Characterization of a novel alkaline arylsulfatase from Marinomonas sp. FW-1 and its application in the desulfation of red seaweed agar

Detection, production, modification, and application of arylsulfatases

Arylsulfatase is a subset of sulfatase which catalyzes the hydrolysis of aryl sulfate ester. Arylsulfatase is widely distributed among microorganisms, mammals and green algae, but the arylsulfatase-encoding gene has not yet been found in the genomes of higher plants so far. Arylsulfatase plays an important role in the sulfur flows between nature and organisms. In this review, we present the maturation and catalytic mechanism of arylsulfatase, and the recent literature on the expression and production of arylsulfatase in wild-type and engineered microorganisms, as well as the modification of arylsulfatase by genetic engineering are summarized. We focus on arylsulfatases from microbial origin and give an overview of different assays and substrates used to determine the arylsulfatase activity. Furthermore, the researches about arylsulfatase application on the field of agar desulfation, soil sulfur cycle and soil evaluation are also discussed. Finally, the perspectives concerning the future research on arylsulfatase are prospected.

Complete genome of Rossellomorea sp. DA94, an agarolytic and orange-pigmented bacterium isolated from mangrove sediment of the South China Sea

Rossellomorea sp. DA94, isolated from mangrove sediment in the South China Sea (Beihai, Guangxi province), is an agarolytic and orange-pigmented bacterium. Here, we present the complete genome sequence of strain DA94, which comprises 4.63 Mb sequences with 43.5% GC content. In total, 4589 CDSs, 33 rRNA genes and 110 tRNA genes were obtained. Genomic analysis of strain DA94 revealed that 108 CAZymes were organized in 4578 PULs involved in polysaccharides degradation, transport, and regulation. Further, we performed the diversity of CAZymes and PULs comparison among Rossellomorea strains. Less CAZymes were organized more PULs, indicating highly efficiently polysaccharides utilization in Rossellomorea. Meanwhile, PUL0459, PUL0460 and PUL0316 related to agar degradation, and exolytic beta-agarase GH50, endo-type beta-agarase GH86 and arylsulfatase were identified in the genome of strain DA94. We verified that strain DA94 can degrade agar to form a bright clear zone around the bacterial colonies in the laboratory. Moreover, the carotenoid biosynthetic pathways were proposed, which may be responsible for orange-pigment of Rossellomorea sp. DA94. This study represents a thorough genomic characterization of CAZymes repertoire and carotenoid biosynthetic pathways of Rossellomorea, provides insight into diversity of related enzymes and their potential biotechnological applications.

Characterization and substrate-accelerated thermal inactivation kinetics of a new serine-type arylsulfatase

Arylsulfatase is useful in industrial agar processing by removing sulfate groups. A full-length arylsulfatase gene, designated ArySMA1, was obtained from marine bacteria Serratia sp. SM1. The ArySMA1 gene encoded a novel serine-type arylsulfatase and the enzymatic properties were characterized. The enzyme presented notable capacity of removing sulfate groups from natural algae substrates. Kinetic study suggested that the microscopic thermal inactivation rate of ArySMA1 in free form was smaller than that of the enzyme-substrate complex. The presence of substrate could unexpectedly accelerate ArySMA1 to deactivate at high temperature. Such phenomenon was opposite to many findings that substrate could stabilize enzymes against heat. Molecular dynamics simulation and ANS fluorescent assay indicated the substrate led the hydrophobic regions of the active site more flexible and the sulfate group of the substrate could retard the processivity of ArySMA1 catalysis. This study provides guidance for agar desulfation and down-stream processing industry.

A Novel Auxiliary Agarolytic Pathway Expands Metabolic Versatility in the Agar-Degrading Marine Bacterium Colwellia echini A3T

