Acetate Accumulation Research Articles

Ethanol vapor treatment inhibits apple ripening at room temperature even with the presence of ethylene

Abstract The present study aimed to evaluate the effect of two ethanol vapor doses (250 and 500 ppm), 1-methylcyclopropene (1-MCP) (0.650 ppm) with or without ethylene application (150 ppm) on the aerobic and anaerobic metabolism and quality of ‘Elstar’, a fast ripening apple cultivar, and ‘Nicoter’, a slowly ripening apple cultivar, over 14 d of holding at room temperature (20 ± 2 °C). Fruit were subjected to treatments for 24 h and analyses performed after 0, 7 and 14 d holding at room temperature (20 ± 2 °C). For both cultivars studied, ethanol vapor treatments, especially 500 ppm, inhibited the ripening of apples even when combined with 150 ppm of ethylene, but not as much as 1-MCP treatment in ‘Nicoter’ apples. Fruit treated with ethanol vapor maintained lower electrolyte leakage, higher flesh firmness, greener color and had more healthy fruit. However, its application increased the pyruvate decarboxylase (PDC) and alcohol dehydrogenase (ADH) activity, acetaldehyde and ethyl acetate accumulation, but in concentrations below the odor threshold reported in the literature. The 1-MCP treatment increased decay incidence, reducing the healthy fruit amount in ‘Nicoter’ apples after 14 d, but maintained a very low ethylene production and respiration rate, which allowed higher acidity maintenance after 14 d holding at room temperature. There was no incidence of external and internal physiological disorders in both cultivars.

PSII-20 Effects of aerobically exposed corn silage treated with medium chain fatty acids on rumen fermentation in vitro

Abstract Medium chain fatty acid (MCFA) treatment of aerobically exposed silage during feed-out is a potential strategy to prevent growth of spoilage and pathogenic microbes. To evaluate the effects of feeding MCFA-treated silage on the rumen fermentability, we incubated 0.02 g of overnight air-exposed corn silage that had been treated individually without or with (0.75% wt/wt) C6, C8, C10 or C12 or with equal proportion mixtures of C6:C8:C10:C12 or C8:C10 with 10 mL freshly collected ruminal fluid. Additions were made while flushing with CO2 and tubes (3 tubes/treatment) were then capped and sealed. After 24 h incubation at 39oC, headspace gases and fluid volatile fatty acids were measure using gas chromatography techniques. Results from a completely randomized analysis of variance revealed higher hydrogen accumulations (P < 0.05) only in incubations containing silage treated with the C8:C10 MCFA mixture when compared to controls, with mean ± SD concentrations (µmol/mL incubation fluid) being 2.19 ± 1.6 versus 0.08 ± 0.04, respectively. Treatment effects were not observed (P > 0.05) on accumulations (µmol/mL) of methane (13.25 ± 2.5), acetate (19.66 ± 5.6), propionate (7.27 ± 2.0), butyrate (12.36 ± 2.7) or stochiometric estimates of amounts of hexose fermented (41.39 ± 9.7), although the acetate:propionate ratios of incubations of silage treated with C8 or the C8:C10 mixture were higher (P < 0.05) than those of untreated controls (3.46 ± 0.7, 3.46 ± 0.5 and 2.35 ± 0.1, respectively). Consequently, correspondingly estimates of fermentation efficiency, calculated based caloric energy values of amounts of acetate, propionate and butyrate relative to glucose, were slightly lower (P < 0.05) for the incubations of silage treated with C8 and the C8:C10 mix compared to controls (74.36 ± 1.1, 74.82 ± 0.2 and 76.55 ± 0.3 %, respectively). Results reveal little negative effect of MCFA treatment on ruminal fermentability of silage.

Regulation of Enteroendocrine Cell Networks by the Major Human Gut Symbiont Bacteroides thetaiotaomicron.

Gut microbes have critical roles in maintaining host physiology, but their effects on epithelial chemosensory enteroendocrine cells (EEC) remain unclear. We investigated the role that the ubiquitous commensal gut bacterium Bacteriodes thetaiotaomicron (Bt) and its major fermentation products, acetate, propionate, and succinate (APS) have in shaping EEC networks in the murine gastrointestinal tract (GIT). The distribution and numbers of EEC populations were assessed in tissues along the GIT by fluorescent immunohistochemistry in specific pathogen free (SPF), germfree (GF) mice, GF mice conventionalized by Bt or Lactobacillus reuteri (Lr), and GF mice administered APS. In parallel, we also assessed the suitability of using intestinal crypt-derived epithelial monolayer cultures for these studies. GF mice up-regulated their EEC network, in terms of a general EEC marker chromogranin A (ChrA) expression, numbers of serotonin-producing enterochromaffin cells, and both hormone-producing K- and L-cells, with a corresponding increase in serum glucagon-like peptide-1 (GLP-1) levels. Bt conventionalization restored EEC numbers to levels in SPF mice with regional specificity; the effects on ChrA and L-cells were mainly in the small intestine, the effects on K-cells and EC cells were most apparent in the colon. By contrast, Lr did not restore EEC networks in conventionalized GF mice. Analysis of secretory epithelial cell monolayer cultures from whole small intestine showed that intestinal monolayers are variable and with the possible exclusion of GIP expressing cells, did not accurately reflect the EEC cell makeup seen in vivo. Regarding the mechanism of action of Bt on EECs, colonization of GF mice with Bt led to the production and accumulation of acetate, propionate and succinate (APS) in the caecum and colon, which when administered at physiological concentrations to GF mice via their drinking water for 10 days mimicked to a large extent the effects of Bt in GF mice. After withdrawal of APS, the changes in some EEC were maintained and, in some cases, were greater than during APS treatment. This data provides evidence of microbiota influences on regulating EEC networks in different regions of the GIT, with a single microbe, Bt, recapitulating its role in a process that may be dependent upon its fermentation products.

