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A novel thermotolerant caproic acid-producing bacterial strain, Clostridium M1NH, was successfully isolated from sewage sludge. Ethanol and acetic acid at a molar ratio of 4:1 proved to be the optimal substrates, yielding a maximum caproic acid production of 3.5 g/L. Clostridium M1NH exhibited remarkable tolerance to high concentrations of ethanol (up to 5% v/v), acetic acid (up to 5% w/v), and caproic acid (up to 2% w/v). The strain also demonstrated a wide pH tolerance range (pH 5.5-7.5) and an elevated temperature optimum between 35 and 40 °C. Phylogenetic analysis based on 16S rRNA gene sequences revealed that Clostridium M1NH shares a 98% similarity with Clostridium luticellarii DSM 29923  T . The robustness of strain M1NH and its efficient caproic acid production from low-cost substrates highlight its potential for sustainable bio-based chemical production. The maximum caproic acid yield achieved by Clostridium M1NH was 1.6-fold higher than that reported for C. kluyveri under similar fermentation conditions. This study opens new avenues for valorizing waste streams and advancing a circular economy model in the chemical industry., (© 2024. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.)

The fermentation of synthesis gas (including carbon monoxide, carbon dioxide, and hydrogen) with anaerobic acetogens is an established biotechnological process that has recently been transferred to a commercial scale. The natural product spectrum of acetogens is natively restricted to acetate, ethanol, and 2,3-butanediol but is rapidly expanding to heterologous products. Syngas fermentation can achieve high carbon-efficiencies; however, the underlying metabolism is operating at a thermodynamic limit. This necessitates special enzymatic properties for energy conservation by acetogens. Therefore, the availability of cellular energy is considered to restrain the efficient production of energy-intense products with complex production pathways. The optimization of the feed-gas composition and other process parameters, genetic engineering, and integration with other biotechnologies is required to overcome this limitation., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

Technological solutions to reduce greenhouse gas (GHG) emissions from anthropogenic sources are required. Heavy industrial processes, such as steel making, contribute considerably to GHG emissions. Fermentation of carbon monoxide (CO)-rich off gases with wild-type acetogenic bacteria can be used to produce ethanol, acetate, and 2,3-butanediol, thereby, reducing the carbon footprint of heavy industries. Here, the processes for the production of ethanol from CO-rich off gases are discussed and a perspective on further routes towards an integrated biorefinery at a steel mill is given. Recent achievements in genetic engineering as well as integration of other biotechnology platforms to increase the product portfolio are summarized. Already, yields have been increased and the portfolio of products broadened. To develop a commercially viable process, however, the extraction from dilute product streams is a critical step and alternatives to distillation are discussed. Finally, another critical step is waste(water) treatment with the possibility to recover resources., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

Fermentation of syngas from renewable biomass, which is part of the syngas platform, is gaining momentum. Here, the objective was to evaluate a proof-of-concept bioprocessing system with diluted ethanol and acetic acid in actual syngas fermentation effluent as the substrate for chain elongation into the product n-caproic acid, which can be separated with less energy input than ethanol. Chain elongation is performed with open cultures of microbial populations (reactor microbiomes) as part of the carboxylate platform. The highest concentration of n-caproic acid of ~1 g L(-1) was produced at a pH of 5.44 and a production rate of 1.7 g L(-1) day(-1). A higher n-butyrate production rate of 20 g L(-1) day(-1) indicated that product toxicity was limiting the chain elongation step from n-butyric acid to n-caproic acid. This result shows that the syngas and carboxylate platforms can be integrated within a biorefinery, but that product separation is necessary., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

Short-chain carboxylic acids generated by various mixed- or pure-culture fermentation processes have been considered valuable precursors for production of bioalcohols. While conversion of carboxylic acids into alcohols is routinely performed with catalytic hydrogenation or with strong chemical reducing agents, here, a biological conversion route was explored. The potential of carboxydotrophic bacteria, such as Clostridium ljungdahlii and Clostridium ragsdalei, as biocatalysts for conversion of short-chain carboxylic acids into alcohols, using syngas as a source of electrons and energy is demonstrated. Acetic acid, propionic acid, n-butyric acid, isobutyric acid, n-valeric acid, and n-caproic acid were converted into their corresponding alcohols. Furthermore, biomass yields and fermentation stoichiometry from the experimental data were modeled to determine how much metabolic energy C. ljungdahlii generated during syngas fermentation. An ATP yield of 0.4-0.5 mol of ATP per mol CO consumed was calculated in the presence of hydrogen. The ratio of protons pumped across the cell membrane versus electrons transferred from ferredoxin to NAD(+) via the Rnf complex is suggested to be 1.0. Based on these results, we provide suggestions how n-butyric acid to n-butanol conversion via syngas fermentation can be further improved., (Copyright © 2012 Wiley Periodicals, Inc.)

A simple potentiostat was constructed as a strategy to enhance solvent production in a mediatorless and oxygen-exposed fermentation inoculated with the aerotolerant strain Clostridium sp. C10. Elevated n-butanol and acetone titers were recorded in all fermentations with either glucose or xylose in the presence of electrodes poised at + 500 mV (+ 814 mV vs SHE) relative to cells plus substrate only controls. Respective butanol titers and volumetric butanol productivities in studies performed with 30 g/L glucose or 30 g/L xylose were 1.67 and 2.27 times and 1.90 and 6.13 times greater in the presence of electrodes compared to controls. Glucose and xylose utilization in the presence of electrodes was 61 and 125% greater than no-electrode controls, respectively. Increasing substrate concentrations to 60 g/L decreased the butanol yields relative to the studies performed at 30 g/L. These data suggest that it may be more efficient to alter reactor reduction potential than increase substrate concentration for solvent output during industrial fermentations, which favors higher yield with few additional inputs.

The vast majority of the food we eat comes from land-based agriculture, but recent technological advances in agriculture and food technology offer the prospect of producing food using substantially less or even virtually no land. For example, indoor vertical farming can achieve very high yields of certain crops with a very small area footprint, and some foods can be synthesized from inorganic precursors in industrial facilities. Animal-based foods require substantial land per unit of protein or per calorie and switching to alternatives could reduce demand for some types of agricultural land. Plant-based meat substitutes and those produced through fermentation are widely available and becoming more sophisticated while in the future cellular agricultural may become technically and economical viable at scale. We review the state of play of these potentially disruptive technologies and explore how they may interact with other factors, both endogenous and exogenous to the food system, to affect future demand for land. [ABSTRACT FROM AUTHOR]

Bioproduction of short chain carboxylic acids (SCCAs) and medium chain carboxylic acids (MCCAs) has emerged as an alternative strategy to upgrade low-value organic waste and reduce fossil fuels requirement. Using synthesis gas (syngas) to generate SCCAs and MCCAs by microbial communities would be an option to address part of the current energy challenge. Syngas fermentation offers a pathway for the sustainable synthesis of fuels and chemicals with advantages over catalytic syngas conversion. In the same way, chain elongation is an anaerobic microbial process driven by ethanol, carbohydrates, and SCCAs (e.g., acetate, lactate) to obtain high-value MCCAs (e.g., caproate, valerate). Because these technologies use organic wastes as feedstocks, mixed microbial communities are often considered biocatalysts. However, the management of microbial communities is the biggest bottleneck for efficient and simultaneous production of SCCAs and MCCAs. Understanding and steering these microbiomes is critical to optimize bioprocess performance. Therefore, this review discusses the metabolic pathways of both syngas fermentation and chain elongation. Also, to examine the overall performance of microbial communities involved in syngas fermentation and chain elongation, the influence of reactor parameters on the growth and metabolic activity of the key microorganisms is presented. The experimental strategies for simultaneous syngas fermentation and chain elongation processes are also presented and discussed. Finally, the use of multi-omics to better understand both syngas fermentation and chain elongation processes is discussed to steer these bioproduction processes towards full-scale applications. [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]