Marine microorganisms encode a complex repertoire of carbohydrate-active enzymes (CAZymes) for the catabolism of algal cell wall polysaccharides. While the core enzyme cascade for degrading agar is conserved across agarolytic marine bacteria, gain of novel metabolic functions can lead to the evolutionary expansion of the gene repertoire. Here, we describe how two less-abundant GH96 α-agarases harbored in the agar-specific polysaccharide utilization locus (PUL) of Colwellia echini strain A3^T facilitate the versatility of the agarolytic pathway. The cellular and molecular functions of the α-agarases examined by genomic, transcriptomic, and biochemical analyses revealed that α-agarases of C. echini A3^T create a novel auxiliary pathway. α-Agarases convert even-numbered neoagarooligosaccharides to odd-numbered agaro- and neoagarooligosaccharides, providing an alternative route for the depolymerization process in the agarolytic pathway. Comparative genomic analysis of agarolytic bacteria implied that the agarolytic gene repertoire in marine bacteria has been diversified during evolution, while the essential core agarolytic gene set has been conserved. The expansion of the agarolytic gene repertoire and novel hydrolytic functions, including the elucidated molecular functionality of α-agarase, promote metabolic versatility by channeling agar metabolism through different routes. IMPORTANCE Colwellia echini A3^T is an example of how the gain of gene(s) can lead to the evolutionary expansion of agar-specific polysaccharide utilization loci (PUL). C. echini A3^T encodes two α-agarases in addition to the core β-agarolytic enzymes in its agarolytic PUL. Among the agar-degrading CAZymes identified so far, only a few α-agarases have been biochemically characterized. The molecular and biological functions of two α-agarases revealed that their unique hydrolytic pattern leads to the emergence of auxiliary agarolytic pathways. Through the combination of transcriptomic, genomic, and biochemical evidence, we elucidate the complete α-agarolytic pathway in C. echini A3^T. The addition of α-agarases to the agarolytic enzyme repertoire might allow marine agarolytic bacteria to increase competitive abilities through metabolic versatility.

Advances in agaro-oligosaccharides preparation and bioactivities for revealing the structure-function relationship

Agaro-oligosaccharides originating from red algae have attracted increasing attention in both basic theoretical research and applied fields due to their excellent bioactivities, which indicates the wide prospects of agaro-oligosaccharides for application in the food, pharmaceutical and cosmetic industries. Thus, a considerable number of studies regarding functional agaro-oligosaccharides preparation as well as the bioactivities exploration have been carried out. Based on these studies, this review first introduced different methods that have been used in agar extraction from red algae, and further provided research progress on arylsulfatase. Then, different methods used for agaro-oligosaccharides production were summarized. Moreover, the abundant bioactivities of agaro-oligosaccharides were described in detail. Finally, this review has discussed current research problems and further provided critical aspects, which may be helpful for revealing the structure-function relationship of agaro-oligosaccharide.

A mutant of Pseudoalteromonas carrageenovora arylsulfatase with enhanced enzyme activity and its potential application in improvement of the agar quality

Enzymatic desulfation using arylsulfatase provides an attractive approach to improve agar quality. We have previously characterized a functional arylsulfatase from Pseudoalteromonas carrageenovora. To further improve its enzymatic performance, we isolated a mutant arylsulfatase of K253Q with improved enzyme activity from a random mutant library. Compared to wild-type arylsulfatase (WT), K253Q showed 33% increase in enzyme activity, with optimal temperature and pH of 55 °C and 8.0, respectively. K253Q demonstrated better substrate binding ability with lower K_m value. Structure analysis indicated that a combination of the additional hydrogen bond and the enhanced substrate binding affinity could account for the improved enzyme activity of K253Q. K253Q exhibited about 54% sulfate removal against agar, resulting in additional 8% increase in 3,6-AG content and 20% increase in gel strength compared to WT. Scanning electron microscopy showed that K253Q treatment led to a stronger crosslinking structure of agar.

A Novel Enzyme Portfolio for Red Algal Polysaccharide Degradation in the Marine Bacterium Paraglaciecola hydrolytica S66T Encoded in a Sizeable Polysaccharide Utilization Locus

Marine microbes are a rich source of enzymes for the degradation of diverse polysaccharides. Paraglaciecola hydrolytica S66^T is a marine bacterium capable of hydrolyzing polysaccharides found in the cell wall of red macroalgae. In this study, we applied an approach combining genomic mining with functional analysis to uncover the potential of this bacterium to produce enzymes for the hydrolysis of complex marine polysaccharides. A special feature of P. hydrolytica S66^T is the presence of a large genomic region harboring an array of carbohydrate-active enzymes (CAZymes) notably agarases and carrageenases. Based on a first functional characterization combined with a comparative sequence analysis, we confirmed the enzymatic activities of several enzymes required for red algal polysaccharide degradation by the bacterium. In particular, we report for the first time, the discovery of novel enzyme activities targeting furcellaran, a hybrid carrageenan containing both β-carrageenan and κ/β-carrageenan motifs. Some of these enzymes represent a new subfamily within the CAZy classification. From the combined analyses, we propose models for the complete degradation of agar and κ/β-type carrageenan by P. hydrolytica S66^T. The novel enzymes described here may find value in new bio-based industries and advance our understanding of the mechanisms responsible for recycling of red algal polysaccharides in marine ecosystems.

