[Research Progress on Distribution Characteristics and Formation Mechanisms of Microplastics in the Environment].

The extensive application of plastic products leads to the increasingly significant harm of plastic wastes to the ecological environment, which is also a focus of global environmental issues. Due to the lack of a sound plastic waste management system, most plastic waste is still treated by the traditional mode or remains in the environment, with low recycling efficiency, and the plastic life cycle has not yet formed. Plastics in the environment will age and degrade under the actions of physical (wear, waves), chemical (ultraviolet radiation, hydrolysis), and biological (fungi, bacteria) factors for a long time and generate micro (nano) plastics. Due to their small particle size, large specific surface area, and charged characteristics, in addition to their own toxicity, they can also be used as carriers or covert carriers of pollutants (heavy metals, persistent organic pollutants, polycyclic aromatic hydrocarbons, bacteria, etc.) to migrate in the environment through runoff, sewage discharge, and hydrometeorology, causing ecological environmental pollution. MPs pollution has been listed as the second largest scientific problem in the field of environmental and ecological science by the United Nations Environment Programme. MPs are widely distributed, and there are different degrees of MPs pollution in the global water (freshwater, ocean), soil, and atmospheric environment. Traces of MPs have also been found in human placentas, human breastmilk, living lungs, and blood in recent years. Therefore, the formation mechanisms of MPs under the actions of physics, chemistry, and microorganisms, as well as their abundance levels and migration characteristics in water, soil, and atmosphere environment were comprehensively reviewed, with the hope of providing reference for monitoring the pollution levels of MPs in the environment, exploring their transport laws in the environment, proposing the management strategy of MPs pollution, and revealing the degradation mechanisms of MPs under different effects.

Relationship between gastric xanthoma, gastric precancerous lesions, and gastric cancer: A retrospective study.

OBJECTIVE: To evaluate the relationship between gastric cancer and its precancerous lesions and gastric xanthoma. METHODS: Medical records of 47 736 patients who underwent gastroscopy in our center from January 2020 to December 2021 were reviewed. Patients' age, sex, endoscopic and histopathological findings, and the presence, number and location of gastric xanthoma were recorded. To investigate the detection rate of gastric xanthoma at different stages of gastric lesions, the participants were further divided into the chronic gastritis group (n = 42 758), the precancerous lesion group (n = 3672), and the gastric cancer group (n = 1306), respectively. RESULTS: The overall detection rate of gastric xanthoma was 2.85%, and it was most commonly observed in the gastric antrum (52.50%). In addition, gastric xanthoma was more common in men and more likely to be single lesion. It was most detected in the precancerous lesion group (8.39%), followed by the gastric cancer group (5.44%), and least in the chronic gastritis group (2.29%). Multivariate analysis showed that gastric xanthoma was closely related to precancerous lesions (odds ratio [OR] 3.197, 95% confidence interval [CI] 2.791-3.662, P < 0.001) and gastric cancer (OR 1.794, 95% CI 1.394-2.309, P < 0.001). CONCLUSION: Gastric xanthoma is closely related to gastric precancerous lesions and gastric cancer.

Electrochemical sensor for sensitive detection of bisphenol A based on molecularly imprinted TiO2 with oxygen vacancy.

Bisphenol A (BPA) is an endocrine disrupting chemical and broadly used in plastics. The leakage of BPA in food and water cycles poses a significant risk to the environment and human health. Thus, monitoring the concentration of BPA to avoid its potential risk is highly important. In this work, a simple and efficient oxygen deficient molecularly imprinted TiO2 electrochemical sensor was proposed for the detection of BPA. The introduction both oxygen vacancies and molecular imprinting evidently enhanced the electrochemical oxidation signal of BPA. The sensor had a good linear response ranging from 0.01 µM to 20 µM with a limit of detection of 3.6 nM. Additionally, the sensor showed remarkable stability, reproducibility and interference resistant ability. It also exhibits excellent recovery during the detection of real water. These findings suggested that the sensor has the potential to be developed as a simple, efficient and low-cost monitoring system for the monitoring of BPA in water.

