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Acids play a crucial role in enhancing the flavor of strong-aroma Baijiu, and among them, caproic acid holds significant importance in determining the flavor of the final product. However, the metabolic synthesis of caproic acid during the production process of Baijiu has received limited attention, resulting in fluctuations in caproic acid content among fermentation batches and generating production instability. Acid-producing bacteria found in the cellar mud are the primary microorganisms responsible for caproic acid synthesis, but there is a lack of research on the related microbial resources and their metabolic properties. Therefore, it is essential to identify and investigate these acid-producing microorganisms from cellar mud to ensure stable caproic acid synthesis. In this study, a unique strain was isolated from the cellar mud, exhibiting a 98.12 % similarity in its 16 S rRNA sequence and an average nucleotide identity of 79.57 % with the reference specie, together with the DNA-DNA hybridization of 23.20 % similarity, confirming the distinct species boundaries. The strain was able to produce 1.22 ± 0.55 g/L caproic acid from glucose. Through genome sequencing, annotation, and bioinformatics analysis, the complete pathway of caproic acid synthesis from glucose was elucidated, and the catalytic mechanism of the key thiolase for caproic acid synthesis was investigated. These findings provide useful fundamental data for revealing the metabolic properties of caproic acid-producing bacteria found in cellar mud. • A potential new species is isolated from cellar mud of Baijiu. • The species could produce caproic acid from glucose. • The possible key thiolase for caproic acid production is identified. • The work offers a valuable strain for producing caproic acid in Baijiu fermentation. [ABSTRACT FROM AUTHOR]

Abstract Although addition of pyrolyzed organic materials (biochars) to soil generally results in increased growth and physiological performance of plants, neutral and negative responses have also commonly been detected. Toxicity of organic compounds generated during pyrolysis, sorbed by biochars, and then released into the soil solution, has been implicated as a possible mechanism for such negative effects. Conversely, water-soluble biochar constituents have also been suggested to have “hormetic” effects (positive effects on plants at low concentrations); however, no specific compounds responsible have been identified. We investigated the relative phytotoxicity—and possible hormetic effects—of 14 organic compounds common in aqueous extracts of freshly produced lignocellulosic biochars, using seed germination bioassays. Of the compounds examined, volatile fatty acids (VFAs: acetic, propionic, butyric, valeric, caproic, and 2-ethylbutyric acids) and phenol, showed acute phytotoxicity, with germination-based ED50 values of 1–30 mmol L−1, and 2-ethylbutyric acid showed ED50 values of 0.1–1.0 mmol L−1. Other compounds (benzene, benzoic acid, butanone, methyl salicylate, toluene, and 2,4-di-tert-butylphenol) showed toxic effects only at high concentrations close to solubility limits. Although phytotoxic at high concentrations, valeric and caproic acid also showed detectable hormetic effects on seedlings, increasing radicle extension by 5–15% at concentrations of ~ 0.01–0.1 mmol L−1. These data support the hypothesis that VFAs are the main agents responsible for phytotoxic effects of lignocellulosic biochar leachates, but that certain VFAs also have hormetic effects at low concentrations and may contribute to positive effects of biochar leachates on early plant development in some cases. Graphical Abstract

Although addition of pyrolyzed organic materials (biochars) to soil generally results in increased growth and physiological performance of plants, neutral and negative responses have also commonly been detected. Toxicity of organic compounds generated during pyrolysis, sorbed by biochars, and then released into the soil solution, has been implicated as a possible mechanism for such negative effects. Conversely, water-soluble biochar constituents have also been suggested to have "hormetic" effects (positive effects on plants at low concentrations); however, no specific compounds responsible have been identified. We investigated the relative phytotoxicity—and possible hormetic effects—of 14 organic compounds common in aqueous extracts of freshly produced lignocellulosic biochars, using seed germination bioassays. Of the compounds examined, volatile fatty acids (VFAs: acetic, propionic, butyric, valeric, caproic, and 2-ethylbutyric acids) and phenol, showed acute phytotoxicity, with germination-based ED50 values of 1–30 mmol L−1, and 2-ethylbutyric acid showed ED50 values of 0.1–1.0 mmol L−1. Other compounds (benzene, benzoic acid, butanone, methyl salicylate, toluene, and 2,4-di-tert-butylphenol) showed toxic effects only at high concentrations close to solubility limits. Although phytotoxic at high concentrations, valeric and caproic acid also showed detectable hormetic effects on seedlings, increasing radicle extension by 5–15% at concentrations of ~ 0.01–0.1 mmol L−1. These data support the hypothesis that VFAs are the main agents responsible for phytotoxic effects of lignocellulosic biochar leachates, but that certain VFAs also have hormetic effects at low concentrations and may contribute to positive effects of biochar leachates on early plant development in some cases. Highlights: 151 compounds were identified in leachates from 13 biochars. Among common compounds, volatile fatty acids (VFAs) and phenol showed the most pronounced phytotoxic effects. Some VFAs also had hormetic effects, enhancing radicle extension growth at low concentrations. Effects were consistent among test plant species but the smallest-seeded species showed the highest sensitivity. [ABSTRACT FROM AUTHOR]

Bioconversion of CO2 into liquid fuels or chemicals, preferred medium chain carboxylic acids (caproic and caprylic acid), is an attractive CO2 utilization technology. The present study aims to investigate the effects of different ratios of H2/CO2 on regulating the distribution of C2‐C8 carboxylic acid products, while the headspace pressure of 1.5 bar was set to amplify the effect of different ratios. The H2/CO2 ratio of 4:1 was more suitable for preparing acetic acid, where the highest acetic acid yield was 17.5 g/L. And the H2/CO2 ratio of 2:1 showed excellent chain elongation ability with the highest n‐caprylic yield of 2.4 g/L. Additionally, the actual H2/CO2 ratios of 4:1 reactors were higher than that in 2:1 may be course chain elongation often accompanied by H2 production. The 16S rRNA genes analysis shows that the genus Terrisporobacter and Coriobacteriales may be related to acetic acid production enriched in H2/CO2 ratio 4:1 reactors, and the genus Clostridium and Paenibacillaceae may associate with the chain elongation pathway were enriched in H2/CO2 ratio 2:1 reactors. [ABSTRACT FROM AUTHOR]

The potato dry rot disease caused by Fusarium spp. seriously reduces potato yield and threatens human health. However, potential biocontrol agents cannot guarantee the stability and activity of biocontrol. Here, 18 synthetic microbial communities of different scales were constructed, and the synthetic microbial communities with the best biocontrol effect on potato dry rot disease were screened through in vitro and in vivo experiments. The results show that the synthetic community composed of Paenibacillus amylolyticus, Pseudomonas putida, Acinetobacter calcoaceticus, Serratia proteamaculans, Actinomycetia bacterium and Bacillus subtilis has the best biocontrol activity. Metabolomics results show that Serratia protoamaculans interacts with other member strains to produce caproic acid and reduce the disease index to 38.01%. Furthermore, the mycelial growth inhibition after treatment with caproic acid was 77.54%, and flow cytometry analysis showed that the living conidia rate after treatment with caproic acid was 11.2%. This study provides potential value for the application of synthetic microbial communities in potatoes, as well as the interaction mechanisms between member strains of synthetic microbial communities. [ABSTRACT FROM AUTHOR]

[Objective] This work aims to elucidate the growth and caproic acid metabolism mechanism of Rummeliibacillus suwonensis from protein level, and to further improve its metabolic capacity. It provides a technical basis for the genetic engineering of R. suwonensis.[Method] The differential expression proteins(DEPs)of strain R. suwonensis 3B-1 were extracted by tandem mass tags(TMT)proteomics in aerobic and anaerobic conditions. Its subcellular localization analysis, Gene Ontology(GO)functional analysis, KEGG signaling pathway annotation analysis, and protein-protein interaction were analyzed.[Result] A total of 810 DEPs were identified, including 423 up-regulated proteins and 387 down-regulated proteins. A total of 725 DEPs were subcellular mapped to 6 items, mainly involving cytoplasmic proteins, cytoplasmic membrane proteins and cellwall proteins. GO enrichment of function analysis indicated that, biological processes such as peptide biosynthesis, translation, and peptide metabolism, molecular functions such as structural constituent and structural molecular activity of ribosomes, and cellular components such as ribosomes and ribonucleoprotein complexes have undergone significant changes. A total of 810 DEPs were annotated into 113 KEGG signaling pathways in KEGG database, which mainly were involved cofactor biosynthesis, two-component system, pentose phosphate pathway, glycolysis/gluconeogenesis and oxidative phosphorylation. The phenylalanine-tRNA ligase β subunit and the riboflavin biosynthesis protein RibD had the highest correlation in the protein interaction network.[Conclusion] Under anaerobic conditions, the expression of pyruvate dehydrogenase and pyruvate kinase in the glycolytic pathway was down-regulated. Additionally, proteins related to amino acid metabolism and biotin protein ligase cofactors were also downregulated. This indicates that the bacterium is better suited for growth in an aerobic conditions. Regarding the synthesis of caproic acid, the expression of acyl-CoA thioesterase was significantly up-regulated. In addition, the glycolysis/gluconeogenesis pathway, the tricarboxylic acid cycle and the pentose phosphate pathway provided sufficient precursors and reduction equivalents for caproic acid synthesis, which jointly promoted caproic acid synthesis. [ABSTRACT FROM AUTHOR]