Objective: The aim of this study was to investigate the impact of dietary nicotinic acid (NA) on apparent nutrient digestibility, rumen fermentation, and rumen microbiota in uncastrated Xiangzhong black cattle. Methods: Twenty-one uncastrated Xiangzhong black cattle (385.08±15.20 kg) aged 1.5 years were randomly assigned to the control group (CL, 0 mg/kg NA in concentrate diet), NA1 group (800 mg/kg NA in concentrate diet) and NA2 group (1,200 mg/kg NA in concentrate diet). All animals were fed a 60% concentrate diet and 40% dried rice straw for a 120-day feeding experiment. Results: Supplemental NA not only enhanced the apparent nutrient digestibility of acid detergent fiber (p<0.01), but also elevated the rumen acetate and total volatile fatty acid concentrations (p<0.05). 16S rRNA gene sequencing analysis of rumen microbiota revealed that dietary NA changed the diversity of rumen microbiota (p<0.05) and the abundance of bacterial taxa in the rumen. The relative abundances of eight Erysipelotrichales taxa, five Ruminococcaceae taxa, and five Sphaerochaetales taxa were decreased by dietary NA (p< 0.05). However, the relative abundances of two taxa belonging to Roseburia faecis were increased by supplemental 800 mg/kg NA, and the abundances of seven Prevotella taxa, three Paraprevotellaceae taxa, three Bifidobacteriaceae taxa, and two operational taxonomic units annotated to Fibrobacter succinogenes were increased by 1,200 mg/kg NA in diets. Furthermore, the correlation analysis found significant correlations between the concentrations of volatile fatty acids in the rumen and the abundances of bacterial taxa, especially Prevotella. Conclusion: The results from this study suggest that dietary NA plays an important role in regulating apparent digestibility of acid detergent fiber, acetate, total volatile fatty acid concentrations, and the composition of rumen microbiota. [ABSTRACT FROM AUTHOR]

Background: Lignocellulosic biomass plays a crucial role in creating a circular bioeconomy and minimizing environmental impact. Enset biomass is a byproduct of traditional Ethiopian Enset food processing that is thrown away in huge quantities. This study aimed to produce caproate from Enset fiber using Neocallimastix cameroonii strain G341 and Clostridium kluyveri DSM 555 in one-pot two-step fermentation. Results: The process started by growing N. cameroonii on Enset fiber as a carbon source for 7 days. Subsequently, the fungal culture was inoculated with active C. kluyveri preculture and further incubated. The results showed that N. cameroonii grew on 0.25 g untreated Enset fiber as the sole carbon source and produced 1.16 mmol acetate, 0.51 mmol hydrogen, and 1.34 mmol formate. In addition, lactate, succinate, and ethanol were detected in small amounts, 0.17 mmol, 0.08 mmol, and 0.7 mmol, respectively. After inoculating with C. kluyveri, 0.3 mmol of caproate and 0.48 mmol of butyrate were produced, and hydrogen production also increased to 0.95 mmol compared to sole N. cameroonii fermentation. Moreover, after the culture was supplemented with 2.18 mmol of ethanol during C. kluyveri inoculation, caproate, and hydrogen production was further increased to 1.2 and 1.36 mmol, respectively, and the consumption of acetate also increased. Conclusion: A novel microbial cell factory was developed to convert untreated lignocellulosic Enset fiber into the medium chain carboxylic acid caproate and H2 by a co-culture of the anaerobic fungi N. cameroonii and C. kluyveri. This opens a new value chain for Enset farmers, as the process requires only locally available raw materials and low-price fermenters. As the caproate production was mainly limited by the available ethanol, the addition of locally produced ethanol-containing fermentation broth ("beer") would further increase the titer. [ABSTRACT FROM AUTHOR]

Syngas is created through the thermochemical conversion of biomass using gasification or pyrolysis and from CO‐rich off‐gases obtained from industries such as steel mills. The Wood–Ljungdahl metabolic pathway, or one of its variations, is used by acetogenic bacteria to convert syngas components (CO, H2, and CO2) to alcohols and other compounds. Many factors affect how well syngas is fermented, including the bacteria species used, syngas composition, medium components, bioreactor type, operational parameters used and the gas–liquid mass transfer rate. These parameters impact carbon and electron flow in the bacteria, influencing the distribution, concentration and metabolic end‐product yield, which determines process feasibility. This article focuses on gas composition, microorganisms, gas–liquid mass transfer fermentation strategies, medium design and commercialization activities to develop the syngas fermentation processes. © 2023 Society of Industrial Chemistry and John Wiley & Sons Ltd. [ABSTRACT FROM AUTHOR]

Background: The product of current syngas fermentation systems is an ethanol/acetic acid mixture and the goal is to maximize ethanol recovery. However, ethanol currently has a relatively low market value and its separation from the fermentation broth is energy intensive. We can circumvent these disadvantages of ethanol production by converting the dilute ethanol/acetic acid mixture into products with longer carbon backbones, which are of higher value and are more easily extracted than ethanol. Chain elongation, which is the bioprocess in which ethanol is used to elongate short-chain carboxylic acids to medium-chain carboxylic acids (MCCAs), has been studied with pure cultures and open cultures of microbial consortia (microbiomes) with several different substrates. While upgrading syngas fermentation effluent has been studied with open cultures, to our knowledge, no study exists that has performed this with pure cultures. Results: Here, pure cultures of Clostridium kluyveri were used in continuous bioreactors to convert ethanol/acetic acid mixtures into MCCAs. Besides changing the operating conditions in regards to substrate loading rates and composition, the effect of in-line product extraction, pH, and the use of real syngas fermentation effluent on production rates were tested. Increasing the organic loading rates resulted in proportionally higher production rates of n-caproic acid, which were up to 40 mM day-1 (4.64 g L-1 day-1) at carbon conversion efficiencies of 90% or higher. The production rates were similar for bioreactors with and without in-line product extraction. Furthermore, a lower ethanol/acetic acid ratio (3:1 instead of 10:1) enabled faster and more efficient n-caproic acid production. In addition, n-caprylic acid production was observed for the first time with C. kluyveri (up to 2.19 ± 0.34 mM in batch). Finally, the use of real effluent from syngas fermentation, without added yeast extract, but with added defined growth factors, did maintain similar production rates. Throughout the operating period, we observed that the metabolism of C. kluyveri was inhibited at a mildly acidic pH value of 5.5 compared to a pH value of 7.0, while reactor microbiomes perform successfully at mildly acidic conditions. Conclusions: Clostridium kluyveri can be used as a biocatalyst to upgrade syngas fermentation effluent into MCCAs at pH values above 5.5. [ABSTRACT FROM AUTHOR]

