A CRISPR/dCpf1-based transcriptional repression system for Gluconobacter oxydans / 生物工程学报

Gluconobacter oxydans are widely used in industrial due to its ability of oxidizing carbohydrate rapidly. However, the limited gene manipulation methods and less of efficient gene editing tools impose restrictions on its application in industrial production. In recent years, the clustered regularly interspaced short palindromic repeats (CRISPR) system has been widely used in genome editing and transcriptional regulation which improves the efficiency of genome editing greatly. Here we constructed a CRISPR/dCpf1-mediated gene transcriptional repression system, the expression of a nuclease inactivation Cpf1 protein (dCpf1) in Gluconobacter oxydans together with a 19 nt direct repeats showed effective repression in gene transcription. This system in single gene repression had strong effect and the relative repression level had been increased to 97.9%. While it could be applied in multiplex gene repression which showed strong repression ability at the same time. Furthermore, this system was used in the metabolic pathway of L-sorbose and the regulatory of respiratory chain. The development of CRISPR transcriptional repression system effectively covered the shortage of current gene regulation methods in G. oxydans and provided an efficient gene manipulation tool for metabolic engineering modification in G. oxydans.

Synthesis of pyrroloquinoline quinone by recombinant Gluconobacter oxydans / 生物工程学报

Pyrroloquinoline quinone (PQQ), an important redox enzyme cofactor, has many physiological and biochemical functions, and is widely used in food, medicine, health and agriculture industry. In this study, PQQ production by recombinant Gluconobacter oxydans was investigated. First, to reduce the by-product of acetic acid, the recombinant strain G. oxydans T1 was constructed, in which the pyruvate decarboxylase (GOX1081) was knocked out. Then the pqqABCDE gene cluster and tldD gene were fused under the control of endogenous constitutive promoter P0169, to generate the recombinant strain G. oxydans T2. Finally, the medium composition and fermentation conditions were optimized. The biomass of G. oxydans T1 and G. oxydans T2 were increased by 43.02% and 38.76% respectively, and the PQQ production was 4.82 and 20.5 times higher than that of the wild strain, respectively. Furthermore, the carbon sources and culture conditions of G. oxydans T2 were optimized, resulting in a final PQQ yield of (51.32±0.899 7 mg/L), 345.6 times higher than that of the wild strain. In all, the biomass of G. oxydans and the yield of PQQ can be effectively increased by genetic engineering.

Biosynthesis of α-lipoic acid in Gluconobacter oxydans increases the production of vitamin C by one-step fermentation / 生物工程学报

In a one-step fermentation system of vitamin C production with Gluconobacter oxydans and Ketogulonicigenium vulgare, a functional module of α-lipoic acid biosynthesis was constructed in G. oxydans. The engineered G. oxydans was co-cultured with K. vulgare to enhance the growth and 2-keto-L-gulonic acid (2-KGA) production of K. vulgare. This one-step fermentation system alleviated the growth inhibition during the mono-culture of K. vulgare and strengthened the interaction between the two bacteria. Moreover, the yield of vitamin C precursor (2-KGA) increased to 73.34 g/L (the control group was 59.09 g/L), and the conversion of D-sorbitol to 2-KGA increased to 86.0%. This study provides a new idea for further optimizing the one-step fermentation system of vitamin C production.

Utilization of a waste glycerol fraction using and reusing immobilized Gluconobacter oxydans ATCC 621 cell extract

Background: Depletion of petroleum resources has enforced the search for alternative sources of renewable energy. Introduction of biofuels into the market was expected to become a solution to this disadvantageous situation. Attempts to cover fuel demand have, however, caused another severe problem­the waste glycerol generated during biodiesel production at a concentration of approximately 10% w/w. This, in turn, prompted a global search for effective methods of valorization of the waste fraction of glycerol. Results: Utilization of the waste fraction at 48 h with an initial glycerol concentration of 30 g·L-1 and proceeding with 62% efficiency enabled the production of 9 g·L-1 dihydroxyacetone at 50% substrate consumption. The re-use of the immobilized biocatalyst resulted in a similar concentration of dihydroxyacetone (8.7 g·L-1) in two-fold shorter time, with an efficiency of 85% and lower substrate consumption (35%). Conclusions: The method proposed in this work is based on the conversion of waste glycerol to dihydroxyacetone in a reaction catalyzed by immobilized Gluconobacter oxydans cell extract with glycerol dehydrogenase activity, and it could be an effective way to convert waste glycerol into a valuable product.

Optimization of the fermentation conditions for 5-keto-D-gluconic acid production / 生物工程学报

Gluconobacter oxydans converts glucose to gluconic acid and subsequently to 5-keto-D-gluconic acid (5-KGA), a precursor of industrially important L(+)-tartaric acid. To increase the yield of 5-KGA, fermentation conditions of 5-KGA production was optimized. Under the optimum medium and culture conditions in the shake flask, the highest 5-KGA production reached 19.7 g/L, increased by 43.8% after optimization. In a 5-L bioreactor, the pH was controlled at 5.5 and dissolved oxygen (DO) at 15%, 5-KGA production reached 46.0 g/L, raised at least 1.3 times than in the shake flask. Glucose feeding fermentation process was further developed, and the highest 5-KGA production of 75.5 g/L with 70% of yield was obtained, 32.0% higher than the highest reported value. Therefore, this newly developed fermentation process provided a practical and effective alternative for the commercial production of 5-KGA, and further of L(+)-tartaric acid.