The effects of hydraulic retention time (HRT) on the performance of two-phase anaerobic fermentation for caproic acid production from Chinese cabbage waste (CCW) were investigated. In the electron donor phase, yeast was inoculated to achieve efficient autopoietic ethanol, providing electron donors for the chain elongation process. Shorter HRT led to drastic fluctuations in microorganisms, thus resulting in lower acid yields at HRT of 6 days. At HRT of 10 days, the balanced collaboration of various key bacteria avoided the accumulation of intermediate by-products, and the caproic acid production reached 4660 mg COD/L, which was 119.5% and 154.8% higher than that at HRTs of 6 and 14 days, respectively. At HRT of 14 days, the low ethanol loading rate resulted in ethanol excessive-oxidation to acetic acid. Acetic acid accounted for 41.5% of the total product, while the selectivity of caproic acid was only 15.3%. The main contributor to the production process of caproic acid was Caproiciproducens , while the Ruminalococcaceae also played a role in the process. This study provided a theoretical basis for the efficient production of caproic acid through continuous fermentation with autopoietic electron donors. • Efficient autopoietic electron donors were achieved by inoculating yeast. • The highest caproic acid yield of 4660 mg COD/L was obtained at HRT of 10 days. • Low ethanol loading rate tended to produce acetic acid. • HRT has a selection effect on microorganisms. [ABSTRACT FROM AUTHOR]

The Leach Bed Reactor (LBR) application is a promising alternative for the anaerobic digestion of solid waste and wastewater. In this study, the LBR was continuously operated for 160 days in four different phases, for co-fermentation of solid and liquid waste from the citrus agroindustry, at 37 °C, evaluating the effect of hydraulic retention time (HRT) and organic loading rate (OLR). The maximum volumetric hydrogen production (VHPR) was observed at an HRT of 12h (958.3 mLH 2.L-1.d-1); however, the highest hydrogen yield (HY) was identified at an HRT of 24h (104.9 mLH 2.g-1CHO). Based on the metabolic characteristics of microorganisms identified in higher relative abundance, by 16S rRNA sequencing, such as Lactobacillus, Caproicoproducens, Bifidobacterium, Olsenella, and Solobacterium, an occurrence of chain elongation pathways in the production of butyric and caproic acids was inferred, with hydrogen production resulting from the lactic acid oxidation. The maximum electricity production potential of 16.3 kWh.m-3 liquor was estimated. [Display omitted] • The leach bed reactor was applied to the dark fermentation of citrus waste. • The highest H 2 yield was obtained in a hydraulic retention time (HRT) of 24h. • The highest volumetric H 2 production rate was verified in HRT of 12h. • Lactobacillus was predominant in the fixed bed and leachate tank at HRT of 12h. • Caproiciproducens were identified with high relative abundance in HRT of 36h. [ABSTRACT FROM AUTHOR]

In this study, we explored different bacterial strains (Clostridium beijerinckii, C. acetobutylicum, C. oryzae, and C. kainantoi) belonging to the Clostridium group and produced butyric acid (C4) using acetate as a carbon source. All the strains produced significant amounts of C4, but C. beijerinckii produced 1.54 g/L of C4, which is almost equivalent to the production capacity (1.63 g/L) of C. kluyveri. Further experiments were performed using diluted raw cheese whey (CW) by inoculating mixed bacterial cultures containing Clostridia, Bacillus, and Desulfobacteraceae groups. Clostridium kluyveri was added to the mixed culture, and it stimulated the caproic acid (C6) production. Mixed bacterial culture produced 13.97 g/L, 10.83 g/L, and 6.81 g/L of C6 when incubated with two times, five times, and ten times diluted CW, respectively, within a 20-day incubation period. Compared to our previous study, the C6 production was higher and faster. These results indicated the dilution ratio of CW is an important factor in facilitating the C6 production, and higher fatty acids are produced with mixed culture than that of a single culture, i.e., C. kluyveri. Results have depicted the potential of employing the bio-augmentation strategy for the valorization of bioresources into valuable products like butyric acid and caproic acid. [ABSTRACT FROM AUTHOR]

Abstract Bioconversion of CO2 into liquid fuels or chemicals, preferred medium chain carboxylic acids (caproic and caprylic acid), is an attractive CO2 utilization technology. The present study aims to investigate the effects of different ratios of H2/CO2 on regulating the distribution of C2‐C8 carboxylic acid products, while the headspace pressure of 1.5 bar was set to amplify the effect of different ratios. The H2/CO2 ratio of 4:1 was more suitable for preparing acetic acid, where the highest acetic acid yield was 17.5 g/L. And the H2/CO2 ratio of 2:1 showed excellent chain elongation ability with the highest n‐caprylic yield of 2.4 g/L. Additionally, the actual H2/CO2 ratios of 4:1 reactors were higher than that in 2:1 may be course chain elongation often accompanied by H2 production. The 16S rRNA genes analysis shows that the genus Terrisporobacter and Coriobacteriales may be related to acetic acid production enriched in H2/CO2 ratio 4:1 reactors, and the genus Clostridium and Paenibacillaceae may associate with the chain elongation pathway were enriched in H2/CO2 ratio 2:1 reactors.

Microbial electrosynthesis (MES) enables the production of carbon-neutral chemicals using CO2 as a carbon source. Acetic acid is the main MES product, but recent studies show the direct production of elongated carboxylic acids, e.g., butyric and caproic acid. However, the production of elongated acids in MES systems is still inefficient due to the low growth rates of acetogenic bacteria and to limited solventogenic rates. Subsequently, researchers have produced elongated carboxylic acids directly from acetic acid or have operated MES systems at low pH to favor solventogenesis. However, the effect the addition of different chain elongation precursors and the operation pH exerts in the bioelectrochemical production of elongated acids remains unclear. To investigate this, three pH-controlled MES systems were operated in this study with continuous liquid and gas supply. MES systems elongating acetic acid at pH 6 achieved higher butyric (0.71 vs. 0.42 g L−1) and caproic acid (0.71 vs. 0.42 g L−1) titers in the absence of CO2 sparging. Additionally, lowering the pH to 5 in the MES systems fed with CO2 and acetic acid improved the elongated acids titers, reaching 0.72 g L−1 butyric and 0.33 g L−1 caproic acid. The 16 S rRNA analysis showed the community was dominated by Oscillibacter at pH 6, and by Clostridium at pH 5. Furthermore, the first scanning electron microscopy pictures revealing biofilm stratification in MES cathodes were taken in this study, where homogeneous rod-shaped bacteria biofilm layers, in contact with the graphite cathode, were covered by heterogeneous biofilm layers.