Background: Hydrogen gas (H2) is a common product of carbohydrate fermentation in the human gut microbiome and its accumulation can modulate fermentation. Concentrations of colonic H2 vary between individuals, raising the possibility that H2 concentration may be an important factor differentiating individual microbiomes and their metabolites. Butyrate-producing bacteria (butyrogens) in the human gut usually produce some combination of butyrate, lactate, formate, acetate, and H2 in branched fermentation pathways to manage reducing power generated during the oxidation of glucose to acetate and carbon dioxide. We predicted that a high concentration of intestinal H2 would favor the production of butyrate, lactate, and formate by the butyrogens at the expense of acetate, H2, and CO2. Regulation of butyrate production in the human gut is of particular interest due to its role as a mediator of colonic health through anti-inflammatory and anti-carcinogenic properties. Results: For butyrogens that contained a hydrogenase, growth under a high H2 atmosphere or in the presence of the hydrogenase inhibitor CO stimulated production of organic fermentation products that accommodate reducing power generated during glycolysis, specifically butyrate, lactate, and formate. Also as expected, production of fermentation products in cultures of Faecalibacterium prausnitzii strain A2-165, which does not contain a hydrogenase, was unaffected by H2 or CO. In a synthetic gut microbial community, addition of the H2-consuming human gut methanogen Methanobrevibacter smithii decreased butyrate production alongside H2 concentration. Consistent with this observation, M. smithii metabolic activity in a large human cohort was associated with decreased fecal butyrate, but only during consumption of a resistant starch dietary supplement, suggesting the effect may be most prominent when H2 production in the gut is especially high. Addition of M. smithii to the synthetic communities also facilitated the growth of E. rectale, resulting in decreased relative competitive fitness of F. prausnitzii. Conclusions: H2 is a regulator of fermentation in the human gut microbiome. In particular, high H2 concentration stimulates production of the anti-inflammatory metabolite butyrate. By consuming H2, gut methanogenesis can decrease butyrate production. These shifts in butyrate production may also impact the competitive fitness of butyrate producers in the gut microbiome. 3hTM6nso89x7h1g_xY7TKk Video Abstract [ABSTRACT FROM AUTHOR]

The growing global population and higher living standards instantly demand the transition in the direction of a sustainable food system. A substantial section of means and agricultural lands are presently committed to protein-rich feed production to rear livestock for human consumption. Conversely, accelerated farming activities and the food industry have rendered a drastic increase in waste which impair the economic and environmental sustainability of the ecosystem. This situation emerges the need for developing an integrated technology for waste management and to improve sustainability footprints. Microbial protein (MP) production based on renewable electron and carbon sources has the potential as a substitute protein source. MP production for animal feed use is growing fast and is derived from bacteria, algae, and fungi including yeast. MP produced from all types of microbes is currently commercialized and in use. However, novel methods and processes are also under investigation to make MP production more economical and sustainable. Current research on MP has concentrated on the valorization of waste materials by using high protein content-containing microorganisms, which can then be used in animal feed. Using such kind of integrated approach, the agroindustry waste resources upcycling can contribute towards finding sustainable, cheaper, and environment-friendly protein sources. This review first describes the potential waste feedstock for MP production and summarizes the recent progress in the application of MP-producing microorganisms including fungus, yeast, bacteria, and phototrophic microbes. Bioprocesses, and production technology advances for MP production have been explored and discussed in detail. Finally, the MP application as animal feed, its challenges, and future perspectives in research have been evaluated. [ABSTRACT FROM AUTHOR]

The purpose of this research is to experimentally evaluate the anaerobic co-digestion in the city of Guaranda of slaughterhouse residues (RM) with straw residues from agriculture, such as amaranth residues (AM), quinoa residues (QU) and residues of wheat (TR), to reduce slaughterhouse discharges and prevent contamination of the city. The study was carried out on a laboratory scale in 311-ml biodigesters under mesophilic conditions of 37 °C. In addition, sewage sludge was used as inoculum with two relationships between substrate and inoculum (SIR 1:1 and SIR 1:2). The design was completed using three relationships between substrate (RM) and co-substrate (AM, QU and TR): 25:75, 50:50 and 75:25. Anaerobic co-digestion resulted in methane yields of 407 ml CH4/g VS, with a methane content in the biogas of 77% for the mixture of RM and QU (RM-QU (25:75)). The increase in inoculum in the mixtures composed of RM and QU increased the biodegradability between 17 and 22%. However, in the mixtures of slaughterhouse waste and amaranth (RM-AM (25:75)), a further increase in inoculum reduced biodegradability by 5%. The results revealed that there is a greater synergy between the RM and QU as the percentage of QU in the mixture is increased. This meant that the co-digestion of the RM with the QU accelerates the biodegradability of the mixture, increasing the production of biogas. [ABSTRACT FROM AUTHOR]

Lignocellulose degradation (LCD) was the key factor limiting the development of anaerobic fermentation (AF) by the cow dung (CD). In the research, the effects of cellulase pretreatment (CP) and microvoltage (MV) alone and combination on the gas production and LCD during the AF were investigated. The results showed that both CP and MV had an significant effect on the AF, though the synergistic reaction was more pronounced. The total biogas yield (TBY) could reach 11521 mL, and the highest methane production rate was 73% in the synergistic reactions, which was increased by 18.7% and 10.0% compared to CP and MV alone respectively. Meanwhile, the degradation rates of cellulose and lignin could be increased by 33.44% and 22.23%, respectively. The results of SEM, FT-IR and excitation emission matrix demonstrated that CP and MV played an important role in improving the fermentation efficiency. The microbial biomass change results indicated that the synergistic effect of CP and 0.8 V MV on the LCD was achieved by promoting the growth of lignocellulose-degrading bacteria. Moreover, the electricity could not only accelerate the movement of microorganisms and enzymes, but also promoted and enhanced the activity of enzymes, which provided an important reference for further development of the AF technology and the biogas industry. [ABSTRACT FROM AUTHOR]

Rice straw is an abundant lignocellulosic biomass used to produce biogas. However, its resistant structure hinders biogas production. In this study, three pretreatments, microwave, ammoniation, and microwave-assisted ammoniation (MAA), were evaluated for their use in improving biogas production from rice straw. After an 18-day digestion, methane production by rice straw pretreated with MAA was 281.56 mL/g (volatile solids of substrate), which was 25.43%, 7.96%, and 18.18% more than that produced following the control, microwave, and ammoniation pretreatments, respectively. These increases were mainly attributed to the change in the resistant structure of rice straw following the MAA pretreatment and a more stable anaerobic digestion system. The degradation rate for the volatile solids of the rice straw pretreated with MAA during anaerobic digestion was 71.20%, which was 4.71%, and 4.86% higher than the rates observed using microwave and ammoniation pretreatments, respectively. In addition, the MAA method had a T90 fermentation cycle of 6 days, which was 33.3%, 25.0%, and 33.3% shorter than those for the control, microwave, and ammoniation methods, respectively. This technology shows the potential to enhance biogas production from the anaerobic digestion of rice straw. [ABSTRACT FROM AUTHOR]

Background: The intestinal microbes in mammals play a key role in host metabolism and adaptation. As a subterranean rodent, zokor digs tunnels for foraging and mating. These digging activities of zokors increase the energy expenditure relative to their aboveground counterparts. However, relatively little is known regarding intestinal microbes of zokor and how they make full use of limited food resources underground for high energy requirements. Results: Eospalax cansus and Eospalax rothschildi had distinct intestinal microbes. Although the composition of intestinal microbes is similar in two species, the proportion of bacterium are distinctly different between them. At phylum level, 11 phyla were shared between two species. Firmicutes and Bacteroidota were two dominant microbes in both of two species, while Eospalax cansus have a significantly high proportion of Firmicutes/Bacteroidota than that of Eospalax rothschildi. At genus level, norank_f_Muribaculaceae were dominant microbes in both of two zokor species. The relative abundance of 12 genera were significantly different between two species. Some bacterium including unclassified_f__Lachnospiraceae, Lachnospiraceae_NK4A136_group, Ruminococcus and Eubacterium_siraeum_group associated with cellulose degradation were significantly enriched in Eospalax cansus. Although alpha diversity was with no significant differences between Eospalax cansus and Eospalax rothschildi, the intestinal microbes between them are significant distinct in PCoA analysis. We have found that trapping location affected the alpha diversity values, while sex and body measurements had no effect on alpha diversity values. PICRUSt metagenome predictions revealed significant enrichment of microbial genes involved in carbohydrate metabolism in Eospalax cansus rather than Eospalax rothschildi. Conclusions: Our results demonstrate that Eospalax cansus harbor a stronger ability of fermentation for dietary plants than Eospalax rothschildi. The stronger ability of fermentation and degradation of cellulose of intestinal microbes of Eospalax cansus may be a long-time adaptation to limited food resources underground. [ABSTRACT FROM AUTHOR]

