Acetogenic Research Articles

Metagenomics profiling of the microbial community and functional differences in solid-state fermentation vinegar starter (seed Pei) from different Chinese regions.

The starter used in solid-state fermentation (SSF) vinegar, known as seed Pei is a microbial inoculant from the previous batch that is utilized during the acetic acid fermentation stage. The seed Pei, which has a notable impact on vinegar fermentation and flavor, is under-researched with comparative studies on microorganisms. Herein metagenomics was employed to reveal the microbes and their potential metabolic functions of four seed Pei from three regions in China. The predominant microbial taxa in all four starters were bacteria, followed by viruses, eukaryotes, and archaea, with Lactobacillus sp. or Acetobacter sp. as main functional taxa. The seed Pei used in Shanxi aged vinegar (SAV) and Sichuan bran vinegar (SBV) exhibited a higher similarity in microbial composition and distribution of functional genes, while those used in two Zhenjiang aromatic vinegar (ZAV) differed significantly. Redundancy analysis (RDA) of physicochemical factors and microbial communities indicated that moisture content, pH, and reducing sugar content are significant factors influencing microbial distribution. Moreover, seven metagenome-assembled genomes (MAGs) that could potentially represent novel species were identified. There are distinctions in the microbiome and functional genes among different seed Pei. The vinegar starters were rich in genes related to carbohydrate metabolism. This research provides a new perspective on formulating vinegar fermentation starters and developing commercial fermentation agents for vinegar production.

Chain elongation in continuous microbial electrosynthesis cells: The effect of pH and precursors supply

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.

Study on the Effect of Inoculation of Mixed Inoculation on Hydrolysis and Acidification Performance of Kitchen Waste

The effect of a mixture of different inoculants as inoculum on the hydrolytic and acidification process was investigated in order to improve the hydrolytic and acidification properties of kitchen waste. The results showed that the inoculation of Baijiu pit mud had the feasibility to improve the hydrolytic acidification performance during the hydrolytic acidification process of kitchen waste. At the end of the hydrolytic acidification process, the SCOD of the 1:0, 3:1,1:1, and 1;3 group increased by 55.97%, 48.67%, 30.82% and 7.03%, respectively, compared with that of the 1:0 group; the hydrolysis rate increased by 2.44%, 7.07%, 2.01% and 2.2% compared with that of the 0:1 group. The highest concentration of VFAs was found in the group with 1:3 ratio of Baijiu pit mud and anaerobic sludge, which was 11353.46 mg/L. The highest acidification rate was found in the 1:3 group, which was 68.57%, and 16.14% higher than that in the 1:0 group. The highest concentration of VFAs was found in the group with 1:3 ratio of Baijiu pit mud and anaerobic sludge, which was 11353.46 mg/L. The highest acidification rate was found in the 1:3 group, which was 68.57%, and 16.14% higher than that in the 1:0 group. Inoculation of Baijiu pit mud was able to change the fraction of VFAs during the hydrolytic acidification of kitchen waste. The fermentation type of the hydrolytic acidification system was ethanol-type fermentation, and the ethanol concentration was increased by 8.64, 8.59, 7.36, and 2.81 times in the groups with the ratio of Baijiu pit mud to anaerobic sludge of 1:0, 3:1, and 1:1, respectively. However, in the Baijiu pit mud and anaerobic sludge ratio of 1:3 and 0:1 group, the main type of fermentation was acetic acid type fermentation. The experimental groups inoculated with Baijiu pit mud.

Unveiling the impact of temperature shift on microbial community dynamics and metabolic pathways in anaerobic digestion

Anaerobic digestion (AD) technology is a viable solution to the challenges attributed to sewage sludge, but its specific impact on biogas production and the dynamics of methanogenic bacteria has not been widely understood. This research investigated the effects of shifts in AD operational temperatures on microbial communities and biogas production. This was achieved by incrementally raising the temperature from 37 °C to 45 °C in 2 °C increments. Within the temperature range of 37 – 41 °C, there was a notable disturbance in the abundance of acetogenic bacteria and methanogens, leading to a considerable reduction in methane production. However, with further elevation of temperature, the increasing activity of acetogens and methanogens was discerned following the increase in methane production. Methanothrix was identified as the predominant methanogen in the present study, marking the domination of the acetoclastic pathway. In functional analysis, the acetate decarboxylation enzymes demonstrated resilience at 43 °C and 45 °C, in contrast to hydrogenotrophic pathway enzymes. The acetoclastic pathway played a primary role in methane production under temperature shift conditions while the hydrogenotrophic pathway was more susceptible to temperature fluctuations. The findings highlight the potential adaptation of microbial communities when subjected to changing temperatures which led to robustness of digestion in AD processes.

