Chain Elongation Research Articles

Discovery of a novel methionine biosynthetic route via O-phospho-l-homoserine.

Methionine (Met), a sulfur-containing amino acid, is essential for the underlying biological processes in living organisms. In addition to its importance as a starting building block for peptide chain elongation in protein biosynthesis, Met is a direct precursor of S-adenosyl-l-methionine, an indispensable methyl donor molecule in primary and secondary metabolism. Streptomyces bacteria are well known to produce diverse secondary metabolites, but many strains lack canonical Met pathway genes for l-homocysteine, a direct precursor of Met in bacteria, plants, and archaea. Here, we report the identification of a novel gene (metM) responsible for the Met biosynthesis in Streptomyces strains and demonstrate the catalytic function of the gene product, MetM. We further identified the metO gene, a downstream gene of metM, and showed that it encodes a sulfur-carrier protein (SCP). In in vitro analysis, MetO was found to play an important role in a sulfur donor by forming a thiocarboxylated SCP. Together with MetO (thiocarboxylate), MetM directly converted O-phospho-l-homoserine to l-homocysteine. O-Phospho-l-homoserine is also known as an intermediate for threonine biosynthesis in bacteria and plants, and MetM shares sequence homology with threonine synthase. Our findings thus revealed that MetM seizes O-phospho-l-homoserine from the threonine biosynthetic pathway and uses it as an intermediate of the Met biosynthesis to generate the sulfur-containing amino acid. Importantly, this MetM/MetO pathway is highly conserved in Streptomyces bacteria and distributed in other bacteria and archaea.IMPORTANCEMethionine (Met) is a sulfur-containing proteinogenic amino acid. Moreover, Met is a direct precursor of S-adenosyl-l-methionine, an indispensable molecule for expanding the structural diversity of natural products. Because Met and its derivatives benefit humans, the knowledge of Met biosynthesis is important as a basis for improving their fermentation. Streptomyces bacteria are well known to produce diverse and valuable natural products, but many strains lack canonical Met pathway genes. Here, we identified a novel l-homocysteine synthase (MetM) in Streptomyces and demonstrated that it converts O-phospho-L-homoserine to l-homocysteine using a thiocarboxylated sulfur-carrier protein as a sulfur donor. Since the metM is distributed in other bacteria and archaea, our pioneering study contributes to understanding Met biosynthesis in these organisms.

Hexanoic acid production from anaerobic fermentation of Chinese cabbage waste with exogenous lactic acid as electron donor

The lack of electron donors is one of the key factors hindering hexanoic acid production from anaerobic fermentation. In this study, three different types of lactic acids were supplemented as exogenous electron donors to the anaerobic fermentation system of Chinese cabbage waste (CCW). The yields of hexanoic acid in the reactors supplemented with CCW lactic acid pre-fermentation broth (PFB), lactic acid diluent (LAD) and chemical lactic acid (LA) were 6996.8 mg COD/L, 4534.8 mg COD/L and 6777.1 mg COD/L, respectively. Compared with the reactor supplemented with LA, the electron efficiency of hexanoic acid in reactor supplemented with PFB increased by 188 %. Supplementing PFB shifted the microbial communities towards a direction favorable to hydrolysis and chain elongation, thereby facilitating the synthesis of hexanoic acid.

Caproic acid production from short-chained carboxylic acids produced by arrested anaerobic digestion of green waste: Development and optimization of a mixed caproic acid producing culture

Caproic acid is an important compound for producing a variety of chemicals and a potential precursor for Sustainable Aviation Fuels (SAF). This study aimed at developing a stable mixed culture producing caproic acid using short-chain carboxylic acids (SCCAs) derived from arrested anaerobic digestion (AAD) of green waste and optimizing chain elongation (CE) conditions. The results showed that the mixed culture was dominated by Clostridium sensu stricto 12 (53.09 %), optimally producing caproic acid at 37 °C, pH 7.20, with a 15 % inoculum concentration. Under these conditions, 75.59 % of the consumed electrons contributed to caproic acid formation. Gradual ethanol feeding in bioreactor experiments resulted in caproic acid titer of 13.36 g/L, with carbon conversion efficiency (CCE) of 81.91 % and electron transfer efficiency (ETE) of 76.39 %, surpassing batch experiments without gradual ethanol addition. These findings demonstrate that the effectiveness of a mixed culture can be improved, resulting in increased caproic acid production.

