaraoligosaccharide under low-cost conditions.

Expression and Characterization of a Methylated Galactose-Accommodating GH86 β-Agarase from a Marine Bacterium

Agarose is the major component of agar, in which galactose units could be naturally modified by methyl groups. Although numerous agarases have been characterized, the capacity of agarases for accommodating methylated galactoses has been rarely investigated. In this study, we cloned, expressed, and characterized a novel GH86 family agarase Aga86A_Wa from a marine bacterium Wenyingzhuangia aestuarii OF219. The enzyme exhibited maximum activity at 30 °C and pH 6.5. Aga86A_Wa was a random endo-acting β-agarase. The smallest products of Aga86A_Wa were disaccharides. Besides typical agarose oligosaccharides, methylated oligosaccharides were also identified in the products by using liquid chromatography coupled with high-resolution mass spectrometry. It was confirmed that Aga86A_Wa could accommodate methylated galactoses at its -1 and +2 subsites. This is the first report on the sequence of the methyl group-tolerating agarase. Aga86A_Wa could be utilized as a biotechnological tool for producing methylated oligosaccharides and for the structural investigation of agarose.

Implications of agar and agarase in industrial applications of sustainable marine biomass

Agar, a major component of the cell wall of red algae, is an interesting heteropolysaccharide containing an unusual sugar, 3,6-anhydro-L-galactose. It is widely used as a valuable material in various industrial and experimental applications due to its characteristic gelling and stabilizing properties. Agar-derived oligosaccharides or mono-sugars produced by various agarases have become a promising subject for research owing to their unique biological activities, including anti-obesity, anti-diabetic, immunomodulatory, anti-tumor, antioxidant, skin-whitening, skin-moisturizing, anti-fatigue, and anti-cariogenic activities. Agar is also considered as an alternative sustainable source of biomass for chemical feedstock and biofuel production to substitute for the fossil resource. In this review, we summarize various biochemically characterized agarases, which are useful for industrial applications, such as neoagarooligosaccharide or agarooligosaccharide production and saccharification of agar. Additionally, we succinctly discuss various recent studies that have been conducted to investigate the versatile biological activities of agar-derived saccharides and biofuel production from agar biomass. This review provides a basic framework for understanding the importance of agarases and agar-derived saccharides with broad applications in pharmaceutical, cosmetic, food, and bioenergy industries.

Properties and Applications of Extremozymes from Deep-Sea Extremophilic Microorganisms: A Mini Review

The deep sea, which is defined as sea water below a depth of 1000 m, is one of the largest biomes on the Earth, and is recognised as an extreme environment due to its range of challenging physical parameters, such as pressure, salinity, temperature, chemicals and metals (such as hydrogen sulphide, copper and arsenic). For surviving in such extreme conditions, deep-sea extremophilic microorganisms employ a variety of adaptive strategies, such as the production of extremozymes, which exhibit outstanding thermal or cold adaptability, salt tolerance and/or pressure tolerance. Owing to their great stability, deep-sea extremozymes have numerous potential applications in a wide range of industries, such as the agricultural, food, chemical, pharmaceutical and biotechnological sectors. This enormous economic potential combined with recent advances in sampling and molecular and omics technologies has led to the emergence of research regarding deep-sea extremozymes and their primary applications in recent decades. In the present review, we introduced recent advances in research regarding deep-sea extremophiles and the enzymes they produce and discussed their potential industrial applications, with special emphasis on thermophilic, psychrophilic, halophilic and piezophilic enzymes.

Biochemical Characterization of a New β-Agarase from Cellulophaga Algicola

Cellulophaga algicola DSM 14237, isolated from the Eastern Antarctic coastal zone, was found to be able to hydrolyze several types of polysaccharide materials. In this study, a predicted β-agarase (CaAga1) from C. algicola was heterologously expressed in Escherichia coli. The purified recombinant CaAga1 showed specific activities of 29.39, 20.20, 14.12, and 8.99 U/mg toward agarose, pure agar, and crude agars from Gracilaria lemaneiformis and Porphyra haitanensis, respectively. CaAga1 exhibited an optimal temperature and pH of 40 °C and 7, respectively. CaAga1 was stable over a wide pH range from 4 to 11. The recombinant enzyme showed an unusual thermostability, that is, it was stable at temperature below or equal to 40 °C and around 70 °C, but was thermolabile at about 50 °C. With the agarose as the substrate, the K_m and V_max values for CaAga1 were 1.19 mg/mL and 36.21 U/mg, respectively. The reducing reagent (dithiothreitol) enhanced the activity of CaAga1 by more than one fold. In addition, CaAga1 was salt-tolerant given that it retained approximately 70% of the maximum activity in the presence of 2 M NaCl. The thin layer chromatography results indicated that CaAga1 is an endo-type β-agarase and efficiently hydrolyzed agarose into neoagarotetraose (NA4) and neoagarohexaose (NA6). A structural model of CaAga1 in complex with neoagarooctaose (NA8) was built by homology modeling and explained the hydrolysis pattern of CaAga1.