Production of vinegar from waste fruits using <i>Acetobacter</i> species

Vinegar is an organic substance that contains about 5% acetic acid and is made from the oxidative fermentation of alcohol by acetic acid bacteria. The aim of this study was to produce vinegar from the juices of waste fruits. Proximate and physicochemical analysis was carried out on the juices of orange, sugarcane, tomato, and pineapple using standard techniques. Twenty-one (21) species of acetic acid bacteria were isolated and identified using glucose-yeast-Calciumcarbonate (GYC) agar. The juices were fermented for 7 days using Saccharomyces cerevisiae, and subsequently, for 28 days, four alcohol-tolerant Acetobacterspecies were selected and inoculated into the fermenting media. The produced vinegar was sensory evaluated, following a nine-point hedonic scale. The antibacterial and antifungal effects of the vinegar were tested on fresh cabbage at various contact times (0, 5, and 10 min) and concentrations (5, 10, and 15 % v/v). The physicochemical parameters analyzed in fermentation using S. cerevisiae showed a decrease in pH, specific gravity, and brix, while the percentage of alcohol content increased. As the fermentation using Acetobacter species progressed, pH further decreased, titratable acidity increased in a range of 6.6-7.7%, and specific gravity also decreased while specific gravity increased in Acetic acid fermentation. Sensory evaluation showed a score range of 5.7–6.8 for pungency, 6.8–7.4 for appearance, 6.4–7.9 for aroma, 5.8–7.4 for taste, and 6.9–7.9 for acceptability. The best results for bacterial and fungal loads 5 on cabbage were at a concentration of 15% at 10 min. Drastic reduction of bacterial load was from 2.07×10 to 4 4 3 2.7×10 CFU/g, while fungal load reduced from 4.9×10 to 6.7× 10 CFU/g. To evaluate significance, an ANOVA was performed (p<0.05) and Duncan's test was used for multiple comparisons. Vinegar was successfully tested to be effective as an antimicrobial agent. Future research should look into process optimization, strain improvement, and the adoption of agro-allied wastes for biotechnology.

Deciphering the core microbiota in open environment solid-state fermentation of Beijing rice vinegar and its correlation with environmental factors.

Rice vinegar is a popular cereal vinegar worldwide and is typically produced in an open environment, and the ecosystem of solid-state fermentation is complicated and robust. The present study aimed to reveal the shaping force of the establishment of the ecosystem of Beijing rice vinegar, the core function microbiota and their correlation with critical environmental factors. [Correction added after first online publication on 29 May 2024; the word "worldwide" has been removed from the first sentence under the section Background.] RESULTS: The experimental findings revealed the changes in environmental factors, major metabolites and microbial patterns during Beijing rice vinegar fermentation were obtained. The major metabolites accumulated at the middle and late acetic acid fermentation (AAF) periods. Principal coordinates and t-test analyses revealed the specific bacterial and fungal species at corresponding stages. Kosakonia, Methlobacterium, Sphingomonas, unidentified Rhizobiaceae, Pseudozyma and Saccharomycopsis dorminated during saccharification and alcohol fermentation and early AAF, whereas Lactococcus, Acetobacter, Rhodotorula and Kazachstania dominated the later AAF stages. Canonical correspondence analysis of environmental factors with core microbiota. Temperature and total acid were the most significant factors correlated with the SAF bacterial profile (Pediococcus, Weissella, Enterococcus and Kosakonia). Ethanol was the most significant factor between AAF1 and AAF3, and mainly affected Acetobacter and Lactobacillus. Conversely, ethanol was the most significant factor in the SAF, AAF1 and AAF3 fungi communities; typical microorganisms were Saccharomyces and Malassezia. Furthermore, the predicted phenotypes of bacteria and their response to environmental factors were evaluated. In conclusion, the present study has provided insights into the process regulation of spontaneous fermentation and distinguished the key driving forces in the microbiota of Beijing rice vinegar fermentation. © 2024 Society of Chemical Industry.

