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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.

The genus Izhakiella was established and designated as a member of the family Enterobacteriaceae in 2016. Although the taxonomical classification of most members in this family has been relatively resolved after two reclassifications in 2016 and 2017, the classification of the genus Izhakiella remains ambiguous. In this study, a polyphasic approach was used to provide evidence supporting the fact that the genus Izhakiella should no longer be considered a member of Enterobacteriaceae and proposes its reclassification into the family Erwiniaceae . The phylogenetic tree of type species in the families Enterobacteriaceae and Erwiniaceae based on the sequences of the 16S rRNA gene, rpoB housekeeping gene, and the whole-genome comprising the 92 core genes revealed that the genus Izhakiella forms a phylogenetic lineage within the family Erwiniaceae . The average nucleotide identity (ANI) value of the type species with genus Izhakiella was found to be higher for the family Erwiniaceae than that for the family Enterobacteriaceae . Notably, 12 conserved signature indels (CSIs) that are exclusively shared among the Erwiniaceae clade members were found in the type strains of the genus Izhakiella . Based on these analyses, this study suggests the reclassification of I. capsodis and I. australiensis into the family Erwiniaceae .

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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 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 Bacillus subtilis CS13 was previously isolated for 2,3-butanediol (2,3-BD) and poly-γ-glutamic acid (γ-PGA) co-production. When culturing this strain without L-glutamic acid in the medium, 2,3-BD is the main metabolic product. 2,3-BD is an important substance and fuel with applications in the chemical, food, and pharmaceutical industries. However, the yield and productivity for the B. subtilis strain should be improved for more efficient production of 2,3-BD. Results The medium composition, which contained 281.1 g/L sucrose, 21.9 g/L ammonium citrate, and 3.6 g/L MgSO4·7H2O, was optimized by response surface methodology for 2,3-BD production using B. subtilis CS13. The maximum amount of 2,3-BD (125.5 ± 3.1 g/L) was obtained from the optimized medium after 96 h. The highest concentration and productivity of 2,3-BD were achieved simultaneously at an agitation speed of 500 rpm and aeration rate of 2 L/min in the batch cultures. A total of 132.4 ± 4.4 g/L 2,3-BD was obtained with a productivity of 2.45 ± 0.08 g/L/h and yield of 0.45 g2,3-BD/gsucrose by fed-batch fermentation. The meso-2,3-BD/2,3-BD ratio of the 2,3-BD produced by B. subtilis CS13 was 92.1%. Furthermore, 89.6 ± 2.8 g/L 2,3-BD with a productivity of 2.13 ± 0.07 g/L/h and yield of 0.42 g2,3-BD/gsugar was achieved using molasses as a carbon source. Conclusions The production of 2,3-BD by B. subtilis CS13 showed a higher concentration, productivity, and yield compared to the reported generally recognized as safe 2,3-BD producers. These results suggest that B. subtilis CS13 is a promising strain for industrial-scale production of 2,3-BD.

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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