Volatile Fatty Acid Metabolism Research Articles

Comparative study of the quick action effect of multiple enzyme-based nano-emulsified oils in enhancing nitrate contamination remediation in groundwater

Emulsified vegetable oil (EVO), as a novel green slow-releasing substrate, has performed great potential in subsurface bioremediation due to its slow release and longevity. Nevertheless, the long time it takes to initiate this process still exposed some limitations. Herein, multiple enzyme-based EVOs (EN-EVOs) were developed to enhance the quick-acting effect in nitrate-contaminated bioremediation. This study demonstrated that EN-EVOs loaded with cellulose (c-EVO) and protein enzymes (p-EVO) performed best, not only did not change the advantages of traditional EVO, but also optimized the stability and particle size to the level of 0.8–0.9 and 247.95–252.25 nm, respectively. Nitrate (NO3–N) degradation further confirmed the superiority of c-EVO in rapidly initiating degradation and achieving stable denitrification. Compared with traditional EVO, the maximum start-up efficiency and the rapid achieving stable denitrification efficiency were improved by 37.6% and 1.71 times, respectively. In such situation, the corresponding NO3–N removal efficiency, kinetics rate constant (k1), and half-life period (t1/2) reached as high as 85.39%, as quick as 1.079 d−1, and as short as 0.64 d after 30-day cultivation. Meanwhile, the rapid conversion efficiency of NO2–N was observed (k2 = 0.083 d−1). High-throughput 16S rRNA gene sequencing indicated that the quick-acting process of NO3–N reduction coupled to c-EVO was mediated by microbial reducers (e.g., Ralstonia, Gulbenkiania, and Sphingobacterium) with regulations of narG, nirS and norB genes. Microorganisms with these genes could achieve quick-acting not only by enhancing microbial activity and the synthesis and metabolism of volatile fatty acids, but also by reducing the production and accumulation of loosely bound-extracellular polymeric substances (LB-EPS). These findings advance our understanding on fast-acting of NO3–N degradation supported by c-EVO and also offer a promising direction for groundwater remediation.

Impact of abscisic acid treatment on postharvest storage quality and volatile flavor substances in blueberries

AbstractTo investigate the impact of abscisic acid (ABA) on the postharvest flavor and quality of blueberries, this study employed different concentrations of ABA (400 μM ABA, 600 μM ABA, and 800 μM ABA) to treat the blueberries. The treated blueberries were then stored at 4°C (~80% relative humidity) for 35 day. Subsequently, genes associated with the metabolism of volatile aromatic substances and fatty acids in postharvest blueberries were assessed using real‐time PCR. Our results revealed that the treatment of ABA could maintain a high level of nutrient and aromatic substances in blueberries. Particularly, 600 μM ABA caused most significant changes in fatty acid metabolism‐related enzyme activities, such as lipoxygenase, hydroperoxide lyase, alcohol dehydrogenase, as well as related gene expressions, like VcLOX2S, VcHPL, VcADH1‐1, VcADH1‐2, VcADH1‐3, and VcADH1‐4. In addition, Furthermore, the blueberries treated with 600 μM ABA exhibited a superior quality when compared to the control group. This superior quality included higher levels of total acid, ascorbic acid, total phenol, anthocyanin, soluble sugar contents, and so forth. In conclusion, postharvest ABA treatment decelerated the decrease in volatile aroma substances and effectively maintained the flavor of blueberries.

Effects of Fe–N co-modified biochar on methanogenesis performance, microbial community, and metabolic pathway during anaerobic co-digestion of alternanthera philoxeroides and cow manure

