The glucose oxidation pathway is important for glucose catabolism in Klebsiella pneumoniae. Gluconic acid and 2-ketogluconic acid are intermediates of this pathway, and the production of these two chemicals has been developed in K. pneumoniae mutants. Catalysis characteristic research in this study has shown that xylose is a suitable substrate of the glucose dehydrogenase of this pathway. Here, using xylose as substrate, xylonic acid was accumulated in the broth of K. pneumoniae culture, and this process was dependent upon acidic conditions. Using a mixture of glucose and xylose as substrates, a mixture of xylonic acid and gluconic acid was produced by the Δgad mutant of K. pneumoniae; gluconic acid was synthesized early, and xylonic acid synthesis began after most glucose was consumed. Using the hydrolysate of bamboo as substrate, mixture of 33 g/L gluconic acid and 14 g/L xylonic acid were produced by K. pneumoniae Δgad. In fed-batch fermentation, 103 g/L xylonic acid was produced after 79 h culture, with a conversion ratio of 1.11 g/g. This is the first report of xylonic acid produced by K. pneumoniae. Production of xylonic acid and gluconic acid using bamboo hydrolysate is a novel approach for biomass utilization.

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Background: 1,3-propanediol (1,3-PDO) is the most widely studied value-added product that can be produced by feeding glycerol to bacteria, including Lactobacillus sp. However, previous research reported that L. reuteri only produced small amounts and had low productivity of 1,3-PDO. It is urgent to develop procedures that improve the production and productivity of 1,3-PDO. Results:We identified a novel L. reuteri CH53 isolate that efficiently converted glycerol into 1,3-PDO, and performed batch co-fermentation with glycerol and glucose to evaluate its production of 1,3-PDO and other products. We optimized the fermentation conditions and nitrogen sources to increase the productivity. Fed-batch fermentation using corn steep liquor (CSL) as a replacement for beef extract led to 1,3-PDO production (68.32 ± 0.84 g/L) and productivity (1.27 ± 0.02 g/L/h) at optimized conditions (unaerated and 100 rpm). When CSL was used as an alternative nitrogen source, the activity of the vitamin B12-dependent glycerol dehydratase (dhaB) and 1,3-propanediol oxidoreductase (dhaT) increased. Also, the productivity and yield of 1,3-PDO increased as well. These results showed the highest productivity in Lactobacillus species. In addition, hurdle to 1,3-PDO production in this strain were identified via analysis of the half-maximal inhibitory concentration for growth (IC50) of numerous substrates and metabolites. Conclusions:We used CSL as a low-cost nitrogen source to replace beef extract for 1,3-PDO production in L. reuteri CH53. These cells efficiently utilized crude glycerol and CSL to produce 1,3-PDO. This strain has great promise for the production of 1,3-PDO because it is generally recognized as safe (GRAS) and non-pathogenic. Also, this strain has high productivity and high conversion yield.

Klebsiella pneumoniae produces many economically important chemicals. Using glucose as a carbon source, the main metabolic product in K. pneumoniae is 2,3-butanediol. Gluconic acid is an intermediate of the glucose oxidation pathway. In the current study, a metabolic engineering strategy was used to develop a gluconic acid-producing K. pneumoniae strain. Deletion of gad, resulting in loss of gluconate dehydrogenase activity, led to the accumulation of gluconic acid in the culture broth. Gluconic acid accumulation by K. pneumoniae Δgad was an acid-dependent aerobic process, with accumulation observed at pH 5.5 or lower, and at higher levels of oxygen supplementation. Under all other conditions tested, 2,3-butanediol was the main metabolic product of the process. In fed batch fermentation, a final concentration of 422 g/L gluconic acid was produced by K. pneumoniae Δgad, and the conversion ratio of glucose to gluconic acid reached 1 g/g. The K. pneumoniae Δgad described in this study is the first genetically modified strain used for gluconic acid production, and this optimized method for gluconic acid production may have important industrial applications. Gluconic acid is an intermediate of this glucose oxidation pathway. Deletion of gad, resulting in loss of gluconate dehydrogenase activity, led to the accumulation of gluconic acid in the culture broth. In fed batch fermentation, a final concentration of 422 g/L gluconic acid was produced by the K. pneumoniae Δgad strain, and the conversion ratio of glucose to gluconic acid reached 1 g/g.