Detection of bacterial sulfatase activity through liquid- and solid-phase colony-based assays

Bacterial arylsulfatases are crucial to biosynthesis in many microorganisms, as bacteria often utilize aryl sulfates as a source of sulfur. The bacterial sulfatases are associated with pathogenesis and are applied in many areas such as industry and agriculture. We developed an activity-based probe 1 for detection of bacterial sulfatase activity through liquid- and solid-phase colony-based assays. Probe 1 is hydrolyzed by sulfatase to generate fluorescent N-methyl isoindole, which is polymerized to form colored precipitates. These fluorescent and colorimetric properties of probe 1 induced upon treatment of sulfatases were successfully utilized for liquid-phase sulfatase activity assays for colonies and lysates of Klebsiella aerogenes, Mycobacterium avium and Mycobacterium smegmatis. In addition, probe 1 allowed solid-phase colony-based assays of K. aerogenes through the formation of insoluble colored precipitates, thus enabling accurate staining of target colonies under heterogeneous conditions.

Diversity and characterization of bacteria associated with the deep-sea hydrothermal vent crab Austinograea sp. comparing with those of two shallow-water crabs by 16S ribosomal DNA analysis

For deep-sea hydrothermal vent crabs, recent investigations have revealed some epibiotic bacteria, but no study has described the bacterial community associated with the gill and intestine. In this study, the microbiota attached to the gill and intestine of the hydrothermal vent crab Austinograea sp. and two shallow-water crab species (Eriocheir sinensis and Portunus trituberculatus) were compared by high-throughput sequencing of 16S rDNA genes. The highest and lowest diversity in bacterial communities were observed in the gill and intestine of Austinograea sp., respectively. Non-metric multidimensional scaling (NMDS) analysis indicated that Austinograea sp. harbored a distinct microbial community. Operational taxonomic units (OTUs) for phylum Fusobacteria, class Epsilonproteobacteria, and genera Leucothrix, Polaribacter, Fusibacter, etc. were dominant in Austinograea sp. Of these, Leucothrix, Sulfurospirillum, and Arcobacter may be involved in oxidizing reduced sulfur compounds and sulfur metabolism; Marinomonas, Polaribacter adapted to the low temperature, and Fusibacter and Psychrilyobacter may survive well under hypoxic conditions. Bacteria commonly present in seawater were dominant in the gill, whereas anaerobic bacteria showed strikingly high abundance in the intestine. Interestingly, Firmicutes and Epsilonproteobacteria may complement each other in Austinograea sp., forming an internal environment. The diversified microbial community of Austinograea sp. reveals adaptation to the hydrothermal vent environment.

Improvement thermostability of Pseudoalteromonas carrageenovora arylsulfatase by rational design

This study aimed to improve the thermostability of arylsulfatase from Pseudoalteromonas carrageenovora. A total of 10 single-site mutants were chosen using the PoPMuSiC program, and two mutants of K253N and P314T showed enhanced thermal stability. By saturation mutagenesis and thermostability analysis, K253H and P314T were the best mutants at the two sites. Combinational mutations of K253H, P314T and H260L were subsequently introduced, and the best mutant of K253H/H260L was selected. Thermal inactivation analysis showed the half-life (t_1/2) value at 55°C for K253H/H260L was 7.7-fold that of the wild-type enzyme (WT), meanwhile this mutant maintained the specific enzyme activity. Structure modeling demonstrated that the additional hydrogen bonds, optimization of surface charge-charge interactions, and increasing of hydrophobic interaction could account for the improved thermostability imparted by K253H/H260L.

Heterologous expression in Pichia pastoris and biochemical characterization of the unmodified sulfatase from Fusarium proliferatum LE1

Sulfatases are a family of enzymes (sulfuric ester hydrolases, EC 3.1.6.-) that catalyze the hydrolysis of a wide array of sulfate esters. To date, despite the discovery of many sulfatase genes and the accumulation of data on numerous sulfated molecules, the number of characterized enzymes that are key players in sulfur metabolism remains extremely limited. While mammalian sulfatases are well studied due to their involvement in a wide range of normal and pathological biological processes, lower eukaryotic sulfatases, especially fungal sulfatases, have not been thoroughly investigated at the biochemical and structural level. In this paper, we describe the molecular cloning of Fusarium proliferatum sulfatase (F.p.Sulf-6His), its recombinant expression in Pichia pastoris as a soluble and active cytosolic enzyme and its detailed characterization. Gel filtration and native electrophoretic experiments showed that this recombinant enzyme exists as a tetramer in solution. The enzyme is thermo-sensitive, with an optimal temperature of 25°C. The optimal pH value for the hydrolysis of sulfate esters and stability of the enzyme was 6.0. Despite the absence of the post-translational modification of cysteine into Cα-formylglycine, the recombinant F.p.Sulf-6His has remarkably stable catalytic activity against p-nitrophenol sulfate, with kcat = 0.28 s-1 and Km = 2.45 mM, which indicates potential use in the desulfating processes. The currently proposed enzymatic mechanisms of sulfate ester hydrolysis do not explain the appearance of catalytic activity for the unmodified enzyme. According to the available models, the unmodified enzyme is not able to perform multiple catalytic acts; therefore, the enzymatic mechanism of sulfate esters hydrolysis remains to be fully elucidated.