The performance of anaerobic digestion (AD) is susceptible to disturbances in feedstock degradation, intermediates accumulation, and methanogenic archaea activity. To improve the methanogenesis performance of the AD system, Fe–N co-modified biochar was prepared under different pyrolysis temperatures (300,500, and 700 °C). Meanwhile, pristine and Fe-modified biochar were also derived from alternanthera philoxeroides (AP). The aim was to compare the effects of Fe–N co-modification, Fe modification, and pristine biochar on the methanogenic performance and explicit the responding mechanism of the microbial community in anaerobic co-digestion (coAD) of AP and cow manure (CM). The highest cumulative methane production was obtained with the addition of Fe-N-BC500 (260.38 mL/gVS), which was 42.37 % higher than the control, while the acetic acid, propionic acid, and butyric acid concentration of Fe-N-BC were increased by 147.58 %, 44.25 %, and 194.06 % compared with the control, respectively. The co-modified biochar enhanced the abundance of Chloroflexi and Methanosarcina in the AD system. Metabolic pathway analysis revealed that the increased methane production was related to the formation and metabolism of volatile fatty acids and that Fe-N-BC500 enhanced the biosynthesis of coenzyme A and the cell activity of microorganisms, accelerating the degradation of propionic acid and enhancing the hydrogenotrophic methanogenesis pathway. Overall, Fe–N co-modified biochar was proved to be an effective promoter for accelerated methane production during AD.

Integrated genome-centric metagenomic and metaproteomic analyses unravel the responses of the microbial community to ammonia stress

Ammonia is a major inhibitor in anaerobic digestion of nitrogen-rich organic wastes. In this study, integrated genome-centric metagenomic and metaproteomic analyses were used to identify the key microorganisms and metabolic links causing instability by characterizing the process performance, microbial community, and metabolic responses of key microorganisms during endogenous ammonia accumulation. The identification of 89 metagenome-assembled genomes and analysis of their abundance profile in different operational phases permitted the identification of key taxa (Firmicutes and Proteobacteria) causing poor performance. Metabolic reconstruction indicated that the key taxa had the genetic potential to participate in the metabolism of C2C5 volatile fatty acids (VFAs). Further investigation suggested that during Phase I, the total ammonia nitrogen (TAN) level was maintained below 2000 mg N/L, and the reactor showed a high methane yield (478.30 ± 33.35 mL/g VS) and low VFAs concentration. When the TAN accumulated to > 2000 mg N/L, acid accumulation, mainly of acetate, began to occur, and the methane yield gradually decreased to 330.44 mL/g VS (Phase II). During this phase, the VFA degradation functions of the community were mainly mediated by Firmicutes. Approximately 61.54% of significant differentially expressed proteins (DEPs) related to acetate metabolism in Firmicutes were down-regulated, which led to an increase in acetate concentration to 4897.91 ± 1558.96 mg/L. However, the reactor performance showed spontaneous recovery without any interference (Phase III), during which Firmicutes gradually adapted to the high ammonia conditions. Approximately 75% of the significant DEPs related to acetate metabolism of Proteobacteria were also up-regulated in Phase III compared with Phase II; thus, VFA-related metabolic functions of the community were enhanced, which resulted in a decrease in the total VFA concentration to 195.39 mg/L. When the TAN increased above 4000 mg N/L, the system gradually showed acid accumulation dominated by propionate, accompanied by a second decrease in methane yield (Phase IV). During this phase, the number of up-regulated and down-regulated proteins related to acetate metabolism of Firmicutes and butyrate/valerate metabolism of Proteobacteria was comparable with that of Phase III, indicating that the metabolic functions related to acetate, butyrate, and valerate of the microbial community were not significantly affected. However, for propionate metabolism, the expression activity of fumarate hydratase from Firmicutes and Proteobacteria was severely inhibited by ammonia, as shown by down-regulation ratios of 63.64% and 85.71%, respectively. No protein with the same function that was not inhibited by ammonia could be detected, and the fumarate degradation function of the microbial community was severely damaged, leading to blocked propionate metabolism and irreversible deterioration of reactor performance. This study has provided a new perspective on the microecological mechanisms of ammonia inhibition.

