Characterization of a novel alkaline Arxula adeninivorans urate oxidase expressed in Escherichia coli and its application in reducing uric acid content of food

A programmable oral bacterial hydrogel for controllable production and release of nanovaccine for tumor immunotherapy

Oral protein vaccines are mainly used to prevent the infection of intestinal pathogens in clinic due to their high safety and strong compliance. However, it is necessary to design the efficient delivery systems to overcome the harsh gastrointestinal environment in the application process. Here we established a programmable oral bacterial hydrogel system for spatiotemporally controllable production and release of nanovaccines. The system was divided into three parts: (1) Engineered bacteria were encapsulated in chitosan-sodium alginate microcapsules, which offered protection against the extreme acid conditions in the stomach. (2) Microcapsules were dissolved, and then engineered bacteria were released and colonized in the intestine. (3) The release of nanovaccines was controlled periodically by a synchronous lysis genetic circuit for tumor immunotherapy. Compared to control groups, tumor volume of subcutaneous tumor-bearing mice treated with bacterial microgels releasing optimized nanovaccine was almost inhibited by 75% and T cell response was activated at least 2-fold. We believe that this programmable bacterial hydrogel will offer a promising way for the application of oral nanovaccines.

Single-atom nanozyme-based electrochemical sensors for health and food safety monitoring

Electrochemical sensors and biosensors play an important role in many fields, including biology, clinical trials, and food industry. For health and food safety monitoring, accurate and quantitative sensing is needed to ensure that there is no significantly negative impact on human health. It is difficult for traditional sensors to meet these requirements. In recent years, single-atom nanozymes (SANs) have been successfully used in electrochemical sensors due to their high electrochemical activity, good stability, excellent selectivity and high sensitivity. Here, we first summarize the detection principle of SAN-based electrochemical sensors. Then, we review the detection performances of small molecules on SAN-based electrochemical sensors, including H₂O₂, dopamine (DA), uric acid (UA), glucose, H₂S, NO, and O₂. Subsequently, we put forward the optimization strategies to promote the development of SAN-based electrochemical sensors. Finally, the challenges and prospects of SAN-based sensors are proposed.

Removal of substrate inhibition of Acinetobacter baumannii xanthine oxidase by point mutation at Gln-201 enables efficient reduction of purine content in fish sauce

Xanthine oxidase is an oxidase that has a molybdopterin structure with substrate inhibition. Here, we show that a single point mutation (Q201) in the Acinetobacter baumannii xanthine oxidase (AbXOD) obtained mutant Q201E (k cat =799.44 s-1, no inhibition) with high enzyme activity and decrease of substrate inhibition in 5 mmol/L high substrate model, and which cause two loops structure change at active center, characterized by complete loss of substrate inhibition without reduction of enzymatic activity. Molecular docking results showed that the change of flexible loop increased the affinity between substrate and enzyme, and the formation of a π-π bond and two hydrogen bonds made the substrate more stable in the active center. Ultimately, Q201E can still maintain better enzyme activity under high purine content (an approximately 7-fold improvement over the wild-type), indicating a broader application prospect in the manufacture of low-purine food.

Urate oxidase from tea microbe Colletotrichum camelliae is involved in the caffeine metabolism pathway and plays a role in fungal virulence

Tea is one of the most well-known, healthy beverages in the world. Tea plants produce caffeine as a secondary metabolite. Colletotrichum camelliae is one of the most important microbes frequently isolated from tea fields, and it causes anthracnose disease in tea plant. In the present work, we performed molecular microbiology and transcriptomic analyses of the C. camelliae - tea plant interaction to investigate the mechanism of fungal virulence and plant defense. Upon infection of tea plant with C. camelliae, we observed alterations in the expression of fungal transcripts, including those of many genes associated with caffeine metabolism, such as those encoding various transporters, xanthine dehydrogenase, and urate oxidase (UOX). In particular, the deletion of C. camelliae urate oxidase (CcUOX), which is involved in the caffeine metabolism pathway, reduced fungal tolerance to caffeine, and impaired fungal virulence. CcUOX is involved in caffeine metabolism by the degradation of uric acid contents. C. camelliaeΔCcUOX mutants impaired uric acid degradation in vivo. The CcUOX gene was cloned from C. camelliae, overexpressed in Escherichia coli, and the recombinant CcUOX protein displayed maximum activity at 30°C and a pH of 4.0. The recombinant CcUOX efficiently reduced uric acid in vitro suggesting a promising application in caffeine-contaminated environment management and in producing food with low purine contents to prevent uric acid related human diseases, such as hyperuricemia and gout.