Modification and comparison of three Gracilaria spp. agarose with methylation for promotion of its gelling properties

In order to improve the gelling properties of agarose, we modified it by methylation. The agarose was prepared from Gracilaria asiatica, G. bailinae, and G. lemaneiformis with alkaline, treated with diatomaceous earth and activated carbon, and anhydrous alcohol precipitation. The methylation reaction process of agarose was performed with dimethyl sulfate while the chemical structure of low-gelling temperature of agarose was also studied by ¹³C-NMR and FT-IR spectra. Results showed that the quality of agarose from G. asiatica is optimal. Its electroendosmosis is 0.116, sulfate content is 0.128%, and its gel strength (1.5%, w/v) is 1024 g cm^-2, like those of the Sigma product (A9539). The gelling temperature, melting temperature, and gel strength of the low-gelling temperature agarose is 28.3, 67.0 °C, and 272.5 g cm^-2, respectively. FT-IR Spectra and ¹³C-NMR spectra also showed that agarose was successfully methylated. Overall, this work suggests that low-gelling temperature agarose may have potential uses as an agar embedding material in various applications such as biomedicine, food, microbiology, and pharmaceutical.

Purification and characterization of glutamate decarboxylase from Enterococcus raffinosus TCCC11660

Glutamate decarboxylase (GAD) is the sole enzyme that synthesizes γ-aminobutyric acid through the irreversible decarboxylation of L-glutamate. In this study, the purification and characterization of an unreported GAD from a novel strain of Enterococcus raffinosus TCCC11660 were investigated. The native GAD from E. raffinosus TCCC11660 was purified 32.3-fold with a recovery rate of 8.3%, using ultrafiltration and ammonium sulfate precipitation, followed by ion-exchange and size-exclusion chromatography. The apparent molecular weight of purified GAD, as determined by SDS-PAGE and size-exclusion chromatography was 55 and 110 kDa, respectively, suggesting that GAD exists as a dimer of identical subunits in solution. In the best sodium citrate buffer, metal ions of Mo⁶⁺ and Mg²⁺ had positive effects, while Cu²⁺, Fe²⁺, Zn²⁺ and Co²⁺ showed significant adverse effects on enzyme activity. The optimum pH and temperature of GAD were determined to be 4.6 and 45 °C, while the K _m and V _max values for the sole L-glutamate substrate were 5.26 and 3.45 μmol L^-1 min^-1, respectively.

Characterization of an arylsulfatase from a mutant library of Pseudoalteromonas carrageenovora arylsulfatase

A library of Pseudoalteromonas carrageenovora arylsulfatase mutants was constructed by introducing random mutagenesis using error-prone PCR. After screening, one mutant strain was obtained whose arylsulfatase had improved thermal stability. Protein sequence analysis revealed one amino acid substitution of H260L. The mutant arylsulfatase (named H260L) retained higher residual activity than wild-type enzyme (named WT) after incubation at 45, 50, 55 and 60°C for 60min. Thermal inactivation analysis showed that the half-life (t_1/2) value at 55°C for H260L was 40.6min, while that of WT was 9.1min. When p-nitrophenyl sulfate was used as a substrate, the optimal reaction temperature and pH for the mutant enzyme were 55°C and pH 8.0, respectively. H260L was stable over the pH range of 6.0-9.0. Inhibition assay with EDTA indicated that metal ions play an important role during the catalytic process of the mutant enzyme. The desulfation ratio against agar of Gracilaria lemaneiformis was 82%.

Detection, production, and application of microbial arylsulfatases

Arylsulfatases are enzymes which catalyze the hydrolysis of arylsulfate ester bonds to release a free sulfonate. They are widespread in nature and are found in microorganisms, most animal and human tissues, and plant seeds. However, this review focuses on arylsulfatases from microbial origin and gives an overview of different assays and substrates used to determine the arylsulfatase activity. Furthermore, the production of microbial arylsulfatases using wild-type organisms as well as the recombinant production using Escherichia coli and Kluyveromyces lactis as expression hosts is discussed. Finally, various potential applications of these enzymes are reviewed.