Is There Re-staging Surgery Necessity for Borderline Ovarian Tumors.

OBJECTIVE: This study assessed the necessity of surgical re-staging in women with borderline ovarian tumors (BOTs) and evaluated the impact of complete surgical staging, lymphadenectomy, and omentectomy on disease recurrence and survival. METHODS: We retrospectively reviewed the medical records of patients with BOTs. A total of 901 patients were eligible for inclusion in the study, and we evaluated some of the variables and clinical/surgical characteristics of the cases. The effects of the type of surgical procedure, surgical staging, and complete or incomplete staging on recurrence were calculated. The rates of disease-free survival, overall survival, and recurrence were compared according to complete surgical staging. A Cox regression analysis was performed to identify potential prognostic factors, and survival curves were constructed using the Kaplan-Meier method. RESULTS: The overall recurrence rate was 13.9%, and recurrence was comparable between the complete surgical staging group and the incomplete groups (P>0.05). The performance of complete surgical staging did not show an effect on long-term survival, and complete surgical staging, omentectomy, and lymphadenectomy had no effect on recurrence. In multivariate analyses, only radical surgery and adjuvant chemotherapy were risk factors for the recurrence of BOTs. Furthermore, we found that omentectomy led to a relatively low recurrence rate in patients with International Federation of Gynecology and Obstetrics (FIGO) stage > I (P=0.022). CONCLUSION: Our results suggest that complete surgical staging should be considered a standard treatment for patients with advanced stage BOTs but not for those at FIGO stage I. It might be safe to reduce the scope of surgical procedures in patients with early-stage BOTs. However, it is not necessary to perform re-staging operations for BOTs with a macroscopically normal extra-ovarian appearance.

λ/12 Super Resolution Achieved in Maskless Optical Projection Nanolithography for Efficient Cross-Scale Patterning.

The emerging demand for device miniaturization and integration prompts the patterning technique of micronano-cross-scale structures as an urgent desire. Lithography, as a sufficient patterning technique, has been playing an important role in achieving functional micronanoscale structures for decades. As a promising alternative, we have proposed and demonstrated the maskless optical projection nanolithography (MLOP-NL) technique for efficient cross-scale patterning. A minimum feature size of 32 nm, which is λ/12 super resolution breaking the optical diffraction limit, has been achieved by a single exposure. Furthermore, multiscale two-dimensional micronano-hybrid structures with the size over hundreds of micrometers and the precision at tens of nanometers have been fabricated by simply controlling the exposure conditions. The proposed MLOP-NL technique provides a powerful tool for achieving cross-scale patterning with both large-scale and precise configuration with high efficiency, which can be potentially used in the fabrication of multiscale integrated microsystems.

[Effect of breastfeeding on the development of infection-related diseases during hospitalization in late preterm infants in 25 hospitals in Beijing, China].

OBJECTIVE: To investigate the incidence rate of infectious diseases during hospitalization in late preterm infants in Beijing, China, as well as the risk factors for infectious diseases and the effect of breastfeeding on the development of infectious diseases. METHODS: Related data were collected from the late preterm infants who were hospitalized in the neonatal wards of 25 hospitals in Beijing, China, from October 23, 2015 to October 30, 2017. According to the feeding pattern, they were divided into a breastfeeding group and a formula feeding group. The two groups were compared in terms of general status and incidence rate of infectious diseases. A multivariate logistic regression analysis was used to investigate the risk factors for infectious diseases. RESULTS: A total of 1 576 late preterm infants were enrolled, with 153 infants in the breastfeeding group and 1 423 in the formula feeding group. Of all infants, 484 (30.71%) experienced infectious diseases. The breastfeeding group had a significantly lower incidence rate of infectious diseases than the formula feeding group (22.88% vs 31.55%, P=0.033). The multivariate logistic regression analysis showed that breastfeeding was an independent protective factor against infectious diseases (OR=0.534, P=0.004), while male sex, premature rupture of membranes, gestational diabetes mellitus, and asphyxia were risk factors for infectious diseases (OR=1.328, 5.386, 1.535, and 2.353 respectively, P < 0.05). CONCLUSIONS: Breastfeeding can significantly reduce the incidence of infectious diseases and is a protective factor against infectious diseases in late preterm infants. Breastfeeding should therefore be actively promoted for late preterm infants during hospitalization.

