Accumulation Of Short-chain Fatty Acids Research Articles

Free ammonia pretreatment assists potassium ferrate to enhance the production of short-chain fatty acids from waste activated sludge: Performance, mechanisms and applications

Anaerobic fermentation of waste activated sludge (WAS) is often limited by low disintegration rates of WAS and quick consumptions of short-chain fatty acids (SCFAs) by methanogens. This work proposed a novel, efficient and harmless pretreatment approach i.e., using potassium ferrate (PF) combined with free ammonia (FA), to enhance the disintegration of WAS and the accumulation of SCFAs from WAS anaerobic fermentation. It was found in this work, the best pretreating condition of WAS is 0.10 g PF/g VSS + 180 mg FA/L, under which the SCFAs consistence reached its maximum value (342.5 mg COD/g VSS), which was respectively 7.45-fold, 3.50-fold and 2.06-fold of that from the Blank, FA and PF reactor. Further in-depth mechanism study showed that the disintegration of WAS promoted and the biodegradability of fermentation broth enhanced under the PF + FA pretreatment condition. Moreover, the populations of fecal coliforms in WAS reduced significantly when PF + FA was adopted. Considering that FA could be produced in situ during the ammoniating process, the findings in this work promoted the utilization of PF-based pretreatment method in actual operations.

Enhancing the decomposition of extracellular polymeric substances and the recovery of short-chain fatty acids from waste activated sludge: Analysis of the performance and mechanism of co-treatment by free nitrous acid and calcium peroxide

At present, the bioproduction of short-chain fatty acids (SCFAs) from waste activated sludge (WAS) has attracted worldwide attention due to the demand of carbon neutrality during waste treatment. Calcium peroxide (CaO2) has been reported to be an effective method for the solubilization of WAS and the accumulation of SCFAs, but the high reagent cost limits its industrial application. Therefore, free nitrous acid (FNA) was introduced into the WAS pretreatment system to assist with CaO2 for enhancing the disruption of extracellular polymeric substances (EPS) and the subsequent acidogenesis process. The results showed that FNA and CaO2 synergistically enhanced EPS decomposition and the release of biodegradable organic compounds during pretreatment. The highest soluble chemical oxygen demand (3.1- and 2.6-fold higher compared to individual pretreatments at the same concentrations) after pretreatment and the highest SCFAs accumulation (2.0- and 6.4-fold compared to individual pretreatments at the same concentrations) after a 2-day fermentation period was observed in the FNA + CaO2 (0.15 g/g VSS) co-treated group. Therefore, the FNA + CaO2 (0.15 g/g VSS) co-treatment was determined to be the optimal strategy for ensuring the disintegration of the EPS matrix and enhancing the accumulation of SCFAs in pretreated sludge during anaerobic digestion.

Insight into the enhancing short-chain fatty acids (SCFAs) production from waste activated sludge via polyoxometalates pretreatment: Mechanisms and implications

Polyoxometalates (POMs), a versatile and environmentally-friendly inorganic material, have been extensively studied and applied in chemical catalytic oxidation and biological nutrients removal processes. However, little is known about effects of POMs pretreatment on anaerobic sludge fermentation. This study thereby filled such knowledge gap and provided insights into the underlying mechanisms. Results demonstrated the maximal short-chain fatty acids (SCFAs) production increased by 6.18 times with POMs rising from 0 to 0.05 g/g TSS. Mechanistic investigations revealed that the oxidation stress of POMs as well as reactive oxygen species (ROS) activated by POMs were responsible for the disintegration of waste activated sludge (WAS). More importantly, POMs pretreatment improved the biodegradability of organics released, providing more biodegradable substrates for SCFAs generation. Furthermore, the inhibition of POMs to SCFAs producers was less severe than that to SCFAs consumers, leading to SCFAs accumulation. Microbial community analysis exhibited that increased the population of hydrolysis (i.e., Longilinea) and SCFAs generation microbes (i.e., Acinetobacter and Fusibacter). Further evaluation showed that the POMs-based technology is economically and environmentally attractive for the pretreatment of WAS. Finally, a “closed-loop” concept of the reutilization of renewable POMs may provide an important implication of WAS management in the future.