Acetic Fermentation of Cagaita Pulp: Technological and Chemical Characteristics

The Brazilian Cerrado region has a rich plant diversity, with fruits that have peculiar and unique sensory characteristics. For these reasons, using these fruits for biotechnological production is a promising alternative, mainly to protect this biome from deforestation and degradation. The production of fermented acetic acid is an option to add value to native fruits and offer the market beverages with better nutritional quality and bioactive compounds. This work aimed to characterize fruits and to develop cagaita (Eugenia dysenterica DC.) acetic fermented beverage. The fruits were subjected to physical-chemical analyses in the first part. Subsequently, different treatments for fermentation were tested using two types of enzymes (amylase and pectinase), two subspecies of Saccharomyces cerevisiae yeast (UFLA CA11 and thermoresistant LNF Angel), and the chaptalization of the must with sucrose (16 °Brix). Alcoholic fermentation was carried out in an incubator with temperature control at 34 ± 1 °C. The pH, total soluble solids, titratable acidity, alcohol content, and density of the fermented products were monitored daily. The chaptalized must with amylase addition and thermoresistant yeast had the best performance during alcoholic fermentation, demonstrating that thermoresistant yeast is an economically advantageous and efficient alternative for the cagaita juice fermentation process. Subsequently, acetic fermentation was carried out using the slow method. Heat-resistant yeast without added enzymes was used to produce cagaita acetic fermented beverages within the parameters of the Brazilian legislation. Furthermore, phenolic compounds and antioxidant activity in the final product were observed. The work demonstrated the possibility of using cagaita fruits in biotechnological processes to produce new food products.

Aged to Perfection: The Scientific Symphony behind Port Wine, Vinegar, and Acetic Acid Bacteria

This review critically examines the multifaceted role of acetic acid bacteria (AAB) in the intricate production process of port wine vinegar, particularly in its transformative process from port wine. With the emergence of port wine vinegar as a distinctive agricultural product in 2018, producers have been faced with a diverse array of challenges, ranging from reducing the high alcohol content to preserving the inherent sweetness. Through an exhaustive exploration of acetic fermentation processes and the indispensable role of AAB, this review meticulously elucidates the complex biochemistry underlying vinegar formation, delving into the nuanced interactions between microbial activity and chemical composition. Furthermore, this review underscores the importance of sensory characteristics and consumer perception derived from vinegar production, providing invaluable insights into these fermented products’ sensory profiles and marketability. In summary, this study offers valuable insights into the evolution of port wine into vinegar, highlighting its significance in agricultural and culinary contexts.

Quality comparison of non-thermal sterilized raw apple vinegar and commercial apple vinegar products

A nonthermally sterilized raw apple vinegar was manufactured using an ultra-fine filtration process (0.2 μm membrane filter) and its quality was comparable to commercially available vinegar products. First, using apple concentrate as a raw material, it was possible to produce non-thermal sterilized Using a two-stage fermentation process of alcohol and acetic acid fermentations, a non-thermally sterilized raw apple vinegar with pH 2.94 and an acidity of 6.20% was produced from an apple concentrate. The fermentation process increased the browning index significantly. However, the fundamental quality parameters of the non-thermal sterilized raw apple vinegar (A) with sterilized apple vinegar (B) did not differ significantly. The pH (2.92-2.95) of apple vinegar (A and B) was higher than that (pH 2.65-2.70) of commercial vinegar (C and D), and the total acidity, which is in the range of 6.20-6.21% and 6.53-6.90%, respectively, was higher in samples C and D than in samples A and B. However, four kinds of organic acids were detected in non-thermal sterilized raw apple vinegar (A), and its total organic acid content (6,245.00 mg%) was significantly higher than that of other samples (B, C, D) (p<0.05). In particular, malic acid content, as a main organic acid in apples, was very high in sample (A) (244.83 mg%) and sample (B) (210.21 mg%), compared to commercial products C (125.78 mg%) and D (86.90 mg%). The total polyphenol content and antioxidant activity of fermented apple vinegar (A, B) were more than twice as high as those of commercial products (C, D). Vinegar A had higher total polyphenol content than vinegar B. The above results suggest it is possible to manufacture and commercialize non-thermal sterilized raw apple vinegar with higher organic acid content and antioxidant properties using ultra-fine filtration.