Protein Arginine Methyltransferase 2 Inhibits Angiotensin II-Induced Proliferation and Inflammation in Vascular Smooth Muscle Cells.

OBJECTIVES: Protein arginine methyltransferase 2 (PRMT2) protects against vascular injury-induced intimal hyperplasia; however, little is known about the role of PRMT2 in angiotensin II (Ang II)-induced VSMCs proliferation and inflammation. This research aims to determine whether PRMT2 inhibits Ang II-induced proliferation and inflammation of vascular smooth muscle cells (VSMCs). MATERIALS AND METHODS: PRMT2 overexpression was used to elucidate the role of PRMT2 in Ang II-induced VSMCs proliferation and inflammation. Western blotting and reverse transcriptional PCR were adopted to detect protein and mRNA expression severally. Cell viability was evaluated by 3-(4,5-Dimethylthiazol-2-yl)-2,5-Diphenyltetrazolium Bromide (MTT) assay and cell cycle distribution by flow cytometry. RESULTS: Ang II significantly reduced mRNA and protein levels of PRMT2 in VSMCs in time-dependent and dose-dependent manner. Results of PRMT2 overexpression indicated that PRMT2 inhibited proliferation of VSMCs stimulated with 100 nmol/L Ang II for 24 hours. Furthermore, overexpression of PRMT2 reduced Ang II-induced production of proinflammatory cytokines such as interleukin 6 (IL-6) and interleukin 1ß (IL-1ß) in VSMCs. CONCLUSIONS: These findings suggest that PRMT2 alleviates Ang II-induced VSMCs proliferation and inflammation, providing a new mechanism about how Ang II mediated VSMCs proliferation and inflammation.

Cultivation of Chlorella vulgaris on anaerobically digested swine manure with daily recycling of the post-harvest culture broth.

In this work, a cultivation system with daily recycling of the post-harvest culture broth was set up and performed in order to reuse the water and nutrients in pretreated anaerobically digested swine manure, which was used as media to cultivate Chlorella vulgaris (UTEX 2714) at different recycling ratios. Results showed that the alga grew well in the system with an accumulative algal biomass and productivity of 1.68-3.47g/L and 234.1-532.2mg/L/d, respectively, at the end of the cultivation. Additionally, chemical compositions in this alga varied with the change of recycling ratios, and the highest productivities of carbohydrate, protein and lipids (76.4, 257.2 and 183.7mg/L/d, respectively) were obtained in the system with a recycling ratio of 1/4 or 1/6. Fatty acid profiles indicated that this alga could be used as a good-quality biodiesel feedstock with a biodiesel productivity of 9.65-40.1mg/L/d.

Bamboo (Phyllostachys pubescens) as a Natural Support for Neutral Protease Immobilization.

Lignin polymers in bamboo (Phyllostachys pubescens) were decomposed into polyphenols at high temperatures and oxidized for the introduction of quinone groups from peroxidase extracted from bamboo shoots and catalysis of UV. According to the results of FT-IR spectra analysis, neutral proteases (NPs) can be immobilized on the oxidized lignin by covalent bonding formed by amine group and quinone group. The optimum condition for the immobilization of NPs on the bamboo bar was obtained at pH 7.0, 40 °C, and duration of 4 h; the amount of immobilized enzyme was up to 5 mg g-1 bamboo bar. The optimal pH for both free NP (FNP) and INP was approximately 7.0, and the maximum activity of INP was determined at 60 °C, whereas FNP presented maximum activity at 50 °C. The Km values of INP and FNP were determined as 0.773 and 0.843 mg ml-1, respectively; INP showed a lower Km value and Vmax, than FNP, which demonstrated that INP presented higher affinity to substrate. Compared to FNP, INP showed broader thermal and storage stability under the same trial condition. With respect to cost, INP presented considerable recycling efficiency for up to six consecutive cycles.