This study aims to evaluate the effects of the co‐digestion of agricultural residues with manure from camelids from the Andean zone. Different combinations of llama manure (LM) and vicuñas (VM) were made with amaranth (AS), quinoa (QS), and wheat (WS) residues. They were fermented using sewage sludge as inoculum. The co‐digestion was evaluated under mesophilic conditions for 40 days. The ratios of volatile substances of substrate / co‐substrate evaluated were 0:100; 25:75; 50:50, 75:25, and 100:0. Two substrate / inoculum ratios (SIR 1:1 and SIR1:2) were also evaluated. The results indicate that the maximum methane accumulation rate is obtained in SIR 1:1 for a VM‐AS ratio (25:75) with 540 mL/g volatile solid (VS). In general, the results did not increase with the increase in inoculum; rather, the tendency to improve methane yield is associated with an increase in the amount of agricultural residues, mainly AS. Regarding the kinetic modeling, the transfer model is the one that best adjusted the predicted values to those observed with an r2 between 0.991 and 0.999, and an RMSE value between 2.06 and 13.62 mL/g (volatile solid) VS. Finally, all the trials presented synergistic effects in their co‐digestion except the digesters formed by LM‐AS, LM‐QS and LM‐WS of SIR 1:2. These presented antagonistic effects in which the addition of the co‐substrate generated competition with the substrates, reducing methane production. © 2021 Society of Chemical Industry and John Wiley & Sons, Ltd [ABSTRACT FROM AUTHOR]

The aim of this study was to evaluate the effect of different inoculum ratio on the dark fermentation of kitchen waste in terms of volatile fatty acids (VFAs) and H2 production. The experiments were performed in batch bioreactors of effective volume 1 L without pH regulation. The ratio between the DS and KW was being increased from 0.11 to 0.51 on a volatile solids (VS) basis, while the initial content of KW was equal to 34.1 g VS/L. Increase of the DS/KW ratio from 0.11 to 0.28 resulted in the rise of VFAs and H2 production. Further increase in the amount of added DS did not cause a significant change in the production of VFAs and H2. In the bioreactor with the DS/KW ratio of 0.28, the production of VFAs and H2 was equal to 16.0 g/L and 68.1 mL/g VS, respectively. Acetic and butyric acids were produced in the largest amount and their content, for DS/KW ratio of 0.28, were equal 37% and 43%, respectively. At the ratio of DS/KW above 0.4, the caproic acid content attained the level of 25%. Based on the DS and KW microbiological analysis, it was observed that dominant bacteria were Bacteroidetes, Firmicutes, Proteobacteria, Spirochaetes and WWE1 at the phylum level. [ABSTRACT FROM AUTHOR]

Coffee beans derived from feces of the civet cat are used to brew coffee known as kopi luwak (the Indonesian words for coffee and palm civet, respectively), which is one of the most expensive coffees in the world owing to its limited supply and strong market demand. Recent metabolomics studies have revealed that kopi luwak metabolites differ from metabolites found in other coffee beans. To produce kopi luwak, coffee beans are first eaten by civet cats. It has been proposed that fermentation inside the civet cat digestive tract may contribute to the distinctively smooth flavor of kopi luwak, but the biological basis has not been determined. Therefore, we characterized the microbiome of civet cat feces using 16S rRNA gene sequences to determine the bacterial taxa that may influence fermentation processes related to kopi luwak. Moreover, we compared this fecal microbiome with that of 14 other animals, revealing that Gluconobacter is a genus that is, uniquely found in feces of the civet cat. We also found that Gluconobacter species have a large number of cell motility genes, which may encode flagellar proteins allowing colonization of the civet gut. In addition, genes encoding enzymes involved in the metabolism of hydrogen sulfide and sulfur-containing amino acids were over-represented in Gluconobacter. These genes may contribute to the fermentation of coffee beans in the digestive tract of civet cats. [ABSTRACT FROM AUTHOR]

Background: Ethanol production through fermentation of gas mixtures containing CO, CO2 and H2 has just started operating at commercial scale. However, quantitative schemes for understanding and predicting productivities, yields, mass transfer rates, gas flow profiles and detailed energy requirements have been lacking in literature; such are invaluable tools for process improvements and better systems design. The present study describes the construction of a hybrid model for simulating ethanol production inside a 700 m3 bubble column bioreactor fed with gas of two possible compositions, i.e., pure CO and a 3:1 mixture of H2 and CO2. Results: Estimations made using the thermodynamics-based black-box model of microbial reactions on substrate threshold concentrations, biomass yields, as well as CO and H2 maximum specific uptake rates agreed reasonably well with data and observations reported in literature. According to the bioreactor simulation, there is a strong dependency of process performance on mass transfer rates. When mass transfer coefficients were estimated using a model developed from oxygen transfer to water, ethanol productivity reached 5.1 g L−1 h−1; when the H2/CO2 mixture is fed to the bioreactor, productivity of CO fermentation was 19% lower. Gas utilization reached 23 and 17% for H2/CO2 and CO fermentations, respectively. If mass transfer coefficients were 100% higher than those estimated, ethanol productivity and gas utilization may reach 9.4 g L−1 h−1 and 38% when feeding the H2/CO2 mixture at the same process conditions. The largest energetic requirements for a complete manufacturing plant were identified for gas compression and ethanol distillation, being higher for CO fermentation due to the production of CO2. Conclusions: The thermodynamics-based black-box model of microbial reactions may be used to quantitatively assess and consolidate the diversity of reported data on CO, CO2 and H2 threshold concentrations, biomass yields, maximum substrate uptake rates, and half-saturation constants for CO and H2 for syngas fermentations by acetogenic bacteria. The maximization of ethanol productivity in the bioreactor may come with a cost: low gas utilization. Exploiting the model flexibility, multi-objective optimizations of bioreactor performance might reveal how process conditions and configurations could be adjusted to guide further process development. [ABSTRACT FROM AUTHOR]

This study is focused on the effects of pH on the production of volatile fatty acids (VFAs) and their distribution through the acidogenic fermentation of source-sorted organic fraction of municipal solid waste (OFMSW) from a mechanical-biological treatment (MBT) plant, and food waste (FW) from a university canteen. In semi-continuous lab-scale digesters using OFMSW at a hydraulic retention time (HRT) of 3.5 days under acidic conditions (pH 6.0), the VFA concentration in the effluent increased to 9.8–11.5 g L−1 (VS content of the feedstock between 4.2 and 5.2% w/w), while its individual VFA profiling was similar to the influent which was already pre-fermented (namely, C2 35–41%, C3 18–22%, C4 17–21%, and C5 9–12%). When working with the same conditions but using FW as feedstock, an effluent with a VFA concentration up to 11.5 g VFA L−1 (FW with a VS content of 5.5% w/w) and a stable distribution of C2 and C4 acids (up to 60.3% and 12.9%, respectively) but with very low quantities of C3 and C5 acids (lower than 1.8 and 2.7%, respectively) was obtained. Anaerobic batch tests using FW revealed that alkaline pH near 9 could lead to higher VFA production with high acetic acid content when compared to pH 6. In the semi-continuous fermenters working at alkaline conditions (pH 9.5–10) using OFMSW and FW, an enhanced solubilization of organic matter was registered with respect to the fermenters working under acidic conditions. This fact was not reflected in a higher VFA production when using OFMSW as feedstock, probably due to free ammonia inhibition, since OFMSW was mixed in the MBT plant with supernatant from anaerobic digestion of this biowaste. However, when using FW, alkaline conditions lead to an enhanced VFA production with respect to the reactor working under acidic conditions, being acetic acid the predominant product, which represented up to 91% of the VFA spectrum obtained. [ABSTRACT FROM AUTHOR]