Formaldehyde: An Essential Intermediate for C1 Metabolism and Bioconversion.

Formaldehyde is an intermediate metabolite of methylotrophic microorganisms that can be obtained from formate and methanol through oxidation-reduction reactions. Formaldehyde is also a one-carbon (C1) compound with high uniquely reactive activity and versatility, which is more amenable to further biocatalysis. Biosynthesis of high-value-added chemicals using formaldehyde as an intermediate is theoretically feasible and promising. This review focuses on the design of the biosynthesis of high-value-added chemicals using formaldehyde as an essential intermediate. The upstream biosynthesis and downstream bioconversion pathways of formaldehyde as an intermediate metabolite are described in detail, aiming to highlight the important role of formaldehyde in the transition from inorganic to organic carbon and carbon chain elongation. In addition, challenges and future directions of formaldehyde as an intermediate for the chemicals are discussed, with the expectation of providing ideas for the utilization of C1.

Beyond Anaerobic Digestion: New Perspectives for the Development of a Biorefinery Platform for the Simultaneous Production of Medium-Chain Fatty Acids by Chain Elongation and Biogas from Food Wastes

Beyond Anaerobic Digestion: New Perspectives for the Development of a Biorefinery Platform for the Simultaneous Production of Medium-Chain Fatty Acids by Chain Elongation and Biogas from Food Wastes

Radical Isomerization Homopolymerization of Linear α‐Olefins to Access C5, C6 or C7 Polymers

AbstractNon‐activated linear α‐olefins are valuable building blocks for organic transformation or olefin (co)polymerization, but they are recognized as textbook knowledge for non‐homopolymerizable monomers under radical conditions. In this article, we disclose our effort to achieve an unprecedented library of all carbon‐bonded sequence‐regulated polymers via radical isomerization homopolymerization of α‐olefin derivatives. The success of this distinctive polymerization is attributed to the remarkable efficiency and selectivity exhibited during the cyano group migration or hydrogen atom transfer, which is greatly enhanced by the precise engineering of their monomer structures. This polymerization process enables the elongation of polymer chains by five, six, or seven carbon atoms at each propagation step. These polymers, obtained through the cyano group migration or hydrogen atom transfer involved radical isomerization polymerization processes, emerge as promising candidates resembling polyethylene or polyacrylonitrile copolymers.

Radical Isomerization Homopolymerization of Linear α-Olefins to Access C5, C6 or C7 Polymers.

Non-activated linear α-olefins are valuable building blocks for organic transformation or olefin (co)polymerization, but they are recognized as textbook knowledge for non-homopolymerizable monomers under radical conditions. In this article, we disclose our effort to achieve an unprecedented library of all carbon-bonded sequence-regulated polymers via radical isomerization homopolymerization of α-olefin derivatives. The success of this distinctive polymerization is attributed to the remarkable efficiency and selectivity exhibited during the cyano group migration or hydrogen atom transfer, which is greatly enhanced by the precise engineering of their monomer structures. This polymerization process enables the elongation of polymer chains by five, six, or seven carbon atoms at each propagation step. These polymers, obtained through the cyano group migration or hydrogen atom transfer involved radical isomerization polymerization processes, emerge as promising candidates resembling polyethylene or polyacrylonitrile copolymers.

Comparative analysis of transcriptome in oil biosynthesis between seeds and non-seed tissues of Symplocos paniculata fruit.