Growing Chlorella vulgaris on thermophilic anaerobic digestion swine manure for nutrient removal and biomass production.

Liquid swine manure was subjected to thermophilic anaerobic digestion, ammonia stripping and centrifugation in order to increase the available carbon sources and decrease the ammonia concentration and turbidity. Chlorella vulgaris (UTEX 2714) was grown on minimally diluted (2×, 3× and 4×) autoclaved and non-autoclaved pretreated anaerobic digestion swine manure (PADSM) in a batch-culture system for 7days. Results showed that C. vulgaris (UTEX 2714) grew best on 3× PADSM media, and effectively removed NH4+-N, TN, TP and COD by 98.5-99.8%, 49.2-55.4%, 20.0-29.7%, 31.2-34.0% and 99.8-99.9%, 67.4-70.8%, 49.3-54.4%, 73.6-78.7% in differently diluted autoclaved and non-autoclaved PADSM, respectively. Results of chemical compositions indicated that contents of pigment, carbohydrate, protein and lipid in C. vulgaris (UTEX 2714) changed with the culture conditions. Moreover, its fatty acid profiles suggested that this alga could be used as animal feed if cultivated in autoclaved PADSM or as good-quality biodiesel feedstock if cultivated in non-autoclaved PADSM.

Efficient yeast cell-surface display of an endoglucanase of Aspergillus flavus and functional characterization of the whole-cell enzyme.

The endoglucanase gene endo753 from Aspergillus flavus NRRL3357 strains was cloned, and the recombinant Endo753 was displayed on the cell surface of Saccharomyces cerevisiae EBY100 strain by the C-terminal fusion using Aga2p protein as anchor attachment tag. The results of indirect immunofluorescence and Western blot confirmed the expression and localization of Endo753 on the yeast cell surface. The hydrolytic activity test of the whole-cell enzyme revealed that Endo753 immobilized on the yeast cell surface had high endoglucanase activity. The functional characterization of the whole-cell enzyme was investigated, and the whole-cell enzyme displayed the maximum activity at pH 8 and 50 °C. The enzyme was stable in a pH range of 7.0-10.0. Furthermore, the whole-cell enzyme displayed high thermostability below 50 °C and moderate stability between 50 and 70 °C. These properties make endo753 a good candidate in bioethanol production from lignocellulosic materials after displaying on the yeast cell surface.

Structures of a glucose-tolerant ß-glucosidase provide insights into its mechanism.

Cellulose can be converted to ethanol via the fermentation of glucose, which is considered as a promising green alternative for transportation fuels. The conversion of cellulose to glucose needs three enzymes, in which ß-glucosidase (BGL) plays an essential role. However, BGL is inhibited by its own product glucose, greatly limiting its applications in industry. We previously obtained a novel BGL named Bgl6 with a high glucose tolerance. Further engineering through random mutagenesis produced a triple mutant M3 with improved thermostability. This enzyme shows promising properties for wide applications but the structural basis of the unusual properties of Bgl6 is not clear. In this study, we determined the crystal structures of Bgl6 and variants at high resolution, which provide insights into its glucose-tolerant mechanism and thermostability. Particularly, Bgl6 forms an extra channel that could be used as a secondary binding site for glucose, which may contribute to glucose tolerance. Additionally, the triple mutations could strengthen the hydrophobic interactions within the enzyme and may be responsible for the enhanced thermostability exhibited by M3, which was further confirmed by dynamic light scattering data. Lastly, structural comparison to other orthologs allows us to formulate new strategies on how to improve the catalytic efficiency of Bgl6.