Anaerobic digestion of chicken manure: Sequences of chemical structures in dissolved organic matter and its effect on acetic acid production

The use of chicken manure (CM) leads to serious environmental pollution due to the existence of bacteria and insect pests. Anaerobic digestion (AD) is one of the important technologies of CM treatment. However, methane production is limited by the accumulation of short-chain fatty acids (SCFAs) from AD. Therefore, the study explored the possible formation mechanism of acetic acid by understanding the effect of sequences of chemical structure variation in DOM on acetic acid production. The chemical structures of DOM were observed. The tyrosine-like substances (C1, 53.53–29.99%) and humic-like substances (C3, 18.38–5.96%) showed a tendency to decrease. Tryptophan-like substances (C2, 28.09–64.04%) showed the increasing trend. The results indicated that C2 was unwilling to biodegrade. In DOM, the order of biodegradability was C2< C1< C3. AD resulted in the enrichment of N–H in-plane (0–22.75%) and COO- stretch (7.53–18.57%) and the loss of O–H stretch (19.39–13.72%), C–H stretch (4.56%-0), CC stretch (12.04–9.61%) and C–O stretch (10.02–5.03%). Two-dimensional correlation spectroscopy is applied to investigate the sequences of chemical structures in DOM, the order is as follows: CC stretch > COO- stretch > N–H in-plane > C–O stretch. The result confirmed that protein was rapidly decomposed and utilized, which would result in the increase of microorganism metabolism and hydrolysis rate, polysaccharide was hydrolyzed to form phenol and carboxylic acid. Four possible pathways were identified in AD by the structural equation model. C1and hydroxyl can promote propionic and butyric acid formation by the pathway of valeric or iso-butyric acid production and further effected acetic acid production. This study proposed the possible formative mechanisms of acetic acid according to sequences of chemical structures variation in DOM during AD, which can provide the theoretical basis for directional regulating the conversion of different chemical structures of DOM into acetic acid in AD.

Insight into the roles of ferric chloride on short-chain fatty acids production in anaerobic fermentation of waste activated sludge: Performance and mechanism

• The effect of ferric chloride on short chain fatty acids production was evaluated. • Solubilization, hydrolysis, and acidogenesis were promoted by ferric chloride. • Ferric chloride promoted acetogenesis and high molecular organic acids conversion. • Ferric chloride changed the acid-fermentation to propionic acid-type fermentation. • Excessive ferric chloride inhibited acid-fermentation by strong aggregation. Ferric chloride (FC) is widely used in sewage treatment and sludge conditioning, which could be inevitably accumulated in waste-activated sludge (WAS). However, its effect on short-chain fatty acids (SCFAs) production from WAS anaerobic fermentation has yet to be thoroughly investigated. This study aims to reveal how different dosages of FC affect the production of SCFAs and elucidate the corresponding mechanism. Experimental results showed that 16 mg Fe/g total suspended solids (TSS) of FC was favorable for SCFAs production, with the maximum production was 3.3 times of the control. Mechanistic study revealed that FC induced dissimilatory iron reduction (DIR) and enhanced hydrolase activities, contributing to the disintegration of WAS flocs and the hydrolysis of complex organics. Moreover, FC stimulated the productivity of HAc by promoting the release of carbon-rich substrates and accepting the intermediate electrons generated in acetogenesis process. Further study indicated FC inhibited the methanogenesis and changed the acid-fermentation type by affecting pH and ORP, which was conducive to SCFAs accumulation. Microbial community analysis confirmed that FC enriched the bacterial microorganisms related to hydrolysis and acidogenesis, and increased the abundance of Fe(III)-reducing genera. However, excessive FC (>16 mg Fe/g TSS) inhibited SCFAs production, due to the strong aggregation increased mass transfer resistance and the “over-acidification” damaged the microbial community.

Chlorogenic Acid Alleviates Colon Mucosal Damage Induced by a High-Fat Diet via Gut Microflora Adjustment to Increase Short-Chain Fatty Acid Accumulation in Rats.