One-Step Process for Environment-Friendly Preparation of Agar Oligosaccharides From Gracilaria lemaneiformis by the Action of Flammeovirga sp. OC4

Oligosaccharides extracted from agar Gracilaria lemaneiformis (G. lemaneiformis) have stronger physiological activities and a higher value than agar itself, but the pollution caused by the extraction process greatly restricts the sustainable use of agar. In this study, four bacterial strains with a high ability to degrade G. lemaneiformis were isolated from seawater by in situ enrichment in the deep sea. Among them, Flammeovirga sp. OC4, identified by morphological observation and its 16S rRNA sequencing (98.07% similarity to type strain JL-4 of Flammeovirga aprica), was selected. The optimum temperature and pH of crude enzyme produced by Flammeovirga sp. OC4 were 50°C and 8, respectively. More than 60% of the maximum enzyme activity remained after storage at pH 5.0-10.0 for 60 min. Both Mn²⁺ and Ba²⁺ could enhance the enzyme activity. A "one-step process" for preparation of oligosaccharides from G. lemaneiformis was established using Flammeovirga sp. OC4. After optimization of the Plackett-Burman (PB) design and response surface methodology (RSM), the yield of oligosaccharides was increased by 36.1% from 2.71 to 3.09 g L^-1 in a 250-mL fermenter with optimized parameters: 30 g L^-1 G. lemaneiformis powder, 4.84 g L^-1 (NH4)₂SO₄, 44.8-mL working medium volume at 36.7°C, and a shaking speed of 200 × g for 42 h. The extracted oligosaccharides were identified by thin layer chromatography (TLC) and ion chromatography, which consisted of neoagarobiose, agarotriose, neoagarotetraose, agaropentaose, and neoagarohexaose. These results provided an alternative approach for environment-friendly and sustainable utilization of algae.

Mutagenesis on the surface of a β-agarase from Vibrio sp. ZC-1 increased its thermo-stability

The recombinant rAgaZC-1 was a family GH50 β-agarase from Vibrio sp. ZC-1 (CICC 24670). In this paper, the mutant D622G (i.e., mutate the aspartic acid at position 622 to glycine) had better thermo-stability than rAgaZC-1, showing 1.5℃ higher T₅₀¹⁰ (the temperature at which the half-time is 10 min) and 4-folds of half-time at 41℃, while they had almost same optimum temperature (38.5℃), optimum pH (pH6.0) and catalytic efficiency. Thermal deactivation kinetical analysis showed that D622G had higher activation energy for deactivation, enthalpy and Gibbs free energy than rAgaZC-1, indicating that more energy is required by D622G for deactivation. Substrate can protect agarase against thermal inactivation, especially D622G. Hence the yield of agarose hydrolysis catalyzed by D622G was higher than that by rAgaZC-1. The models of D622G and rAgaZC-1 predicted by homology modeling were compared to find that it is the improved distribution of surface electrostatic potential, great symmetric positive potential and more hydrophobic interactions of D622G that enhance the thermo-stability.

Extracellular expression of agarase rAgaM1 in Bacillus subtilis and its ability for neoagaro-oligosaccharide production

An agarase gene (agaM1) was cloned, expressed and characterized by using Escherichia coli as host strain, revealing the outstanding properties of recombinant AgaM1 (rAgaM1) in agarose degradation and neoagaro-oligosaccharides (NAs) production in our previous work. In current study, agaM1 was extracellularly expressed in Bacillus subtilis, and we aim to assess the ability of the supernatant of recombinant B. subtilis fermentation broth containing rAgaM1 to degrade agarose without protein purification, which would save the cost of purification and avoid the activity loss during purification. The pH and temperature optima for the supernatant were 7.0 and 50 °C, respectively. The supernatant containing rAgaM1 has outstanding stability against 40 °C and 50 °C. Besides, we detailedly studied the possible influence factors of rAgaM1 expression in the supernatant, including pH, temperature, isopropyl β-D-thiogalactoside (IPTG) concentration, initial optical density at a wavelength of 600 nm (OD₆₀₀ ), and induction time, and the optimum conditions for rAgaM1 expression by B. subtilis were confirmed. Moreover, the supernatant was able to produce NAs by using the Gracilaria lemaneiformis, whose cells were broken by autoclaving, as substrate, and a total of 1.41 µmol ml^-1 of NA, including neoagarotetraose and neoagarohexaose, was produced after degradation for 48 h. This ability could save the cost of substrates in NA production, although the method requires a further study. Our results reveal that the NAs with great potential in food and pharmaceutical industries could be inexpensive to make by the supernatant containing rAgaM1 of B. subtilis fermentation broth in the foreseeable future.