[Display omitted] The possibility of using reverse microemulsion based on sodium dodecyl sulfate containing an extractant caproic acid for the selective recovery of non-ferrous metals and their separation from iron in the process of microemulsion leaching has been demonstrated. Using a model system with a mixture of oxides, the following recovery factors of metals are achieved in 5 h of leaching (%): Cu, 47.6; Mn, 12.8; Ni, 9.4; Co, 9.1; Fe, 4.3. When leaching from a sample of oxidized cobalt–copper concentrate, the recovery of metals is as follows (%): Cu, 60.0; Co, 51.3; Mn, 16.5; Fe, 10.0; Ni, 9.3. [ABSTRACT FROM AUTHOR]

Abstract Background Diabetic retinopathy (DR) development is associated with disturbances in the gut microbiota and related metabolites. Butyric acid is one of the short-chain fatty acids (SCFAs), which has been found to possess a potential antidiabetic effect. However, whether butyrate has a role in DR remains elusive. This study aimed to investigate the effect and mechanism of sodium butyrate supplementation on DR. Methods C57BL/6J mice were divided into three groups: Control group, diabetic group, and diabetic with butyrate supplementation group. Type 1 diabetic mouse model was induced by streptozotocin. Sodium butyrate was administered by gavage to the experimental group daily for 12 weeks. Optic coherence tomography, hematoxylin–eosin, and immunostaining of whole-mount retina were used to value the changes in retinal structure. Electroretinography was performed to assess the retinal visual function. The tight junction proteins in intestinal tissue were evaluated using immunohistochemistry. 16S rRNA sequencing and LC–MS/MS were performed to determine the alteration and correlation of the gut microbiota and systemic SCFAs. Results Butyrate decreased blood glucose, food, and water consumption. Meanwhile, it alleviated retinal thinning and activated microglial cells but improved electroretinography visual function. Additionally, butyrate effectively enhanced the expression of ZO-1 and Occludin proteins in the small intestine. Crucially, only butyric acid, 4-methylvaleric acid, and caproic acid were significantly decreased in the plasma of diabetic mice and improved after butyrate supplementation. The deeper correlation analysis revealed nine genera strongly positively or negatively correlated with the above three SCFAs. Of note, all three positively correlated genera, including norank_f_Muribaculaceae, Ileibacterium, and Dubosiella, were significantly decreased in the diabetic mice with or without butyrate treatment. Interestingly, among the six negatively correlated genera, Escherichia-Shigella and Enterococcus were increased, while Lactobacillus, Bifidobacterium, Lachnospiraceae_NK4A136_group, and unclassified_f_Lachnospiraceae were decreased after butyrate supplementation. Conclusion Together, these findings demonstrate the microbiota regulating and diabetic therapeutic effects of butyrate, which can be used as a potential food supplement alternative to DR medicine.

Efficient waste management is necessary to transition towards a more sustainable society. An emerging trend is to use mixed culture biotechnology to produce chemicals from organic waste. Insights into the metabolic interactions between community members and their growth characterization are needed to mediate knowledge-driven bioprocess development and optimization. Here, a granular sludge bioprocess for the production of caproic acid through sugar-based chain elongation metabolism was established. Lactic acid and chain-elongating bacteria were identified as the two main functional guilds in the granular community. The growth features of the main community representatives (isolate Limosilactobacillus musocae G03 for lactic acid bacteria and type strain Caproiciproducens lactatifermentans for chain-elongating bacteria) were characterized. The measured growth rates of lactic acid bacteria (0.051 ± 0.005 h−1) were two times higher than those of chain-elongating bacteria (0.026 ± 0.004 h−1), while the biomass yields of lactic acid bacteria (0.120 ± 0.005 g biomass/g glucose) were two times lower than that of chain-elongating bacteria (0.239 ± 0.007 g biomass/g glucose). This points towards differential growth strategies, with lactic acid bacteria resembling that of a r-strategist and chain-elongating bacteria resembling that of a K-strategist. Furthermore, the half-saturation constant of glucose for L. mucosae was determined to be 0.35 ± 0.05 g/L of glucose. A linear trend of caproic acid inhibition on the growth of L. mucosae was observed, and the growth inhibitory caproic acid concentration was predicted to be 13.6 ± 0.5 g/L, which is the highest reported so far. The pre-adjustment of L. mucosae to 4 g/L of caproic acid did not improve the overall resistance to it, but did restore the growth rates at low caproic acid concentrations (1–4 g/L) to the baseline values (i.e., growth rate at 0 g/L of caproic acid). High resistance to caproic acid enables lactic acid bacteria to persist and thrive in the systems intended for caproic acid production. Here, insights into the growth of two main functional guilds of sugar-based chain elongation systems are provided which allows for a better understanding of their interactions and promotes future bioprocess design and optimization.

The production of Volatile Fatty Acids (VFAs) from wastewater holds significant importance in the context of biorefinery concepts due to their potential as valuable precursors for various bio-based processes. Therefore, the primary objective of this research is to investigate the fermentation of Winery Wastewater (WW) in an Upflow Anaerobic Sludge Blanket (UASB) reactor to generate VFAs, with particular emphasis on Caproic Acid (HCa) production and the dynamics of the microbiota, under varying Hydraulic Retention Time (HRT) periods (8, 5, and 2.5 h). The change from an 8 h to a 5 h HRT period resulted in an approximately 20% increase in total VFA production. However, when the HRT was further reduced to 2.5 h, total VFA production decreased by approximately 50%. Concerning the specific production of HCa, expressed in grams of Chemical Oxygen Demand (gCOD), the maximum yield was observed at around 0.9 gCOD/L for a 5-h HRT. Microbial population analysis revealed that Eubacteria outnumbered Archaea across all HRTs. Population dynamics analysis indicated that the Firmicutes Phylum was predominant in all cases. Within this phylum, bacteria such as Clostridium kluyveri and Clostridium sp., known for their ability to produce HCa, were identified. Based on the results obtained, the application of the UASB reactor for WW treatment, within the biorefinery framework, has the potential to provide a practical alternative for HCa production when operated with a 5 h HRT. [ABSTRACT FROM AUTHOR]

The carboxylate platform is a sustainable and cost-effective way to valorize wastes into biochemicals that replace those of fossil origin. Short-chain fatty acids (SCFAs) are intermediates generated during anaerobic fermentation (AF) and are considered high-value-added biochemicals among carboxylates. This investigation aimed to produce SCFAs through the AF of sugar beet molasses at 25 °C and semi-continuous feeding mode in completely stirred tank reactors. A particular focus was devoted to the role of hydraulic retention time (HRT) variation in SCFAs production and distribution profile. The highest SCFAs concentration (44.1 ± 2.3 gCOD/L) was reached at the HRT of 30 days. Caproic acid accounted for 32.5–35.5% (COD-concentration basis) at the long HRTs of 20 and 30 days due to the carbon chain elongation of shorter carboxylic acids. The findings of this study proved that HRT could be used to steer the anaerobic process toward the targeted SCFAs for specific uses. Furthermore, the successful operation at low-temperature conditions (i.e., 25 °C) makes the process economically promising. [ABSTRACT FROM AUTHOR]

Aims To determine the fermentation quality, aerobic stability, and chemical composition of Italian ryegrass silage prepared with Lactobacillus plantarum (LP), caproic acid (CA), and their combination during ensiling and feed-out phase. Methods and results Six treatments: control (CON), LP, 0.15% caproic acid (LCA), 0.2% caproic acid (HCA), LCA + LP, and HCA + LP were employed for 30 days ensiling and an 8-days aerobic stability test. LP had similar pH value and lactic acid content with LCA + LP, while the contents of NH3-N and total VFAs in LCA + LP were significantly lower than those in LP and CON, and the fermentation quality of LCA + LP performed best among all silages. As air-exposure extended, contents of water-soluble carbohydrates (WSC), lactic, and acetic acids decreased, while pH, and NH3-N content increased significantly. The population of lactic acid bacteria gradually decreased in contrast to increased counts of aerobic bacteria and yeasts. Compared with LCA, 0.2% CA delayed the aerobic deterioration as judged by a slower increase in pH and high residual of WSC and lactic acid, and negligible ethanol content and anaerobe spores counts remained in HCA at the end of air exposure. Compared with CON (73 h), LP showed less aerobic stability (38 h), whereas HCA and HCA + LP prolonged aerobic stability for 210 and 152 h, better than LCA (109 h) and LCA + LP (146 h). Conclusions Lactobacillus plantarum apparently improved the fermentation quality, and combined with CA exhibited greater efficiency in inhibiting undesirable microorganism during ensiling. CA at 0.2% optimally extended the aerobic stability. [ABSTRACT FROM AUTHOR]

