Expression and Biochemical Characterization of a Novel Marine Chitosanase from Streptomyces niveus Suitable for Preparation of Chitobiose

It is known that bioactivities of chitooligosaccharide (COS) are closely related to the degree of polymerization (DP); therefore, it is essential to prepare COS with controllable DP, such as chitobiose showing high antioxidant and antihyperlipidemia activities. In this study, BLAST, sequence alignment and phylogenetic analysis of characterized glycoside hydrolase (GH) 46 endo-chitosanases revealed that a chitosanase Sn1-CSN from Streptomyces niveus was different from others. Sn1-CSN was overexpressed in E. coli, purified and characterized in detail. It showed the highest activity at pH 6.0 and exhibited superior stability between pH 4.0 and pH 11.0. Sn1-CSN displayed the highest activity at 50 °C and was fairly stable at ≤45 °C. Its apparent kinetic parameters against chitosan (DDA: degree of deacetylation, >94%) were determined, with Km and kcat values of 1.8 mg/mL and 88.3 s-1, respectively. Cu2+ enhanced the activity of Sn1-CSN by 54.2%, whereas Fe3+ inhibited activity by 15.1%. Hydrolysis products of chitosan (DDA > 94%) by Sn1-CSN were mainly composed of chitobiose (87.3%), whereas partially acetylated chitosan with DDA 69% was mainly converted into partially acetylated COS with DP 2-13. This endo-chitosanase has great potential to be used for the preparation of chitobiose and partially acetylated COS with different DPs.

Exploring Effects of Chitosan Oligosaccharides on the DSS-Induced Intestinal Barrier Impairment In Vitro and In Vivo

Intestinal barrier dysfunction is an essential pathological change in inflammatory bowel disease (IBD). The mucus layer and the intestinal epithelial tight junction act together to maintain barrier integrity. Studies showed that chitosan oligosaccharide (COS) had a positive effect on gut health, effectively protecting the intestinal barrier in IBD. However, these studies usually focused on its impact on the intestinal epithelial tight junction. The influence of COS on the intestinal mucus layer is still poorly understood. In this study, we explored the effect of COS on intestinal mucus in vitro using human colonic mucus-secreted HT-29 cells. COS relieved DSS (dextran sulfate sodium)-induced mucus defects. Additionally, the structural characteristics of COS greatly influenced this activity. Finally, we evaluated the protective effect of COS on intestinal barrier function in mice with DSS-induced colitis. The results indicated that COS could manipulate intestinal mucus production, which likely contributed to its intestinal protective effects.

Detecting SARS-CoV-2 in the Breath of COVID-19 Patients

In the COVID-19 outbreak year 2020, a consensus was reached on the fact that SARS-CoV-2 spreads through aerosols. However, finding an efficient method to detect viruses in aerosols to monitor the risk of similar infections and enact effective control remains a great challenge. Our study aimed to build a swirling aerosol collection (SAC) device to collect viral particles in exhaled breath and subsequently detect SARS-CoV-2 using reverse transcription polymerase chain reaction (RT-PCR). Laboratory tests of the SAC device using aerosolized SARS-CoV-2 pseudovirus indicated that the SAC device can produce a positive result in only 10 s, with a collection distance to the source of 10 cm in a biosafety chamber, when the release rate of the pseudovirus source was 1,000,000 copies/h. Subsequent clinical trials of the device showed three positives and 14 negatives out of 27 patients in agreement with pharyngeal swabs, and 10 patients obtained opposite results, while no positive results were found in a healthy control group (n = 12). Based on standard curve calibration, several thousand viruses per minute were observed in the tested exhalations. Furthermore, referring to the average tidal volume data of adults, it was estimated that an exhaled SARS-CoV-2 concentration of approximately one copy/mL is detectable for COVID-19 patients. This study validates the original concept of breath detection of SARS-CoV-2 using SAC combined with RT-PCR.