Waste volatile fatty acids as a good electron donor in microbial fuel cell with the iron-modified anode

The commercialization of microbial fuel cell technology is limited by high operating costs and low electricity production due to poor electron transfer to the anode. Operational costs can be lowered by utilizing waste materials, and cell performance can be improved by anode modification. This study investigated how anode modification with iron compounds changed the efficiency of energy generation and the microbiome of microbial fuel cells fueled with waste volatile fatty acids from a full-scale anaerobic digestion. Anode modification with 2.5 g Fe2O3/m2 increased the power density, current density, and voltage by 3.6-fold, 1.8-fold, and 1.4-fold, respectively. In the microbial fuel cell influent, propionic, enanthic, and iso-caproic acids predominated (60, 15, and 13% of all volatile fatty acids, respectively); in the outflow, propionic (71%) and valeric acids (17%) predominated. In anodic biofilms, Acidovorax sp. were most abundant; they have a great capacity for volatile fatty acids decomposition, and their abundance doubled in the microbial fuel cell with an iron-modified anode. The presence of iron significantly increased the abundance of the genera Pseudomonas and Geothrix, which were mainly responsible for electricity production. These results indicate that anode modification with iron changes the anode microbiome, favoring efficient volatile fatty acids metabolism and a greater abundance of electrogens in the biofilm, which ensures better electricity generation.

Metabolome profiling of plasma reveals different metabolic responses to acute cold challenge between Inner-Mongolia Sanhe and Holstein cattle.

Low-temperature conditions influence cattle productivity and survivability. Understanding the metabolic regulations of specific cattle breeds and identifying potential biomarkers related to cold challenges are important for cattle management and optimization of genetic improvement programs. In this study, 28 Inner-Mongolia Sanhe and 22 Holstein heifers were exposed to -25°C for 1 h to evaluate the differences in metabolic mechanisms of thermoregulation. In response to this acute cold challenge, altered rectal temperature was only observed in Holstein cattle. Further metabolome analyses showed a greater baseline of glycolytic activity and mobilization of AA in Sanhe cattle during normal conditions. Both breeds responded to the acute cold challenge by altering their metabolism of volatile fatty acids and AA for gluconeogenesis, which resulted in increased glucose levels. Furthermore, Sanhe cattle mobilized the citric acid cycle activity, and creatine and creatine phosphate metabolism to supply energy, whereas Holstein cattle used greater AA metabolism for this purpose. Altogether, we found that propionate and methanol are potential biomarkers of acute cold challenge response in cattle. Our findings provide novel insights into the biological mechanisms of acute cold response and climatic resilience, and will be used as the basis when developing breeding tools for genetically selecting for improved cold adaptation in cattle.

Simulated seasonal diets alter yak rumen microbiota structure and metabolic function.

Yak is the only ruminant on the Qinghai-Tibetan Plateau that grazes year-round. Although previous research has shown that yak rumen microbiota fluctuates in robust patterns with seasonal foraging, it remains unclear whether these dynamic shifts are driven by changes in environment or nutrient availability. The study examines the response of yak rumen microbiota (bacteria, fungi, and archaea) to simulated seasonal diets, excluding the contribution of environmental factors. A total of 18 adult male yaks were randomly divided into three groups, including a nutrition stress group (NSG, simulating winter pasture), a grazing simulation group (GSG, simulating warm season pasture), and a supplementation group (SG, simulating winter pasture supplemented with feed concentrates). Volatile fatty acids (VFAs) profiling showed that ruminal acetate, propionate and total VFA contents were significantly higher (p < 0.05) in GSG rumen. Metagenomic analysis showed that Bacteroidetes (53.9%) and Firmicutes (37.1%) were the dominant bacterial phyla in yak rumen across dietary treatments. In GSG samples, Actinobacteriota, Succinivibrionaceae_UCG-002, and Ruminococcus albus were the most abundant, while Bacteroides was significantly more abundant in NSG samples (p < 0.05) than that in GSG. The known fiber-degrading fungus, Neocallimastix, was significantly more abundant in NSG and SG samples, while Cyllamyces were more prevalent in NSG rumen than in the SG rumen. These findings imply that a diverse consortium of microbes may cooperate in response to fluctuating nutrient availability, with depletion of known rumen taxa under nutrient deficiency. Archaeal community composition showed less variation between treatments than bacterial and fungal communities. Additionally, Orpinomyces was significantly positively correlated with acetate levels, both of which are prevalent in GSG compared with other groups. Correlation analysis between microbial taxa and VFA production or between specific rumen microbes further illustrated a collective response to nutrient availability by gut microbiota and rumen VFA metabolism. PICRUSt and FUNGuild functional prediction analysis indicated fluctuation response of the function of microbial communities among groups. These results provide a framework for understanding how microbiota participate in seasonal adaptations to forage availability in high-altitude ruminants, and form a basis for future development of probiotic supplements to enhance nutrient utilization in livestock.