Preparation and mechanical properties of Portland cement composites filled with bamboo fibres modified by acetic acid and fermentation treatment

To improve the compatibility between Portland cement and bamboo fibre, bamboo fibres were modified by acetic acid and fermentation treatment and the modified bamboo fibres/Porland cement composites were prepared. The hydration curves of the bamboo fibres/Porland cement composites were measured and the area ratio under the cement hydration heat curve was used as the compatibility coefficient to evaluate the compatibility of bamboo fiber and cement. The hydration products at different hydration times were characterized by XRD, FTIR, and SEM. Moreover, the mechanical strengths of standard test blocks of Portland cement/bamboo fibre composites were tested to further verify the improved compatibility of bamboo fiber and Portland cement. The study shows that the compatibility between bamboo fibre and Portland cement was improved from 9% to 87%, the bending strength of Portland cement/bamboo fibre composite was increased from 638 N to 3678 N, and the compressive strength was increased from 1.5 MPa to 34.35 MPa.

Lactiplantibacillus plantarum and Komagataeibacter europaeus enhance energy metabolism, acetic acid and aromatic amino acids catabolism flux in cider vinegar fermentation

Fruit vinegar is typically produced through a two-stage submerged fermentation involving Saccharomyces cerevisiae (alcohol fermentation) and Acetobacter pasteurianus (acetic acid fermentation). In order to enhance its flavor and nutritional properties, Lactiplantibacillus plantarum and Komagataeibacter europaeus were introduced into the respective stages. The fermentation process was monitored to assess their individual and combined effects, while non-targeted metabolomic analysis aided amino acids and organic acids analysis was applied to characterize the metabolic profiles and identify the differential metabolites.Lactic acid accumulated by L. plantarum, enhanced energy metabolism and ethanol respiratory chain, thereby promoting the K. europaeus growth. In the presence of K. europaeus, A. pasteurianus biomass increased 36–57%, leading to elevated acetic acid synthesis. The co-fermentation systems, especially those containing K. europaeus, exhibited enhanced conversion of shikimic acid to aromatic amino acids and their derivatives such as ferulic acid, isoferulic acid, serotonin, l-kynuanine, phenylacetaldehyde and benzaldehyde. The co-fermentation with K. europaeus and L. plantarum resulted in an enhancement of ethyl phenylacetate, ethyl lactate and ethyl hexanoate production, thereby intensifying the fruity aroma profile. The findings presented here contributed to a deeper comprehension of bioconversion mechanism involving multiple species in cider vinegar fermentation processes.

Biochar-mediated synergistic promotion of DIET and IHT: Kinetic and thermodynamic insights into propionate two-step syntrophic methanogenesis

Biochar can effectively enhance the thermophilic anaerobic degradation of propionate. Nevertheless, previous studies frequently ascribed this enhancement to direct interspecies electron transfer (DIET) without considering the underlying kinetics and thermodynamics involved. Additionally, quantitative evaluation of biochar’s impact on interspecies electron transfer (IET) has been limited. In this study, we developed and optimized models for analyzing thermodynamics and electron transfer flux to elucidate the mechanism by which biochar enhances the two-step syntrophic methanogenesis of propionate. Findings revealed that biochar primarily facilitated DIET (1.78 × 10−4 A), leveraging its redox capacity. Additionally, it synergistically enhanced interspecies hydrogen transfer (4.08 × 10−10 A), significantly improving IET efficiency. This synergistic effect led to accelerated oxidative degradation rates of propionate (39.2 %) and intermediate acetate (13.5 %), expanding the thermodynamic windows for their syntrophic methanogenesis (221 % and 103 %, respectively). Accordingly, biochar increased the maximum rate of propionate methanation (71.9 %) and reduced the lag phase time (51.1 %). Moreover, biochar promoted the specific growth rates of acetogenic bacteria and methanogens while significantly increasing the abundance of Pelotomaculum, Methanoculleus, and Methanosarcina. These findings provide new insights and theoretical support for the use of biochar in promoting anaerobic digestion and facilitating IET during the process.