Caproic acid is a value-added product that has many uses in the preservation and synthesis of bio-energy. It is obtained via reverse β-oxidation reaction using electron donors and acceptors through the process of carbon chain elongation. The short-chain fatty acids are converted to high-value medium-chain fatty acids (such as caproic acid with six carbon chains). To improve the production yield of caproic acid, it is essential to clarify the relationship between reductase and energy supply, as well as the appropriate range of influencing factors and their mechanism in the biosynthesis process. This review paper describes the mechanisms of carbon chain elongation with lactic acid and ethanol as electron donors. Excessive ethanol oxidation, methanogenesis, and the lactate–acrylate pathways were introduced as competitive pathways during electron donor oxidation, and the corresponding inhibition methods were also reviewed. The reductase supply relationship between electron donor oxidation and electron acceptor reduction during the reverse β oxidation was discussed. In addition, this study clarified the utilization of energy by anaerobic microorganisms during the biosynthesis of caproic acid and two types of ATP synthesis: substrate level phosphorylation and electron transport phosphorylation. Electron bifurcation in the reverse β oxidation (a phenomenon in which two electrons from the same molecule are separated and redox potential is converted into energy to drive thermodynamically adverse reactions) and the role of different electron bifurcations in the production of caproic acid were evaluated. The influence of pH on the production of caproic acid driven by different electron donors was analyzed from the perspectives of competitive pathways, the growth range of functional microorganisms, and product inhibition. Regulating the collaboration between different bacterial communities and exploiting product separation techniques may enhance the production of caproic acid, and this should be investigated in the future. The role of CO2 and H2 as headspace in reverse β oxidation was investigated from the perspectives of substrates, competitive pathways, and thermodynamics. Relevant studies of the CO2 loading rate and H2 partial pressure were also reviewed. The development and current status of bioelectrochemical enhancement in the synthesis of caproic acid were examined, with emphasis on the fixation of CO2. Future research should focus on synthesizing caproic acid using lactic acid as an electron donor and organic wastewater as a substrate by bioelectrochemistry. This review summarized the advantages and disadvantages of the biosynthesis of caproic acid, providing theoretical guidance on how to produce it and improve its yield.

The potato dry rot disease caused by Fusarium spp. seriously reduces potato yield and threatens human health. However, potential biocontrol agents cannot guarantee the stability and activity of biocontrol. Here, 18 synthetic microbial communities of different scales were constructed, and the synthetic microbial communities with the best biocontrol effect on potato dry rot disease were screened through in vitro and in vivo experiments. The results show that the synthetic community composed of Paenibacillus amylolyticus, Pseudomonas putida, Acinetobacter calcoaceticus, Serratia proteamaculans, Actinomycetia bacterium and Bacillus subtilis has the best biocontrol activity. Metabolomics results show that Serratia protoamaculans interacts with other member strains to produce caproic acid and reduce the disease index to 38.01%. Furthermore, the mycelial growth inhibition after treatment with caproic acid was 77.54%, and flow cytometry analysis showed that the living conidia rate after treatment with caproic acid was 11.2%. This study provides potential value for the application of synthetic microbial communities in potatoes, as well as the interaction mechanisms between member strains of synthetic microbial communities.

The aqueous enzymatic method is a form of green oil extraction technology with limited industrial application, owing to the need for the demulsification of the oil body intermediate product. Existing demulsification methods have problems, including low demulsification rates and high costs, such that new methods are needed. The free fatty acids produced by lipid hydrolysis can affect the stability of peanut oil body (POB) at a certain concentration. After screening even-carbon fatty acids with carbon chain lengths below ten, caproic acid was selected for the demulsification of POB using response surface methodology and a Box–Behnken design. Under the optimal conditions (caproic acid concentration, 0.22%; solid-to-liquid ratio, 1:4.7 (w/v); time, 61 min; and temperature, 79 °C), a demulsification rate of 97.87% was achieved. Caproic acid not only adjusted the reaction system pH to cause the aggregation of the POB interfacial proteins, but also decreased the interfacial tension and viscoelasticity of the interfacial film with an increasing caproic acid concentration to realize POB demulsification. Compared to pressed oil and soxhlet-extracted oil, the acid value and peroxide value of the caproic acid demulsified oil were increased, while the unsaturated fatty acid content and oxidation induction time were decreased. However, the tocopherol and tocotrienol contents were higher than those of the soxhlet-extracted oil. This study provides a new method for the demulsification of POB. [ABSTRACT FROM AUTHOR]

Background: Diabetic retinopathy (DR) development is associated with disturbances in the gut microbiota and related metabolites. Butyric acid is one of the short-chain fatty acids (SCFAs), which has been found to possess a potential antidiabetic effect. However, whether butyrate has a role in DR remains elusive. This study aimed to investigate the effect and mechanism of sodium butyrate supplementation on DR. Methods: C57BL/6J mice were divided into three groups: Control group, diabetic group, and diabetic with butyrate supplementation group. Type 1 diabetic mouse model was induced by streptozotocin. Sodium butyrate was administered by gavage to the experimental group daily for 12 weeks. Optic coherence tomography, hematoxylin–eosin, and immunostaining of whole-mount retina were used to value the changes in retinal structure. Electroretinography was performed to assess the retinal visual function. The tight junction proteins in intestinal tissue were evaluated using immunohistochemistry. 16S rRNA sequencing and LC–MS/MS were performed to determine the alteration and correlation of the gut microbiota and systemic SCFAs. Results: Butyrate decreased blood glucose, food, and water consumption. Meanwhile, it alleviated retinal thinning and activated microglial cells but improved electroretinography visual function. Additionally, butyrate effectively enhanced the expression of ZO-1 and Occludin proteins in the small intestine. Crucially, only butyric acid, 4-methylvaleric acid, and caproic acid were significantly decreased in the plasma of diabetic mice and improved after butyrate supplementation. The deeper correlation analysis revealed nine genera strongly positively or negatively correlated with the above three SCFAs. Of note, all three positively correlated genera, including norank_f_Muribaculaceae, Ileibacterium, and Dubosiella, were significantly decreased in the diabetic mice with or without butyrate treatment. Interestingly, among the six negatively correlated genera, Escherichia-Shigella and Enterococcus were increased, while Lactobacillus, Bifidobacterium, Lachnospiraceae_NK4A136_group, and unclassified_f_Lachnospiraceae were decreased after butyrate supplementation. Conclusion: Together, these findings demonstrate the microbiota regulating and diabetic therapeutic effects of butyrate, which can be used as a potential food supplement alternative to DR medicine. [ABSTRACT FROM AUTHOR]

Caproic acid is the precursor material of ethyl hexanoate, a representative flavor substance in strong flavor baijiu (SFB). Increasing the content of caproic acid in SFB helps to improve its quality. In the present study, caproic acid-producing bacteria from the pit mud of an SFB ecosystem were isolated, purified, and characterized. Strain BF-1 with the highest caproic acid yield (0.88 g/l) was selected. The morphological and molecular identification analysis showed that strain BF-1 was Enterococcus casseliflavus. The genome of E. casseliflavus BF-1 was sequenced and was found to be 2,968,377 bp in length with 3,270 open reading frames (ORFs). The caproic acid biosynthesis pathway in E. casseliflavus BF-1 was predicted based on the KAAS annotation. The virulence factors in the genome of strain BF-1 were annotated, which showed that E. casseliflavus BF-1 is safe at the genetic level. After adding essential nutrients based on the KAAS annotation, the optimum medium conditions for acid production by strain BF-1 were obtained by performing orthogonal experiments. The caproic acid yield of strain BF-1 reached 3.03 g/l, which was 3.44-fold higher than the initial yield. The optimized fer-

In contrast to the other components of the medium-chain triglycerides ketogenic diet (MCT KD), i.e., caprylic acid (CA8), a comprehensive evaluation of caproic (CA6) and lauric acids' (CA12) properties in standard chemical and electrical seizure tests in mice has not yet been performed. We investigated their effects in maximal electroshock seizure threshold (MEST), 6 Hz seizure threshold and intravenous (i.v.) pentylenetetrazole (PTZ) seizure tests. Since ketone body production can be regulated by the activation of 5′AMP-activated protein kinase (AMPK), we hypothesized that metformin (an AMPK activator) enhance ketogenesis and would act synergistically with the fatty acids to inhibit convulsions. We assessed the effects of acute and chronic co-treatment with metformin and CA6/CA8 on seizures. CA6 and CA12 (p.o.) increased seizure threshold in the 6 Hz seizure test. CA6 at the highest tested dose (30 mmol/kg) developed toxicity in several mice, impaired motor performance and induced ketoacidosis. Acute and chronic co-treatment with metformin and CA6/CA8 did not affect seizure thresholds. Moreover, we observed the pro-convulsive effect of the acute co-administration of CA8 (5 mmol/kg) and metformin (100 mg/kg). Since this co-treatment was pro-convulsive, the safety profile and risk/benefit ratio of MCT KD and metformin concomitant therapy in epileptic patients should be further evaluated. [ABSTRACT FROM AUTHOR]