Size-dependent effects of polystyrene microplastics on anaerobic digestion performance of food waste: Focusing on oxidative stress, microbial community, key metabolic functions

Polystyrene (PS) microplastics (MPs) are widely existed in food waste (FW) due to the usage of plastic food-packaging. However, the effects and mechanisms of PS MPs with different sizes on anaerobic digestion (AD) performance of FW have not been comprehensively studied yet. Herein, the impacts of different PS MPs sizes (1 mm, 100 µm and 1 µm) with 20, 200 particles/g-TS were investigated. Results showed that 20 particles/g-TS PS MPs decreased cumulative methane production by 1.46–18.11 %, while the higher levels (200 particles/g-TS) significantly inhibited by 9.14–33.08 % (p < 0.05) compared with control group. The inhibiting effects were enhanced as particle size smaller. Physicochemical analysis indicated that MPs prolonged organic matter hydrolysis, weakened the volatile fatty acids metabolism and inhibited methanogenesis-related microorganisms (Synergistetes, Proteiniphilum and Methanosarcina). Small-sized MPs could induce more reactive oxygen species causing cell toxicity and suppressed key enzymes (α–glucoside, protease, acetate kinases and F420) activities, thereby restraining methane production. The analyses of acetyl-CoA synthase and methyl-coenzyme M reductase functional genes illustrated that small-sized MPs negatively affected acetoclastic methanogenesis pathways. Overall, these results provide new insights into the size-dependent effects on AD performance induced by PS MPs.

Protective Roles of Sodium Butyrate in Lipopolysaccharide-Induced Bovine Ruminal Epithelial Cells by Activating G Protein-Coupled Receptors 41

This study aimed to evaluate whether sodium butyrate (SB) attenuates the ruminal response to LPS-stimulated inflammation by activating GPR41 in bovine rumen epithelial cells (BRECs). We examined the SB regulation of GPR41 and its impact on LPS-induced inflammation using GPR41 knockdown BRECs. The LPS-induced BRECs showed increases in the expression of genes related to pro-inflammation and decreases in the expression of genes related to tight junction proteins; these were attenuated by pretreatment with SB. Compared with that in LPS-stimulated BRECs, the ratio of phosphorylated NF-κB (p65 subunit) to NF-κB (p65 subunit) and the ratio of phosphorylated IκBα to IκBα were suppressed with SB pretreatment. The LSB group abated LPS-induced apoptosis and decreased the expression of Bax, Caspase 3, and Caspase 9 mRNA relative to the LPS group. In addition, the LSB group had a lower proportion of cells in the G0–G1 phase and a higher proportion of cells in the S phase than the LPS group. The mRNA expression of ACAT1 and BDH1 genes related to volatile fatty acid (VFA) metabolism were upregulated in the LSB group compared to those in LPS-induced BRECs. In addition, pretreatment with SB promoted the gene expression of GPR41 in the LPS-induced BRECs. Interestingly, SB pretreatment protected BRECs but not GPR41KD BRECs. Our results suggest that SB pretreatment protects against the changes in BRECs LPS-induced inflammatory response by activating GPR41.

Understanding the role of rumen epithelial host-microbe interactions in cattle feed efficiency.