The Advantage of Citrus Residues as Feedstock for Biogas Production: A Two-Stage Anaerobic Digestion System

Anaerobic digestion (AD) is an important step in waste recovery. In Colombia, the production of citrus food significantly contributes to environmental impact via waste generation. In 2021, the waste produced, specifically citrus rind, amounted to 725,035 tons/year. During degradation, wastes generate leachate and greenhouse gases (GHGs), which negatively impact water sources (leachate), soil, and human and animal health. This article describes the design of a two-phase biodigestion system for the degradation of organic matter and biogas production. The system uses citrus waste to produce biogas with neutral emissions. The biodigestion process begins with the stabilization of the methanogenesis reactor (UASB), which takes approximately 19 days. During this period, the biogas produced contains approximately 60% methane by volume. Subsequently, the packed bed reactor operates for 7 days, where hydrolytic and acetogenic bacteria decompose the citrus waste, leading to the production and accumulation of volatile fatty acids. The final step involves combining the two phases for 5 days, resulting in a daily biogas production ranging from 700 to 1100 mL. Of this biogas, 54.90% is methane (CH4) with a yield of 0.51 LCH4gSV−1. This study assesses the methane production capacity of citrus waste, with the process benefiting from the pH value of the leachate, enhancing its degradability. Consequently, this approach leads to a notable 27.30% reduction in solids within the digestion system. The two-phase anaerobic biodigestion system described in this article demonstrates a promising method to mitigate the environmental impact of citrus waste while concurrently producing a renewable source of energy.

Recombinant Production of Pseudomonas aeruginosa Rhamnolipids in P. putida KT2440 on Acetobacterium woodii Cultures Grown Chemo-Autotrophically with Carbon Dioxide and Hydrogen.

The establishment of sustainable processes for the production of commodity chemicals is one of today's central challenges for biotechnological industries. The chemo-autotrophic fixation of CO2 and the subsequent production of acetate by acetogenic bacteria via anaerobic gas fermentation represents a promising platform for the ecologically sustainable production of high-value biocommodities via sequential fermentation processes. In this study, the applicability of acetate-containing cell-free spent medium of the gas-fermenting acetogenic bacterium A. woodii WP1 as the feeder strain for growth and the recombinant production of P. aeruginosa PAO1 mono-rhamnolipids in the well-established nonpathogenic producer strain P. putida KT2440 were investigated. Additionally, the potential possibility of a simplified production process without the necessary separation of feeder strain cells was elucidated via the cultivation of P. putida in cell-containing A. woodii culture broth. For these cultures, the content of both strains was investigated by examining the relative quantification of strain-exclusive genes via qPCR. The recombinant production of mono-rhamnolipids was successfully achieved with maximum titers of approximately 360-400 mg/L for both cell-free and cell-containing A. woodii spent medium. The reported processes therefore represent a successful proof of principle for gas fermentation-derived acetate as a potential sustainable carbon source for future recombinant rhamnolipid production processes by P. putida KT2440.