The Symplocos paniculata, a woody oil plant, has garnered attention for its oil-rich fruit, which exhibits potential for both oil production and ecological restoration endeavors, thereby presenting substantial developmental value. However, the comprehension of the distinctive oil biosynthesis and deposition strategies within the fruit's various compartments, coupled with the tissue-specific biosynthetic pathways yielding optimal fatty acid profiles, remains in its infancy. This investigation was designed to delineate the tissue specificity of oil biosynthetic disparities and to elucidate the molecular underpinnings within the fruit mesocarp and seeds of S. paniculata, employing lipidomic and transcriptomic analyses. The results revealed that oil biosynthesis within the fruit mesocarp commences approximately 40 days prior to that within the seeds, with a concomitant higher lipid content observed in the mesocarp, reaching 43% as opposed to 30% in the seeds. The fruit mesocarp was found to be enriched with palmitic acid (C16:0) and exhibited a harmonious ratio of saturated, monounsaturated, to polyunsaturated fatty acids (SFA: MUFA: PUFA=1:1:1), in stark contrast to the seed oil, which is predominantly composed of unsaturated fatty acids, accounting for 90% of its total FA content. Microstructural assessments have unveiled divergent oil deposition modalities; the fruit mesocarp oils are predominantly sequestered within oil cells (OC) and a spectrum of lipid droplets (LD), whereas the seeds predominantly harbor uniformly-sized LD. The expression patterns of pivotal genes implicated in oil biosynthesis were observed to be markedly contingent upon the tissue type and developmental stage. Notably, the light-responsive fatty acid synthase (FAS) gene demonstrated preferential transcription within the fruit mesocarp. In contrast, genes pivotal for carbon chain elongation, such as 3-ketoacyl-ACP synthase II (KASII) and fatty acyl-ACP thioesterase A (FATA), and desaturation, typified by Stearoyl-ACP desaturase (SAD) and Fatty Acid Desaturase (FAD), were noted to be more robustly transcribed within the seeds. Furthermore, isoenzyme gene families integral to the assembly of triacylglycerol (TAG), including long-chain acyl-CoA synthetases (LACSs), glycerol-3-phosphate acyltransferases (GPATs), and lysophosphatidic acid acyltransferases (LPATs), exhibited pronounced tissue specificity. This research endeavors to clarify the molecular regulatory mechanisms that oversee oil biosynthesis within both seed and non-seed tissues of oilseed-bearing plants with entire fruits. Collectively, these findings lay the groundwork and offer technical scaffolding for future targeted cultivation of woody oil plants, with the ultimate aim of augmenting fruit oil yield and refining FA compositions.

Divergent Synthesis and Antigenicity Evaluation of Core Oligosaccharides of the Lipopolysaccharides from Acinetobacter baumannii SMAL and ATCC 19606.

Acinetobacter baumannii poses a serious threat to human health. Pathogenic bacterial lipopolysaccharides (LPSs) are potent immunogens for the development of antibacterial vaccines. To investigate the antigenic properties of A. baumannii LPS, five well-defined core oligosaccharide fragments from the LPS of A. baumannii SMAL and ATCC 19606 were synthesized. A divergent synthesis strategy based on orthogonally protected α-(2 → 5)-linked Kdo dimer 6 was developed. Selective exposure of different positions in this key precursor and then elongation of sugar chains via stereocontrolled formation of both 1,2-trans and 1,2-cis-2-aminoglycosidic linkages permitted the efficient synthesis of the targets. The synthetic route also highlights a 4-O and then 7-O glycosylation sequence for assembly of the novel 4,7-branched Kdo framework. Antigenicity assay using the glycan microarray technique disclosed that tetrasaccharide 3 featuring both 4,7-branch and α-(2 → 5)-Kdo-Kdo structural elements was a potential antigenic determinant.

Unlocking Oxetane Potential: Modular Synthetic Platform for the Concise Synthesis of Acyclic Oligo-Isoprenoids and Terpenoids.