Feed efficiency is one of the economically important traits for the cattle industry that affects profit (feed costs) and the environment (production of manure and methane). Due to that feed efficiency is driven by multi-factors, mechanisms contributing to the animal to animal variation in this trait have not been well defined, limiting the development of precision feeding strategies to improve the herd production efficiency. Rumen microbial fermentation and volatile fatty acids (VFA) production have been recently reported to be associated with cattle feed efficiency, however the roles of rumen epithelial function in feed efficiency are less studied although the rumen epithelium has an important function in VFA absorption and metabolism which can affect host feed efficiency. Rumen epithelium is colonized with a diverse microbial population, termed epimural microbiota, which has proposed functions in tissue development, barrier and inflammation, urea transport, and oxygen scavenging, suggesting that they can affect rumen epithelial functions and subsequently cattle feed efficiency. Especially, prospective functions of epimural microbiota, enhanced rumen immunity and increased rumen epithelial thickness, might contribute to less nutritional requirement for tissue recuperation. Thus, the understanding of the functions of rumen epithelium, epimural microbiota, and rumen epithelial host-microbe interactions is essential to identify their roles in contributing to feed efficiency. In this review, we will focus on to date research findings on the structure of rumen epithelium, epimural microbiota, and epithelial host-microbe interactions together with their functions and how these are associated with feed efficiency, aiming to provide insights on future directions to study rumen epithelial host-microbe interactions and improve the rumen functions in cattle.

Physicochemical pretreatment selects microbial communities to produce alcohols through metabolism of volatile fatty acids

Physicochemical pretreatment selects microbial communities to produce alcohols through metabolism of volatile fatty acids

Single-cell transcriptomic landscape of the sheep rumen provides insights into physiological programming development and adaptation of digestive strategies

As an important evolutionary innovation and unique organ, the rumen has played a crucial role in ruminant adaptation to complex ecological environments. However, the cellular basis of its complex morphology and function remains largely unknown. In this study, we identified eight major cell types from seven representative prenatal and postnatal rumen samples using ~56 600 single-cell transcriptomes. We captured the dynamic changes and high heterogeneity in cellular and molecular profiles before, during, and after the appearance of keratinized stratified squamous epithelium with neatly arranged papillae and functional maturity. Basal cells, keratinocytes, differentiating keratinocytes, terminally differentiated keratinocytes, and special spinous cells provided the cellular basis for rumen epithelium formation. Notably, we obtained clear evidence of two keratinization processes involved in early papillogenesis and papillae keratinization and identified TBX3 as a potential marker gene. Importantly, enriched stratum spinosum cells played crucial roles in volatile fatty acid (VFA) metabolism and immune response. Our results provide a comprehensive transcriptional landscape of rumen development at single-cell resolution, as well as valuable insight into the interactions between dietary metabolism and the rumen.

Mechanisms of Anaerobic Soil Disinfestation: Volatile Fatty Acids Reduce Viability of Athelia (Sclerotium) rolfsii Sclerotia in Acidic Soil Conditions and Have Limited Effects on Endemic Trichoderma spp.

Volatile fatty acids (VFAs), such as acetic and n-butyric acid, released during anaerobic decomposition of organic soil amendments during anaerobic soil disinfestation (ASD) likely play a role in soilborne plant pathogen inoculum suppression. However, research is limited on the direct effects of soil VFA exposure on fungal plant pathogen inoculum, effects on pathogen antagonists such as Trichoderma spp., and the role of soil microbial VFA metabolism on reducing exposure effects. The present study addresses these limitations through a series of studies evaluating the effects of VFA (acetic or n-butyric acid), VFA concentration (4, 8, or 16 mmol/kg soil), soil sterilization by autoclaving, and soil amendment on the viability of Athelia rolfsii (Sclerotium rolfsii) sclerotia post VFA exposure, and soil populations of Trichoderma spp. HCl and water-only controls were included. After 4-days exposure in an acidic, anaerobic environment, sclerotial viability, and colonization by culturable fungi or bacteria were assessed with standard procedures. Greenhouse experiments were similarly conducted to evaluate endemic soil populations of Trichoderma spp. following soil exposure to VFAs and Trichoderma spp. populations assessed with standard soil dilution plating onto semi-selective medium. Sclerotial germination was generally reduced by soil exposure to acetic (35.1% germination) or n-butyric (21.9% germination) acids compared to water (74.3% germination) and HCl (62.7% germination). Germination was reduced as VFA concentration increased from 4 to 8 and 16 mmol/kg (39.5, 29.1, and 16.9%, respectively). In amended soils, there was no difference in sclerotial germination compared to non-amended soils, but in the greenhouse experiment there was a Trichoderma spp. population increase of over 300% in amended soil [3.4 × 106 colony forming units (CFU)/g soil] compared to the non-amended soil (9.6 × 105 CFU/g soil). Soil autoclaving had no effect on sclerotial germination at low VFA concentrations, but sclerotial germination was reduced at higher VFA concentrations compared to non-autoclaved soil. Our results suggest that VFAs contribute to sclerotial mortality in strongly acidic soil environments, and mortality is influenced by VFA components and environment. Antifungal activity is less for acetic acid than for n-butyric, and less in non-sterile soil environments more typical of field conditions than in sterile laboratory conditions.