(1) Background: Microbial conversion of gaseous molecules, such as CO2, CO and H2, to valuable compounds, has come to the forefront since the beginning of the 21st century due to increasing environmental concerns and the necessity to develop alternative technologies that contribute to a fast transition to a more sustainable era. Research efforts so far have focused on C1–C2 molecules, i.e., ethanol and methane, while interest in molecules with higher carbon atoms has also started to emerge. Research efforts have already started to pay off, and industrial installments on ethanol production from steel-mill off-gases as well as methane production from the CO2 generated in biogas plants are a reality. (2) Methodology: The present study addresses C4–C6 acids and butanol as target molecules and responds to how the inherent metabolic potential of mixed microbial consortia could be revealed and exploited based on the application of different enrichment methods (3) Results and Conclusions: In most of the enrichment series, the yield of C4–C6 acids was enhanced with supplementation of acetic acid and ethanol together with the gas substrates, resulting in a maximum of 43 and 68% (e-mol basis) for butyric and caproic acid, respectively. Butanol formation was also enhanced, to a lesser degree though and up to 9% (e-mol basis). Furthermore, the microbial community exhibited significant shifts depending on the enrichment conditions applied, implying that a more profound microbial analysis on the species level taxonomy combined with the development of minimal co-cultures could set the basis for discovering new microbial co-cultures and/or co-culturing schemes. [ABSTRACT FROM AUTHOR]

Caproic acid is an important fatty acid with diverse applications. In this study, the biomass growth and metabolites of Lacrimispora celerecrescens JSJ-1 were investigated under different carbon sources (ethanol, starch, sucrose, and glucose), with a focus on the effect of the coexistence of glucose and ethanol on the synthesis of caproic acid. The results showed that starch, glucose, and sucrose all contributed to the biomass of L. celerecrescens JSJ-1. Under the three carbon sources, L. celerecrescens JSJ-1 produced acetic acid, butyric acid, lactic acid, ethanol, and butanol, but caproic acid was not produced. Ethanol was the optimal substrate for the production of caproic acid. When glucose and ethanol coexisted, the generation time of caproic acid was delayed compared with that in ethanol sodium acetate medium (ES medium). This was because glucose was preferentially consumed over ethanol. Lactic acid was generated as a result of glucose consumption, which led to a significant decrease in pH from 6.45 to 4.68. The low pH (< 5) inhibited the synthesis of caproic acid. Then, the strain's usage of lactic acid and the reaction between CaCO3 and lactic acid caused the pH to increase. L. celerecrescens JSJ-1 did not start producing caproic acid using ethanol and acetic acid until the pH increased to 5.8. This research enriches the knowledge regarding the metabolism of L. celerecrescens JSJ-1 and provides guidelines for the industrial production of caproic acid by using L. celerecrescences JSJ-1. Key points: • Ethanol is the optimal substrate for the synthesis of caproic acid by Lacrimispora celerecrescens JSJ-1. • Lacrimispora celerecrescens JSJ-1 produced lactic acid rapidly when it used glucose, causing a sharp drop in pH. • pH is a crucial factor affecting the synthesis of caproic acid from ethanol by Lacrimispora celerecrescens JSJ-1. [ABSTRACT FROM AUTHOR]

Background: Individuals who experience the prodromal phase of schizophrenia (SCZ), a common and complex psychiatric disorder, are referred to as ultra-high-risk (UHR) individuals. Short-chain fatty acid (SCFA) is imperative in the microbiota-gut-brain axis and brain function. Accumulating amount of evidence shows the connections between psychiatric disorders and SCFAs. This study aims to explore the underlying roles SCFAs play in SCZ by investigating the association of alterations in SCFAs concentrations with common cognitive functions in both the SCZ and UHR populations. Methods: The study recruited 59 SCZ patients (including 15 participants converted from the UHR group), 51 UHR participants, and 40 healthy controls (HC) within a complete follow-up of 2 years. Results of cognitive functions, which were assessed by utilizing HVLT-R and TMT, and serum concentrations of SCFAs were obtained for all participants and for UHR individuals at the time of their conversion to SCZ. Methods: The study recruited 59 SCZ patients (including 15 participants converted from the UHR group), 51 UHR participants, and 40 healthy controls (HC) within a complete follow-up of 2 years. Results of cognitive functions, which were assessed by utilizing HVLT-R and TMT, and serum concentrations of SCFAs were obtained for all participants and for UHR individuals at the time of their conversion to SCZ. Conclusion: Our study suggests that alterations in concentrations of SCFAs may be associated with the pathogenesis and the cognitive impairment of schizophrenia. Further researches are warranted to explore this association. The clinical implications of our findings were discussed. [ABSTRACT FROM AUTHOR]

The production of Volatile Fatty Acids (VFAs) from wastewater holds significant importance in the context of biorefinery concepts due to their potential as valuable precursors for various bio-based processes. Therefore, the primary objective of this research is to investigate the fermentation of Winery Wastewater (WW) in an Upflow Anaerobic Sludge Blanket (UASB) reactor to generate VFAs, with particular emphasis on Caproic Acid (HCa) production and the dynamics of the microbiota, under varying Hydraulic Retention Time (HRT) periods (8, 5, and 2.5 h). The change from an 8 h to a 5 h HRT period resulted in an approximately 20% increase in total VFA production. However, when the HRT was further reduced to 2.5 h, total VFA production decreased by approximately 50%. Concerning the specific production of HCa, expressed in grams of Chemical Oxygen Demand (gCOD), the maximum yield was observed at around 0.9 gCOD/L for a 5-h HRT. Microbial population analysis revealed that Eubacteria outnumbered Archaea across all HRTs. Population dynamics analysis indicated that the Firmicutes Phylum was predominant in all cases. Within this phylum, bacteria such as Clostridium kluyveri and Clostridium sp., known for their ability to produce HCa, were identified. Based on the results obtained, the application of the UASB reactor for WW treatment, within the biorefinery framework, has the potential to provide a practical alternative for HCa production when operated with a 5 h HRT.

In this study, we explored different bacterial strains (Clostridium beijerinckii, C. acetobutylicum, C. oryzae, and C. kainantoi) belonging to the Clostridium group and produced butyric acid (C4) using acetate as a carbon source. All the strains produced significant amounts of C4, but C. beijerinckii produced 1.54 g/L of C4, which is almost equivalent to the production capacity (1.63 g/L) of C. kluyveri. Further experiments were performed using diluted raw cheese whey (CW) by inoculating mixed bacterial cultures containing Clostridia, Bacillus, and Desulfobacteraceae groups. Clostridium kluyveri was added to the mixed culture, and it stimulated the caproic acid (C6) production. Mixed bacterial culture produced 13.97 g/L, 10.83 g/L, and 6.81 g/L of C6 when incubated with two times, five times, and ten times diluted CW, respectively, within a 20-day incubation period. Compared to our previous study, the C6 production was higher and faster. These results indicated the dilution ratio of CW is an important factor in facilitating the C6 production, and higher fatty acids are produced with mixed culture than that of a single culture, i.e., C. kluyveri. Results have depicted the potential of employing the bio-augmentation strategy for the valorization of bioresources into valuable products like butyric acid and caproic acid.

The carboxylate platform is a sustainable and cost-effective way to valorize wastes into biochemicals that replace those of fossil origin. Short-chain fatty acids (SCFAs) are intermediates generated during anaerobic fermentation (AF) and are considered high-value-added biochemicals among carboxylates. This investigation aimed to produce SCFAs through the AF of sugar beet molasses at 25 °C and semi-continuous feeding mode in completely stirred tank reactors. A particular focus was devoted to the role of hydraulic retention time (HRT) variation in SCFAs production and distribution profile. The highest SCFAs concentration (44.1 ± 2.3 gCOD/L) was reached at the HRT of 30 days. Caproic acid accounted for 32.5–35.5% (COD-concentration basis) at the long HRTs of 20 and 30 days due to the carbon chain elongation of shorter carboxylic acids. The findings of this study proved that HRT could be used to steer the anaerobic process toward the targeted SCFAs for specific uses. Furthermore, the successful operation at low-temperature conditions (i.e., 25 °C) makes the process economically promising.