Terpenes occupy a unique place among the secondary metabolites due to their broad utility and extraordinary structural diversity. Their synthesis via polyene cyclization, either biomimetic or enzymatic, represents the cutting edge of modern synthetic chemistry. However, these endeavors have been inherently tied to the availability of natural and non-natural acyclic polyene starting materials. Herein, we report an oxetane-based platform for the modular construction of oxygenated polyolefins with precise geometric control. This "tail-to head" iterative method leverages the site-selective cross-metathesis of terminal olefins to form an alkylidene oxetane moiety and the regioselective ring opening of alkenyl-oxetanes for chain elongation. In addition, the unique and peculiar propensity of alkylidene oxetane fragment in various reactions was also revealed and exploited for site-selective functionalization, cyclization, and as a protecting group in polyenes.

Enhancing medium-chain fatty acids production via alkyl polyglucose modulation of electron acceptor generation, microbial community and metabolic traits in anaerobic fermentation of waste activated sludge

Production of medium chain fatty acids (MCFAs) through anaerobic fermentation is an essential pathway for efficient resource recovery and utilization of waste activated sludge (WAS). In this study, a novel strategy utilizing polyglucose (APG) to enhance MCFAs production from WAS by anaerobic fermentation was proposed. The results showed that the maximum MCFAs production reached 14745.0 mg COD/L with 0.3 g APG/g TSS, which was 20.2 times of that without APG treatment. The transformation of intermediates demonstrated that APG promoted the generation of electron acceptors (i.e., short-chain fatty acids) and conversion of substrate to MCFAs. Microbial community analysis indicated that APG selectively enriched microbe involved in hydrolysis, acidogenesis and chain elongation (CE). Also, the presence of APG had a negative impact on methanogens and potential excessive ethanol oxidation (EEO) microbe, which were competitors of CE bacteria in mixed-culture system. Metagenomic analysis showed an increase in relative abundance of genes encoding metabolic functions responsible for hydrolysis, acidogenesis, CE and energy generation, thus maintained high microbial activity in MCFAs biosynthesis. These enhanced metabolic functions were accompanied by a reduction in relative abundance of genes encoding methanogenesis and EEO metabolism, which together result in boosting the efficiency of substrate and energy flow to MCFAs production. This study presents a promising approach to improve the biotransformation of polysaccharides and proteins from WAS into MCFAs.

Effect of inoculum sources on caproic acid production from food waste through lactate-based chain elongation: Properties and microbial succession

Caproic acid (CA) production is a promising way to valorize food waste (FW), but the low CA yield seriously restricts its application. Inoculum source as a key factor can affect the microbial communities and CA fermentation processes, but was not fully explored. In the present study, three common inoculum sources namely anaerobic digestion sludge (AD), pit mud (PM) and raw FW (RFW) were selected as inocula to initiate CA production from FW. The organics conversion properties, microbial community succession processes and bacterial metabolism pathways were investigated. Results showed that carbohydrates were effectively degraded into lactic acid and then to CA based on lactate-based chain elongation. The CA yield (0.37 g-COD/g-VS) using AD was higher than that inoculated with PM (0.26 g-COD/g-VS) and RFW (0.32 g-COD/g-VS). Although microbial communities in inocula were totally different, they exhibited similar succession with Firmicutes and Bacteroidetes as the dominant functional phyla. Logically, lactic acid-producing bacteria (e.g. Lactobacillus, Limosilactobacillus and Sporolactobacillus) were enriched at the early stage to prepare electron donor (lactate), and then were replaced by chain elongation bacteria for CA production. However, unclassified_Ruminococcaceae was dominant in reactor with AD, unclassified_Ruminococcaceae, Bifidobacterium, Clostridium_sensu_stricto and unclassified_Prevotellaceae were largely detected in reactors inoculated with PM and RFW, which resulted in different CA yield. This study provides useful information for caproate production from FW, and widens the knowledge of cleaner production from wastes.

