S-Adenosylmethionine (SAM) is a valuable compound extensively used in depression treatment and biological methyl donor, which is biosynthesized from ATP and L-methionine with SAM synthase (SAM-s) as a catalyst. In this research, the weak SAM-s activity was a key factor and led to low SAM titer in Saccharomyces cerevisiae. Then, a novel K+ uptake channel was introduced to the SAM production pathway of Saccharomyces cerevisiae, activated by K+ in molasses to enhance the SAM synthase (SAM-s) activity and thereby improve the production efficiency of SAM. As a result, the intracellular K+ concentration and SAM-s activity were 1.23-and 1.31-fold higher than the control leading to a 24 % increase to 0.93 +/- 0.04 g/L in SAM titer. In combination with bio-process optimization resulted in a final yield of 2.22 +/- 0.01 g/L in shake flasks and 15.37 +/- 0.89 g/L in a 5-L bioreactor from pretreated molasses. This work provides a practical and cost-effective strategy for the large-scale biosynthesis of SAM from cane molasses.

Geraniol has versatile applications in the fragrance, pharmacy, and biofuel industries. This monoterpene is produced via the mevalonate pathway in the yeast Saccharomyces cerevisiae. However, carbon flux leakage restricts the efficient biosynthesis of target compounds via this pathway. In this work, the mevalonate pathway of the recombinant S. cerevisiae was reprogrammed by introducing an isopentenyl phosphate kinase (IPK) and to establish an isopentenyl phosphate utilization (IPU) bypass that can utilise the isopentenyl phosphate (IP) produced from phosphomevalonate decarboxylase (PMD). Geraniol production was increased by 225% in the engineered strain. The yield of geraniol was further enhanced to 156.2 +/- 6.6 mg/L through optimisation of key rate-limiting enzymes of the mevalonate pathway. Using pretreated molasses as a carbon source yielded 180.9 +/- 2.9 mg/L of geraniol under optimal fermentation conditions, the highest reported titre to date using molasses medium. Modification of the mevalonate pathway can provide a commercially feasible strategy for monoterpene synthesis in engineered S. cerevisiae.

Microbial engineering based on synthetic biology can facilitate large-scale production of target products. In this study, the introduction of lactate dehydrogenase (LDH) enabled Saccharomyces cerevisiae to acquire the capacity for L-lactic acid (LA) production and the NADH/NAD + ratio from 0.228 to 0.156, while the subsequent modification of carbon metabolism pathway led to a rapid increase of NADH/NAD + even up to 0.337. By testing the effectiveness of four different redox systems, we demonstrated that dynamic regulation of additional redox genes to consume excessive NADH is more beneficial for LA accumulation, alleviating the negative effects of metabolic modification on hosts, and altering the distribution of metabolic flow. We first reported expression of GLT1 which coding glutamate synthase has the strongest ability to increase LA production and reduce NADH/NAD + . Combining metabolic engineering and cofactor engineering, the LA yield reached from 0.04 g/g to 0.37 g/g in YNB medium. Subsequently, strain PK27 produced 37.94 g/L LA with production yield of 0.66 g/g in YPD medium. Finally, the results could provide a reference that the potential under poor nutrient culture conditions and the direction and intensity of regulation of intracellular NADH/NAD + for LA accumulation.

Recently, the biosynthesis of silver nanoparticles (AgNPs) by microbes to develop biocompatible nanomaterials for use in environmental protection and biomedicine has become popular. The fabrication of AgNPs for application in monotherapy or combination therapy will open avenues to produce new antibacterial drugs. The synthesis of AgNPs by endophytic bacteria is a less explored field. In the present study, an eco-friendly and economical method was developed for the formation of AgNPs by using the endophytic bacterium Bacillus zanthoxyli GBE11, isolated from the leaves of Ginkgo biloba , to estimate their antibacterial potential. The change of the mixture from colorless to dark brown verifies the initial formation of AgNPs. Endophytic B. zanthoxyli -produced AgNPs (Bz-AgNPs) were characterized using UV–vis spectrometry and surface plasmon resonance at 439 nm. X-ray diffraction analysis yielded diffraction intensities with 2θ angles of 27.66°, 32.06°, 38.10°, 46.11°, and 77.13°, confirming the crystalline nature of nanoparticles. Especially, the Fourier transform infrared spectra revealed the existence of probable bioreduction molecules required for the synthesis of Bz-AgNPs. Transmission electron microscopy indicated the polydispersity of the Bz-AgNPs with a size of 3.68–31.60 nm. Our results indicated that the Bz-AgNPs had a strong antibacterial effect against Staphylococcus aureus ATCC6538P, Salmonella typhi enterica ATCC25922, Escherichia coli DH5α, Bacillus subtilis WB800, and Pseudomonas aeruginosa ATCC27853. The data showed that Bz-AgNPs are prospective antimicrobial agents that are available for the manufacture of new drugs to overcome multidrug resistance.

d-Allulose is a desirable sucrose substitute with potential applications in food and health care. d-Allulose can be synthesized using d-glucose as a substrate through coupling glucose isomerase with d-allulose 3-epimerase (DAEase); however, the product yield is typically less than 20% at reaction equilibrium and thus limits its use in industrial applications. Here, a 3R-ketose phosphorylation pathway coupled with an adenosine triphosphate (ATP) regeneration system was developed for the efficient synthesis of d-allulose in Escherichia coli using d-glucose as a substrate. The l-rhamnulose kinase (RhaB) was used to break the inherent reaction equilibrium due to its substrate specificity, resulting in increases in d-allulose titer by 69.9% to 4.96 ± 0.49 g/L. By optimizing the whole cell transformation conditions and designing an ATP regeneration module, d-allulose production reached 17.62 ± 0.77 g/L from 30 g/L d-glucose with a final yield of 0.73 g/g without the addition of exogenous ATP. To evaluate the potential industrial application of this multienzyme cascade system, d-allulose was produced from cane molasses (124.16 ± 2.69 g/L glucose equivalent) with a final d-allulose titer of 62.60 ± 3.76 g/L. The present study provides a practical enzymatic approach for the economical synthesis of d-allulose.

The microbial production of dextranase using cheap carbon sources is beneficial to solve the economic loss caused by the accumulation of dextran in syrup. A food‐grade microbial cell factory was constructed by introducing the dextranase encoding gene DEX from Chaetomium gracile to the chromosome of Bacillus subtilis, and the antibiotic resistance marker gene was subsequently deleted via the Cre/loxP strategy. The dual‐promoter system with a sequentially arranged constitutive P43 promoter resulted in an 85 % increase in DEX expression. Under the optimal fermentation conditions of 10 g/L maltose, 15 g/L casein, 1 g/L Na2HPO4, 1 g/L FeSO4 and 8 g/L NaCl, DEX activity was increased from 2.625 to 64.34 U/mL. Recombinant DEX was purified 5.98‐fold with a recovery ratio of 26.67 % and specific activity of 3935.02 U/mg. Enzyme activity was optimal at 55 °C and pH 5.0 and remained 80.34 % and 71.36 % of the initial activity at 55 °C and pH 4.0 after 60 min, respectively. The enzyme possessed high activity in the presence of Co2+, while Ag+ showed the strongest inhibition ability. The optimal substrate was 20 g/L dextran T‐2000. The findings could facilitate the low‐cost, large‐scale production of food‐grade DEX for use in the sugar industry.