Caproic acid is the precursor of ethyl caproate, the main representative flavor substance of strong-flavor baijiu (SFB). Caproic acid-producing bacteria are considered to be the most important type of acid-producing microorganisms in the pit mud of the SFB ecosystem. In this study, the Rummeliibacillus suwonensis 3B-1 with a high yield of caproic acid (4.064 g/L) was screened from SFB pit mud. The genome of the R. suwonensis 3B-1 was sequenced, the total size was found to be 4117,671 bp and a calculated GC content of 35.86%. The caproic acid biosynthesis pathway was identified and analyzed, and it showed that 3B-1 could not only use ethanol, but it could also use glucose and other carbon sources as substrates to produce caproic acid. According to the genome analysis and with an optimized medium, the optimal conditions for caproic acid production were yeast powder at 3 g/L, sodium acetate at 15 g/L, and 1% biotin at 8 mL/100 mL. The yield of caproic acid reached 4.627 g/L, an increase of 13.9%, which was higher than that of general caproic acid bacteria. This is the first report of the synthesis of caproic acid by R. suwonensis. This strain could be used to produce caproic acid, an artificial pit mud preparation, and/or an enhanced inoculum in the production of SFB. [Display omitted] • Rummeliibacillus suwonensis was reported as the caproic acid producing bacteriu-m for the first time. • Caproic acid biosynthetic pathway of Rummeliibacillus suwonensis was identified. • The yield of caproic acid reached 4.627 g/L based on the pathway analysis and fermentation medium optimization. [ABSTRACT FROM AUTHOR]

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Organic solid waste (OSW) significantly harms the environment and threatens human health. Producing caproic acid (CA) from OSW presents a cost-effective, sustainable, and resource-efficient solution. This study comprehensively examines the various methods for synthesizing CA from OSW, focusing on waste material selection, pretreatment processes to improve dissolution and hydrolysis of OSW, key substrates, and optimization strategies. Using OSW resources has been extensively studied and applied across numerous industries, presenting a promising solution for reducing environmental pollution. This study provides insights into CA synthesis pathways and substrate selection while emphasizing the optimization of CA production from OSW. It also highlights key areas for future research., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Single-stage fermentation was characterized by low medium chain carboxylic acids concentrations and different mesophilic temperatures had little effect on the process performance, whereas thermophilic conditions and pH 5.5 led to lactate and ethanol accumulation. Two-stage fermentation enabled almost twofold increase in the caproate productivity, that reached 0.8 g/L-d (1.7 ± 0.1 gCOD/L-d) with a caproate concentration of 4.0 g/L (8.4 gCOD/L) at specificity of 37% and led to a reduced release of carbon dioxide. Under pH 6.5 and temperature of 37°C the production of medium chain carboxylic acids required higher concentrations of ethanol. Number of genes annotated to fatty acid biosynthesis pathway exceeded the number of sequences assigned to the reverse β-oxidation pathway. Core microorganisms encoding these pathways belonged to Caproiciproducens, Caproicibacterium and Clostridium. This study provides a valuable insight for valorisation of organic fraction of municipal solid waste into carboxylates in a single- and two-stage systems., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024. Published by Elsevier Ltd.)

The aqueous enzymatic method is a form of green oil extraction technology with limited industrial application, owing to the need for the demulsification of the oil body intermediate product. Existing demulsification methods have problems, including low demulsification rates and high costs, such that new methods are needed. The free fatty acids produced by lipid hydrolysis can affect the stability of peanut oil body (POB) at a certain concentration. After screening even-carbon fatty acids with carbon chain lengths below ten, caproic acid was selected for the demulsification of POB using response surface methodology and a Box–Behnken design. Under the optimal conditions (caproic acid concentration, 0.22%; solid-to-liquid ratio, 1:4.7 (w/v); time, 61 min; and temperature, 79 °C), a demulsification rate of 97.87% was achieved. Caproic acid not only adjusted the reaction system pH to cause the aggregation of the POB interfacial proteins, but also decreased the interfacial tension and viscoelasticity of the interfacial film with an increasing caproic acid concentration to realize POB demulsification. Compared to pressed oil and soxhlet-extracted oil, the acid value and peroxide value of the caproic acid demulsified oil were increased, while the unsaturated fatty acid content and oxidation induction time were decreased. However, the tocopherol and tocotrienol contents were higher than those of the soxhlet-extracted oil. This study provides a new method for the demulsification of POB.

[Display omitted] • ZVI addition boosted caproic acid production by 186% in co-culture experiments. • Co-culturing A. woodii and M. hexanoica optimized carbon flux towards caproic acid. • 3 g/L ZVI maximized CA yield while balancing biomass and carbon flux. • Automated bioreactor validation confirmed stable caproic acid production with ZVI. • ZVI as an electron donor enhanced lactate oxidation and chain elongation processes. Acetobacterium woodii and Megasphaera hexanoica were co-cultured for caproic acid (CA) production from lactic acid (LA) and CO 2. Also, various concentrations (1 g/L, 3 g/L, 5 g/L, and 10 g/L) of Zero Valent Iron (ZVI) were supplied to study its impact on the co-culture system. In flask experiments, 10 g/L LA and 1.0 bar CO 2 produced 0.6 g/L CA with some biomass growth. ZVI increased LA consumption and CA production. Indeed, 3 g/L ZVI boosted CA production by 186 % and biomass accumulation by 103 %, suggesting that ZVI controls the carbon flux. Subsequent automated bioreactor studies showed that 3 g/L ZVI produced 1.842 g/L CA at stable pH, compared to 0.969 g/L without ZVI (control). Further, metabolic activity showed that both bacteria could directly use H 2 , generated by ZVI (3 g/L), as electron donor. Higher ZVI concentrations (10 g/L) resulted in Fe2+ causing excessive oxidation pressure on M. hexanoica , with its carbon flux flowing preferentially towards biomass. Enzyme assays confirmed that A. woodii preferred 10 g/L ZVI while M. hexanoica preferred 3 g/L for optimal bioconversion. [ABSTRACT FROM AUTHOR]

BACKGROUND: n-Caproic acid (CA), as a medium-chain carboxylic acid, is a valuable chemical feedstock for various industrial applications. The fermentative production of CA from renewable carbon sources has attracted a lot of attentions. Lactate is a significant intermediate waste in the anaerobic breakdown of carbohydrates that comprise 18-70% of the chemical oxygen demand (COD) in municipal and some industrial wastewaters. Recently, researchers (including our own group) reported the CA production using lactate as electron donor with newly identified microbiome systems. However, within such processes, it was hard to determine whether the CA production was completed by a single strain or by the co-metabolism of different microorganisms. RESULTS: Here, we report the CA production using lactate as electron donor using the strain CPB6, which we isolated from a microbiome for CA production as described previously. Strain CPB6 is affiliated with Clostridium cluster IV of the family of Ruminococcaceae based on 16S rRNA gene sequence analysis. The strain prefers acidic initial pH condition (pH 5.0-6.5), and the temperature ranging from 30 to 40 °C for CA production. In a fed-batch fermentation with non-sterilized lactate-containing organic wastewater as feedstock, strain CPB6 produced 16.6 g/L CA (from 45.1 g/L lactate) with a maximum productivity of 5.29 g/L/day. Enzyme assays with crude cell extract showed that CPB6 can metabolize acetate and butyryl-CoA to produce n-butyric acid, and acetate/n-butyrate and caproyl-CoA to produce CA, respectively. CONCLUSION: This study demonstrated that high concentration of CA production can be obtained by a newly isolated pure culture CPB6. This strain can be employed as a powerful workhorse for high-efficient CA recovery from lactate-containing waste streams. Our preliminary investigation suggested that the CA production from lactate in strain CPB6 might be via the chain elongation pathway of the reverse β-oxidation; the detailed mechanism, however, warrants further investigation using various molecular microbiology techniques.