The micro-organisms which inhabit the human gut (i.e. the intestinal microbiota) influence numerous human biochemical pathways and physiological functions. The present review focuses on two questions, 'Are intestinal microbiota effects measurable and meaningful?' and 'What research methods and variables are influenced by intestinal microbiota effects?'. These questions are considered with respect to doubly labelled water measurements of energy expenditure, heat balance calculations and models, measurements of RMR via indirect calorimetry, and diet-induced energy expenditure. Several lines of evidence suggest that the intestinal microbiota introduces measurement variability and measurement errors which have been overlooked in research studies involving nutrition, bioenergetics, physiology and temperature regulation. Therefore, we recommend that present conceptual models and research techniques be updated via future experiments, to account for the metabolic processes and regulatory influences of the intestinal microbiota. [ABSTRACT FROM AUTHOR]

Syngas fermentation has been successfully implemented in commercial-scale plants and can enable the biochemical conversion of the driest fractions of biomass through synthesis gas (H2, CO2, and CO). The process relies on optimized acetogenic strains able to reach and maintain high productivity of ethanol and acetate. In parallel, microbial communities have shown to be the best choice for the production of valuable medium-chain carboxylates through anaerobic fermentation of biomass, demanding low technical complexity and being able to realize simultaneous hydrolysis of the substrate. Each of the two technologies benefits from different strong points and has different challenges to overcome. This review discusses the rationales for merging these two seemingly disparate technologies by analyzing previous studies and drawing opinions based on the lessons learned from such studies. For keeping the technical demands of the resulting process low, a case is built for using microbial communities instead of pure strains. For that to occur, a shift from conventional syngas-based to "syngas-aided" anaerobic fermentation is suggested. Strategies for tackling the intricacies of working simultaneously with communities and syngas, such as competing pathways, and thermodynamic aspects are discussed as well as the stoichiometry and economic feasibility of the concept. Overall, syngas-aided anaerobic fermentation seems to be a promising concept for the biorefinery of the future. However, the effects of process parameters on microbial interactions have to be understood in greater detail, in order to achieve and sustain feasible medium-chain carboxylate and alcohol productivity. [ABSTRACT FROM AUTHOR]

Clostridia are Gram-positive, spore-forming, obligate anaerobic bacteria that can produce solvents such as acetone, ethanol, and butanol, which can be used as biofuels or building block chemicals. Many successful attempts have been made to improve solvent yield and titer from sugars through metabolic engineering of solventogenic and acidogenic clostridia. More recently, cellulolytic and acetogenic clostridia have also attracted high interests for their ability to utilize low-cost renewable substrates such as cellulose and syngas. Process engineering such as in situ butanol recovery and consolidated bioprocessing (CBP) has been developed for improved solvent titer and productivity. This review focuses on metabolic and process engineering strategies for solvent production from sugars, lignocellulosic biomass, and syngas by various clostridia, including conventional solventogenic Clostridium acetobutylicum, engineered acidogens such as C. tyrobutyricum and C. cellulovorans, and carboxydotrophic acetogens such as C. carboxidivorans and C. ljungdahlii. [ABSTRACT FROM AUTHOR]

Solid-state fermentation is a potential technology for developing lignocellulosic biomass-based biorefineries. This work dealt with solid-state fermentation for carboxylates production from corn stover, as building blocks for a lignocellulosic feedstock-based biorefinery. The effect of extrusion pretreatment, together with the action of a microbial consortia and hydrolytic enzymes as biotic triggers, was investigated on corn stover conversion, microbial metabolic pathways, and populations. The extrusion caused changes in the physical and morphological characteristics, without altering the biochemical composition of the corn stover. Extrusion also led to remarkable differences in the composition of the indigenous microbial population of the substrate. Consequently, it affected the structure of community developed after fermentation and the substrate conversion yield, which increased by 118% (from 23 ± 4 gCOD/kgVSi obtained with raw substrate to 51 ± 1 gCOD/kgVSi with extruded corn stover) with regard to self-fermentation experiments. The use of activated sludge as inoculum further increased the total substrate conversion into carboxylates, up to 60 ± 2 gCOD/kgVSi, and shaped the microbial communities (mainly composed of bacteria from the Clostridia and Bacteroidia classes) with subsequent homogenization of the fermentation pathways. The addition of hydrolytic enzymes into the reactors further increased the corn stover conversion, leading to a maximum yield of 142 ± 1 gCOD/kgVSi. Thus, extrusion pretreatment combined with the use of an inoculum and enzyme addition increased by 506% corn stover conversion into carboxylates. Beside biomass pretreatment, the results of this study indicated that biotic factor greatly impacted solid-state fermentation by shaping the microbial communities and related metabolic pathways. [ABSTRACT FROM AUTHOR]

Chain elongation is one of the common anaerobic fermentation processes in which bacteria convert ethanol and short chain fatty acids (SCFA) into medium chain fatty acids (MCFA). These are single carboxylic acids having six to twelve carbon atoms, with several applications, such as biofuels. Caproate is a promising MCFA, and several technologies were proposed for the valorization of waste to obtain it. Bioelectrochemical systems (BESs) are technologies that are capable of converting the chemical energy of organic/inorganic wastes into value‐added products, using in situ generated H2 or electricity as energy sources. To convert waste biomass into caproate, an electron donor in the form of hydrogen or ethanol should be supplemented within the anaerobic fermentation, which can be used as the electron donor in the cathodic compartment for the conversion of acetate into caproate. This review highlights recent anaerobic and bioelectrochemical processes for the production of caproate. The discussion will also cover the potential applications of this technology, together with obstacles to its use, compared with the conventional anaerobic digestion (AD) process, and considers whether it could be a standalone technology or a complementary one for AD. © 2018 Society of Chemical Industry and John Wiley & Sons, Ltd [ABSTRACT FROM AUTHOR]

The anaerobic digestion of food waste (FW) often leads to acidification inhibition owing to rapid biodegradation, resulting in system instability. In this study, distillers’ grains (DG) and food waste were mixed in accordance with volatile solid (VS) ratios of 0.9:0.1, 0.85:0.15, 0.8:0.2, and 0.7:0.3. The experimental groups adopted yeast to conduct ethanol pre-fermentation and then inoculated sludge to perform anaerobic digestion, while the control groups conducted anaerobic digestion without pre-treatment. Results showed that the experimental groups had lower propionic acid concentrations; higher alkalinities, pH values and methane production rates and shorter stagnation periods than the control groups regardless of the mixing ratio. Specifically, at the DG/FW ratio of 0.7:0.3, compared with the control group, the propionic acid concentration was reduced by 59.6%, the alkalinity was increased by 41.7%. Even under high organic loading, the propionic acid and VFA did not accumulate in the system after ethanol pre-fermentation, and the anaerobic digestion system remained stable. At DG/FW ratios of 0.9:0.1 and 0.85:0.15, a synergistic effect was observed during the co-digestion of DG and FW. And, the synergistic effect of EP was relatively high, especially when the DG/FW ratio was 0.9:0.1, and methane yield increased by 26.8%. [ABSTRACT FROM AUTHOR]