Background: Bacillus subtilis naturally produces large amounts of 2,3-butanediol (2,3-BD) as the main byproduct during poly-γ-glutamic acid (γ-PGA) fermentation using carbon sources. 2,3-BD is a promising platform chemicals in various industries, and co-production has great economic benefits. Thus, co-production of poly-γ-glutamic acid (γ-PGA) and 2,3-butanediol (2,3-BD) by Bacillus subtilis were investigated for the first time. Results: In this study, a novel Bacillus subtilis CS13 was isolated that can efficiently co-production of γ-PGA and 2,3-BD. The fermentation medium and culture parameters by B. subtilis CS13 were optimized using statistical methods. It was observed that sucrose, L-glutamic acid, ammonium citrate, and MgSO 4 •7H 2 O were favorable for γ-PGA and 2,3-BD co-production at pH 6.5 and 37 °C. A medium composed of 119.83 g/L sucrose, 48.85 g/L L-glutamic acid, 21.08 g/L ammonium citrate, and 3.21 g/L MgSO 4 •7H 2 O was optimized by response surface methodology (RSM). The results show that the yields of γ-PGA and 2,3-BD reached 27.79 ± 0.87 g/L at 24 h and 57.05 ± 1.28 g/L at 84 h with the optimized medium, respectively. Conclusions: To our knowledge, the co-production of 2,3-BD and γ-PGA will reduce the costs of production and separation in theory and provide a new perspective for industrial production of γ-PGA and 2,3-BD. B. subtilis CS13 as a generally recognized as safe (GRAS) strain, has great promise for the co-production of 2,3-BD and γ-PGA.

Background: Poly-γ-glutamic acid (γ-PGA) is a promising biopolymer and has been applied in many fields. Bacillus siamensis SB1001 was a newly isolated poly-γ-glutamic acid producer with sucrose as its optimal carbon source. To improve the utilization of carbon source, and then molasses can be effectively used for γ-PGA production, 60 cobalt gamma rays was used to mutate the genes of B. siamensis SB1001. Results: Bacillus siamensis IR10 was screened for the production of γ-PGA from untreated molasses. In batch fermentation, 17.86 ± 0.97 g/L γ-PGA was obtained after 15 h, which is 52.51% higher than that of its parent strain. Fed-batch fermentation was performed to further improve the yield of γ-PGA with untreated molasses, yielding 41.40 ± 2.01 g/L of γ-PGA with a productivity of 1.73 ± 0.08 g/L/h. An average γ-PGA productivity of 1.85 g/L/h was achieved in the repeated fed-batch fermentation. This is the first report of such a high γ-PGA productivity. The analysis of the enzyme activities showed that they were affected by the carbon sources, enhanced ICDH and GDH, and decreased ODHC, which are important for γ-PGA production. Conclusion: These results suggest that untreated molasses can be used for economical and industrial-scale production of γ-PGA by B. siamensis IR10.

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Background: Bacillus subtilis naturally produces large amounts of 2,3-butanediol (2,3-BD) as the main byproduct during poly-γ-glutamic acid (γ-PGA) fermentation using carbon sources. 2,3-BD is a promising platform chemicals in various industries, and co-production has great economic benefits. Thus, co-production of poly-γ-glutamic acid (γ-PGA) and 2,3-butanediol (2,3-BD) by Bacillus subtilis were investigated for the first time. Results: In this study, a novel Bacillus subtilis CS13 was isolated that can efficiently co-production of γ-PGA and 2,3-BD. The fermentation medium and culture parameters by B. subtilis CS13 were optimized using statistical methods. It was observed that sucrose, L-glutamic acid, ammonium citrate, and MgSO4·7H2O were favorable for γ-PGA and 2,3-BD co-production at pH 6.5 and 37 °C. A medium composed of 119.83 g/L sucrose, 48.85 g/L L-glutamic acid, 21.08 g/L ammonium citrate, and 3.21 g/L MgSO4·7H2O was optimized by response surface methodology (RSM). The results show that the yields of γ-PGA and 2,3-BD reached 27.79 ± 0.87 g/L at 24 h and 57.05 ± 1.28 g/L at 84 h with the optimized medium, respectively. Conclusions: To our knowledge, the co-production of 2,3-BD and γ-PGA will reduce the costs of production and separation in theory and provide a new perspective for industrial production of γ-PGA and 2,3-BD. B. subtilis CS13 as a generally recognized as safe (GRAS) strain, has great promise for the co-production of 2,3-BD and γ-PGA.