Model-based driving mechanism analysis for butyric acid production in Clostridium tyrobutyricum

Metabolic Engineering of Clostridium tyrobutyricum for High-Yield n-Butanol Production by Increasing Intracellular Reducing Equivalent with NADPH-Dependent 3-Hydroxybutyryl-CoA Dehydrogenase

Clostridium tyrobutyricum was engineered to overexpress adhE2 encoding the aldehyde/alcohol dehydrogenase and an exogenous NADPH-dependent 3-hydroxybutyryl-CoA dehydrogenase from Clostridium kluyveri (Ckhbd) for n-butanol production. In general, large amounts of butyrate, acetate, and ethanol are also produced from glucose when butanol biosynthesis is hindered by limited intracellular NADH pools. In silico flux balance analysis showed that coupling NADP+/NADPH turnover with butanol production increased the reducing equivalent supply and butanol selectivity over ethanol and acids, thus increasing butanol production from glucose. This was verified with the coexpression of Ckhbd and adhE2 in C. tyrobutyricum wild type (WT), Ack, ΔhydA, and Δcat1 strains. Except for the Δcat1 strains, strains coexpressing Ckhbd showed significant (>5%) increase in reducing equivalents, 50-60% increase in butanol production (butanol yield: 0.24-0.28 vs. 0.15-0.18 g/g), and 2.5- to 4.5-fold increases in butanol/ethanol and alcohols/acids ratios due to increased flux from acetyl-CoA to butyryl-CoA and reducing equivalents compared to the strains expressing only adhE2. In the presence of methyl viologen, the strain Ack-adhE2-Ckhbd produced the highest butanol yield of 0.36 g/g, ∼88% of the theoretical yield from glucose, which was among the highest yields reported for known solventogenic clostridia.

Systems Metabolic Engineering of Clostridium tyrobutyricum for 1,3-Propanediol Production From Crude Glycerol

Clostridium tyrobutyricum has emerged as a non-pathogenic microbial cell factory capable of anaerobic production of various value-added products, such as butyrate, butanol, and butyl butyrate. This study reports the first systematic engineering of C. tyrobutyricum for the heterologous production of 1,3-propanediol (1,3-PDO) from industrial by-product crude glycerol. Initially, the glycerol reductive pathway for 1,3-PDO production was constructed, and the unique glycerol oxidation pathway in C. tyrobutyricum was elucidated. Subsequently, the glycerol metabolism and 1,3-PDO synthesis pathways were enhanced. Furthermore, the intracellular reducing power supply and the fermentation process were optimized to improve 1,3-PDO production. Consequently, 54.06 g/L 1,3-PDO with a yield of 0.64 mol/mol and a productivity of 1.13 g/L·h was obtained using crude glycerol and fish meal. The strategies described herein could facilitate the engineering of C. tyrobutyricum as a robust host for synthesizing valuable chemicals.

Effect of calf separation on gut microbiome and fecal metabolome of mother in the captive Yangtze finless porpoise (Neophocaena asiaeorientalis asiaeorientalis)

Social separation, or the absence of social support, can cause physical and psychological health issues. Social separation is crucial for the welfare of the Yangtze finless porpoise (YFP) in captivity because they face many challenges like frequent social separation, noise from visitors, and animal replacement, which can cause psychological and physiological stress. This research is aimed at assessing the potential negative impacts of social separation on the gut microbiome and metabolome of captive YFP, focusing on the potential imbalances caused by mother-calf separation. The study found that social separation did not alter the alpha and beta diversity of the gut microbes but increased the abundance of disease-associated taxa such as Romboutsia, Terrisporobacter, and Clostridium_sensu_stricto_13 in the MC (mother-calf) group while increasing Paeniclostridium and Clostridium_sensu_stricto_1 associated with host health in the MS (mother-separated) group. The fecal metabolome underwent significant changes during social separation, with stress-associated metabolites like kainic acid, phenethylamine glucuronide, and paxilline upregulated in the MC group and host health-associated metabolites like butyric acid, 6-hydroxyhexanoic acid, and fosinopril downregulated in the MS group. In addition, there was a strong association between the fecal microbiome and the metabolome of captive YFPs. The study enhances our comprehension of the detrimental effects of social separation, which result in disruptions in the gut microbiome and fecal metabolome. The study is aimed at introducing a new method for assessing the health and welfare of endangered mammals in captivity.

Feedstock variability impacts the bioconversion of sugar and lignin streams derived from corn stover by Clostridium tyrobutyricum and engineered Pseudomonas putida

Feedstock variability represents a challenge in lignocellulosic biorefineries, as it can influence both lignocellulose deconstruction and microbial conversion processes for biofuels and biochemicals production. The impact of feedstock variability on microbial performance remains underexplored, and predictive tools for microbial behaviour are needed to mitigate risks in biorefinery scale-up. Here, twelve batches of corn stover were deconstructed via deacetylation, mechanical refining, and enzymatic hydrolysis to generate lignin-rich and sugar streams. These batches and their derived streams were characterised to identify their chemical components, and the streams were used as substrates for producing muconate and butyrate by engineered Pseudomonas putida and wildtype Clostridium tyrobutyricum, respectively. Bacterial performance (growth, product titers, yields, and productivities) differed among the batches, but no strong correlations were identified between feedstock composition and performance. To provide metabolic insights into the origin of these differences, we evaluated the effect of twenty-three isolated chemical components on these microbes, including three components in relevant bioprocess settings in bioreactors, and we found that growth-inhibitory concentrations were outside the ranges observed in the streams. Overall, this study generates a foundational dataset on P. putida and C. tyrobutyricum performance to enable future predictive models and underscores their resilience in effectively converting fluctuating lignocellulose-derived streams into bioproducts.

