Improvement of D-Ribose Production from Corn Starch Hydrolysate by a Transketolase-Deficient Strain Bacillus subtilis UJS0717

Enzyme cascades for high-yield conversion of d-xylose into d-ribose by overcoming equilibrium constraints and enhancing selectivity

d-Ribose is essential for critical cellular functions and the synthesis of antiviral nucleosides. However, traditional chemical synthesis and fermentation methods of d-ribose production suffer from low yields and inefficient resource utilization. Here, we present a highly efficient enzymatic cascade strategy that utilizes selective phosphorylation and dephosphorylation processes, coupled with ATP regeneration to convert d-xylose into d-ribose with high yield. By optimizing this enzyme cascade, we achieved a substantial increase in d-ribose yield from 23.4 % to 93.5 % mol/mol, effectively overcoming the equilibrium limitations of sugar conversion processes. Notably, our approach allows for the selective conversion of d-xylose to d-ribose in lignocellulosic hydrolysates, even in the presence of d-glucose. This work demonstrates the highly efficient enzymatic conversion of d-xylose into d-ribose offering a competitive alternative to existing chemical synthesis methods. Our findings provide a novel approach to cellulosic biomass valorization and represent a significant contribution to the field of biorefinery.

Xylose Metabolism and Transport in Bacillus subtilis and Its Application to D-Ribose Production

Xylose is a five-carbon sugar and the second abundant mono-saccharide in lignocellulosic biomass. Xylose is not only a sugar substitute by itself, but also a good carbon source for the microbial and enzymatic synthesis of various valuable biomaterials. Most microorganisms are able to uptake and consume xylose as a sole carbon source because they possess specific transport systems and metabolic enzymes. Bacillus subtilis is a representative Gram-positive bacterium commercially used for enzyme and food production. Even though B. subtilis is popular in genetic and protein engineering, its application for metabolic engineering has been limited. Meanwhile, D-ribose is a five-carbon sugar and essential component in nucleotides, ATP, NAD, coenzyme A and so on. It boosts healthy effects on the human body such as enhancement of muscle performance and tolerance to myocardial ischemia. To produce D-ribose from xylose in B. subtilis, a comprehensive review on xylose metabolic regulation, xylose transport, and D-ribose biosynthetic engineering and fermentation process was provided. It would be useful for production of other valuable metabolites from xylose in B. subtilis.

Producing D-Ribose from D-Xylose by Demonstrating a Pentose Izumoring Route

D-Ribose plays fundamental roles in all living organisms and has been applied in food, cosmetics, health care, and pharmaceutical sectors. At present, D-ribose is predominantly produced by microbial fermentation based on the pentose phosphate pathway (PPP). However, this method suffers from a long synthetic pathway, severe growth defect of the host cell, and carbon catabolite repression (CCR). According to the Izumoring strategy, D-ribose can be produced from D-xylose through only three steps. Being not involved in the growth defect or CCR, this shortcut route is promising to produce D-ribose efficiently. However, this route has never been demonstrated in engineering practice, which hinders its application. In this study, we stepwise demonstrated this route and screened out higher active enzymes for each step. The first D-ribose production from D-xylose through the Izumoring route was achieved. By stepwise enzyme dosage tuning and process optimization, 6.87 g/L D-ribose was produced from 40 g/L D-xylose. Feeding D-xylose further improved the D-ribose titer to 9.55 g/L. Finally, we tested the coproduction of D-ribose and D-allose from corn stalk hydrolysate using the route engineered herein. In conclusion, this study demonstrated a pentose Izumoring route, complemented the engineering practices of the Izumoring strategy, paved the way to produce D-ribose from D-xylose, and provided an approach to comprehensively utilize the lignocellulosic sugars.

Pentose metabolism and conversion to biofuels and high-value chemicals in yeasts

Pentose sugars are widespread in nature and two of them, D-xylose and L-arabinose belong to the most abundant sugars being the second and third by abundance sugars in dry plant biomass (lignocellulose) and in general on planet. Therefore, it is not surprising that metabolism and bioconversion of these pentoses attract much attention. Several different pathways of D-xylose and L-arabinose catabolism in bacteria and yeasts are known. There are even more common and really ubiquitous though not so abundant pentoses, D-ribose and 2-deoxy-D-ribose, the constituents of all living cells. Thus, ribose metabolism is example of endogenous metabolism whereas metabolism of other pentoses, including xylose and L-arabinose, represents examples of the metabolism of foreign exogenous compounds which normally are not constituents of yeast cells. As a rule, pentose degradation by the wild-type strains of microorganisms does not lead to accumulation of high amounts of valuable substances; however, productive strains have been obtained by random selection and metabolic engineering. There are numerous reviews on xylose and (less) L-arabinose metabolism and conversion to high value substances; however, they mostly are devoted to bacteria or the yeast Saccharomyces cerevisiae. This review is devoted to reviewing pentose metabolism and bioconversion mostly in non-conventional yeasts, which naturally metabolize xylose. Pentose metabolism in the recombinant strains of S. cerevisiae is also considered for comparison. The available data on ribose, xylose, L-arabinose transport, metabolism, regulation of these processes, interaction with glucose catabolism and construction of the productive strains of high-value chemicals or pentose (ribose) itself are described. In addition, genome studies of the natural xylose metabolizing yeasts and available tools for their molecular research are reviewed. Metabolism of other pentoses (2-deoxyribose, D-arabinose, lyxose) is briefly reviewed.

Bacteria counting method based on polyaniline/bacteria thin film

A simple and rapid bacteria counting method based on polyaniline (PANI)/bacteria thin film was proposed. Since the negative effects of immobilized bacteria on the deposition of PANI on glass carbon electrode (GCE), PANI/bacteria thin films containing decreased amount of PANI would be obtained when increasing the bacteria concentration. The prepared PANI/bacteria film was characterized with cyclic voltammetry (CV) technique to provide quantitative index for the determination of the bacteria count, and electrochemical impedance spectroscopy (EIS) was also performed to further investigate the difference in the PANI/bacteria films. Good linear relationship of the peak currents of the CVs and the log total count of bacteria (Bacillus subtilis) could be established using the equation Y=-30.413X+272.560 (R(2)=0.982) over the range of 5.3×10(4) to 5.3×10(8)CFUmL(-1), which also showed acceptable stability, reproducibility and switchable ability. The proposed method was feasible for simple and rapid counting of bacteria.