A high-fat diet (HFD) has been previously associated with the development of diseases such as chronic colitis. While chlorogenic acid (CGA) is known to exhibit potent antioxidant, antibacterial, and anti-inflammatory properties, little is known about its effects on intestinal inflammation. In this study, we investigated the effects of CGA on intestinal inflammation in an HFD-induced obesity rat model and assessed whether these effects were related to changes in gut microbiota composition. This was achieved by examining physiological and biochemical indicators, the liver transcriptome, and the structure of the fecal microflora. CGA treatment significantly reduced HFD-induced internal organ weight gain, promoted colon tissue repair, downregulated the expression of inflammatory cytokines, and promoted the accumulation of the tight junction protein. KEGG enrichment analysis of differentially expressed genes, applied to data from the RNA-seq of rat liver tissue, revealed that CGA treatment significantly affected amino acid and lipid metabolism in the liver. Furthermore, CGA decreased the abundance of bacteria belonging to the genera Blautia, Sutterella, and Akkermansia and increased butyric acid levels, which were positively correlated with the abundance of Ruminococcus (butyric acid producer). Moreover, the beneficial changes observed in the HFD group were not as pronounced as those in the CGA treatment group. In summary, CGA can alleviate colitis in HFD-induced obesity through its anti-inflammatory effects associated with changes in gut microbiota composition and an increase in the production of short-chain fatty acids and thus can be used as a potential drug for the treatment of this pathology.

Response of anaerobic digestion of waste activated sludge to residual ferric ions

This study was conducted to investigate the effects of residual ferric ions (FI), released from iron or its oxides for wastewater or waste activated sludge (WAS) treatment, on anaerobic digestion of WAS. Herein it was found that the anaerobic digestion process was greatly affected by FI dosages as well as FI distributions. The responses of performance and microorganism suggested that a low FI (e.g., 0.125 mmol/g volatile suspended solid (VSS)) enhanced methane production by 29.3%, and a medium FI (e.g., 0.3 mmol/g VSS) promoted short chain fatty acids accumulation to reach the maximum of 247 mg chemical oxygen demand /g VSS, conversely, a high FI (e.g., 0.9 mmol/g VSS) led to severe inhibition on acidogenesis and methanogenesis. The findings may provide some new insights for mechanism understanding on anaerobic digestion process influenced by iron or its oxides, as well as the disposal of WAS contained FI.

Xylooligosaccharides from steam-exploded barley straw: Structural features and assessment of bifidogenic properties

The biorefinery concept integrates the production of energy and bioproducts from biomass. In this philosophy, barley straw samples were used as raw material for the production of xylooligosaccharides (XOS) mixtures from soluble hemicelluloses by steam-explosion pretreatment. This fraction was treated by ion-exchange (XOS1) and a combination of membrane filtration, enzymatic hydrolysis, and ion-exchange processes (XOS2) to produce prebiotic compounds. The afforded products were then characterized by using analytical techniques, including HPAEC-PAD, FTIR, and MALDI-TOF-MS. XOS2 is composed of a backbone of xylopyranosyl branched, which including acetyl-esterified oligosaccharides and feruloyl substituted arabino-oligosaccharides.Further, the prebiotic potential was evaluated by in vitro fermentation experiments using as inocula human fecal samples from volunteers in which the short-chain fatty acids production, total bacteria growth, and the bifidobacteria numbers were quantified and compared to the results obtained with commercial fructooligosaccharides.The accumulation of short-chain fatty acids was similar for XOS1 and XOS2 (102.7 and 117.2 mM). An increase of 1.50 and 1.43 log cell number/mL-fold was observed for media containing XOS1 and XOS2, respectively. Results obtained confirm that the production and use of XOS derived from steam-exploded barley straw such as functional ingredient is an alternative for the valorization of its hemicelluloses fraction into the “biorefinery” context.

Insights on the microbial communities developed during the anaerobic fermentation of raw and pretreated microalgae biomass