Chitosan Oligosaccharides Coupling Inhibits Bacterial Biofilm-Related Antibiotic Resistance against Florfenicol

The formation of bacterial biofilms has increased the resistance of bacteria to various environmental factors and is tightly associated with many persistent and chronic bacterial infections. Herein we design a strategy conjugating florfenicol, an antibiotic commonly used in the treatment of streptococcus, with the antimicrobial biomaterial, chitosan oligosaccharides. The results demonstrated that the florfenicol-COS conjugate (F-COS) efficiently eradicated the mature Streptococcus hyovaginalis biofilm, apparently inhibiting drug resistance to florfenicol. A quantity of 250 μg/mL F-COS showed effective inhibitory activity against planktonic cells and biofilm of the bacteria, and a 4-fold improvement of the F-COS compared to unmodified florfenicol was observed. Furthermore, the conjugate showed a broad-spectrum activity against both Gram-positive and Gram-negative bacteria. It suggested that F-COS might have a potential for application in the treatment of biofilm-related infections.

Blood-Brain Barrier Permeable Chitosan Oligosaccharides Interfere with β-Amyloid Aggregation and Alleviate β-Amyloid Protein Mediated Neurotoxicity and Neuroinflammation in a Dose- and Degree of Polymerization-Dependent Manner

It is proven that β-amyloid (Aβ) aggregates containing cross-β-sheet structures led to oxidative stress, neuroinflammation, and neuronal loss via multiple pathways. Therefore, reduction of Aβ neurotoxicity via inhibiting aggregation of Aβ or dissociating toxic Aβ aggregates into nontoxic forms might be effective therapeutic methods for Alzheimer's disease (AD) treatment. This study was designed to explore interference of chitosan oligosaccharides (COS) on β-(1-42)-amyloid protein (Aβ42) aggregation and Aβ42-induced cytotoxicity. Here it was demonstrated that COS showed good blood-brain barrier (BBB) penetration ability in vitro and in vivo. The experimental results showed that COS efficiently interfered with Aβ42 aggregation in dose- and degree of polymerization (DP)-dependent manners, and COS monomer with DP6 showed the best effect on preventing conformational transition into β-sheet-rich structures. Based on the binding affinity analysis by microscale thermophoresis (MST), it was confirmed that COS could directly bind with Aβ42 in a DP-dependent manner. Our findings demonstrated that different performance of COS monomers with different DPs against Aβ42 assembly was, to some extent, attributable to their different binding capacities with Aβ42. As a result, COS significantly ameliorated Aβ42-induced cytotoxicity. Taken together, our studies would point towards a potential role of COS in treatment of AD.

Rapid and simple detection of Bacillus cereus in milk by real-time competitive annealing mediated isothermal amplification

Bacillus cereus (B. cereus) is widespread in nature and considered an important foodborne pathogen, which can lead to emetic syndrome and diarrheal illness. Therefore, appropriate detection methods are needed to effectively monitor this pathogenic bacterium. Competitive annealing mediated isothermal amplification (CAMP) is a novel nucleic-acid-based detection technology that amplifies DNA with high sensitivity and specificity under isothermal conditions. The aim of this study was to develop a real-time CAMP assay for the rapid and simple detection of B. cereus in milk. In this system, a pair of primers was designed to specifically target the entFM gene of B. cereus. Compared with the conventional PCR method, the CAMP assay has higher sensitivity, the same specificity and shorter detection time. The detection limits of the CAMP assay for pure bacterial cultures and artificially contaminated milk samples were all 59 CFU mL^-1. And this detection method showed a wide linear range (from 5.9 × 10⁵ to 59 CFU mL^-1) and satisfactory recovery values (from 75.76% to 106.78%). These results indicate that the developed CAMP assay is a potentially useful method for the detection of B. cereus in milk.