Diseases’ bacterial markers in the rumen of Russian Arctic reindeer

The study of symbiotic communities of the reindeers’ rumen remains one of the most interesting topics of microbial ecology. The physiological adaptations of reindeer allow them to use the scarce nutritional resources of the tundra and forest-tundra for feeding. The study is the first attempt to analyze the microbiome of the rumen of Russian Arctic reindeer's in the in terms of searching for microorganisms that are indicators of pathological processes caused by the change of seasons. We have sequenced (Miseq, Illumina) the rumen microbiome of 38 reindeer living in the Nenets and Yamalo-Nenets Autonomous Districts in summer and winter. NMDS analysis revealed significant differences between winter and summer microbiomes of the reindeers’ rumen (p = 0.001). By analyzing sequencing data using the VennDiagram package in the R software, common and unique OTUs were calculated. The share of unique species in winter was 7.1%, and in summer 10.6%. It was found that a number of pathogenic microorganisms that cause diseases develop in the rumen of reindeers in the summer. It is known that the incidence of parasitic diseases, necrobacteriosis, etc. in reindeers’ herds increases in summer. Necrobacteriosis is seasonal in nature and spreads mainly in July-August, when the temperature is highest and the gadflies and blood-sucking insects are active. Venngraph analysis showed the presence of unique DNA sequences of Fusobacterium sp. that were found only for the summer period. Fusobacteria can be called one of the main agents causing necrobacteriosis. In the summer period only, rumen bacteria that contribute to the development of inflammatory reactions in the chronic periodontitis (Parvimonas sp. and Porphyromonas endodontalis) were detected. Sharpea sp. was detected only for the summer period also. These bacteria produce lactic acid and are able to lower the pH of the rumen fluid, which leads to an imbalance in the metabolism of volatile fatty acids. It is known that in cattle, changes associated with a decrease in rumen pH lead to the development of acidosis. Thus, we have shown that in summer, in contrast to winter, various pathogenic bacterial species develop, causing diseases such as necrobacteriosis, chronic periodontitis. This is probably due to an increase in temperature in summer, which provokes the development of different groups of microorganisms, including pathogens, as well as the activity of parasitic insects that contribute to the spread of diseases in reindeer herds. In addition, the animal's body is weakened after a long winter period and a meager diet, which also contributes to the development of various infectious processes. We have identified a number of pathogenic bacteria, such as Fusobacterium sp., Parvimonas sp. and Porphyromonas endodontalis, which appear only in summer and can be distinguished as microorganisms-markers of pathological processes.

Transcriptomic analysis reveals the molecular mechanisms of rumen wall morphological and functional development induced by different solid diet introduction in a lamb model