Meta-Analysis of Chinese Traditional Medicine Bushen Huoxue Prescription for Endometriosis Treatment.

OBJECTIVES: To evaluate the efficacy and safety of Bushen Huoxue prescription (BSHXP) for endometriosis. METHODS: A meta-analysis was performed, and studies were searched from the seven databases from the date of database establishment to April 30, 2017. Randomized controlled trials (RCTs) that explored the efficacy and safety of BSHXP for patients with endometriosis were included. Two assessors independently reviewed each trial. The Cochrane Risk of Bias assessment tool was used for quality assessment. RESULTS: In the 13 included studies, the total effectiveness rates of BSHXP were higher than those of Western medicine (RR, 1.55; 95% CI, 1.03-2.32; P = 0.04), but the dysmenorrhea alleviation rates of the two treatments did not significantly differ (RR, 1.28; 95% CI, 0.70-2.34; P = 0.42). The pregnancy rates of BSHXP were also higher than those of hormone therapy (RR, 1.99; 95% CI, 1.17-3.39; P = 0.01). However, whether BSHXP is more effective than Western medicine in diminishing endometriotic cyst remains unknown. CONCLUSIONS: Our study provides evidence that BSHXP is effective and safe for endometriosis, but this evidence is inconclusive because of the low methodological quality of the included RCTs. Our findings suggest that BSHXP is an alternative drug for endometriosis, but it should be further examined in future clinical research.

Engineering of a thermostable esterase Est816 to improve its quorum-quenching activity and the underlying structural basis.

N-acyl-homoserine lactones (AHLs) are small diffusible molecules called autoinducers that mediate cell-to-cell communications. Enzymatic degradation of AHLs is a promising bio-control strategy known as quorum-quenching. To improve the quorum-quenching activity of a thermostable esterase Est816, which had been previously cloned, we have engineered the enzyme by random mutagenesis. One of the mutants M2 with double amino acid substitutions (A216V/K238N) showed 3-fold improvement on catalytic efficiency. Based on the crystal structure determined at 2.64 Å, rational design of M2 was conducted, giving rise to the mutant M3 (A216V/K238N/L122A). The kcat/KM value of the mutant M3 is 21.6-fold higher than that of Est816. Furthermore, activity assays demonstrated that M3 reached 99% conversion of 10-µM N-octanoyl-DL-homoserine lactone (C8-HSL) to N-octanoyl- DL-homoserine (C8-Hse) in 20 min, in contrast to the 8 h required by wild type Est816. The dramatic activity enhancement may be attributed to the increased hydrophobic interactions with the lactone ring by the mutation A216V, and the reduced steric clashes between the long side chain of L122 and the aliphatic tail of HSL by the mutation L122A, according to the crystal structure. This study sheds lights on the activity-structure relationship of AHL-lactonases, and may provide useful information in engineering AHL-degrading enzymes.

Efficient Secretion of the ß-Galactosidase Bgal1-3 via both Tat-Dependent and Tat-Independent Pathways in Bacillus subtilis.

In this study, the twin-arginine (Tat) signal peptide PhoD was used to direct the secretion of the ß-galactosidase Bgal1-3 into the growth medium of an engineered strain of Bacillus subtilis 168. After 24 h of cultivation, the extracellular activity reached 1.15 U/mL, representing 78% of the total activity. Bgal1-3 was exported via both Tat-dependent and Tat-independent pathways. To improve the secretion amounts, two more copies of the target gene were inserted into the designated loci on the chromosome, further improving the extracellular enzymatic activity to 2.15 U/mL. The engineered strain with three copies of bgal1-3 was genetically stable after 150 generations. To the best of our knowledge, this is the first report on the functional secretion of a heterologous protein via both Tat-dependent and Tat-independent pathways mediated by a Tat signal peptide in B. subtilis. Furthermore, this study provides us with a markerless engineered strain for the production of ß-galactosidase.