Microbial consortium is an alternative for bioconversion of crude glycerol to value-added products whereas concerns about the process stability in long-term operation existed. The aim of this study is to evaluate the feasibility of using an anaerobic microbial consortium as inoculum for continuous conversion of crude glycerol to 1,3-propanediol (1,3-PDO). Performances of continuous fermentations with the consortium inoculum were evaluated under different dilution rates and glycerol feed concentrations. The highest 1,3-PDO production of 57.86 g/L was achieved with a productivity of 5.55 g/(L·h). Analyses of kinetic data showed that the consortium maintained a consistent pattern for 1,3-PDO production under different operating conditions despite changes in community composition. The continuous fermentation by the consortium was able to operate for a longer period of time (31 volume changes) than that using pure culture (24 volume changes) with the average 1,3-PDO concentration of 53.52 g/L and productivity of 6.69 g/(L·h) under glycerol-excess condition, which could be contributed to the intraspecies diversity among Clostridium butyricum in the consortium. Under glycerol-limited conditions, however, a spontaneous oscillation of the consortium was observed after continuous operation for about 120 h, along with severe fluctuations of the microbial community. The oscillatory behavior could be reduced by increasing the dilution rates and was likely the metabolic feature of C. butyricum. [ABSTRACT FROM AUTHOR]

A decade ago, a novel mechanism to drive thermodynamically unfavorable redox reactions was discovered that is used in prokaryotes to drive endergonic electron transfer reactions by a direct coupling to an exergonic redox reaction in one soluble enzyme complex. This process is referred to as flavin-based electron bifurcation, or FBEB. An important function of FBEB is that it allows the generation of reduced low-potential ferredoxin (Fdred) from comparably high-potential electron donors such as NADH or molecular hydrogen (H2). Fdred is then the electron donor for anaerobic respiratory chains leading to the synthesis of ATP. In many metabolic scenarios, Fd is reduced by metabolic oxidoreductases and Fdred then drives endergonic metabolic reactions such as H2 production by the reverse, electron confurcation. FBEB is energetically more economical than ATP hydrolysis or reverse electron transport as a driving force for endergonic redox reactions; thus, it does “save” cellular ATP. It is essential for autotrophic growth at the origin of life and also allows for heterotrophic growth on certain low-energy substrates. [ABSTRACT FROM AUTHOR]

An experiment was conducted to determine the effects of soy isoflavone daidzein on ruminal fermentation, microbial protein synthesis and rumen bacterial community in beef cattle. Six rumen-cannulated adult beef cattle were assigned to three blocks according to similar body weight in a randomised block design, with two cattle each block. Each block randomly received one of the two dietary treatments: control (basal concentrate) and daidzein (supplementation with 500 mg daidzein/kg basal concentrate). High-throughput sequencing data showed that supplemental daidzein increased the relative abundance of bacteria belonging to phylum Bacteroidetes (p = .050), but reduced and tended to reduce the relative abundance of phylum Spirochaetae (p = .030) and Firmicutes (p = .080). At the genus level, the relative abundance of Prevotella (p = .036), RC9_gut_group (p = .019), Succinivibrio (p = .093) and Ruminobacter (p = .085) were increased or tended to be increased by daidzein supplementation. However, supplemental daidzein reduced or tended to reduce some uncultured and unclassified bacteria genus belonging to Ruminococcaceae (p = .028), Prevotellaceae (p = .088) and Lachnospiraceae (p = .068). The ruminal pH (p = .023) and ammonia-N (p = .031) concentration were lower in the daidzein group than in the control group, but the daidzein group tended to have greater ruminal total VFA (p = .063) concentration. Supplemental daidzein increased urinary excretion of allantoin (p = .005) and total purine derivatives (p = .007). Current results suggest that supplemental daidzein can affect ruminal fermentation by changing ruminal microbial community, increase the production of VFA and enhance microbial protein synthesis in the rumen, showing the potential of daidzein for improving ruminal fermentation in beef cattle. [ABSTRACT FROM AUTHOR]

The gut microbiota in mammals plays a key role in host metabolism and adaptation. However, relatively little is known regarding to how the animals adapts to extreme environments through regulating gut microbial diversity and function. Here, we investigated the diet, gut microbiota, short-chain fatty acid (SCFA) profiles, and cellulolytic activity from two common pika (Ochotona spp.) species in China, including Plateau pika (Ochotona curzoniae) from the Qinghai-Tibet Plateau and Daurian pika (Ochotona daurica) from the Inner Mongolia Grassland. Despite a partial diet overlap, Plateau pikas harbored lower diet diversity than Daurian pikas. Some bacteria (e.g., Prevotella and Ruminococcus) associated with fiber degradation were enriched in Plateau pikas. They harbored higher gut microbial diversity, total SCFA concentration, and cellulolytic activity than Daurian pikas. Interestingly, cellulolytic activity was positively correlated with the gut microbial diversity and SCFAs. Gut microbial communities and SCFA profiles were segregated structurally between host species. PICRUSt metagenome predictions demonstrated that microbial genes involved in carbohydrate metabolism and energy metabolism were overrepresented in the gut microbiota of Plateau pikas. Our results demonstrate that Plateau pikas harbor a stronger fermenting ability for the plant-based diet than Daurian pikas via gut microbial fermentation. The enhanced ability for utilization of plant-based diets in Plateau pikas may be partly a kind of microbiota adaptation for more energy requirements in cold and hypoxic high-altitude environments. [ABSTRACT FROM AUTHOR]

Bacterial fermentation of lignocellulose has been regarded as a sustainable approach to butyric acid production. However, the yield of butyric acid is hindered by the conversion efficiency of hydrolysate xylose. A mesophilic alkaline-tolerant strain designated as Clostridium butyricum B10 was isolated by xylose fermentation with acetic and butyric acids as the principal liquid products. To enhance butyric acid production, performance of the strain in batch fermentation was evaluated with various temperatures (20-47 °C), initial pH (5.0-10.0), and xylose concentration (6-20 g/L). The results showed that the optimal temperature, initial pH, and xylose concentration for butyric acid production were 37 °C, 9.0, and 8.00 g/L, respectively. Under the optimal condition, the yield and specific yield of butyric acid reached about 2.58 g/L and 0.36 g/g xylose, respectively, with 75.00% butyric acid in the total volatile fatty acids. As renewable energy, hydrogen was also collected from the xylose fermentation with a yield of about 73.86 mmol/L. The kinetics of growth and product formation indicated that the maximal cell growth rate (μm) and the specific butyric acid yield were 0.1466 h−1 and 3.6274 g/g cell (dry weight), respectively. The better performance in xylose fermentation showed C. butyricum B10 a potential application in efficient butyric acid production from lignocellulose. [ABSTRACT FROM AUTHOR]

A life cycle assessment ( LCA) of a four-stage biorefinery concept, coined H- M- Z- S, that converts 1 t of organic fraction of municipal solid waste ( OFMSW) into bioenergy and bioproducts was performed in order to determine whether it could be an alternative to common disposal of OFMSW in landfills in the Mexican reality. The OFMSW is first fermented for hydrogen production, then the fermentates are distributed 40 % to the methane production, 40 % to enzyme production, and 20 % to the saccharification stage. From hydrogen and methane, up to 267 MJ and 204 kWh of gross heat and electricity were produced. The biorefinery proved to be self-sustainable in terms of power (95 kWh net power), but it presented a deficit of energy for heating services (−155 MJ), which was partially alleviated by digesting the wastes from the bioproducts stages (−84 MJ). Compared to landfill, biorefinery showed lower environmental impacts in global warming (down to −128 kg CO-eq), ozone layer depletion (2.96 × 10 kg CFC-eq), and photochemical oxidation potentials (0.011 kg CH-eq). The landfarming of the digestates increased significantly the eutrophication impacts, up to 20 % below the eutrophication from landfilling (1.425 kg PO-eq). These results suggest that H-M-Z-S biorefinery could be an attractive alternative compared to conventional landfilling for the management of municipal solid wastes, although new alternatives and uses of co-products and wastes should be explored and tested. Moreover, the biorefinery system would benefit from the integration into the market chain of the bioproducts, i.e., enzymes and hydrolysates among others. [ABSTRACT FROM AUTHOR]