Short-chain fatty acids (SCFAs) are considered building blocks for bioproducts in the so-called carboxylate platform. These compounds can be sustainably produced via anaerobic fermentation (AF) of organic substrates, such as microalgae. However, SCFAs bioconversion efficiency is hampered by the hard cell wall of some microalgae. In this study, one thermal and two enzymatic pretreatments (carbohydrases and proteases) were employed to enhance Chlorella vulgaris biomass solubilization prior to AF. Pretreated and non-pretreated microalgae were assessed in continuous stirred tank reactors (CSTRs) for SCFAs production. Aiming to understand microorganisms’ roles in AF depending on the employed substrate, not only bioconversion yields into SCFAs were evaluated but microbial communities were thoroughly characterized. Proteins were responsible for the inherent limitation of raw biomass conversion into SCFAs. Indeed, the proteolytic pretreatment resulted in the highest bioconversion (33.4% SCFAs-COD/CODin), displaying a 4-fold enhancement compared with raw biomass. Population dynamics revealed a microbial biodiversity loss along the AF regardless of the applied pretreatment, evidencing that the imposed operational conditions specialized the microbial community. In fact, a reduced abundance in Euryarchaeota phylum explained the low methanogenic activity, implying SCFAs accumulation. The bacterial community developed in the reactors fed with pretreated microalgae exhibited high acidogenic activities, being dominated by Firmicutes and Bacteroidetes. Firmicutes was by far the dominant phylum when using protease (65% relative abundance) while Bacteroidetes was prevailing in the reactor fed with carbohydrase-pretreated microalgae biomass (40% relative abundance). This fact indicated that the applied pretreatment and macromolecule solubilization have a strong effect on microbial distribution and therefore in SCFAs bioconversion yields.

Ruminal acidosis, bacterial changes, and lipopolysaccharides.

Acute and subacute ruminal acidosis (SARA) are common nutritional problems in both beef and dairy cattle. Therefore, the objective of this review is to describe how ruminal Gram-negative bacteria could contribute to the pathogenesis of ruminal acidoses, by releasing lipopolysaccharides (LPS; a component of their cell wall) in the ruminal fluid. When cattle consume excessive amounts of highly fermentable carbohydrates without prior adaptation, normal fermentation become disrupted. The fermentation of these carbohydrates quickly decreases ruminal pH due to the accumulation of short-chain fatty acids and lactate in the rumen. As a consequence, ruminal epithelium may be damaged and tissue function could be impaired, leading to a possible translocation of pathogenic substances from the rumen into the bloodstream. Such changes in fermentation are followed by an increase in Gram-positive bacteria while Gram-negative bacteria decrease. The lyses of Gram-negative bacteria during ruminal acidosis increase LPS concentration in the ruminal fluid. Because LPS is a highly proinflammatory endotoxin in the circulatory system, past studies have raised concerns regarding ruminal LPS contribution to the pathogenesis of ruminal acidosis. Although animals that undergo these disorders do not always have an immune response, recent studies showed that different Gram-negative bacteria have different LPS composition and toxicity, which may explain the differences in immune response. Given the diversity of Gram-negative bacteria in the rumen, evaluating the changes in the bacterial community during ruminal acidosis could be used as a way to identify which Gram-negative bacteria are associated with LPS release in the rumen. By identifying and targeting ruminal bacteria with possible pathogenic LPS, nutritional strategies could be created to overcome, or at least minimize, ruminal acidosis.

Potential Role of SLC5A8 Expression in the Etiology of Subacute Ruminal Acidosis.

Rumen fluid of cows with subacute ruminal acidosis (SARA) has high concentrations of short chain fatty acids (SCFA). However, the mechanism of SCFA accumulation is unknown. The solute-linked carrier 5a8 (SLC5A8) plays a key role in the transportation and absorption of SCFA in the intestinal epithelium. The objective of the current study was to investigate (1) SLC5A8 gene and protein expression in various parts of the bovine gastrointestinal tract, (2) the effect of SCFA on SLC5A8 expression in rumen epithelial cells, and (3) SLC5A8 gene and protein expression in SARA and healthy cows. A total of 10 dairy cows, 84 ± 26 days in milk and in their second to fourth parity were allocated to control (n = 5) and SARA groups (n = 5). Three cows from the control group and three calves (1-day-old, female, 45–50 kg, healthy, fasting) were chosen to collect a total of 10 sections of digestive tract, from rumen to rectum, and then bovine ruminal epithelial cells were isolated from the three calves. Gene and protein expression of SLC5A8 was detected in all tested regions of the gastrointestinal tract in calves and adult cows by Western blot and quantitative real-time PCR and were both highest in the rumen. Gene and protein expression of SLC5A8 was more than 50% lower in the rumen epithelium of SARA vs. control cows and was partly restored after therapy of SARA cows. Compared with SCFA concentrations typical for control cows (60 mM acetate, 30 mM propionate, and 20 mM butyrate), gene and protein expression of SLC5A8 in rumen epithelium was lower at elevated SCFA concentrations typical for SARA cows (90 mM acetate, 40 mM propionate, and 30 mM butyrate), specifically for elevated concentrations of propionate or butyrate in contrast to elevated concentrations of acetate increased gene and protein expression of SLC5A8 in rumen epithelium. In conclusion, the elevated concentrations of propionate and butyrate inhibit ruminal absorption of SCFA via downregulation of SLC5A8 in SARA cows; the expression of SLC5A8 plays an important role in the etiology of SARA.