[Early predictors of necrotizing pneumonia in children].

OBJECTIVE: To investigate the early predictors of necrotizing pneumonia in children. METHODS: The clinical data of 43 children with necrotizing pneumonia and 83 children with lobar pneumonia were retrospectively analyzed. Sex, age, the number of days with fever, laboratory examination results, and bronchoscopic findings were compared between the two groups. The multiple logistic regression analysis was used to identify the early predictors of necrotizing pneumonia. RESULTS: The necrotizing pneumonia group had a higher percentage of girls than the lobar pneumonia group (P<0.05). Compared with the lobar pneumonia group, the necrotizing pneumonia group had a larger number of days with fever, a higher peripheral blood white blood cell count (WBC), a higher percentage of neutrophils (NE%), and higher serum levels of high-sensitivity C-reactive protein (hs-CRP), albumin (Alb), and lactate dehydrogenase (LDH) (P<0.05). The necrotizing pneumonia group also had higher percentages of children with a large amount of sputum bolt under a bronchoscope which needed to be removed with biopsy forceps and children with rice-water-like bronchoalveolar lavage fluid (P<0.05). The multiple logistic regression analysis showed that being a female, the presence of sputum bolt under a bronchoscope which needed to be removed with biopsy forceps, the number of days with fever, WBC, hs-CRP, and LDH were independent predictors of necrotizing pneumonia. The receiver operating characteristic curve analysis showed that the cut-off values of the latter 4 predictors were 18.5 d, 15.1×10(9)/L, 121.5 mg/L, and 353.5 U/L, respectively. CONCLUSIONS: Increased WBC (≥15.1×10(9)/L), increased hs-CRP (≥121.5 mg/L), increased serum LDH (≥353.5 U/L), and the presence of sputum bolt under a bronchoscope which needs to be removed with biopsy forceps and rice-water-like bronchoalveolar lavage fluid may be the early predictors of necrotizing pneumonia in children.

A novel metagenome-derived gene cluster from termite hindgut: Encoding phosphotransferase system components and high glucose tolerant glucosidase.

Functional screening of a metagenomic library of termite hindgut identified an overlapping gene cluster encoding the phosphotransferase system (PTS) components, which consisted of a glucoside specific PTS enzyme II gene (glu1923) and a glycoside hydrolase gene (glu1392). Hydrolytic experiments revealed that the combined effect of Glu1923 and Glu1392 was responsible for the utilization of glucosidic substrates in recombinant Escherichia coli (E. coli) strains. Yeast two hybrid analysis suggested that there was an interaction between Glu1923 and Glu1392, and the domain EIIA of Glu1923 played an important role for the interaction. In addition, the hydrolase Glu1392 displayed hydrolysis ability toward cellobiose and maltose, and had a very high tolerance to glucose with a Ki value of 2.25M. These properties make Glu1392 an interesting candidate in biotechnology applications after further study.

Engineering a novel glucose-tolerant ß-glucosidase as supplementation to enhance the hydrolysis of sugarcane bagasse at high glucose concentration.