BackgroundThis study aimed to elucidate the molecular mechanisms of solid diet introduction initiating the cellular growth and maturation of rumen tissues and characterize the shared and unique biological processes upon different solid diet regimes.MethodsTwenty-four Hu lambs were randomly allocated to three groups fed following diets: goat milk powder only (M, n = 8), goat milk powder + alfalfa hay (MH, n = 8), and goat milk powder + concentrate starter (MC, n = 8). At 42 days of age, the lambs were slaughtered. Ruminal fluid sample was collected for analysis of concentration of volatile fatty acid (VFA) and microbial crude protein (MCP). The sample of the rumen wall from the ventral sac was collected for analysis of rumen papilla morphology and transcriptomics.ResultsCompared with the M group, MH and MC group had a higher concentration of VFA, MCP, rumen weight, and rumen papilla area. The transcriptomic results of rumen wall showed that there were 312 shared differentially expressed genes (DEGs) between in “MH vs. M” and “MC vs. M”, and 232 or 796 unique DEGs observed in “MH vs. M” or “MC vs. M”, respectively. The shared DEGs were most enriched in VFA absorption and metabolism, such as peroxisome proliferator-activated receptor (PPAR) signaling pathway, butanoate metabolism, and synthesis and degradation of ketone bodies. Additionally, a weighted gene co-expression network analysis identified M16 (2,052 genes) and M18 (579 genes) modules were positively correlated with VFA and rumen wall morphology. The M16 module was mainly related to metabolism pathway, while the M18 module was mainly associated with signaling transport. Moreover, hay specifically depressed expression of genes involved in cytokine production, immune response, and immunocyte activation, and concentrate starter mainly altered nutrient transport and metabolism, especially ion transport, amino acid, and fatty acid metabolism.ConclusionsThe energy production during VFA metabolism may drive the rumen wall development directly. The hay introduction facilitated establishment of immune function, while the concentrate starter enhanced nutrient transport and metabolism, which are important biological processes required for rumen development.

The functional development of the rumen is influenced by weaning and associated with ruminal microbiota in lambs

Rumen development is critical for the development of early lambs. This work aims to evaluate the effects of abrupt weaning at day 21 on rumen fermentation, histomorphological traits and the ruminal microbiota compared with continuous suckling. Twelve pairs of artificially reared full-sib neonatal male Hu lambs were allocated to two groups, one of which was weaned at day 21 (EW group) and the other which was not weaned (CON group). At day 26 and day 49, six lambs from each group were randomly selected and sacrificed to collect ruminal contents and rumen tissue samples. Results showed that weaning influenced the fermentation parameters in the rumen, and altered the microbial community composition on day 49 (p < 0.05). Several genera were associated with rumen fermentation parameters (p < 0.05). Volatile fatty acid (VFA) concentration is the key parameter impacting microbiota composition. Weaning influenced the expression of genes associated with VFA metabolism and regulation of cell proliferation (p < 0.05). In conclusion, weaning significantly influenced the morphological and functional development of the rumen, and bacterial community composition. The microbial community composition was strongly associated with rumen weight and fermentation profiles, but not with morphological development.

Response of process performance and microbial community to ammonia stress in series batch experiments

To further clarify the key stage and microorganisms responsible for ammonia inhibition instability, three sequential batch experiments were conducted with various ammonia concentrations and different exposure modes. Acetate metabolism was most sensitive to ammonia, however, after continuous ammonia exposure, acetate metabolism was well restored by a shift in dominant microorganisms. In contrast, the metabolism of longer-chain volatile fatty acids (LCVFAs, C3–C5) was only inhibited under a high ammonia concentration (≥6000 mg/L), however, once inhibited, continuous exposure neither restored the abundance of functional microbes nor induced new microorganisms to perform metabolic functions. Therefore, LCVFA metabolism was the key stage responsible for process instability under ammonia stress. Moreover, the deterioration of LCVFA metabolism was caused by the inhibition of syntrophic acetogenic bacteria (SAB) induced by total ammonia nitrogen, rather than the feedback inhibition from methanogenesis. That is, SAB were the key microorganisms involved in process instability.