Long-Term Effects of Polyvinyl Chloride Microplastics on Anaerobic Granular Sludge for Recovering Methane from Wastewater.

Polyvinyl chloride microplastics (PVC-MPs) are emerging contaminants affecting biological wastewater treatment processes. However, most of the previous studies mainly focused on their short-term impacts on floc sludge, with little work being conducted to explore their potential effects on more complex anaerobic granular sludge (AGS), which has been widely used for high-strength organic wastewater treatment. In this paper, the long-term effects of PVC-MPs on AGS were investigated via continuous feeding tests that are representative of real wastewater treatment processes. The results of a continuous 264 days test showed that the prolonged exposure of PVC-MPs at 15-150 MPs·L-1 significantly (p = 7.86 × 10-37, 3.44 × 10-43, and 5.29 × 10-46) inhibited the COD removal efficiency of AGS by 13.2%-35.5%, accompanied by a 11.0%-32.3% decreased production of methane and 40.3%-272.7% increased accumulation of short-chain fatty acids (SCFAs). In addition, the PVC-MPs exposure suppressed the secretion of extracellular polymeric substances (EPS), causing AGS and the inside microorganisms to lose the protection of EPS, thereby resulting in granule breakage and decreased cells viability. Aligning with the deteriorated performance, the long-term exposure of PVC-MPs reduced the total microbial populations and the relative abundances of key methanogens and acidogens. A toxicity mechanism assessment revealed that the negative impacts induced by PVC-MPs are mainly attributed to the toxic leachate and excess oxidative stress.

Alterations in fermentation parameters during and after induction of a subacute rumen acidosis in the rumen simulation technique.

Subacute rumen acidosis (SARA) is a common problem in dairy cattle. High-concentrate rations lead to an accumulation of short-chain fatty acids (SCFA) in the rumen and a subsequent decrease in ruminal pH. As SARA impairs animal welfare and productivity, numerous in vivo studies are focusing on evaluation of prevention strategies. In vitro models can support this research and reduce animal numbers and experimental costs. We used different diets and buffer compositions to induce SARA in the rumen simulation technique (Rusitec) and investigated the recovery process. The experiment consisted of an equilibration period (7days), a first control period, a SARA period and a second control period (5days each). During the SARA period, SARA was induced by infusing SARA1 or SARA2 buffer with reduced bicarbonate (20mmol/L and 25mmol/L) and phosphate (both 10mmol/L) contents compared to a modified McDougall's buffer (bicarbonate 97.9mmol/L, phosphates 20mmol/L). Additionally, we compared three feeding strategies, which differed in the concentrate-to-roughage ratio (30:70, 70:30, changing ratio: 30% concentrate in control periods and 70% concentrate in SARA period). During the SARA period, the pH decreased to a constant value below the SARA thresholds of pH 5.8 and 5.6, whereas lactate concentrations remained low. The total SCFA production rate declined 3days after SARA induction, and the molar proportion of acetate decreased. The decrease in pH and SCFA production was more pronounced for SARA1 buffer. The high-concentrate diet reduced the molar proportion of acetate and increased NH3 -N concentrations. During the second control period, most parameters recovered. In conclusion, SARA conditions were successfully induced in the Rusitec. However, we observed a higher influence of buffer composition than of concentrate proportions on most biochemical parameters. Nearly all changes were reversible. This model can be applied to test acidosis prevention strategies prior to animal experiments.