Enhancing kitchen waste anaerobic digestion by recycled aluminum industry waste: Alkali treatment and potential electron transfer mechanism

Kitchen waste has become a significant environmental concern worldwide. Red mud, an industrial solid waste characterized by its porous structure and high iron oxide content, exhibits potential as a conductive conduit in the direct interspecies electron transfer (DIET) pathway. In this study, red mud pretreatment of kitchen waste was conducted to enhance anaerobic digestion (AD). The effect and mechanism of enhancing kitchen waste AD by red mud pretreatment was studied for the first time. Results indicated that red mud pretreatment could accelerate the hydrolysis of organic compounds and alleviate the acid inhibition. Consequently, the methane production rate was increased from 260.7 mL/g VS to 402.3 mL/g VS, i.e., up to 54.3%. And volatile solids removal efficiency was increased from 53.9% to 73.1%, i.e., up to 35.6%. Furthermore, microbial community analysis revealed the enrichment of electrochemically active bacteria (Synergistaceae), acetogenic bacteria (Syntrophomonadaceae) and methanogens (Methanobacterium and Methanosarcina), which played essential roles in interspecies hydrogen transfer (IHT) and DIET. This study showed that red mud pretreatment has the potential to enhance kitchen waste AD which contributes to carbon mitigation. It also threw the potential new insights to the relative mechanism.

Mechanisms of anaerobic treatment of sulfate-containing organic wastewater mediated by Fe0 under different initial pH values.

The anaerobic treatment of sulfide-containing organic wastewater (SCOW) is significantly affected by pH, causing dramatic decrease of treatment efficiency when pH deviates from its appropriate range. Fe0 has proved as an effective strategy on mitigating the impact of pH. However, systematic analysis of the influence mechanism is still lacking. To fill this gap, the impact of different initial pH values on anaerobic treatment efficiency of SCOW with Fe0 addition, the change of fermentation type and methanogens, and intra-extracellular electron transfer were explored in this study. The results showed that Fe0 addition enhanced the efficacy of anaerobic treatment of SCOW at adjusted initial pH values, especially at pH 6. Mechanism analysis showed that respiratory chain-related enzymes and electron shuttle secretion and resistance reduction were stimulated by soluble iron ions generated by Fe0 at pH 6, which accelerated intra-extracellular electron transfer of microorganisms, and ultimately alleviated the impact of acidic pH on the system. While at pH 8, Fe0 addition increased the acetogenic bacteria abundance, as well as optimized the fermentation type and improved the F420 coenzyme activity, resulting in the enhancement of treatment efficiency in the anaerobic system and remission of the effect of alkaline pH on the system. At the neutral pH, Fe0 addition had both advantages as stimulating the secretion ofrespiratory chainand electron transfer-related enzymes at pH 6 and optimizing the fermentation type pH 8, and thus enhanced the treatment efficacy. This study provides important insights and scientific basis for the application of new SCOW treatment technologies.

The energy-converting hydrogenase Ech2 is important for the growth of the thermophilic acetogen Thermoanaerobacter kivui on ferredoxin-dependent substrates.

Acetogens thrive by converting H2+CO2 to acetate. Under environmental conditions, this allows for only very little energy to be conserved (∆G'<-20 kJ mol-1). CO2 serves as a terminal electron acceptor in the ancient Wood-Ljungdahl pathway (WLP). Since the WLP is ATP neutral, energy conservation during growth on H2 + CO2 is dependent on the redox metabolism. Two types of acetogens can be distinguished, Rnf- and Ech-type. The function of both membrane-bound enzyme complexes is twofold-energy conversion and redox balancing. Ech couples the Fd-dependent reduction of protons to H2 to the formation of a proton gradient in the thermophilic bacterium Thermoanaerobacter kivui. This bacterium may be utilized in gas fermentation at high temperatures, due to very high conversion rates and the availability of genetic tools. The physiological function of an Ech hydrogenase in T. kivui was studied to contribute an understanding of its energy and redox metabolism, a prerequisite for future industrial applications.

The Nutritional, Physico-chemical, and Antioxidant Changes during the Production of Soursop Vinegar Influenced by Yeast and Aeration

This study aims to produce soursop vinegar and evaluate how its nutritional composition changes during production. This process offers a solution to convert acidic fruits like soursop into a nutritious product with a longer shelf life. Fresh soursop juice was extracted using a mechanical press, followed by alcoholic and acetous fermentation under different aerobic and anaerobic conditions, with some samples aerated. The nutritional analysis included proximate composition, vitamin C content, acetic acid, pH, and soluble solids (TSS or ºBrix). Results during fermentation showed increased moisture content (90.73–93.99%) compared to the control (78.56%) and a decrease in protein content (0.5–0.61%) when Saccharomyces cerevisiae was present (1.53–1.84% without it). Acetic acid and vitamin C levels remained relatively stable, while ºBrix values significantly decreased (4.83–7.00 ºBrix) compared to the initial 15 ºBrix of the control during fermentation. Aeration during production improved the vinegar’s antioxidative capacity, with the highest enhancement observed when Acetobacter sp. was added. Overall, this study highlights the potential of soursop vinegar to retain the nutritional composition of the fruit, resulting in a healthier, natural product with an extended shelf life.

