Development of a semi-continuous two-stage simultaneous saccharification and fermentation process for enhanced 2,3-butanediol production by Klebsiella oxytoca

Microbial Succession and Interactions During the Manufacture of Fu Brick Tea

Fu Brick tea is a very popular post-fermented tea that is known for its "golden flower fungus," Aspergillus cristatus, which becomes the dominant microbe during the maturation process. This study used both culture-dependent methods and high-throughput sequencing to track microbial succession and interactions during the development of the golden flower fungus, a crucial component of the manufacturing process of Fu Brick tea. Among the bacterial communities, Klebsiella and Lactobacillus were consistently cultured from both fresh tea leaves and in post-fermentation Fu Brick tea. Methylobacterium, Pelomonas, and Sphingomonas were dominant genera in fresh tea leaves but declined once fermentation started, while Bacillus, Kluyvera, and Paenibacillus became dominant after piling fermentation. The abundance of A. cristatus increased during the manufacturing process, accounting for over 98% of all fungi present after the golden flower bloom in the Fu Brick tea product. Despite their consistent presence during culture work, network analysis showed Lactobacillus and Klebsiella to be negatively correlated with A. cristatus. Bacillus spp., as expected from culture work, positively correlated with the presence of golden flower fungus. This study provides complete insights about the succession of microbial communities and highlights the importance of co-occurrence microbes with A. cristatus during the manufacturing process of Fu Brick tea.

Efficient 2,3-butanediol production from whey powder using metabolically engineered Klebsiella oxytoca

BACKGROUND

Whey is a major pollutant generated by the dairy industry. To decrease environmental pollution caused by the industrial release of whey, new prospects for its utilization need to be urgently explored. Here, we investigated the possibility of using whey powder to produce 2,3-butanediol (BDO), an important platform chemical.

RESULTS

Klebsiella oxytoca strain PDL-0 was selected because of its ability to efficiently produce BDO from lactose, the major fermentable sugar in whey. After deleting genes pox, pta, frdA, ldhD, and pflB responding for the production of by-products acetate, succinate, lactate, and formate, a recombinant strain K. oxytoca PDL-K5 was constructed. Fed-batch fermentation using K. oxytoca PDL-K5 produced 74.9 g/L BDO with a productivity of 2.27 g/L/h and a yield of 0.43 g/g from lactose. In addition, when whey powder was used as the substrate, 65.5 g/L BDO was produced within 24 h with a productivity of 2.73 g/L/h and a yield of 0.44 g/g.

CONCLUSION

This study demonstrated the efficiency of K. oxytoca PDL-0 for BDO production from whey. Due to its non-pathogenicity and efficient lactose utilization, K. oxytoca PDL-0 might also be used in the production of other important chemicals using whey as the substrate.

The current strategies and parameters for the enhanced microbial production of 2,3-butanediol

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2,3-Butanediol (2,3-BD) is a propitious compound with many industrial uses.

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2,3-BD production has always been hampered by low fermentation yields and high production costs.

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2,3-BD production may be enhanced by optimization of culture conditions and use of high-producing strains.

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TMetabolic engineering tools are currently used to generate high-yielding strains.

2,3-Butanediol (2,3-BD) is a propitious compound with many industrial uses ranging from rubber, fuels, and cosmetics to food additives. Its microbial production has especially attracted as an alternative way to the petroleum-based production. However, 2,3-BD production has always been hampered by low yields and high production costs. The enhanced production of 2,3-butanediol requires screening of the best strains and a systematic optimization of fermentation conditions. Moreover, the metabolic pathway engineering is essential to achieve the best results and minimize the production costs by rendering the strains to use efficiently low cost substrates. This review is to provide up-to-date information on the current strategies and parameters for the enhanced microbial production of 2,3-BD.

Simultaneous saccharification and fermentation of oil palm front for the production of 2,3-butanediol

The present study aims to develop a process for the production of 2,3-butanediol by Simultaneous Saccharification and Fermentation (SSF) of Oil Palm Front (OPF) biomass. The study compares SSF with Separate Hydrolysis and Fermentation (SHF) of oil palm biomass and batch fermentation using glucose. The results showed that SSF is one of the most attractive techniques for the microbial production of 2,3-butanediol using lignocellulosic biomass. The enzymatic digestibility and fermentative efficiency of alkali pre-treated OPF biomass was checked and the role of various experimental parameters like enzyme loading and inoculum loading were optimized. SSF experiments could give 30.74 g/l of BDO in shake flask and 12.53 g/l in 500 ml bioreactor with a productivity of 0.32 and 0.13 g/l/h respectively.

Production of 2,3-butanediol from glucose and cassava hydrolysates by metabolically engineered industrial polyploid Saccharomyces cerevisiae

BACKGROUND

2,3-Butanediol (2,3-BDO) is a valuable chemical for industrial applications. Bacteria can produce 2,3-BDO with a high productivity, though most of their classification as pathogens makes them undesirable for the industrial-scale production. Though Saccharomyces cerevisiae (GRAS microorganism) was engineered to produce 2,3-BDO efficiently in the previous studies, their 2,3-BDO productivity, yield, and titer were still uncompetitive compared to those of bacteria production. Thus, we propose an industrial polyploid S. cerevisiae as a host for efficient production of 2,3-BDO with high growth rate, rapid sugar consumption rate, and resistance to harsh conditions. Genetic manipulation tools for polyploid yeast had been limited; therefore, we engineered an industrial polyploid S. cerevisiae strain based on the CRISPR-Cas9 genome-editing system to produce 2,3-BDO instead of ethanol.

RESULTS

Endogenous genes coding for pyruvate decarboxylase and alcohol dehydrogenase were partially disrupted to prevent declined growth rate and C₂-compound limitation. A bacterial 2,3-BDO-producing pathway was also introduced in engineered polyploid S. cerevisiae. A fatal redox imbalance was controlled through the heterologous NADH oxidase from Lactococcus lactis during the 2,3-BDO production. The resulting strain (YG01_SDBN) still retained the beneficial traits as polyploid strains for the large-scale fermentation. The combination of partially disrupted PDC (pyruvate decarboxylase) and ADH (alcohol dehydrogenase) did not cause the severe growth defects typically found in all pdc- or adh-deficient yeast. The YG01_SDBN strain produced 178 g/L of 2,3-BDO from glucose with an impressive productivity (2.64 g/L h). When a cassava hydrolysate was used as a sole carbon source, this strain produced 132 g/L of 2,3-BDO with a productivity of 1.92 g/L h.

CONCLUSIONS

The microbial production of 2,3-BDO has been limited to bacteria and haploid laboratorial S. cerevisiae strains. This study suggests that an industrial polyploid S. cerevisiae (YG01_SDBN) can produce high concentration of 2,3-BDO with various advantages. Integration of metabolic engineering of the industrial yeast at the gene level with optimization of fed-batch fermentation at the process scale resulted in a remarkable achievement of 2,3-BDO production at 178 g/L of 2,3-BDO concentration and 2.64 g/L h of productivity. Furthermore, this strain could make a bioconversion of a cassava hydrolysate to 2,3-BDO with economic and environmental benefits. The engineered industrial polyploid strain could be applicable to production of biofuels and biochemicals in large-scale fermentations particularly when using modified CRISPR-Cas9 tools.