Establishment and Application of Peristaltic Human Gut-Vessel Microsystem for Studying Host-Microbial Interaction

Intestinal floras influence a lot of biological functions of the organism. Although animal model are strong tools for researches on the relationship between host and microbe, a physiologically relevant in vitro human gut model was still required. Here, a novel human gut-vessel microfluidic system was established to study the host–microbial interaction. Peristaltic motion of the cells on the chip was driven by a pneumatic pump. When intestinal epithelial cells (Caco2) were co-cultured with vascular endothelial cells (HUVECs) on the peristaltic microfluidic chip, Caco2 showed normal barrier and absorption functions after 5 days cultivation, which generally took 21 days in static Transwell models. Intestinal microvilli and glycocalyx layer were seen after 4 days cultivation, and Lactobacillus casei was successfully co-cultured for a week in the intestinal cavity. A model for intestinal damage and inflammatory responses caused by E. coli was set up on this chip, which were successfully suppressed by Lactobacillus casei or antibiotic. In summary, this human gut-vessel microfluidic system showed a good potential for investigating the host–microbial interaction and the effect and mechanism of microbiome on intestinal diseases in vitro.

Fabrication of a Cartilage Patch by Fusing Hydrogel-Derived Cell Aggregates onto Electrospun Film

Irregular defects at sites of degenerative cartilage often accompany osteoarthritis (OA). The development of novel cell-/biomaterial-based cartilage tissue engineering methods to address these defects may provide a durable approach to hinder the development of OA. In this study, we fabricated a neocartilage patch by fusing cell aggregates onto a biodegradable nanofiber film for degenerative cartilage repair. Human mesenchymal stem/stromal cell (MSC) aggregates were prepared and induced for chondrogenesis in a thermosensitive hydrogel, poly (N-isopropylacrylamide-co-acrylic acid (p(NIPAAm-AA)). Cell migration mediated the formation of cell aggregates in the thermosensitive hydrogel and led to a cell-dense hollow shell structure. The chondrocytes derived from MSC aggregates in the hydrogel were evidenced by the expression of chondrogenesis-related genes and extracellular matrices. They were fused onto an electrospun film by mechanical force and spatial confinement to generate a neo-cartilage patch. The fabricated neocartilage patches may be able to integrate into the irregular defects under compressive stresses and achieve cartilage regeneration in vivo. Impact statement The formation of human mesenchymal stem/stromal cells aggregates in thermosensitive hydrogels was mechanistically examined. These in situ formed cell aggregates with enhanced chondrogenesis were bioengineered into a neocartilage patch for regeneration of superficial irregular cartilage defects.

Extraction, Characterization, Antitumor and Immunological Activities of Hemicellulose Polysaccharide from Astragalus radix Herb Residue

Astragalus radix (radix) have been frequently used for clinical application in China, and the herb residues of radix turn out to be a waste of resources. To escape from this, the medicine value of radix herb residues is mined in this article. We isolated hemicellulose polysaccharide AX-I-3b from radix herb residues by fractional extraction. Monosaccharide-composition analysis revealed that AX-I-3b consisted of arabinose, xylose, and glucose with a molar ratio of 10.4:79.3:1.1. Methylation, NMR and FT-IR analyses showed that AX-I-3b monosaccharide residue was linked as follows: →2,3,4)-β-d-Xylp-(1→, →4)-β-d-Arap-(1→, →4)-β-d-Glcp-(1→. Then, we found that AX-I-3b exhibited antitumor activity against lung cancer in vitro and vivo through MTT assay and xenograft tumor model. Mechanistically, AX-I-3b induced apoptosis in lung cancer cells and xenograft tumors, which is evidenced by the up-regulation of p53, Bax and cleaved caspase-3, and the down-regulation of Bcl-2. Moreover, AX-I-3b synergistically improved the therapeutic ability of cisplatin in xenograft tumors model. Furthermore, AX-I-3b treatment effectively improved the immune organ index, the percentage of spleen lymphocyte subsets and serum cytokine levels in lung cancer mice, supporting that AX-I-3b showed immunomodulatory activity. In conclusion, our results identified AX-I-3b as an antitumor and immunomodulatory agent, providing a new insight into the reutilization of radix herb residue.