Alkaline aided thermophiles pretreatment of waste activated sludge to increase short chain fatty acids production: Microbial community evolution by alkaline on hydrolysis and fermentation

Adding alkaline into an anaerobic waste activated sludge (WAS) fermentation with thermophilic bacteria pretreatment could efficiently improve short-chain fatty acids (SCFAs) accumulation to 3550 ± 120 mg COD/L. The acidification rate in combined test was 21.2%, while that was 15.6% and 10.7% in sole thermophilic bacteria pretreatment and control tests respectively. Four distinct groups of microbes could be identified with noticeable shifts using the combined pretreatments, and tremendous effects were analyzed on organic content especially of the soluble proteins and SCFAs concentrations. Particularly, alkaline addition would significantly change the functional microbial structures, including the decrease of Caloramator with the function of thermophilic proteolytic and the increase of Acidobacteria TM7 and Petrimonas sp. The results above suggested that alkaline addition could decrease the hydrolytic substances consume by thermotolerance bacteria and final improve SCFAs accumulation in fermentation process.

Shifts in short-chain fatty acid profile, Fe(III) reduction and bacterial community with biochar amendment in rice paddy soil.

Biochar, a valuable product from the pyrolysis of agricultural and forestry residues, has been widely applied as soil amendment. However, the effect of different types of biochar on soil microorganisms and associated biochemical processes in paddy soil remains ambiguous. In this study, we investigated the impact of biochars derived from different feedstocks (rice straw, orange peel and bamboo powder) on the dynamics of short-chain fatty acids (SCFAs), iron concentration and bacterial community in paddy soil within 90 days of anaerobic incubation. Results showed that biochar amendment overall inhibited the accumulation of SCFAs while accelerating the Fe(III) reduction process in paddy soil. In addition, 16S rRNA gene sequencing results demonstrated that the α-diversity of the bacterial community significantly decreased in response to biochar amendments at day 1 but was relatively unaffected at the end of incubation, and incubation time was the major driver for the succession of the bacterial community. Furthermore, significant correlations between parameters (e.g. SCFAs and iron concentration) and bacterial taxa (e.g. Clostridia, Syntrophus, Syntrophobacter and Desulfatiglans) were observed. Overall, our findings demonstrated amendment with different types of biochar altered SCFA profile, Fe(III) reduction and bacterial biodiversity in rice paddy soil.

Enhancing biomethane production and pyrene biodegradation by addition of bio-nano FeS or magnetic carbon during sludge anaerobic digestion

ABSTRACT Pyrene exerts toxic effects on methanogens during anaerobic digestion of sludge, thus affecting the efficiency of sludge treatment. This study evaluated the facilitated direct interspecific electron transfer (DIET) between bacteria and methanogens when bio-nano FeS or magnetic carbon is added into anaerobic reactors. Results showed that adding 200 mg/L bio-nano FeS or magnetic carbon clearly reduced the accumulation of short-chain fatty acids and avoided acidification during 25 days of anaerobic digestion. The methane productions were 98.38 L/kg total solid (TS) and 73.69 L/kg TS in the bio-nano FeS and magnetic carbon systems, respectively, which accelerated methane production by 58.1% and 33.4%, respectively, compared with the control system (40.26 L/kg TS). The pyrene removal rates reached 77.5% and 72.1% in the bio-nano FeS and magnetic carbon systems, whereas it was only 40.8% in the control system. Analysis of microbial community structure revealed that methanogens (e.g. Methanosarcina and Methanosaeta) and extracellular electron-transfer bacteria (e.g. Pseudomonas, Cloastridia, and Synergistetes) were enriched in the reactors added with bio-nano FeS or magnetic carbon. This result indicates that the addition of bio-nano FeS or magnetic carbon may promote the activity and growth of microorganisms to improve the efficiency of methane production and pyrene degradation by enhancing DIET.