Outstanding enhancement of caproate production with microwave pyrolyzed highly reductive biochar addition

The integration of biochar into microbial Chain Elongation (CE) proves to be an effective tool of producing high-value bio-based products. This study innovatively applied biochar fabricated under microwave irradiation with carbon fiber cloth assistance into CE system. Results highlighted that microwave biochar achieved maximal CE efficiency yielding 8 g COD/L, with 3-fold increase to the blank group devoid of any biochar. Microwave biochar also obtained the highest substrate utilization rate of 94 %, while conventional biochar group recorded 90 % and the blank group was of 74 %. Mechanistic insights revealed that the reductive surface properties facilitated CE performance, which is relevant to fostering dominant genera of Parabacteroides, Bacteroides, and Macellibacteroides. By metagenomics, microwave biochar up-regulated functional genes and enzymes involved in CE process including ethanol oxidation, the reverse β-oxidation pathway, and the fatty acid biosynthesis pathway. This study effectively facilitated caproate production by utilizing a new microwave biochar preparation strategy.

Bioaugmentation of microalgae fermentation with yeast for enhancing microbial chain elongation: In-situ ethanol production and metabolic potential

Anaerobic microalgae fermentation, leveraging its cost-effectiveness and the adaptability of mixed cultures, holds promise for carboxylate biosynthesis. Microalgae, with their abundant carbohydrates and proteins, stand out as an optimal substrate for this process among various options. Furthermore, microalgae fermentation not only shows the potential to mitigate risks associated with algae blooms but also aligns with the need for sustainable practices. However, the limited utilization rate of microalgae in anaerobic fermentation poses challenges to achieving high production rates of desired products. In this study, we implemented a bioaugmentation process with yeast to enhance carboxylate production performance of microalgae fermentation. The results demonstrated a fourfold increase in carboxylate yield with the addition of yeast. In-situ ethanol production facilitated the conversion of short-chain carboxylic acids into medium-chain carboxylates, achieving a yield of 46.3 mM-C/g VS. The presence of yeast significantly enhanced substrate utilization from 20 % to 80 %, steering the metabolic pathway towards chain elongation. Metagenomic analysis further revealed metabolic shifts following yeast addition, particularly an increased abundance of genes involved in acetyl-CoA production. Notably, the aldehyde:ferredoxin oxidoreductase (AOR) pathway emerged as a key driver in butanol production. These findings highlight the improved performance of anaerobic microalgae fermentation with yeast, enabling efficient production of higher value bioproducts while eliminating the need for external electron donors.

On the use of vibrations and temperatures for the monitoring of plastic chain conveyor systems

In industrial automation, the transportation of unit loads plays a crucial role. This paper addresses the under-explored area of plastic chain conveyors, a versatile and efficient means of transport within production processes. Despite their widespread use, these conveyors suffer from wear and tear due to continuous contact between the chain and guide rails, often leading to unscheduled shutdowns and increased costs. The literature on monitoring solutions for such systems is sparse, particularly for plastic chains. This paper aims to bridge this gap by surveying the most common wear mechanisms for these systems and presenting a physical model that describes the interaction between the chain links and guide rails, based on chain of masses, springs and dampers and the Archard wear model. This model allows to relate the variations due to wear with other physical quantities, such as passage frequencies of the links and heat generated due to friction. The comprehensive model provides analytical formulas to understand the vibrations induced by the chain on the platform and the guide-rail temperatures. To validate the model and evaluate how the measurements are affected by the degradation of the system, an extensive experimental campaign was conducted on a conveyor test rig, acquiring vibration and temperature data. The end goal is to identify and discuss methodologies suitable for estimating the wear mechanisms of conveyor systems, with a focus on the constraints of industrial environments. Hence, this study aims to lay the groundwork for defining monitoring solutions that enhance the maintenance efficiency of plastic chain conveyor systems. The results suggest that the power Spectral Densities (PSD) of the platform’s accelerations are sufficient to estimate the average links pitch, which in turn could be used to assess the chain elongation. Besides, the local temperatures confirmed the model observations, making them suitable for estimating the slide-rail thinning.