The mixed culture fermentation is an important environmental biotechnology that converts biodegradable organic wastes to valuable chemicals such as hydrogen, methane, acetate, ethanol, propionate, and so on. For the multistep process of hydrolysis, acidogenesis, acetogenesis/homoacetogensis, and methanogenesis, the typical metabolic reactions are firstly summarized. And then, since the final metabolites are always a mixture, the separation and purification processes are necessary to couple with anaerobic fermentation. Therefore, several typical coupling technologies including biogas upgrading, two-stage fermentation, gas stripping, membrane technology of pervaporation, membrane distillation, electrodialysis, bipolar membrane electrodialysis, and microbial fuel cells are summarized to separate the metabolites and recover energy. At last, the novel technologies such as the controlled metabolite production, medium chain carboxylic acid production, and high temperature ethanol recovery in thermophilic mixed culture fermentation are also reviewed. However, the novel concepts are still needed to meet the demands of better overall performances and lower total costs. [ABSTRACT FROM AUTHOR]

Oilseed rape straw (ORS) is a kind of biorefractory waste widely existing in the rural area of China, which is highly suitable to mix with kitchen waste (KW) and duck droppings (DD) in two-phase anaerobic digestion (AD). This research introduced the importance of KW and DD addition to improve the biogas production and biodegradation of ORS. A set of comparative experiments were conducted on two-phase mono- and co-digestion with organic load of 60 g VS/L. The total methane yield (TMY) and the biodegradation of ORS of co-digestions were obviously improving, and the synergistic effect found in the two-phase co-digestions. The optimum mixing ratio of ORS, KW and DD was 50:40:10, and the corresponding TMY and VS degradation rate of ORS were 374.5 mL/g VS and 49.7%, respectively. Addition of KW and DD maintained the pH within the optimal range for the hydrolyzing-acidification, improved the phase separation and buffering capacity of AD system. [ABSTRACT FROM AUTHOR]

Background: Medium chain carboxylic acids, such as caproic acid, are conventionally produced from food materials. Caproic acid can be produced through fermentation by the reverse β-oxidation of lactic acid, generated from low value lignocellulosic biomass. In situ extraction of caproic acid can be achieved by membrane electrolysis coupled to the fermentation process, allowing recovery by phase separation. Results: Grass was fermented to lactic acid in a leach-bed-type reactor, which was then further converted to caproic acid in a secondary fermenter. The lactic acid concentration was 9.36 ± 0.95 g L-1 over a 33-day semi-continuous operation, and converted to caproic acid at pH 5.5-6.2, with a concentration of 4.09 ± 0.54 g L-1 during stable production. The caproic acid product stream was extracted in its anionic form, concentrated and converted to caproic acid by membrane electrolysis, resulting in a >70 wt% purity solution. In a parallel test exploring the upper limits of production rate through cell retention, we achieved the highest reported caproic acid production rate to date from a lignocellulosic biomass (grass, via a coupled process), at 0.99 ± 0.02 g L-1 h-1. The fermenting microbiome (mainly consisting of Clostridium IV and Lactobacillus) was capable of producing a maximum caproic acid concentration of 10.92 ± 0.62 g L-1 at pH 5.5, at the border of maximum solubility of protonated caproic acid. Conclusions: Grass can be utilized as a substrate to produce caproic acid. The biological intermediary steps were enhanced by separating the steps to focus on the lactic acid intermediary. Notably, the pipeline was almost completely powered through electrical inputs, and thus could potentially be driven from sustainable energy without need for chemical input. [ABSTRACT FROM AUTHOR]

Hemicelluloses are major components of plant biomass, but their fermentation in the rumens of cattle and other ruminants is poorly understood. We compared four species of the ruminally dominant genus Prevotella and the well-known hemicellulose utilizer, Butyrivibrio fibrisolvens, with respect to degradation of several isolated hemicelluloses (xylans, glucomannan, and xyloglucan). We also performed Illumina sequencing of the V3/V4 region of 16S rRNA genes to determine the relative proportions of Prevotella and Butyrivibrio in hemicellulose-fed enrichment cultures inoculated from ruminal contents of dairy cattle fed a total mixed ration (TMR) rich in hemicelluloses. Results confirmed the xylan fermentation and butyrate production abilities of B. fibrisolvens. Despite their reputation as generalist fermenters, the Prevotella strains poorly fermented these hemicelluloses but exhibited dramatic differences in fermentation end products. Prevotella was much less abundant in mixed bacterial enrichment cultures fed the same TMR than in the ruminal inoculum, yet Prevotella was again the most abundant genus in enrichment cultures fed xylans. By contrast, glucomannan fermentations were dominated by Streptococcus sp. Genera known for hemicellulose degradation ( Butyrivibrio, Ruminococcus, and Fibrobacter) were not significantly enriched on these hemicelluloses. Substantial differences in fermentation end product distribution from the different hemicelluloses were observed, which would likely affect nutrient partitioning in the host animal. Differences in community composition between in vitro hemicellulose enrichments and inoculum samples emerged at every phylogenetic level, suggesting that in vitro conditions provide unique selective pressures on the bacterial community and also that ruminal bacteria exhibit specialization with respect to hemicellulose utilization. [ABSTRACT FROM AUTHOR]

This study aimed to enhance hydrogen production from sugarcane syrup by biogas sparging. Two-stage continuous stirred tank reactor (CSTR) and upflow anaerobic sludge blanket (UASB) reactor were used to produce hydrogen and methane, respectively. Biogas produced from the UASB was used to sparge into the CSTR. Results indicated that sparging with biogas increased the hydrogen production rate (HPR) by 35% (from 17.1 to 23.1 L/L.d) resulted from a reduction in the hydrogen partial pressure. A fluctuation of HPR was observed during a long term monitoring because CO2 in the sparging gas and carbon source in the feedstock were consumed by Enterobacter sp. to produce succinic acid without hydrogen production. Mixed gas released from the CSTR after the sparging can be considered as bio-hythane (H2+CH4). In addition, a continuous sparging biogas into CSTR release a partial pressure in the headspace of the methane reactor. In consequent, the methane production rate is increased. [ABSTRACT FROM AUTHOR]

The sustainable recovery of resources from wastewater streams can provide many social and environmental benefits. A common strategy to recover valuable resources from wastewater is to harness the products of fermentation by complex microbial communities. In these fermentation bioreactors high microbial community diversity within the inoculum source is commonly assumed as sufficient for the selection of a functional microbial community. However, variability of the product profile obtained from these bioreactors is a persistent challenge in this field. In an attempt to address this variability, the impact of inoculum on the microbial community structure and function within the bioreactor was evaluated using controlled laboratory experiments. In the course of this work, sequential batch reactors were inoculated with three complex microbial inocula and the chemical and microbial compositions were monitored by HPLC and 16S rRNA amplicon analysis, respectively. Microbial community dynamics and chemical profiles were found to be distinct to initial inoculate and highly reproducible. Additionally we found that the generation of a complex volatile fatty acid profile was not specific to the diversity of the initial microbial inoculum. Our results suggest that the composition of the original inoculum predictably contributes to bioreactor community structure and function. [ABSTRACT FROM AUTHOR]