Subacute ruminal acidosis in dairy cows - physiological background, risk factors and diagnostic methods

According to the latest studies, the prevalence of subacute ruminal acidosis (SARA) is around 20% in early and mid- lactation dairy cows, generating annual losses in the United States of approximately USD 500 million to 1 billion. The diagnosis of SARA is still difficult due to lack of pathognomonic clues and the delayed appearance of certain clinical signs. Therefore, SARA remains neglected or even unrecognized in many dairy herds. SARA is characterized by daily episodes of low ruminal pH, when the pH remains in the range of 5.2 to 6 for a prolonged period due to the accumulation of short-chain fatty acids and insufficient rumen buffering. The causes of SARA are related to high-grain diets, such as feeding excessive amounts of non-structural carbohydrates and highly fermentable forages, and insufficient dietary coarse fibre. SARA is associated with the inflammation of several organs and tissues in dairy cows, and its main long-term health and economic consequences are the fluctuation of feed intake, reduced fibre digestion, depression of milk yield and milk fat content, gastrointestinal damage, diarrhoea, laminitis, liver abscesses, and lameness. The aim of this review is to summarize the information available on the physiological aspects, risk factors, prevalence and possible indicators of SARA in dairy cattle. Basedon the existing literature, rumenocentesis and the use of an oral stomach tube are reliable field techniques to detect SARA. Nowadays, improved field techniques allowing the continuous measurement of reticuloruminal pH are also available for better diagnosis of SARA. Wireless indwelling pH probes may become important tools for the continuous measurement of ruminal pH in the coming years.

Effects of fibers and gut microbiota on low-grade inflammatory human disease

Obesity represents a major public health problem, as it leads to metabolic disorders involved in the development of type 2 diabetes, fatty liver diseases, cardiovascular diseases and cancer (1). The Western lifestyle, including over-feeding of highly refined diets and sedentary behavior, is associated with systemic low-grade inflammation, responsible for chronic degenerative disease. Moreover, animal and human data have demonstrated the impact of high-fat diet feeding on the onset of metabolic endotoxemia. This latter, being characterized by increase blood lipopolysaccharide (LPS) levels, triggers low-grade inflammation and contributes to the development of obesity. The gut microbiota are a candidate sources of plasma LPS. Indeed, LPS is a major component of the outer membrane in Gram-negative bacteria and its plasma levels are correlated with changes in intestinal microbiota where the Gram-negative to Grampositive ratio is increased by high fat feeding (1). Not surprising that in humans, obesity is characterized by dysbiosis, i.e. imbalances in the composition and function of the intestinal microbes. Currently, many studies are being conducted to assess the contribution of intestinal microflora metabolites [mainly short-chain fatty acids (SCFAs)] to the organism’s homeostasis. Dietary fibers have been promoted for their health benefits and high-fiber intake has been reported as beneficial in numerous chronic diseases (2). However, we have to keep in mind that consumption of dietary fiber significantly alters the composition of the gut microbiota. For instance, addition of fibers to the diet increases the abundance of butyrate-producing bacteria Roseburia species and Eubacterium rectale , whereas a lowfiber diet is associated to a major decrease in this group, with Faecalibacterium prausnitzii becoming the main butyrate-producer. Hence, a greater understanding of the interaction between dietary fibers and the intestinal microbiota could represent a mean of maintaining or improving the community of gut microorganisms, particularly when dysbiosis exists. In addition, although various data indicate that increased SCFAs production positively affects the host by exerting antiobesity and antidiabetic effects, some in vitro and in vivo studies have indicated that overproduction or accumulation of SCFAs in the bowel may lead to obesity and cancer development, owing to increased energy accumulation and elevation of the inflammatory state. As correctly pointed out in the recent paper by Wen and Schwabe , more experimental and epidemiologic data are needed to completely elucidate the link among dietary fibers, gut microbiota and the onset of low-grade inflammatory diseases (3). However, the authors commented about the recent study by Singh et al. (4) and based only on these results stated that soluble fibers could be associated to liver disease and hepatocellular carcinoma. Specifically, it will be a great achievement to shed light on the influence that SCFAs exert on the intestinal environment as well as on distal tissues and organs. SCFAs, mainly acetate, propionate and butyrate, are organic acid produced by intestinal microbial fermentation of dietary fibers. Various mechanisms have been highlighted to justify the biological effects of butyrate: (I) inhibition of histone deacetylase (HDAC); (II) downregulation of neuropilin-1 (NRP-1); (III) activation of G-protein-coupled receptors, GPR41, GPR43 and GPR109A, and of the peroxisome proliferator-activated receptor γ (PPARγ); (IV) modulation of canonical Wnt signaling pathway; (V) activation of AIM2 and NLRP3 inflammasomes, enhancing production of interleukin-18 (IL-18) and epithelial barrier function; (VI) differentiation of T lymphocytes into effector (Te) and regulatory (T reg) T cells; and (VII) modulation of T lymphocytes and dendritic cell functions (5). In the meantime, SCFAs can reach the liver through the portal vein and directly promote hepatic triglyceride accumulation and gluconeogenesis. In addition, various data have demonstrated that butyrate appears to have “paradoxical” effects on colonic epithelial proliferation due to the fact that the response of proliferative cells to butyrate are affected by the dose of butyrate, the physiological conditions under which the study was performed and the phenotype of the target cells (3). Butyrate can instead suppress proliferation in hyperproliferation situations (i.e., colon cancers cells), or stimulate proliferation in impaired energy status (i.e., atrophic colon) or having no effect in normal tissues. Similarly, butyrate can promote or inhibit apoptosis (1).