Syngas fermentation allows for the conversion of wastes into useful commodity chemicals. To target higher value products, the conditions can be tuned to be favourable for both acetogenic and reverse beta-oxidation pathways and produce, in one stage, butyric and caproic acid. Studies in CSTR have shown the crucial role of pH, which must be low enough to allow for ethanol generation in the acetogenic step while avoiding the inhibition of reverse β-oxidation in acidic conditions. However, no studies have investigated the effect of pH in reactor configurations suitable for syngas fermentation (i.e., allowing for cell retention and exhibiting high mass transfer rates at low operating costs), such as Trickle Bed Reactors, TBR. In this study, two TBR were used to study the pH effect on the fermentation of syngas to produce C4 and C6 acids, using undefined mixed cultures. Five pH values were tested in the range 4.5–7.5, and pH 6 was found to be the most favourable for simultaneous production of C4 & C6 acids from syngas, which agrees with what was found in suspended growth systems. In addition, the highest titers in literature so far were achieved in the TRB. 16S rRNA analysis was performed showing Clostridium and Rummenliibacillus to be the key genus for the efficient process at pH 6. Finally, the experimental methodology followed, and data collected proved the robustness of mixed culture biofilm reactors in respect to pH changes, as the same reactor performance and bacterial community were achieved regardless of the operation history. [Display omitted] • High titers, productivities, and yields of C4 & C6 acids were obtained. • pH 6 was most favourable for chain elongation in trickle bed reactors. • Microbial community and performance were not affected by the operation history. • Clostridium and Rummeliibacillus dominated the community at pH 6. [ABSTRACT FROM AUTHOR]

Lactic acid bacteria fermentation generates pyroglutamic and butyric acid, two metabolites that influence the flavour of foods and could significantly benefit human health. In literature, data on the ability of lactic acid bacteria to produce these molecules is limited. Therefore, in this study, single strains were inoculated in milk to determine the quantity of butyric and pyroglutamic acid produced and the effect of glutamine enrichment substrate was evaluated. In addition to Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus , which are used in traditional yoghurt, other strains (including some probiotics) isolated from different sources were studied. L. bulgaricus E1 and the probiotic L. casei ATCC393 generated the most butyric acid (110 and 108 mg 100 g−1 d.m., respectively) in media without glutamine. The highest quantity of pyroglutamic acid was produced by Lactobacillus delbruekii subsp. bulgaricus MY (700 mg 100 g−1 d.m.) and the probiotic Lacticaseibacillus casei Shirota (1786 mg 100 g−1 d.m.), respectively. Most of the inoculated strains produced a greater quantity of pyroglutamic acid in the substrate with glutamine. These results are an interesting starting point for researchers to utilize selected strains of lactic acid bacteria to develop new dairy products with functional properties due to the presence of pyroglutamic and butyric acid. [Display omitted] • Pyroglutamic and butyric acid have beneficial effects on human health. • The production of these metabolites by 22 lactic acid bacteria strains was studied in fermented milk. • Fortification of milk with glutamine before the inoculation caused increase of pyroglutamic acid. • The MY and the probiotic Shirota strains produced the highest quantity of pyroglutamic acid in presence of glutamine. • The E1 and the probiotic ATCC393 strains produced the highest quantity of butyric acid in absence of glutamine. [ABSTRACT FROM AUTHOR]

In contrast to the other components of the medium-chain triglycerides ketogenic diet (MCT KD), i.e., caprylic acid (CA8), a comprehensive evaluation of caproic (CA6) and lauric acids’ (CA12) properties in standard chemical and electrical seizure tests in mice has not yet been performed. We investigated their effects in maximal electroshock seizure threshold (MEST), 6 Hz seizure threshold and intravenous (i.v.) pentylenetetrazole (PTZ) seizure tests. Since ketone body production can be regulated by the activation of 5′AMP-activated protein kinase (AMPK), we hypothesized that metformin (an AMPK activator) enhance ketogenesis and would act synergistically with the fatty acids to inhibit convulsions. We assessed the effects of acute and chronic co-treatment with metformin and CA6/CA8 on seizures. CA6 and CA12 (p.o.) increased seizure threshold in the 6 Hz seizure test. CA6 at the highest tested dose (30 mmol/kg) developed toxicity in several mice, impaired motor performance and induced ketoacidosis. Acute and chronic co-treatment with metformin and CA6/CA8 did not affect seizure thresholds. Moreover, we observed the pro-convulsive effect of the acute co-administration of CA8 (5 mmol/kg) and metformin (100 mg/kg). Since this co-treatment was pro-convulsive, the safety profile and risk/benefit ratio of MCT KD and metformin concomitant therapy in epileptic patients should be further evaluated.

(1) Background: Microbial conversion of gaseous molecules, such as CO2, CO and H2, to valuable compounds, has come to the forefront since the beginning of the 21st century due to increasing environmental concerns and the necessity to develop alternative technologies that contribute to a fast transition to a more sustainable era. Research efforts so far have focused on C1–C2 molecules, i.e., ethanol and methane, while interest in molecules with higher carbon atoms has also started to emerge. Research efforts have already started to pay off, and industrial installments on ethanol production from steel-mill off-gases as well as methane production from the CO2 generated in biogas plants are a reality. (2) Methodology: The present study addresses C4–C6 acids and butanol as target molecules and responds to how the inherent metabolic potential of mixed microbial consortia could be revealed and exploited based on the application of different enrichment methods (3) Results and Conclusions: In most of the enrichment series, the yield of C4–C6 acids was enhanced with supplementation of acetic acid and ethanol together with the gas substrates, resulting in a maximum of 43 and 68% (e-mol basis) for butyric and caproic acid, respectively. Butanol formation was also enhanced, to a lesser degree though and up to 9% (e-mol basis). Furthermore, the microbial community exhibited significant shifts depending on the enrichment conditions applied, implying that a more profound microbial analysis on the species level taxonomy combined with the development of minimal co-cultures could set the basis for discovering new microbial co-cultures and/or co-culturing schemes.

Mixed microbial cultures have become a preferred choice of biocatalyst for chain elongation systems due to their ability to convert complex substrates into medium-chain carboxylates. However, the complexity of the effects of process parameters on the microbial metabolic networks is a drawback that makes the task of optimizing product selectivity challenging. Here, we studied the effects of small air contaminations on the microbial community dynamics and the product formation in anaerobic bioreactors fed with lactate, acetate and H2/CO2. Two stirred tank reactors and two bubble column reactors were operated with H2/CO2 gas recirculation for 139 and 116 days, respectively, at pH 6.0 and 32°C with a hydraulic retention time of 14 days. One reactor of each type had periods with air contamination (between 97 ± 28 and 474 ± 33 mL O2 L−1 d−1, lasting from 4 to 32 days), while the control reactors were kept anoxic. During air contamination, production of n-caproate and CH4 was strongly inhibited, whereas no clear effect on n-butyrate production was observed. In a period with detectable O2 concentrations that went up to 18%, facultative anaerobes of the genus Rummeliibacillus became predominant and only n-butyrate was produced. However, at low air contamination rates and with O2 below the detection level, Coriobacteriia and Actinobacteria gained a competitive advantage over Clostridia and Methanobacteria, and propionate production rates increased to 0.8–1.8 mmol L−1 d−1 depending on the reactor (control reactors 0.1–0.8 mmol L−1 d−1). Moreover, i-butyrate production was observed, but only when Methanobacteria abundances were low and, consequently, H2 availability was high. After air contamination stopped completely, production of n-caproate and CH4 recovered, with n-caproate production rates of 1.4–1.8 mmol L−1 d−1 (control 0.7–2.1 mmol L−1 d−1). The results underline the importance of keeping strictly anaerobic conditions in fermenters when consistent n-caproate production is the goal. Beyond that, micro-aeration should be further tested as a controllable process parameter to shape the reactor microbiome. When odd-chain carboxylates are desired, further studies can develop strategies for their targeted production by applying micro-aerobic conditions.