The impact of temperature on the metabolism of volatile fatty acids by polyphosphate accumulating organisms (PAOs)

This study investigated the effects of different carbon sources on enriched Accumulibacter PAO cultures at high temperature (30 °C) and compared the carbon transformation with low temperature (20 °C) cases reported in literature, revealing several key metabolic differences. While PAOs seemed to prefer propionate anaerobically as compared to other VFAs at high temperature, high aerobic glycogen replenishment was realized with propionate as the anaerobic carbon source, a trait not previously observed at low temperatures. Therefore, it was found that propionate is not correlated with high P removal by Accumulibacter PAO at high temperatures. A combined substrate of acetate, propionate and perhaps butyrate seemed to be a better carbon source combination, since the total VFA uptake rate increased by up to 46%, and this increased the aerobic P-removal efficiency by up to 38.4% and reduced the glycogen recovery by more than 63% compared to the use of only propionate as substrate. This study improves our understanding of how to stimulate successful EBPR operation in warm climates by augmenting the P removal performance of PAOs.

Adding Appropriate Fiber in Diet Increases Diversity and Metabolic Capacity of Distal Gut Microbiota Without Altering Fiber Digestibility and Growth Rate of Finishing Pig.

The digestion ability of pigs to dietary fiber is derived from their intestinal microbiota, especially hindgut microbiota. However, tolerance of pigs to high dietary fiber and the changes of microbiota profile with fiber levels are still unclear. To investigate the changes of gut microbiota with dietary fiber and its relationship with fiber digestibility, we conducted comparative analyses of growth rate, apparent fiber digestibility, gut microbiota and volatile fatty acid (VFA) profiles in Chinese Suhuai pigs feeding diets with different defatted rice bran (DFRB) fiber levels. We found that dietary fiber level had no effect on the growth rate of Suhuai pigs. Although the apparent digestibility of Cellulose, insoluble dietary fiber (IDF) and total dietary fiber (TDF) decreased with dietary fiber level, we found that the apparent digestibility of Cellulose, IDF and TDF of Suhuai pigs was not changed when provided with diet containing 19.10% TDF (as feed basis). The pigs provided with diet containing 19.10% TDF had higher microbial richness, proportions of several fiber-degrading bacteria taxa at genus level and predicted microbial functions (such as carbohydrate metabolism, energy metabolism) in cecum compared to those fed with basal diet. In addition, the fiber-induced increasing of fiber-degrading bacteria promoted the VFAs metabolism, which potentially helped Suhuai pigs to maintain growth rate. However, as TDF reached to 24.11% (as feed basis), the apparent digestibility of fiber decreased and the positive effect on intestine microbiota in caecum were absent. Together, our data suggest that appropriate fiber level could increase the diversity and metabolic capacity of distal gut microbiota to improve the utilization efficiency of fiber resources without altering the growth rate of pigs.

Response of syntrophic aggregates to the magnetite loss in continuous anaerobic bioreactor

Increasing studies indicate that magnetite addition could accelerate the methanogenesis via enhancing direct interspecies electron transfer (DIET)-based anaerobic syntrophy. However, magnetite is found to run off in continuous bioreactor, and the effect of magnetite loss on syntrophic aggregates is still underreported. In this study, two EGSB reactors (RM with magnetite-enhanced sludge, and RB as a control) were operated to investigate the magnetite behavior in continuous bioreactor and the corresponding response of syntrophic aggregates. Results showed that magnetite in RM was washed out gradually in form of iron ions, and a slightly acidic niche was supposed to be the major cause. Nevertheless, candidate DIET partners like Geobacter and Methanothrix along with syntrophic volatile fatty acids (VFAs)-degrading microbes were enriched in RM. In addition, the improved redox activity of extracellular polymeric substance (EPS), higher sludge conductivity and electron transport activity suggested that the DIET ability of sludge in RM was still enhanced, which favors the syntrophic metabolism of VFAs. Interestingly, syntrophic partners were loosely combined under the condition of high organic loading rate (OLR) in the presence of magnetite, but with gradual loss of magnetite, dense and active anaerobic granular sludge (AGS) was formed in RM. This study provided a comprehensive understanding of magnetite behavior in continuous bioreactor and the response of syntrophic aggregates. The robust DIET-based syntrophy after magnetite adding could favor the high-efficient anaerobic wastewater treatment and resource recovery in the future, and further investigations on magnetite resupply and the mechanism of magnetite enriching candidate DIET partners are recommended.