Recombinant β-agarases: insights into molecular, biochemical, and physiochemical characteristics

Agarases (agarose 4-glycanohydrolase; EC 3.2.1.81) are class of enzymes that belong to glycoside hydrolase (GH) family capable of hydrolyzing agar. Their classification depends on hydrolysis pattern and product formation. Among all the agarases, β-agarases and the oligosaccharides formed by its action have fascinated quite a lot of industries. Ample of β-agarase genes have been endowed from marine sources such as algae, sea water, and marine sediments, and the expression of these genes into suitable host gives rise to recombinant β-agarases. These recombinant β-agarases have wide range of industrial applications due to its improved catalytic efficiency and stability in tough environments with ease of production on large scale. In this review, we have perused different types of recombinant β-agarases in consort with their molecular, physiochemical, and kinetic properties in detail and the significant features of those agarases are spotlighted. From the literature reviewed after 2010, we have found that the recombinant β-agarases belonged to the families GH16, GH39, GH50, GH86, and GH118. Among that, GH39, GH50, and GH86 belonged to clan GH-A, while the GH16 family belonged to clan GH-B. It was observed that GH16 is the largest polyspecific glycoside hydrolase family with ample number of β-agarases and the families GH50 and GH118 were found to be monospecific with only β-agarase activity. And, out of 84 non-catalytic carbohydrate-binding modules (CBMs), only CBM6 and CBM13 were professed in β-agarases. We witnessed a larger heterogeneity in molecular, physiochemical, and catalytic characteristics of the recombinant β-agarases including molecular mass: 32-132 kDa, optimum pH: 4.5-9, optimum temperature 16-60 °C, K _M: 0.68-59.8 mg/ml, and V _max: 0.781-11,400 U/mg. Owing to this extensive range of heterogeneity, they have lion's share in the multibillion dollar enzyme market. This review provides a holistic insight to a few aspects of recombinant β-agarases which can be referred by the upcoming explorers to this area.

Integration of Bacterial Expansin on Agarolytic Complexes to Enhance the Degrading Activity of Red Algae by Control of Gelling Properties

Expansin act by loosening hydrogen bonds in densely packed polysaccharides. This work characterizes the biological functions of expansin in the gelling and degradation of algal polysaccharides. In this study, the bacterial expansin BpEX from Bacillus pumilus was fused with the dockerin module of a cellulosome system for assembly with agarolytic complexes. The assembly of chimeric expansin caused an indicative enhancement in agarase activity. The enzymatic activities on agar substrate and natural biomass were 3.7-fold and 3.3-fold higher respectively than that of agarase as a single enzyme. To validate the effect on the agar degradation, the regulation potential of parameters related to gel rheology by bacterial expansin was experimentally investigated to indicate that the bacterial expansin lowered the gelling temperature and viscosity of agar. Thus, these results demonstrated the possibility of advancing more efficient strategies for utilizing agar as oligo sugar source in the biorefinery field that uses marine biomass as feedstocks.

Biochemical Characteristics and Variable Alginate-Degrading Modes of a Novel Bifunctional Endolytic Alginate Lyase

Bifunctional alginate lyases can efficiently degrade alginate comprised of mannuronate (M) and guluronate (G), but their substrate-degrading modes have not been thoroughly elucidated to date. In this study, we present Aly1 as a novel bifunctional endolytic alginate lyase of the genus Flammeovirga. The recombinant enzyme showed optimal activity at 50°C and pH 6.0. The enzyme produced unsaturated disaccharide (UDP2) and trisaccharide fractions as the final main alginate digests. Primary substrate preference tests and further structure identification of various size-defined final oligosaccharide products demonstrated that Aly1 is a bifunctional alginate lyase and prefers G to M. Tetrasaccharide-size fractions are the smallest substrates, and M, G, and UDP2 fractions are the minimal product types. Remarkably, Aly1 can vary its substrate-degrading modes in accordance with the terminus types, molecular sizes, and M/G contents of alginate substrates, producing a series of small size-defined saturated oligosaccharide products from the nonreducing ends of single or different saturated sugar chains and yielding unsaturated products in distinct but restricted patterns. The action mode changes can be partially inhibited by fluorescent labeling at the reducing ends of oligosaccharide substrates. Deletion of the noncatalytic region (NCR) of Aly1 caused weak changes of biochemical characteristics but increased the degradation proportions of small size-defined saturated M-enriched oligosaccharide substrates and unsaturated tetrasaccharide fractions without any size changes of degradable oligosaccharides, thereby enhancing the M preference and enzyme activity. Therefore, our results provided insight into the variable action mode of a novel bifunctional endolytic alginate lyase to inform accurate enzyme use.