Computer-assisted in vitro reconstitution of purine degradation pathway to lower the purine content in food

BACKGROUND

With the increasing prevalence of gout and its etiological hyperuricemia, dietary control of gout based on low-purine food according to patients' eating habits is becoming a better choice compared to the existing drug treatment such as allopurinol with notorious side effects. Reconstructing the purine metabolic pathway in vitro to degrade purine substances in food into natural functional allantoin appears to be an innovative method for preparing nutritious and healthy food of low purine content. The present study reports a computer-assisted in vitro reconstruction of four purinolytic enzymes metabolizing adenosine into allantoin to reduce purine content in food for personalized dietary control of hyperuricemia and gout.

RESULTS

Under the optimum reaction conditions of 40 °C and pH 7, 0.1 U of enzymes and 0.5 mmol L^-1 adenosine determined by an orthogonal test design, 16 different enzyme complexes were experimentally tested. The tested enzyme composition and allantoin production values were used as input and output to build a three-layer back propagation artificial neural network (BP-ANN) model, which was further optimized by a genetic algorithm (GA). The optimum enzyme complex predicted by the GA-BP-ANN model produced 248.08±7.832 μmol L^-1 allantoin, which was 19.9% higher than equimolar mixture of enzymes, and also more efficiently lowered purine contents in beer, as well as beef and yeast extracts.

CONCLUSION

This is the first in vitro reconstitution of complete purine metabolic pathway by combining ANN and GA technologies, with successful application with respect to lowering the purine content in food, indicating a promising application of computer-assisted in vitro reconstitution of purinolytic pathway in low-purine food to prevent hyperuricemia and gout. © 2022 Society of Chemical Industry.

Characterization of a novel marine microbial uricase from Priestia flexa and evaluation of the effects of CMCS conjugation on its enzymatic properties

A novel uricase producing marine bacterium Priestia flexa alkaAU was isolated and identified. The 16S rDNA and the uricase coding gene were sequenced, analyzed and submitted to GenBank. The uricase from Priestia flexa alkaAU (PFU) was purified, determined to be 58.87 kDa, and conjugated with carboxymethyl chitosan (CMCS) by ionic gelation. CMCS conjugation had no effect on the optimum pH of PFU but decreased the optimum temperature by 10 °C. CMCS conjugation increased the specific activity of PFU by 53% at the human body temperature (37 °C) and small intestine's pH (pH 6.8). Uricase thermostabilizing ability of CMCS was significant in the range of 37-80 °C but not at lower temperatures. For improvement of the pH stability of PFU, CMCS was more effective at pHs 3-5 than pHs 6-11. CMCS increased the half-life of PFU against artificial intestinal fluid by 1.5 folds, which demonstrated the potential capability of CMCS-PFU for oral administration.

Yeasts of the Blastobotrys genus are promising platform for lipid-based fuels and oleochemicals production

Strains of the yeast genus Blastobotrys (subphylum Saccharomycotina) represent a valuable biotechnological resource for basic biochemistry research, single-cell protein, and heterologous protein production processes. Species of this genus are dimorphic, non-pathogenic, thermotolerant, and can assimilate a variety of hydrophilic and hydrophobic substrates. These can constitute a single-cell oil platform in an emerging bio-based economy as oleaginous traits have been discovered recently. However, the regulatory network of lipogenesis in these yeasts is poorly understood. To keep pace with the growing market demands for lipid-derived products, it is critical to understand the lipid biosynthesis in these unconventional yeasts to pinpoint what governs the preferential channelling of carbon flux into lipids instead of the competing pathways. This review summarizes information relevant to the regulation of lipid metabolic pathways and prospects of metabolic engineering in Blastobotrys yeasts for their application in food, feed, and beyond, particularly for fatty acid-based fuels and oleochemicals. KEY POINTS: • The production of biolipids by heterotrophic yeasts is reviewed. • Summary of information concerning lipid metabolism regulation is highlighted. • Special focus on the importance of diacylglycerol acyltransferases encoding genes in improving lipid production is made.