Development of inducible promoters for regulating gene expression in Clostridium tyrobutyricum for biobutanol production

Clostridium tyrobutyricum is an anaerobe known for its ability to produce short-chain fatty acids, alcohols, and esters. We aimed to develop inducible promoters for fine-tuning gene expression in C. tyrobutyricum. Synthetic inducible promoters were created by employing an Escherichia coli lac operator to regulate the thiolase promoter (PCathl) from Clostridium acetobutylicum, with the best one (LacI-Pto4s) showing a 5.86-fold dynamic range with isopropyl β- d-thiogalactoside (IPTG) induction. A LT-Pt7 system with a dynamic range of 11.6-fold was then created by combining LacI-Pto4s with a T7 expression system composing of RNA polymerase (T7RNAP) and Pt7lac promoter. Furthermore, two inducible expression systems BgaR-PbgaLA and BgaR-PbgaLB with a dynamic range of ~40-fold were developed by optimizing a lactose-inducible expression system from Clostridium perfringens with modified 5' untranslated region (5' UTR) and ribosome-binding site (RBS). BgaR-PbgaLB was then used to regulate the expressions of a bifunctional aldehyde/alcohol dehydrogenase encoded by adhE2 and butyryl-CoA/acetate Co-A transferase encoded by cat1 in C. tyrobutyricum wild type and Δcat1::adhE2, respectively, demonstrating its efficient inducible gene regulation. The regulated cat1 expression also confirmed that the Cat1-catalyzed reaction was responsible for acetate assimilation in C. tyrobutyricum. The inducible promoters offer new tools for tuning gene expression in C. tyrobutyricum for industrial applications.

Butyric acid and prospects for creation of new medicines based on its derivatives: a literature review

The widespread use of antimicrobials causes antibiotic resistance in bacteria. The use of butyric acid and its derivatives is an alternative tactic. This review summarizes the literature on the role of butyric acid in the body and provides further prospects for the clinical use of its derivatives and delivery methods to the animal body. Thus far, there is evidence confirming the vital role of butyric acid in the body and the effectiveness of its derivatives when used as animal medicines and growth stimulants. Butyric acid salts stimulate immunomodulatory activity by reducing microbial colonization of the intestine and suppressing inflammation. Extraintestinal effects occur against the background of hemoglobinopathy, hypercholesterolemia, insulin resistance, and cerebral ischemia. Butyric acid derivatives inhibit histone deacetylase. Aberrant histone deacetylase activity is associated with the development of certain types of cancer in humans. Feed additives containing butyric acid salts or tributyrin are used widely in animal husbandry. They improve the functional status of the intestine and accelerate animal growth and development. On the other hand, high concentrations of butyric acid stimulate the apoptosis of epithelial cells and disrupt the intestinal barrier function. This review highlights the biological activity and the mechanism of action of butyric acid, its salts, and esters, revealing their role in the treatment of various animal and human diseases. This paper also discussed the possibility of using butyric acid and its derivatives as surface modifiers of enterosorbents to obtain new drugs with bifunctional action.

Enhancing and monitoring spore production in Clostridium butyricum using pH-based regulation strategy and a robust soft sensor based on back-propagation neural networks

Clostridium butyricum is a probiotic that forms anaerobic spores and plays a crucial role in regulating gut microbiota. However, the total viable cell count and spore yield of C. butyricum in industrial production are comparatively low. To this end, we investigated the metabolic characteristics of the strain and proposed three distinct pH regulation strategies for enhancing spore production. In addition, precise measurement of fermentation parameters such as substrate concentration, total viable cell count, and spore concentration is crucial for successful industrial probiotics production. Nevertheless, online measurement of these intricate parameters in the fermentation of C. butyricum poses a considerable challenge owing to the complex, nonlinear, multivariate, and strongly coupled characteristics of the production process. Therefore, we analyzed the capacitance and conductivity acquired from a viable cell sensor as the core parameters for the fermentation process. Subsequently, a robust soft sensor was developed using a seven-input back-propagation neural network model with input variables of fermentation time, capacitance, conductivity, pH, initial total sugar concentration, ammonium ion concentration, and calcium ion concentration. The model enables the online monitoring of total viable biomass count, substrate concentrations, and spore yield, and can be extended to similar fermentation processes with pH changes as a characteristic feature.

Construction of a Microbial Consortium for the De Novo Synthesis of Butyl Butyrate from Renewable Resources

Butyl butyrate has shown wide applications in food, cosmetic, and biofuel sectors. Currently, biosynthesis of butyl butyrate still requires exogenous addition of precursors and lipase, which increases the production cost and limits further large-scale development. In this study, a microbial consortium was first designed to realize direct butyl butyrate production from lignocellulose. The highest butyl butyrate concentration of 34.42 g/L was detected in the solvent phase from 60 g/L glucose using a microbial coculture system composed of Clostridium acetobutylicum NJ4 and Clostridium tyrobutyricum LD with the elimination of butyric acid supplementation. Meanwhile, 13.52 g/L butyl butyrate was synthesized from 60 g/L glucose using a microbial consortium composed of three strains including strain NJ4, strain LD, and Escherichia coli BL21- pET-29a(+)-LE without the addition of any exogenous precursors and lipase. In addition, 2.94 g/L butyl butyrate could be directly produced from 60 g/L microcrystalline cellulose when Trichoderma asperellum was added to the above-mentioned three-strain microbial consortium. This four-strain microbial consortium represents the first study regarding the direct butyl butyrate production from lignocellulose without the supplementation of exogenous precursors and lipase, which may be extended to the biosynthesis of other short-chain esters, such as ethyl acetate and butyl lactate.