Inhibition of Liver Tumor Cell Metastasis by Partially Acetylated Chitosan Oligosaccharide on A Tumor-Vessel Microsystem

Chitooligosaccharides (COS), the only cationic oligosaccharide in nature, have been demonstrated to have anti-tumor activity. However, the inhibitory effects of COS on different stages of tumor metastasis are still unknown, and it is not clear what stage(s) of tumor metastasis COS targeted. To study the inhibitory effects of a new partially acetylated chitooligosaccharide (paCOS) with fraction of acetylation (FA) 0.46 on each phase of liver cancer cell metastasis, a dynamic tumor-vessel microsystem undergoing physiological flow was leveraged. paCOS (FA = 0.46) significantly inhibited proliferation of HepG2 cells through vascular absorption on the chip, and inhibited migration of HepG2 cells by inhibiting the formation of pseudopod in liver tumor cells. It was also found that paCOS at 10 μg/mL had a stronger inhibitory effect on liver tumor cells invading blood vessels than that of paCOS at 100 μg/mL, and paCOS at 100 μg/mL, which had a significant destructive effect on tumor vascular growth and barrier function. Moreover, paCOS reduced the number of liver tumor cells adhering onto the surface of HUVECs layer after 3 h of treatment. Therefore, the results revealed that paCOS had considerable potential as drugs for anti-tumor metastasis.

Establishment and application of a dynamic tumor-vessel microsystem for studying different stages of tumor metastasis and evaluating anti-tumor drugs

Tumor metastasis is one of the main causes of cancer-related death, and it is difficult to study the whole process of tumor metastasis in vivo due to the complex physiological environment in the body. Therefore, it's crucial to develop simple and physiologically relevant in vitro cancer models to study the metastasis process, especially different phases of tumor metastasis. A novel microfluidic tumor-vessel co-culture system was established to reproduce the different phases of cancer metastasis (proliferation, migration, intravasation and adherence) individually in vitro for the first time. It was observed that blood vessels with fluid flow had big impact on metastasis of liver cancer cells HepG2 and breast ones MDA-MB-231. In particular, it was found that both HepG2 and MDA-MB-231 cells migrated in the direction of “blood flow”. Furthermore, MDA-MB-231 cells invaded through paracellular mode disrupting the intercellular endothelial junctions, whereas HepG2 cells engaged in transcellular intravasation through transcellular process. Compared with traditional assays, much more potent inhibition of 5-fluorouracil (5-Fu) on different phases of tumor metastasis was observed on the microsystem. In summary, the microfluidic device yielded abundant information about each phase of tumor metastasis, and would provide a powerful platform for use in drug screening, toxicology studies, and personalized medicine in future.

The different stages of the cancer metastasis were reproduced individually on a novel tumor-vessel co-culture microsystem.

A review on the preparation of chitosan oligosaccharides and application to human health, animal husbandry and agricultural production

Chitosan oligosaccharides (COS) are the degraded products of chitin or chitosan prepared by chemical or enzymatic hydrolysis. As compared to chitosan, COS not only exhibit some specific physicochemical properties such as excellent water solubility, biodegradability and biocompatibility, but also have a variety of functionally biological activities including anti-inflammation, anti-bacteria, immunomodulation, neuroprotection and so on. This review aims to summarize the preparation and structural characterization methods of COS, and will discuss the application of COS or their derivatives to human health, animal husbandry and agricultural production. COS have been demonstrated to prevent the occurrence of human health-related diseases, enhance the resistance to diseases of livestock and poultry, and improve the growth and quality of crops in plant cultivation. Overall, COS have presented a broad developmental potential and application prospect in the healthy field that deserves further exploration.

N-Acetylcysteine alleviates gut dysbiosis and glucose metabolic disorder in high-fat diet-fed mice

BACKGROUND

N-Acetylcysteine (NAC), an antioxidative reagent for clinical diseases, shows potential in the treatment of diabetes and other metabolic diseases. However, it is unknown how NAC modulates the gut microbiota of mice with metabolic syndrome. The aim of the present study was to demonstrate the preventive effect of NAC on intestinal dysbiosis and glucose metabolic disorder.

METHODS

Mice (C57BL/6J strain) were fed either a normal chow diet (NCD), NCD plus NAC, a high-fat diet (HFD), or HFD plus NAC for 5 months, after which glucose levels, circulating endotoxins and key metabolism-related proteins were determined. Fecal samples were analyzed by 16S rRNA sequencing. A novel analysis was performed to predict functional changes in gut microbiota. In addition, Spearman's correlation analysis was performed between metabolic biomarkers and bacterial abundance.