Effects of carbon and nitrogen sources on 5-keto-gluconic acid production / 生物工程学报

Gluconobacter oxydans is known to oxidize glucose to gluconic acid (GA), and subsequently, to 2-keto-gluconic acid (2KGA) and 5-keto-gluconic acid (5KGA), while 5KGA can be converted to L-(+)-tartaric acid. In order to increase the production of 5KGA, Gluconobacter oxydans HGI-1 that converts GA to 5KGA exclusively was chosen in this study, and effects of carbon sources (lactose, maltose, sucrose, amylum and glucose) and nitrogen sources (yeast extract, fish meal, corn steep liquor, soybean meal and cotton-seed meal) on 5KGA production were investigated. Results of experiment in 500 mL shake-flask show that the highest yield of 5KGA (98.20 g/L) was obtained using 100 g/L glucose as carbon source. 5KGA reached 100.20 g/L, 109.10 g/L, 99.83 g/L with yeast extract, fish meal and corn steep liquor as nitrogen source respectively, among which the optimal nitrogen source was fish meal. The yield of 5KGA by corn steep liquor is slightly lower than that by yeast extract. For the economic reason, corn steep liquor was selected as nitrogen source and scaled up to 5 L stirred-tank fermentor, and the final concentration of 5KGA reached 93.80 g/L, with its maximum volumetric productivity of 3.48 g/(L x h) and average volumetric productivity of 1.56 g/(L x h). The result obtained in this study showed that carbon and nitrogen sourses for large-scale production of 5KGA by Gluconobacter oxydans HGI-1 were glucose and corn steep liquor, respectively, and the available glucose almost completely (85.93%) into 5KGA.

Biosynthesis of 3-hydroxypropionic acid from 1,3-propanediol by Gluconobacter oxydans ZJB09112 / 生物工程学报

3-Hydroxypropionic acid is an important building block to synthesize lots of industrially valuable chemicals. In this study, we firstly investigated the effects of cell, substrate and product concentrations on biosynthesis of 3-hydroxypropionic acid from 1,3-propanediol by Gluconobacter oxydans ZJB09112 in 50-mL shake flask containing 10 mL transformation liquid. To avoid the inhibition of substrate and product, we adopted fed-batch biotransformation and fed-batch biotransformation coupled with in situ product removal in 2-L bubble column reactor containing 1 L transformation liquid. The results show that high concentrations of substrate and product could inhibit the biotransformation by decreasing the initial reaction rate, and the optimal reaction conditions were as follows: cell concentration 6 g/L, pH 5.5. Fed-batch biotransformation in which the substrate concentration was maintained at 15-20 g/L could obtain product concentration of 60.8 g/L after 60 h, which gave a productivity of 1.0 g/(Lh) and a yield of 84.3%. Furthermore, fed-batch biotransformation coupled with in situ product removal could achieve the total product concentration of 76.3 g/L after 50 h, which gave a productivity of 1.5 g/(L x h) and a yield of 83.7%. The results obtained here may be useful for the application of G. oxydans in biocatalysis industry by using its characteristic of incomplete oxidation of alcohols.

Progress in metabolic engineering of microbial production of 1,3-dihydroxyacetone / 生物工程学报

1,3-Dihydroxyacetone is widely used in cosmetics, medicines and food products. We reviewed the recent progress in metabolic pathways, key enzymes, as well as metabolic engineering for microbial production of 1,3-dihydroxyacetone. We addressed the research trend to increase yield of 1,3-dihydroxyacetone by improving the activity of glycerol dehydrogenase with genetic engineering, and regulating of fermentation process based on metabolic characteristic of the strain.

Advance in dihydroxyacetone production by microbial fermentation / 生物工程学报

We reviewed the fermentation for dihydroxyacetone production. Microbial fermentation is better for dihydroxyacetone production as compared to chemical methods. Gluconobacter oxydans was recognized as the most important strain for industrial production of dihydroxyacetone. The dihydroxyacetone yield is associated with many factors such as substrate, product, oxygen and biomass concentration. Repeated fed-batch fermentation and immobilization fermentation were recognized as the most potential process in various fermentation mode. Construction of recombinant microorganism and optimization of process are future directions of dihydroxyacetone production.

Purification of L-sorbose/L-sorbosne dehydrogenase from Ketogulonigenium vulgare and construction and selection of genomic library / 生物工程学报

L-sorbose/L-sorbosone dehydrogenase from Ketogulonigenium vulgare S2 can transform L-sorbose to 2-KLG, which is widely used in production of Vitamin C. In order to obtain the engineering strain producing L-sorbose/L-sorbosone dehydrogenase and simplify the fermentation technology, firstly, this enzyme was purified by the methods of ammonium sulfate precipitation, DEAE Sepharose Fast Flow and Q Sepharose High Performance. Then, the purified L-sorbose/L-sorbosone dehydrogenase was injected to rabbit to obtain antibody. Next, the genomic library of Ketogulonigenium vulgare S2 was constructed by inserting the restriction fragments of chromatosomal DNA digested with Sau3A I into cosmid pKC505 vector digested by Hpa I and Pst I, which were packed with lamda phage package protein and transferred into E. coli DH5alpha in vitro. Finally, the positive strain K719# was selected from more than 12,000 clones via Dot-ELISA. Through the test of SDS-PAGE and thin layer chromatography, the results showed that the engineering strain K719# had the same biological activity as Ketogulonigenium vulgare S2 after adding coenzyme PQQ.