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Clostridium butyricum is an anaerobic bacterium that inhabits broad niches. Clostridium butyricum is known for its production of butyrate, 1,3-propanediol, and hydrogen. This study aimed to present a comparative pangenome analysis of 24 strains isolated from different niches. We sequenced and annotated the genome of C. butyricum 3-3 isolated from the Chinese baijiu ecosystem. The pangenome of C. butyricum was open. The core genome, accessory genome, and strain-specific genes comprised 1011, 4543, and 1473 genes, respectively. In the core genome, Carbohydrate metabolism was the largest category, and genes in the biosynthetic pathway of butyrate and glycerol metabolism were conserved (in the core or soft-core genome). Furthermore, the 1,3-propanediol operon existed in 20 strains. In the accessory genome, numerous mobile genetic elements belonging to the Replication, recombination, and repair (L) category were identified. In addition, genome islands were identified in all 24 strains, ranging from 2 (strain KNU-L09) to 53 (strain SU1), and phage sequences were found in 17 of the 24 strains. This study provides an important genomic framework that could pave the way for the exploration of C. butyricum and future studies on the genetic diversification of C. butyricum.

Clostridium spp. are important microorganisms that can degrade complex biomasses such as lignocellulose, which is a widespread and renewable natural resource. Co-culturing Clostridium spp. and other microorganisms is considered to be a promising strategy for utilizing renewable feed stocks and has been widely used in biotechnology to produce bio-fuels and bio-solvents. In this review, we summarize recent progress on the Clostridium co-culture system, including system unique advantages, composition, products, and interaction mechanisms. In addition, biochemical regulation and genetic modifications used to improve the Clostridium co-culture system are also summarized. Finally, future prospects for Clostridium co-culture systems are discussed in light of recent progress, challenges, and trends.

Clostridium kluyveri is an anaerobic microorganism that is well-known for producing butyrate and hexanoate using ethanol and acetate. It is also an important bacterium in the production of Chinese strong flavour baijiu (SFB). To obtain a comprehensive understanding of its metabolism, a curated genome-scale metabolic model (GSMM) of C. kluyveri, including 708 genes, 994 reactions, and 804 metabolites, was constructed and named iCKL708. This model was used to simulate the growth of C. kluyveri on different carbon substrates and the results agreed well with the experimental data. The butyrate, pentanoate, and hexanoate biosynthesis pathways were also elucidated. Flux balance analysis indicated that the ratio of ethanol to acetate, as well as the uptake rate of carbon dioxide, affected hexanoate production. The GSMM iCKL708 described here provides a platform to further our understanding and exploration of the metabolic potential of C. kluyveri.

2,3-Butanediol (2,3-BD) is widely used in several chemical syntheses as well as the manufacture of plastics, solvents, and antifreeze formulations, and can be manufactured by microbial glucose fermentation. Conventional (2,3-BD) fermentation typically has low productivity, yield, and purity, and is expensive for commercial applications. We aimed to delete the lactate dehydrogenase and acetate kinase (ldhA and ack) genes in Klebsiella pneumoniae HD79 by using λRed homologous recombination technology, to eliminate by-products and thereby improve (2,3-BD) production. We also analyzed the resulting gene changes by using transcriptomics. The yield of (2,3-BD) from the mutant Klebsiella strain was 46.21 g/L, the conversion rate was 0.47 g/g, and the productivity was 0.64 g/L·h, which represented increases of 54.9%, 20.5%, and 106.5% respectively, compared to (WT) strains. Lactate and acetate decreased by 48.2% and 62.8%, respectively. Transcriptomics analysis showed that 4628 genes were differentially expressed (404 significantly up-regulated and 162 significantly down-regulated). Moreover, the (2,3-BD) operon genes were differentially expressed. Our data showed that the biosynthesis of (2,3-BD) was regulated by inducers (lactate and acetate), a regulator (BudR), and carbon flux. Elimination of acidic by-products by ldhA and ack knockdown significantly improved (2,3-BD) production. Our results provide a deeper understanding of the mechanisms underlying (2,3-BD) production, and form a molecular basis for the improvement this process by genetic modification in the future.

Strain Bacillus amyloliquefaciens BH1 was evaluated for the generation of α-amylase. Culture conditions and medium components were optimized by a statistical approach for the optimal generation of α-amylase with response surface methodology (RSM) method. The Plackett-Burman (PB) design was executed to select the fermentation variables and Central composite design (CCD) for optimizing significant factors influencing production. The optimum levels for highest generation of α-amylase activity (198.26 ± 3.54 U/mL) were measured. A 1.69-fold improve generation was acquired in comparison with the non-optimized. Partial characterization of the α-amylase indicated optimal pH and temperature at 7.0 and 40 °C, respectively. Crude α-amylase maintained a constant pH range 5.0-8.0 and 30-70 °C. The α-amylase was independent of Ca