RESULTS

Treatment with NAC significantly reversed the glucose intolerance, fasting glucose concentrations, and gains in body weight and plasma endotoxin in HFD-fed mice. Further, NAC upregulated occludin and mucin glycoprotein levels in the proximal colon of HFD-treated mice. Noticeably, NAC promoted the growth of beneficial bacteria (i.e. Akkermansia, Bifidobacterium, Lactobacillus and Allobaculum) and decreased populations of diabetes-related genera, including Desulfovibrio and Blautia. In addition, NAC may affect the metabolic pathways of intestinal bacteria, including lipopolysaccharide biosynthesis, oxidative stress, and bacterial motility. Finally, the modified gut microbiota was closely associated with the metabolic changes in NAC-treated HFD-fed mice.

CONCLUSIONS

N-Acetylcysteine may be a potential drug to prevent glucose metabolic disturbances by reshaping the structure of the gut microbiota.

[Effect and mechanism of mulberry leaf polysaccharide on type 1 diabetic nephropathy in rats]

Objective: To observe the effects of mulberry leaf polysaccharide (MLP) on insulin-like growth factor 1 (IGF-1) and insulin-like growth factor blinding protein 3 (IGFBP-3) as well as the expression of IGF-1 and IGFBP-3 mRNA in the kidney of type 1 Diabetic Nephropathy (DN) rats, and to investigate its therapeutic effects and underlying mechanisms. Methods: Type 1 DN rat model was established by intraperitoneally injecting streptozocin (STZ). SD rats were randomly divided into the control, model, insulin and MLP groups, with eight rats in each group. Rats in MLP group were given orally with MLP 200 mg/kg daily for 8 weeks and insulin group rats were given subcutaneously injection of short acting insulin 1 U daily for 8 weeks. The changes in body weight, blood and urine parameters were recorded. Extracellular matrix (ECM) was calculated. The contents of IGF-1 and IGFBP-3 in blood serum were evaluated by enzyme-linked immunosorbent assay (ELISA). The mRNA expressions of IGF-1 and IGFBP-3 in the kidney were evaluated by fluorescence quantitative PCR. Results: Compared with rats in control group, blood glucose, triglyceride, total cholesterol, low density lipoprotein, very low density lipoprotein, 24 h urine protein, serum creatinine and urea nitrogen in the model group rats were significantly increased (all P<0.01), and these parameters of MLP group were significantly lower than the model group (all P<0.01). The contents of IGF-1 and IGFBP-3 in the blood serum of the model group were significantly higher than those in the control group (both P<0.001), while in the MLP group they were lower than the model group[IGF-1: (0.777±0.018) ng/ml vs (0.864±0.022) ng/ml, P<0.001; IGFBP-3: (0.759±0.016) ng/ml vs (0.846±0.021) ng/ml, P<0.001]. The mRNA expressions of IGF-1 and IGFBP-3 in the kidney of the model group were significantly higher than those in the control group (both P<0.001), while in the MLP group they were lower than in the model group (IGF-1: 1.450±0.032 vs 1.810±0.090, P<0.001; IGFBP-3: 1.684±0.018 vs 1.968±0.044, P<0.001). Compared with the model group rats, there were fewer pathological changes of kidney in MLP group rats. Conclusion: MLP has a certain therapeutic effect on DN, which may be achieved by decreasing the contents of IGF-1 and IGFBP-3 in the blood serum and down-regulating the over-expression of IGF-1 and IGFBP-3 mRNA in the kidney.