[Display omitted] • Constructed microbial consortia-based strategy enhanced caproic acid production. • Clostridium sensu stricto 1 and Caproiciproducers were key genera. • Lactate platform could contribute to product upgrading in acidogenic fermentation. • EDBM enabled phase separation of caproic acid with a purity of 82.58%. A constructed microbial consortia-based strategy to enhance caproic acid production from one-stage mixed-fermentation of glucose was developed, which incubated with acidogens (Clostridium sensu stricto 1 , 11 dominated) and chain elongators (including Clostridium sensu stricto 12 , Sporanaerobacter, and Caproiciproducens) acclimated from anaerobic sludge. Significant product upgrading toward caproic acid (8.31 g‧L−1) and improved substrate degradation was achieved, which can be greatly attributed to the lactic acid platform. Whereas, a small amount of caproic acid was observed in the control incubating with acidogens, with an average concentration of 2.09 g‧L−1. The strategy accelerated the shape and cooperation of the specific microbial community dominated by Clostridium sensu stricto and Caproiciproducens , which thereby contributed to caproic acid production via the fatty acid biosynthesis pathway. Moreover, the tailored electrodialysis with bipolar membrane enabled progressive up-concentration and acidification, allowing selective separation of caproic acid as an immiscible product with a purity of 82.58 % from the mixture. [ABSTRACT FROM AUTHOR]

To provide a sufficient supply of electron donors for the synthesis of caproic acid, yeast fermentation was employed to increase ethanol production in the anaerobic fermentation of Chinese cabbage waste (CCW). The results showed that the caproic acid yield of CCW with ethanol pre-fermentation was 7750.3 mg COD/L, accounting for 50.2% of the total volatile fatty acids (TVFAs), which was 32.5% higher than that of the CCW without yeast inoculation. The synchronous fermentation of yeast and seed sludge significantly promoted the growth of butyric acid consuming bacterium Bacteroides , resulting in low yields of butyric acid and caproic acid. With yeast inoculation, substrate competition for the efficient ethanol conversion in the early stage of acidogenic fermentation inhibited the hydrolysis and acidfication. Without yeast inoculation, the rapid accumulation of TVFAs severely inhibited the growth of Bacteroidetes. In the reactor with ethanol pre-fermentation, the key microorganism for caproic acid production, Clostridium_sensu_stricto_ 12, was selectively enriched. [Display omitted] • Yeast pre-fermentation increased the yield and selectivity of caproic acid from CCW. • Synchronous fermentation seriously inhibited the production of butyric acid. • Substrate competition for ethanol conversion inhibited the acidfication. • Yeast inoculation method has a significant impact on the microbial community. [ABSTRACT FROM AUTHOR]

[Display omitted] • Acidogenic fermentation for food waste valorisation allows a range of products. • Adjusting only HRT and OLR selected three different fermentation types in STRs. • Higher retention times stimulated secondary fermentation such as chain elongation. • Lactic acid is the dominant product at higher organic load. • Microbial community composition reflected reactor performance. Acidogenic fermentation is attractive for food waste valorisation. A better understanding is required on how operation affects product selectivity. This study demonstrated that the hydraulic retention time (HRT) and organic loading rate (OLR) selected fermentation pathways in a single-stage, semi-continuous stirred tank reactor. Three combinations of HRT and OLR were tested to distinguish the effect of each parameter. Three fermentation profiles with distinct microbial communities were obtained. Predominantly n-butyric acid (13 ± 2 gCOD L−1, 55 ± 14% of carboxylates) was produced at an HRT of 8.5 days and OLR around 12 gCOD L−1d−1. Operating at an HRT two days longer, yet with similar OLR, stimulated chain elongation (up to 13.6 gCOD L−1 of n-caproic acid). This was reflected by a microbial community twice as diverse at longer HRT as indicated by first and second order Hill number (1D = 24 ± 4, 2D = 12 ± 3) and by a higher relative abundance of genera related to secondary fermentation, such as the VFA-elongating Caproiciproducens spp., and secondary lactic acid fermenter Secundilactobacillus spp.. Operating at a higher OLR (20 gCOD L−1d−1) but HRT of 8.5 days, resulted in typical lactic acid fermentation (34 ± 5 gCOD L−1) harbouring a less diverse community (1D = 8.0 ± 0.7, 2D = 5.7 ± 0.9) rich in acid-resistant homofermentative Lactobacillus spp. These findings demonstrate that a flexible product portfolio can be achieved by small adjustments in two key operating conditions. This improves the economic potential of acidogenic fermentation for food waste valorisation. [ABSTRACT FROM AUTHOR]

Background: Intrahepatic cholestasis of pregnancy (ICP) is a pregnancy-specific liver condition that typically arises in the middle and late stages of pregnancy. Short-chain fatty acids (SCFAs), prominent metabolites of the gut microbiota, have significant connections with various pregnancy complications, and some SCFAs hold potential for treating such complications. However, the metabolic profile of SCFAs in patients with ICP remains unclear., Aim: To investigate the metabolic profiles and differences in SCFAs present in the maternal and cord blood of patients with ICP and determine the clinical significance of these findings., Methods: Maternal serum and cord blood samples were collected from both patients with ICP (ICP group) and normal pregnant women (NP group). Targeted metabolomics was used to assess the SCFA levels in these samples., Results: Significant differences in maternal SCFAs were observed between the ICP and NP groups. Most SCFAs exhibited a consistent declining trend in cord blood samples from the ICP group, mirroring the pattern seen in maternal serum. Correlation analysis revealed a positive correlation between maternal serum SCFAs and cord blood SCFAs [r (Pearson) = 0.88, P = 7.93e-95]. In both maternal serum and cord blood, acetic and caproic acids were identified as key metabolites contributing to the differences in SCFAs between the two groups (variable importance for the projection > 1). Receiver operating characteristic analysis demonstrated that multiple SCFAs in maternal blood have excellent diagnostic capabilities for ICP, with caproic acid exhibiting the highest diagnostic efficacy (area under the curve = 0.97)., Conclusion: Compared with the NP group, significant alterations were observed in the SCFAs of maternal serum and cord blood in the ICP group, although they displayed distinct patterns of change. Furthermore, the SCFA levels in maternal serum and cord blood were significantly positively correlated. Notably, certain maternal serum SCFAs, specifically caproic and acetic acids, demonstrated excellent diagnostic efficiency for ICP., Competing Interests: Conflict-of-interest statement: All authors have no conflicts of interest to declare., (©The Author(s) 2024. Published by Baishideng Publishing Group Inc. All rights reserved.)

Caproic acid can be produced by fermentation technology. Reactive extraction method is a promising technology for separating the acid from the carboxylic mixture in the fermenter [1-4]. To achieve it, tri‑butyl phosphate (TBP) is used as the reactive extractant and sunflower and soybean oils are used as the diluents. The performance of both the physical and reactive extraction processes was analysed by different parameters like distribution coefficient, loading ratio, and extraction efficiency. To meet the purpose, concentration of caproic acid in aqueous phase was measured by doing acid-base titration by caustic solution Further, reaction equilibrium constant, stoichiometry and distribution of complex, free acid and dimer concentrations in the organic phase were analysed. The data are related to the published (https://doi.org/10.1016/j.cep.2020.107926) paper in Chemical Engineering and Processing: Process Intensification [5]. The data shown in the current article are not provided in the mentioned published paper. Moreover, data are useful for understanding the physical and chemical behavior of the caproic acid extraction process and also can be used to design the process in industrial scale.

Background: Butyric acid (BA) is a short-chain fatty acid (SCFA) with anti-inflammatory properties, which promotes intestinal barrier function. Medium-chain fatty acids (MCFA), including caproic acid (CA), promote TH1 and TH17 differentiation, thus supporting inflammation.Aim: Since most SCFAs are absorbed in the cecum and colon, the measurement of BA in peripheral blood could provide information on the health status of the intestinal ecosystem. Additionally, given the different immunomodulatory properties of BA and CA the evaluation of their serum concentration, as well as their ratio could be as a simple and rapid biomarker of disease activity and/or treatment efficacy in MS.Methods: We evaluated serum BA and CA concentrations, immune parameters, intestinal barrier integrity and the gut microbiota composition in patients with multiple sclerosis (MS) comparing result to those obtained in healthy controls.Results: In MS, the concentration of BA was reduced and that of CA was increased. Concurrently, the microbiota was depleted of BA producers while it was enriched in mucin-degrading, pro-inflammatory components. The reduced serum concentration of BA seen in MS patients correlated with alterations of the barrier permeability, as evidenced by the higher plasma concentrations of lipopolysaccharide and intestinal fatty acid-binding protein, and inflammation. Specifically, CA was positively associated with CD4+/IFNγ+ T lymphocytes, and the BA/CA ratio correlated positively with CD4+/CD25high/Foxp3+ and negatively with CD4+/IFNγ+ T lymphocytes.Conclusion: The gut microbiota dysbiosis found in MS is possibly associated with alterations of the SCFA/MCFA ratio and of the intestinal barrier; this could explain the chronic inflammation that characterizes this disease. SCFA and MCFA quantification could be a simple biomarker to evaluate the efficacy of therapeutic and rehabilitation procedures in MS.