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• Whole cell bioconversion of L-sorbose to 2-KLG was established. • Expression of PQQ avoided extra addition of the cofactor in E. coli. • 72.4 g/L 2-KLG was obtained from L-sorbose with a conversion ratio of 71.2%. • A co-culture system was performed for direct conversion of D-sorbitol to 2-KLG. The 2-keto-L-gulonic acid (2-KLG) is the direct precursor for industrial vitamin C production. The main biosynthetic method for 2-KLG production is the classical two-step fermentation route. However, disadvantages of this method are emerging, including high consumption of energy, difficulties in strain screening, complex operation, and poor stability. In this study, five recombinant Escherichia coli strains overexpressing different sorbose/sorbosone dehydrogenases were constructed and used for 2-KLG production. By optimizing catalytic conditions and further expressing pyrroloquinoline quinone in the recombinant strain, the titer of 2-KLG reached 72.4 g/L, with a conversion ratio from L-sorbose of 71.2% in a 5-L bioreactor. To achieve direct biosynthesis of 2-KLG from D-sorbitol, a co-culture system consisting of Gluconobacter oxydans and recombinant E. coli was designed. With this co-culture system, 16.8 g/L of 2-KLG was harvested, with a conversion ratio from D-sorbitol of 33.6%. The approaches developed here provide alternative routes for the efficient biosynthesis of 2-KLG. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Created a nitritation-denitritation/denitrification-nitrification. • Spontaneous recovery of permeability can be achieved. • The aerobic granular sludge (AGS) was cultivated successfully. • The deploying of AOB and NOB was reached by the two-stage system. Abstract A novel pilot gravity-driven anoxic/oxic fed-batch membrane bioreactor (AFMBR) was developed to treat real domestic wastewater. In this process, the anoxic and oxic stages created favorable conditions for stable and continuous nitritation-denitritation/denitrification-nitrification links without adding external carbon source. Excellent removals of organic carbon/nitrogen (NH 4 +-N: 71–97%, COD: 78–96%, UV 254 : 70–95%, TN: 20–60%) and spontaneous permeability recovery were achieved simultaneously. It was assessed at micro levels by characterizing sludge particle morphologies, microbiota functional evolutions, fouling layer properties and energy consumptions. It was demonstrated that the aerobic granular sludge (AGS) was cultivated successfully. Notable differences of microbial diversity were observed in different regions of AFMBR. The SEM and AFM spectra suggested the loose cake layers can shed automatically due to low pressure and continue flushing. The energy consumption in AFMBR was around 0.042 kWh/m3, far lower than that of conventional MBR. Overall, the AFMBR has a potential on improvement of domestic wastewater treatment. [ABSTRACT FROM AUTHOR]

[Display omitted] • Novel segmented aerobic/anaerobic fermentation treatments for wheat straw. • AN as the first stage could stabilize straw pH value and retain nutrients. • Aerobic composting as the first stage could help to degrade hemicellulose. • High SiO 2 content in ash results in lower organic matter content in straw. Traditional aerobic composting used for straw treatment shows limited regulation effects and unstable properties, and it is necessary to introduce some co-processing methods to optimize its performance. Herein, segmented aerobic/anaerobic fermentation, combined with chemical treatment with wood vinegar/NaOH, was used to treat wheat straw. The results showed that anaerobic fermentation when used as the first stage could stabilize the wheat straw pH between 5.19 and 6.13 and improve nutrient contents. All treatments had greater effects on substrate aeration porosities (range of 14%) than on total porosity (range of 6%), and the water-holding porosities were improved to a greater extent by NaOH than by wood vinegar. The hemicellulose degradation rate of aerobic-anaerobic treatment was higher than that achieved with anaerobic-aerobic treatment, while the latter method was more effective at removing the neutral detergent-soluble as well as remaining organic matter, which was generated due to a higher KCl content in the ash. [ABSTRACT FROM AUTHOR]

[Display omitted] • Novel biological treatments for wheat straw used as peat substitute. • Mixed anaerobic fermentation led to better pH and EC values in substrates. • Aerobic fermentation retained more nutrients, lignin and cellulose contents. • Cellulase mixed with hemicellulase or laccase increased the straw crystallinity. • Mixed anaerobic fermentation was suggested to treat straw used as substrates. To solve the central problems caused by traditional composting treatments, such as long-time consumption and poor regulation effects, this study used three fermentation methods and four enzymes to develop rapid and directional regulation methods to convert wheat straw into a suitable substrate. The results showed that the mixed anaerobic method led to better pH (4.39–5.75) and EC values (1.27–1.89 mS/cm) in the straw substrates, while the aerobic method retained more nutrients and increased lignin and cellulose contents by 5.07–8.04% and 1.52–3.32%. The cellulase mixed with hemicellulase or laccase treatments all increased the crystallinity by 0.45–7.23%. The TG/DTG results showed that all treatments decreased the initial straw glass transition temperature, particularly when using the mixed anaerobic method, with decreases of 10.63–25.48 °C. Overall, mixed anaerobic fermentation and multiple enzymes, including cellulase, have been suggested as alternative biological modification methods for straw substrates. [ABSTRACT FROM AUTHOR]