[Inhibition of chitin oligosaccharide on dyslipidemia and the potential molecular mechanism exploration]

The inhibitory effect of NACOS on dyslipidemia and potential molecular mechanisms by in vitro and in vivo experiments were investigated. For in vitro study, four experimental groups were designed by using HepG2 cells, including the control group, palmitic acid (PA) treatment alone group, NACOS treatment alone group and NACOS + PA treatment group. For in vivo study, male C57BL/6 mice were divided into four groups (n=5) at random including the normal control group (NCD), high fat diet (HFD) group, NACOS treatment alone group, NACOS+HFD group, which were treated for 20 weeks. The used methods in this study were as follows: the observation of lipid droplet deposition in HepG2 cells by oil red O staining, the detection of mRNA levels of lipid metabolism-related regulators and inflammatory cytokine by RT-PCR method, the monitoring of MAPKs and PI3K/Akt pathway activation by Western blotting method. The in vitro study shows that, NACOS had no toxicity on the viability of HepG2 cells at 25-100 μg/mL and significantly reduced the deposition of lipid droplet. Also, based on both in vitro and in vivo investigation, NACOS evidently down-regulated the expression of lipid metabolism-related regulators (PGC1α, Cox5b, Mcad) and inflammatory cytokine (IL-1β) at mRNA level (P<0.05 or 0.01), and suppressed the activation of p38, ERK1/2 and Akt in HepG2 cells and lever tissues from HFD-fed mice (P<0.05 or 0.01). Based on the above, NACOS may inhibit the oxidation of liver mitochondrial fatty acid and the lipid biosynthesis, block the inflammatory responses and prevent the HepG2 cells and C57BL/6 mice from lipidemia.

Enteromorpha prolifera oligomers relieve pancreatic injury in streptozotocin (STZ)-induced diabetic mice

The polysaccharides of Enteromorpha prolifera (PEP) displayed various bioactivities such as anti-viral, anti-inflammatory and immune-regulative effects. However, no studies were performed on the biological effect of Enteromorpha prolifera oligomers (EPO). In this study, we prepared EPO and evaluated their anti-diabetic effect. By enzymatic degradation, EPO were produced from PEP, and the average molecular weight was identified to be 44.1 kDa by Gel Permeation Chromatography (GPC) analysis. The major monosaccharide units of EPO were measured to be rhamnose, glucuronic acid, glucose, xylose and galactose by capillary electrophoresis assay. Based on the in vitro studies, EPO presented potent reducing power and antioxidant effect such as the scavenging of 1, 1-diphenyl-2-picrylhydrazyl (DPPH), superoxide and NO radicals. The in vivo studies show that EPO relieved the symptoms of polydipsia, polyphagia, emaciation and hyperglycemia in streptozotocin (STZ)-induced diabetic mice to a certain extent. Further, by using the quantitative real-time PCR (qPCR) assay and immunofluorescence staining, EPO was proved to promote the insulin secretion by reducing pancreatic inflammation and apoptosis in diabetic mice. In summary, our results indicate that the mitigation of EPO on pancreatic damage might be an effective way to ameliorate the diabetes mellitus.

Exploring Effects of Chitosan Oligosaccharides on Mice Gut Microbiota in in vitro Fermentation and Animal Model

Chitosan oligosaccharides (COS) have shown positive effects on host gut health and influence on intestinal microbial community. However, the bioactivity and mechanism of COS on gut microbiota is still poorly understood. Here, we presented systematic studies of COS on mice fecal/gut microbiota. During in vitro fermentation of COS by mice gut microbiota, total bacterial population significantly decreased after 8-h COS treatment but was returned to the normal level after extended incubation. Consumption of COS and production of SCFAs suggested that COS were utilized by the microbe, although the consumption of chitosan pentasaccharides was obviously slower than others. COS treatments on mice fecal samples caused the decrease of potential pathogenic genera Escherichia/Shigella and the increase of genus Parabacteroides. In vivo animal study indicated that COS reduced population of probiotic genera Lactobacillus, Bifidobacterium and harmful genus Desulfovibrio, and increased abundance of genus Akkermansia. Phylum Proteobacteria was significantly inhibited by COS both in the animal model and in vitro fermentation. Our findings suggested that COS could reform the community structure of gut microbiota. The relationship among COS, gut microbiota and host health deserve further study.