Performance and interaction mechanism of integrating alkali pretreatment and immobilized electrodes on enhanced sludge digestion for methane production

Introduction of voltage or conductive materials have been proven to be effective strategies for enhancing the stability and efficiency of sludge digestion for methane recovery. This experiment simulated a two-phase anaerobic system, consisting of an acid-producing phase with alkali pretreatment and a methane-producing phase with immobilized electrodes and voltage enhancement. Various effective and comparative experiments were conducted to investigate the crucial roles of immobilized electrodes like carbon brush (CB) and nickel foam (NF), electroactive biofilm and voltage during the sludge methane-producing phase. The experimental results indicate that directly application of immobilized CB and NF electrode to promote sludge anaerobic digestion achieves better performance than additional voltage supply. The electrodes can increase methane production by 38% to 94%, whereas under additional voltage supply, methane production only increases by 22%–53% compared to the control. Through the analysis of key transformations in organic substrates and changes in microbial community structure, the inherent advantages of electrode materials in promoting the syntrophic methanogenesis processes are confirmed. Compared to suspended sludge, the types and relative abundance of typical syntrophic methane-producing microorganisms, Methanosarcina, and acetogenic bacteria, Syntrophomonas on the electrode surface significantly increase by 8.5% and 1.7%. This process is notably superior to the methane generation process dominated by hydrogenotrophic methanogensis after applying voltage. The results indicate that CB and NF are suitable conductive materials to promote anaerobic methane recovery, and their effectiveness surpasses that of applying voltage. These research outcomes provide new insights for the development of novel anaerobic digestion enhancement systems.

Changes in soil microbial functions involved in the carbon cycle response to conventional and biodegradable microplastics

Biodegradable mulch film has become an encouraging alternative to conventional petroleum–based plastic, but it is likely to generate more microplastics (MPs) than conventional films with lower resistance and thus profoundly affects the soil environment. However, the effects of biodegradable (BMPs) and conventional polyethylene MPs (PE–MPs) on soil microbial carbon (C) cycle remain unclear. Here, metagenomic sequencing was used to investigate microbial functional and relative taxonomic traits in response to PE–MP and BMP addition (5 % w/w) via a soil microcosm experiment. The results showed that the presence of BMPs, rather than PE–MPs, significantly changed soil microbial C cycling patterns at the functional and taxonomic levels. In soils, BMP addition significantly increased the abundances of genes regulating aerobic respiration, C decomposition (intracellular), C fixation, fermentation and CO oxidation pathways compared to those in the control and PE–MP added soils. Specifically, BMPs promoted soil starch and PHA (liable C) degradation, acetate and ethanol fermentation, Calvin–Benson–Bassham (CBB) cycle and 3–hydroxypropionate/4–hydroxybutyrate (3HP/4HB) associated with C fixation. Most of these C cycling pathways were further strengthened in the microplastisphere of BMPs. Furthermore, MPs selectively enriched specific taxa on their surface and subsequently increased their abundance in soils; Bradyrhizobium, Ramlibacter and Variovorax (enriched by BMPs) positively regulated labile C degradation, and Amycolatopsis and Nocardia (enriched by PE–MPs) promoted recalcitrant C degradation. Moreover, Pseudonocardia and Variovorax that were enriched by BMPs improved C dissimilation and assimilation by regulating fermentation and C fixation processes, respectively. Taken together, these results improve the understanding of the influence of conventional and biodegradable MPs on soil C cycling pathways and related microbial communities, highlighting that the presence of BMPs rather than PE–MPs accelerates soil C turnover.