Synthesis of medium-chain fatty acids from corn stover by sequential fermentation based on substrate configuration and initial pH optimization

This work describes a novel sequential fermentation method for the production of medium-chain fatty acids (MCFAs) from corn stover, without adding exogenous electron donors/acceptors. The effects of the carbon substrate concentration, ethanol-to-acetate ratio (ED/EA), and initial pH on carbon chain elongation (CCE) by Clostridium kluyveri to produce MCFAs are investigated using ethanol and acetate as the electron donor and acceptor, respectively. A carbon substrate concentration of 300 mM C is sufficient for CCE. An initial weakly alkaline environment significantly enhances the production of caproate through buffering effects and by reducing inhibition of product formation. The maximum caproate production reached 4.41 g/L (initial pH 8.5; 300 mm C; ED/EA = 1:1). The ability of corn stover to generate a suitable ED/EA via two-step fermentation to synthesize MCFAs is also explored. Ultimately, 5.53 g/L butyrate and caproate can be obtained from corn stover, where caproate accounts for 2.79 g/L. This study offers innovative ideas for the sustainable production of bio-based chemicals.

Tuning the Solubility of Soluble Support Constructs in Liquid Phase Oligonucleotide Synthesis.

Solubility of the growing oligonucleotide-soluble support constructs in the liquid phase oligonucleotide synthesis (LPOS) is a critical parameter, which affects coupling efficiency, purity, and recovery of the growing oligonucleotides during the chain elongation. In the present study, oligonucleotides have been assembled on a 4-oxoheptanedioic acid (OHDA) linker-derived tetrapodal soluble support using 5'-O-(2-methoxyprop-2-yl)-protected 2'-deoxyribonucleotide phosphoroamidite building blocks with different nucleobase protecting groups [isobutyryl (Gua), 1-butylpyrrolidin-2-ylidene (Gua, Cyt), 2,4-dimethylbenzoyl (Ade, Cyt), and Bz (Thy)]. The solubility of the oligonucleotide-soluble support constructs (molecular mass varying between 3 and 10 kDa) as models of protected tetra-, octa-, dodeca-, hexadeca-, and eicosa-nucleotides was measured in different solvent systems and in potential antisolvents. By tuning the nucleobase protecting group scheme, the solubility can be improved in aprotic organic solvent systems, while the recovery of the constructs in the precipitation, used for the isolation and purification of the growing oligonucleotide intermediates in a protic antisolvent (2-propanol), remained near quantitative. The precipitation-based yield of the protected tetrapodal oligonucleotides varied from a quantitative to 90% yield. Overall yield (for di-: 95%, tri-: 79-96%, tetra-: 82-88%, and pentanucleotides: 68-75%) and purity of the LPOS were evaluated by RP HPLC and MS-spectroscopy of the released oligonucleotide aliquots. In addition, the orthogonality of the OHDA linker was applied to release authentic protected nucleotides from the soluble supports.

Carbon chain elongation characterizations of electrode-biofilm microbes in electro-fermentation