Conjugation of chitosan oligosaccharides enhances immune response to porcine circovirus vaccine by activating macrophages

Porcine circovirus type 2 (PCV2)-associated diseases have led to great economic losses to the pig industry. Our lab previously found that conjugation of chitosan oligosaccharides (COS) or via a carrier protein enhanced the immunogenicity of PCV2 vaccine against infectious pathogens. However, precise mechanisms and signal transduction pathways underlying the efficacy of COS conjugation remains poorly defined. In this study, to better understand the effects and mechanism of COS conjugates maintain the adjuvant potential in vivo, we investigated its augmentation of macrophage function, including cell activation, NO production, cytokine production and phagocytosis. Additionally, the role of Toll-like receptors (TLR) proteins in this process was also assessed. The results indicate that, as compared to the PCV and PCV/COS, conjugation of COS effectively enhanced the NO production, cytokines generation and phagocytosis activity of macrophages. Noticeably, the generation of NO and proinflammatory cytokines was closely related to the TLR2/4 signaling pathways, strongly suggesting that conjugation of COS regulates innate and adaptive immunity by activation of macrophages, resulting in immune enhancement. In summary, the present study provides a potential mechanism of COS conjugation as a novel adjuvant to improve immune responses against various diseases.

Heterologous expression and biochemical characterization of a GHF9 endoglucanase from the termite Reticulitermes speratus in Pichia pastoris

BACKGROUND

Cellulases are of great significance for full utilization of lignocellulosic biomass. Termites have an efficient ability to degrade cellulose. Heterologous production of the termite-origin cellulases is the first step to realize their industrial applications. The use of P. pastoris for the expression of recombinant proteins has become popular. The endoglucanase from Reticulitermes speratus (RsEG), belonging to glycoside hydrolase family 9 (GHF9), has not been produced in P. pastoris yet.

RESULTS

A mutant RsEGm (G91A/Y97W/K429A) was successfully overexpressed in P. pastoris. RsEGm, with optimum pH 5.0, was active over the pH range of 4.0 to 9.0, and exhibited superior pH stability over between pH 4.0 and pH 11.0. It displayed the highest activity and good stability at 40 °C, but lost activity quickly at 50 °C. The apparent kinetic parameters of RsEGm against Carboxymethyl Cellulose (CMC) were determined, with K m and V max of 7.6 mg/ml and 5.4 μmol/min•mg respectively. Co2+, Mn2+ and Fe2+ enhanced the activity of RsEGm by 32.0, 19.5 and 11.2% respectively, while Pb2+ and Cu2+ decreased its activity by 19.6 and 12.7% separately.

CONCLUSIONS

RsEGm could be overexpressed in P. pastoris. It was stable between pH 4.0 and pH 11.0, and exhibited higher stability at temperatures ≤ 40 °C. This endoglucanase may have potential to be used in the field of laundry, textile and lignocellulose-based biofuels and chemicals.

Helix loop-mediated isothermal amplification of nucleic acids

Isothermal nucleic acid amplification has played a key role in the point of care test (POCT). In this study, a helix loop-mediated isothermal amplification (HAMP) method with high specificity, efficiency and rapidity was developed. The MERS-Cov orf1b gene was chosen for the validation and optimization of HAMP. The HAMP analysis was performed at a constant temperature of 61-65 °C and yielded a self-primed spiral structure with no introduction of exogenous gene sequence by two pairs of specially designed primers. The primers for helix loop formation were composed of two complementary primers including the helix forward primer and the helix reverse primer, the 3' ends of which were complementary to their respective target nucleic acids. HAMP assay can be monitored by fluorescence signals with the addition of Eva Green in the reaction mixture. In addition, an accelerated HAMP was developed after the addition of acceleration probe, which could be finished within 75 min with a sensitivity of 10 copies per reaction. Further, a reverse transcription-HAMP (RT-HAMP) was proven to be feasible for RNA detection by combining the reverse transcriptase with DNA polymerase. Finally, both the HAMP and RT-HAMP assay were visually conducted by using Hydroxynaphthol blue (HNB) as a chromogenic indicator. All in all, it is suggested that the HAMP assay would have great potential in POCT applications.