IMPORTANCE The elucidated endolytic alginate lyases usually degrade substrates into various size-defined unsaturated oligosaccharide products (≥UDP2), and exolytic enzymes yield primarily unsaturated monosaccharide products. However, it is poorly understood whether endolytic enzymes can produce monosaccharide product types when degrading alginate. In this study, we demonstrated that Aly1, a bifunctional alginate lyase of Flammeovirga sp. strain MY04, is endolytic and monosaccharide producing. Using various sugar chains as testing substrates, we also proved that key factors causing Aly1's action mode changes are the terminus types, molecular sizes, and M/G contents of substrates. Furthermore, the NCR fragment's effects on Aly1's biochemical characteristics and alginate-degrading modes and corresponding mechanisms were discovered by gene truncation and enzyme comparison. In summary, this study provides a novel bifunctional endolytic tool and a variable action mode for accurate use in alginate degradation.

Identification and characterization of a thermostable endolytic β-agarase Aga2 from a newly isolated marine agarolytic bacteria Cellulophaga omnivescoria W5C

Research on the enzymatic breakdown of seaweed-derived agar has recently gained attention due to the progress in green technologies for marine biomass utilization. The enzymes known as agarases catalyze the cleavage of glycosidic bonds within the polysaccharide. In this study, a new β-agarase, Aga2, was identified from Cellulophaga omnivescoria W5C. Aga2 is one of four putative agarases from the W5C genome, and it belongs to the glycoside hydrolase 16 family. It was shown to be exclusive to the Cellulophaga genus. Agarase activity assays showed that Aga2 is an endolytic-type β-agarase that produces tetrameric and hexameric neoagaro-oligosaccharides, with optimum activity at 45°C and pH 8.0. Zinc ions slightly enhanced its activity while manganese ions had inhibitory effects even at very low concentrations. Aga2 has a K_m of 2.59mgmL^-1 and V_max of 275.48Umg^-1. The K_cat is 1.73×10²s^-1, while the K_cat/K_m is 8.04×10⁶s^-1M^-1. Aga2 also showed good thermostability at 45°C and above, and retained >90% of its activity after repeated freeze-thaw cycles. Bioinformatic analysis of its amino acid sequence revealed that intrinsic properties of the protein (e.g. presence of certain dipeptides and the relative volume occupied by aliphatic amino acids) and tertiary structural elements (e.g. presence of salt bridges, hydrophobic interactions and H-bonding) contributed to its thermostability.

Biochemical Characterization and Substrate Degradation Mode of a Novel Exotype β-Agarase from Agarivorans gilvus WH0801

Agarases are important hydrolytic enzymes for the biodegradation of agar. Understanding the degradation mode and hydrolysis products of agarases is essential for their utilization in oligosaccharide preparations. Herein, we cloned and expressed AgWH50B, a novel neoagarotetraose-forming β-agarase from Agarivorans gilvus WH0801 that has high specific activity and a fast reaction rate. AgWH50B consists of a C-terminal glycoside hydrolase family 50 catalytic domain with two tandem noncatalytic carbohydrate-binding modules (CBMs) in the N-terminus (residues 45-214 and 236-442). AgWH50B exhibited good enzymatic properties with high specific activity and catalytic efficiency (1523.2 U/mg and a V_max of 1700 μmol/min/mg) under optimal hydrolysis conditions of pH 7.0 and 40 °C. Analysis of the hydrolysis products revealed that this enzyme is an exotype β-agarase and that the dominant product of agarose or oligosaccharide degradation was neoagarotetraose. These findings suggest that AgWH50B could be utilized to yield abundant neoagarotetraose.

Characterization and Applications of Marine Microbial Enzymes in Biotechnology and Probiotics for Animal Health

Marine microorganisms have been recognized as potential sources of novel enzymes because they are relatively more stable than the corresponding enzymes derived from plants and animals. Enzymes from marine microorganisms also differ from homologous enzymes in terrestrial microorganisms based on salinity, pressure, temperature, and lighting conditions. Marine microbial enzymes can be used in diverse industrial applications. This chapter will focus on the biotechnological applications of marine enzymes and also their use as a tool of marine probiotics to improve host digestion (food digestion, food absorption, and mucus utilization) and cleave molecular signals involved in quorum sensing in pathogens to control disease in aquaculture.