The higher efficiency of electro-fermentation in synthesizing medium-chain fatty acids (MCFAs) compared to traditional fermentation has been acknowledged. However, the functional mechanisms of electrode-biofilm enhancing MCFAs synthesis remain research gaps. To address this, this study proposed a continuous flow electrode-biofilm reactor for chain elongation (CE). After 225 days of operation, stable electrode-biofilms formed and notably improved caproate yield by more than 38 %. The electrode-biofilm was enriched with more CE microorganisms and electroactive bacteria compared to the suspended sludge microorganisms, including Caproicibacterium, Oscillibacter and Pseudoramibacter. Besides, the upregulated CE pathways were evaluated by metagenomic analysis, and the results indicated that the pathways such as acetyl-CoA and malonyl-[acp] formation, reverse beta-oxidation, and fatty acid biosynthesis pathway were all markedly enhanced in cathodic biofilm, more than anodic biofilm and suspended microorganisms. Moreover, microbial community regulated processes like bacterial chemotaxis, flagellar assembly and quorum sensing, crucial for electrode-biofilm formation. Electron transfer, energy metabolism, and microbial interactions were found to be prominently upregulated in the cathodic biofilm, surpassing levels observed in anodic biofilm and suspended sludge microorganisms, which further enhanced CE efficiency. In addition, the statistical analyses further highlighted key microbial functions and interactions within the cathodic biofilm. Oscillospiraceae_bacterium was identified to be the most active microbe, alongside pivotal roles played by Caproiciproducens_sp._NJN-50, Clostridiales_bacterium, Prevotella_sp. and Pseudoclavibacter_caeni. Eventually, the proposed microbial collaboration mechanisms of cathodic biofilm were ascertained. Overall, this study uncovered the biological effects of the electrode-biofilm on MCFAs electrosynthesis, thereby advancing biochemicals production and filling the knowledge gaps in CE electroactive biofilm reactors.

Biochar confers significant microbial resistance to ammonia toxicity in n-caproic acid production

Microbial chain elongation integrating innovative bioconversion technologies with organic waste utilization can transition current energy-intensive n-caproic acid production to sustainable circular bioeconomy systems. However, ammonia-rich waste streams, despite their suitability, pose inhibitory challenges to these bioconversion processes. Herein, biochar was employed as an additive to enhance the activity of chain elongating microbes under ammonia inhibition conditions, with an objective to detail underlying mechanisms of improvements. Biochar addition significantly improved chain elongation performance even under severe ammonia stress (exceeding 8 g N/L), increasing n-caproic acid yields by 40 % to 158 % and reducing lag times by 51 % to 90 %, compared with the best-performing group without biochar addition. The material contribution to n-caproic production reached up to 94.3 % (at 4 g N/L). These enhancements were mainly attributed to the new electron syntrophy induced by biochar, which improved electron transfer system activity and electrical conductivity of the fermentation system. This is further substantiated by increased relative abundances of the genus Sporanaerobacter, electroactive bacteria, and up-regulated direct electron transfer-related genes including conductive pili and c-type cytochrome. This study demonstrates that biochar can confer robust resilience to ammonia toxicity in functional microbes, paving a way for efficient and sustainable n-caproic acid production.

Differences on carboxylic acids bioproduction from soluble carbohydrates or proteins in a sequencing batch reactor: Deciphering the influence of the volumetric and specific organic loading rate

Acidogenic fermentation (AF) has been extensively explored. However, the impact of operational parameters on AF has led to inconsistent results. In this work, AF experiments were performed in a sequencing batch reactor (SBR) using simulated wastewaters solely containing soluble carbohydrates or proteins as carbon sources to independently assess the impact of the volumetric organic loading rate (OLRv) and of the specific organic loading rate (OLRs). When only carbohydrates were used, the main effluent components were acetic and butyric acids at OLRv of 6.0 g COD L−1 d−1, while changing OLRv over 11.0 g COD L−1 d−1 gave acetic acid and ethanol as main components. Conversely, if the carbon source consisted solely of proteins, increasing the OLRv or the OLRs had minimal impact on the AF performance and on the effluent composition. Also, in the case of carbohydrate experiments, increasing the OLRs from 2.3 to 3.8 g COD g−1 VSS d−1 promoted chain elongation reactions, as caproic acid formation was also observed. Besides, at the highest OLRv tested in this work for protein experiments (18.5 g COD L−1 d−1), it was obtained the maximum isocaproic acid concentration using mixed microbial cultures and without adding any external electron donor. The SBR configuration proved to be an adequate system, especially when proteins were used as carbon source, since it makes possible to keep low the OLRs and to reduce the hydrolysis limitations. Finally, the bacterial genera detected in the reactors notably changed between both substrates. Future work must be focused on identifying carboxylic acid producing-genera from proteins.