Microbial diversity provides an immense reservoir of functions and supports key steps in maintaining ecosystem balance through matter decomposition processes and nutrient recycling. The use of microorganisms for biomolecule production is now common, but often involves single-strain cultures. In this review, we highlight the significance of using ecosystem-derived microbial diversity for biotechnological researches. In the context of organic matter mineralization, diversity of microorganisms is essential and enhances the degradation processes. We focus on anaerobic production of biomolecules of interest from discarded biomass, which is an important issue in the context of organic waste valorization and processing. Organic waste represents an important and renewable raw material but remains underused. It is commonly accepted that anaerobic mineralization of organic waste allows the production of diverse interesting molecules within several fields of application. We provide evidence that complex and diversified microbial communities isolated from ecosystems, i.e. microbialconsortia, offer considerable advantages in degrading complex organic waste, to yield biomolecules of interest. We defend our opinion that this approach is more efficient and offers enhanced potential compared to the approaches that use single strain cultures. [ABSTRACT FROM AUTHOR]

The acetogen Clostridium ljungdahlii is capable of syngas fermentation and microbial electrosynthesis. Biofilm formation could benefit both these applications, but was not yet reported for C. ljungdahlii. Biofilm formation does not occur under standard growth conditions, but attachment or aggregation could be induced by different stresses. The strongest biofilm formation was observed with the addition of sodium chloride. After 3 days of incubation, the biomass volume attached to a plastic surface was 20 times higher with than without the addition of 200 mM NaCl to the medium. The addition of NaCl also resulted in biofilm formation on glass, graphite and glassy carbon, the latter two being often used electrode materials for microbial electrosynthesis. Biofilms were composed of extracellular proteins, polysaccharides, as well as DNA, while pilus-like appendages were observed with, but not without, the addition of NaCl. A transcriptome analysis comparing planktonic (no NaCl) and biofilm (NaCl addition) cells showed that C. ljungdahlii coped with the salt stress by the upregulation of the general stress response, Na+ export and osmoprotectant accumulation. A potential role for poly-N-acetylglucosamines and D-alanine in biofilm formation was found. Flagellar motility was downregulated, while putative type IV pili biosynthesis genes were not expressed. Moreover, the gene expression analysis suggested the involvement of the transcriptional regulators LexA, Spo0A and CcpA in stress response and biofilm formation. This study showed that NaCl addition might be a valuable strategy to induce biofilm formation by C. ljungdahlii, which can improve the efficacy of syngas fermentation and microbial electrosynthesis applications. [ABSTRACT FROM AUTHOR]

The aim of this research was to estimate the production of hydrogen, organic acids and alcohols by the strain ofClostridium acetobutylicumATCC 824 using residual glycerol as a carbon source. The experiments were carried out in pure and mixed cultures in batch experiments. Three different sources of inocula for mixed culture were used. Ruminal liquid from goats and sludge collected from two upflow anaerobic sludge blanket reactors treating municipal wastewater and brewery effluent were tested for hydrogen, organic acids and alcohols production with or withoutC. acetobutylicumATCC 824. The main detected end-products from the glycerol fermentation were hydrogen, organic acids (acetic, propionic, butyric and caproic) and alcohol (ethanol and 1,3-propanediol – 1,3PD). High hydrogen (0.44 mol H2/mol glycerol consumed) and 1,3PD (0.32 mol 1,3PD/mol glycerol consumed) yields were obtained when the strainC. acetobutylicumATCC 824 was bioaugmented into the sludge from municipal wastewater using 5 g/L of glycerol. Significant concentrations ofn-caproic acid were detected in the ruminal liquid when amended withC. acetobutylicumATCC 824. The results suggest that glycerol can be used for the generation of H2, 1,3PD andn-caproic acid usingC. acetobutylicumATCC 824 as agent in pure or mixed cultures. [ABSTRACT FROM PUBLISHER]

The increasing production of food waste worldwide and new international regulations call for the development of new technologies to treat this biowaste. Anaerobic processes are able to treat efficiently organic wastes, producing at the same time different value-added compounds. In addition, due to the lower costs and environmental impacts associated with these processes when compared to other options, they are among the most promising technologies for food waste treatment. This article reviews the state-of-the-art dealing with treatment of food waste by anaerobic processes, with emphasis on the most recent research carried out. The different processes that are assessed are anaerobic digestion for methane production, anaerobic fermentation for hydrogen and/or volatile fatty acids production and 2-stage systems. The primary issues associated with each alternative are presented, paying special attention to accumulation of ammonia and volatile fatty acids in the reactor. In addition, the latest developments to overcome the complications of each system are also described, focusing on how they improve its stability and performance. Moreover, the relevant economic and environmental research has also been reviewed, including several life cycle analyses that compare anaerobic processes with other technologies used for food waste treatment. Different case studies are also presented. Finally, recommendations for future research for the anaerobic processes studied and options for process integration are discussed. Moving towards the idea of a circular economy, a potential biorefinery for food waste valorization is also proposed. [ABSTRACT FROM AUTHOR]

This study investigated the temporal dynamics of the degradation of organic matter (OM), fibre, protein and remaining organic constituents during anaerobic digestion of silages from maize, sunflower and sorghum-sudangrass that were harvested at different maturity stages. The tests were conducted using an in sacco method in 20 l digesters. The degradation kinetics of fibres showed some similarity for maize and sorghum-sudangrass with a continuous progress, whereas in sunflower it developed with a strong degradation right after incubation to reach a quasi-constant level for the rest of the 35 days lasting fermentation time. The degradation process for crude protein was usually intense from the very beginning and levelled off after only 5 days. Methane yield after 35 days amounted to 358, 278, and 320 l CH/kg OM for maize, sunflower and sorghum-sudangrass respectively but could not be predicted with high accuracy by regression models based on organic constituents. [ABSTRACT FROM AUTHOR]

Acetone-butanol-ethanol (ABE) fermentation by clostridia has shown promise for industrial-scale production of biobutanol. However, the continuous ABE fermentation suffers from low product yield, titer, and productivity. Systems analysis of the continuous ABE fermentation will offer insights into its metabolic pathway as well as into optimal fermentation design and operation. For the ABE fermentation in continuous Clostridium acetobutylicum culture, this paper presents a kinetic model that includes the effects of key metabolic intermediates and enzymes as well as culture pH, product inhibition, and glucose inhibition. The kinetic model is used for elucidating the behavior of the ABE fermentation under the conditions that are most relevant to continuous cultures. To this end, dynamic sensitivity analysis is performed to systematically investigate the effects of culture conditions, reaction kinetics, and enzymes on the dynamics of the ABE production pathway. The analysis provides guidance for future metabolic engineering and fermentation optimization studies. [ABSTRACT FROM AUTHOR]

To enhance the productivity of mixed microbial cultures for fermentative bio-hydrogen production, chemical-physical pre-treatments of the original seed are needed to suppress the activity of hydrogen (H)-consuming microbes. This approach might influence negatively the composition and diversity of the hydrogen-producing community with consequences on the functional stability of the H-producing systems in case of perturbations. In this study, we aimed at investigating the effect of different types of pre-treatment on the performance of hydrogen production systems in the presence of an inhibitor, such as 5-hydroxymethylfurfural (HMF). The efficiency and the microbial community structure of batch reactors amended with HMF and inoculated with non-pretreated and pretreated (acid, heat shock, and aeration) anaerobic sludge were evaluated and compared with control systems. The type of pre-treatments influenced the microbial community assembly and activity in inhibited systems, with significant effect on the performance. Cumulative H production tests showed that the pre-aerated systems (control and HMF inhibited) were the most efficient, while the difference of the lag phase of the pre-acidified control and HMF-added test was negligible. Analyses of the structure of the enriched microbial community in the systems through PCR-denaturing gradient gel electrophoresis (DGGE) followed by band sequencing revealed that the differences in performance were mostly related to shifts in the metabolic pathways rather than in the predominant species. In conclusion, the findings suggest that the use of specific inoculum pre-treatment could contribute to regulate the metabolic activity of the fermentative H-producing bacteria in order to enhance the bio-energy production. [ABSTRACT FROM AUTHOR]