A novel and effective pretreatment to stimulate short‐chain fatty acid production from waste activated sludge anaerobic fermentation by ferrous iron catalyzed peracetic acid

AbstractBACKGROUNDThis study investigates a novel, efficient and green pretreatment approach using ferrous iron catalyzed peracetic acid oxidation (Fe2+/PAA) on anaerobic fermentation of waste activated sludge. The underlying mechanisms are also studied for both the chemical and microbial effects.RESULTSThe results indicate that Fe2+/PAA exhibit significant positive synergistic effect on short‐chain fatty acid (SCFA) generation, especially acetic acid. The maximal SCFA concentration of 272 mg COD g−1 VSS is obtained with Fe2+ (2.7 mmol L–1)/PAA (3.0 mmol L–1), which is 5.2 times that of the control test. Fe2+/PAA can effectively facilitate sludge solubilization due to the disruption of extracellular polymeric substances structure and microbial cells. The biodegradability of released organic substance is also improved due to the oxidation of non‐biodegradable substances. The activity of functional enzymes for hydrolysis and acidification is enhanced but that for methanogenesis is inhibited. Further analysis on microbial community structure indicates that phylum Firmicutes and genera Proteiniclasticum showed the maximal positive correlation with SCFA production, while the abundance of methanogenic archaea especially acetoclastic methanogenic archaea is inhibited by Fe2+/PAA treatment. Moreover, the presence of Fe2+ lengthened the oxygen release period of PAA, the main functional reactive oxygen species are hydroxyl radicals and Fe2+ facilitated PAA generates more hydroxyl radicals thus enhancing the oxidation ability of PAA.CONCLUSIONThis study demonstrated that Fe2+/PAA can be used as an effective pretreatment method for SCFA accumulation in sludge anaerobic fermentation process. The findings obtained in this study will supply information for the application of Fe2+ catalyzed PAA pre‐oxidation in sludge treatment. © 2019 Society of Chemical Industry

Increased anode respiration enhances utilization of short-chain fatty acid and lipid wet-extraction from Scenedesmus acutus biomass in electro-selective fermentation

Electro-selective fermentation (ESF) can improve lipid extraction from Scenedesmus acutus biomass using green solvents like hexane and 1:1 hexane: isopropanol, but accumulation of short-chain fatty acids (SCFAs) wastes useable electrons. To eliminate the electron loss, we designed a flat-plate microbial electrolytic cell (MEC) to have a large anode area for a biofilm of anode respiring bacteria (ARB) that oxidize the SCFAs and generate current that produces H2 gas at the cathode. In 9-day batch tests of ESF in the flat-plate MEC, 18% of the total electrons in the feeding biomass were scavenged by the ARB biofilm and converted to current, leaving minimal concentrations of SCFAs. Extraction with two solvents -- 1:1 hexane:isopropanol and 100% hexane – was evaluated at the end of the 9-day experiments. 30% of the total lipids became hexane-extractable with ESF, compared to <1% in the feeding biomass. Furthermore, hexane had 100% selectivity towards saturated long-chain fatty acids (LCFAs), which are superior for biofuel production. Thus, ESF improved the quantity and quality of extractable FAME-based biofuel from S. acutus, while directing electron equivalents in SCFAs to current and H2 generation at the cathode.