BACKGROUND: Most ß-glucosidases reported are sensitive to the end product (glucose), making it the rate limiting component of cellulase for efficient degradation of cellulose through enzymatic route. Thus, there are ongoing interests in searching for glucose-tolerant ß-glucosidases, which are still active at high glucose concentration. Although many ß-glucosidases with different glucose-tolerance levels have been isolated and characterized in the past decades, the effects of glucose-tolerance on the hydrolysis of cellulose are not thoroughly studied. RESULTS: In the present study, a novel ß-glucosidase (Bgl6) with the half maximal inhibitory concentration (IC 50) of 3.5 M glucose was isolated from a metagenomic library and characterized. However, its poor thermostability at 50 °C hindered the employment in cellulose hydrolysis. To improve its thermostability, random mutagenesis was performed. A thermostable mutant, M3, with three amino acid substitutions was obtained. The half-life of M3 at 50 °C is 48 h, while that of Bgl6 is 1 h. The K cat/K m value of M3 is 3-fold higher than that of Bgl6. The mutations maintained its high glucose-tolerance with IC 50 of 3.0 M for M3. In a 10-h hydrolysis of cellobiose, M3 completely converted cellobiose to glucose, while Bgl6 reached a conversion of 80 %. Then their synergistic effects with the commercial cellulase (Celluclast 1.5 L) on hydrolyzing pretreated sugarcane bagasse (SCB) were investigated. The supplementation of Bgl6 or mutant M3 to Celluclast 1.5 L significantly improved the SCB conversion from 64 % (Celluclast 1.5 L alone) to 79 % (Bgl6) and 94 % (M3), respectively. To further evaluate the application potential of M3 in high-solids cellulose hydrolysis, such reactions were performed at initial glucose concentration of 20-500 mM. Results showed that the supplementation of mutant M3 enhanced the glucose production from SCB under all the conditions tested, improving the SCB conversion by 14-35 %. CONCLUSIONS: These results not only clearly revealed the significant role of glucose-tolerance in cellulose hydrolysis, but also showed that mutant M3 may be a potent candidate for high-solids cellulose refining.

Enhancing the Thermostability of Feruloyl Esterase EstF27 by Directed Evolution and the Underlying Structural Basis.

To improve the thermostability of EstF27, two rounds of random mutagenesis were performed. A thermostable mutant, M6, with six amino acid substitutions was obtained. The half-life of M6 at 55 °C is 1680 h, while that of EstF27 is 0.5 h. The Kcat/Km value of M6 is 1.9-fold higher than that of EstF27. The concentrations of ferulic acid released from destarched wheat bran by EstF27 and M6 at their respective optimal temperatures were 223.2 ± 6.8 and 464.8 ± 11.9 µM, respectively. To further understand the structural basis of the enhanced thermostability, the crystal structure of M6 is determined at 2.0 Å. Structural analysis shows that a new disulfide bond and hydrophobic interactions formed by the mutations may play an important role in stabilizing the protein. This study not only provides us with a robust catalyst, but also enriches our knowledge about the structure-function relationship of feruloyl esterase.

Characterization of the cross-linked enzyme aggregates of a novel ß-galactosidase, a potential catalyst for the synthesis of galacto-oligosaccharides.

A novel ß-galactosidase (Bgal1-3) was isolated from a marine metagenomic library and then its cross-linked enzyme aggregates (CLEAs) were prepared. The enzymatic properties of Bgal1-3-CLEAs were studied and compared with that of the free enzyme. The thermostability and storage stability of Bgal1-3 were significantly improved after it was immobilized as CLEAs. The galactose-tolerance of the enzyme was also enhanced after the immobilization, which could relieve the inhibitory effect and then tends to be beneficial for the galacto-oligosaccharides (GOS) synthesis. Moreover, higher GOS yield was achieved (59.4 ± 1.5%) by Bgal1-3-CLEAs compared to the free counterpart (57.1 ± 1.7%) in an organic-aqueous biphasic system. The GOS content and composition of the syrups synthesized by the free enzyme and Bgal1-3-CLEAs were similar and they both contained at least seven different oligosaccharides with the degree of polymerization (DP) ranging between 3 and 9. Furthermore, Bgal1-3-CLEAs maintained 82.1 ± 2.1% activity after ten cycles of reuse; the GOS yield of the tenth batch was 52.3 ± 0.3%, which was still higher than that of the most former reports. To the best of our knowledge, this is the first report on the GOS synthesis using CLEAs of ß-galactosidase in an organic-aqueous biphasic system. The study not only further expands the application scope of CLEA, but also provides a potential catalyst for the synthesis of GOS with low cost.