Thermophilic biomethanation of sugarcane molasses comparing single and two-stage systems: Process performance and energetic potential

This study compares two- and single-stage thermophilic (55 °C) anaerobic systems as approaches for recovering bioenergy from sugarcane molasses. A bench-scale reactor was initially fed for 344 d with fermented molasses in a two-stage approach (RM-I). The same reactor was further fed with fresh molasses for 192 d, characterizing a single-stage system (RM-II). Increasing organic loading rates (up to 10 kg-COD m−3 d−1) were assessed in both operating modes. Maximum methane production was 1.5-fold higher in RM-I (3912 vs. 2688 NmL-CH4 L−1 d−1), with a global (CH4 + H2) energetic potential 200% higher (7.80 vs. 4.00 MJ kg-molasses−1) than RM-II. Operational stability was maintained in RM-II even when decreasing NaHCO3 supplying from 1.00 to 0.25 g-NaHCO3 g-COD−1. The removal of NaHCO3 dosing stimulated hydrogen production and the accumulation of butyrate and acetate. Methane production was only partially recovered after re-inserting NaHCO3 and acetate accumulation was evidence of impaired acetoclastic methanogenic activity.

Screening of Acetate-Tolerant Yeast and Its Effect on Controlling Bacterial Contamination During Ethanol Production from Sugarcane Molasses

Growth and ethanol fermentation ability of the acetate-tolerant yeast Saccharomyces cerevisiae KU 002-3 strain were investigated in acetate-addition medium. Under simulated industrial conditions, acetate did not affect on sugar consumption and ethanol production of KU 002-3. Moreover, KU 002-3 strain demonstrated a higher capability for ethanol production than other commercial strains. Co-fermentation was conducted with Lactobacillus fermentum IFRPD 2021, the major contaminating bacteria, during the ethanol production at 0.8% (v/v) acetate (130 mM of the undissociated form of acetate). Under these conditions, growth of L. fermentum IFRPD 2021 was inhibited but the growth and ethanol production ability of S. cerevisiae KU 002-3 strain were not significantly affected. Data indicated the possibility of producing ethanol under high acetate accumulation and reducing Lactobacillus sp. in molasses medium or acetate-containing condition. Producing ethanol under high acetate accumulation and lower the contamination of Lactobacillus sp. in a molasses medium can be useful at industrial scale to produce ethanol with S. cerevisiae KU 002-3 under non-sterilized conditions.

Research on the electrocatalytic reduction of CO2 by microorganisms with a nano-titanium carburizing electrode

The reduction of CO2 to organics using microbial electrosynthesis (MES) is currently a popular research direction in the environmental field. In this study, we evaluated the effect of the electrode material on the production of organics from CO2 in microbial electrosynthesis with a mixed-culture biocathode. The electrode material is an important factor influencing electron transfer, since it directly affects the efficiency of CO2 reduction. In this study, we compared the performance of a graphite electrode and a metal-based carbon hybrid material electrode for the electro-reduction of CO2. The cathode potential was set to −0.8 V (vs Ag/AgCl). When the cathode material was changed from a graphite electrode to a nano-titanium carburizing electrode, the current density of MES increased from 1.66 ± 0.2 A·m−2 to 2.75 ± 0.2 A·m−2, acetate accumulation increased from 127 mg/L to 234 mg/L, butyrate accumulation increased from 46 mg/L to 86.5 mg/L, and the total electron recovery of MES increased to nearly 70%. The results show that improving electrode performance can effectively improve the efficiency of MES for reducing CO2. Metal-based carbon hybrid materials have good biological affinity and stability and also have good electrochemical performance.

Enhanced Biosynthesis of Plasmid DNA from Escherichia coli Applying Experimental Design.

Therapeutic applications of plasmid DNA (pDNA) have significantly advanced during the last years. Currently, several pDNA-based drugs are already in the market, whereas several others have entered phases 2 and 3 of clinical trials. The present and future demand for pDNA requires the development of efficient bioprocesses to produce it. Commonly, pDNA is produced by cultures of Escherichia coli. It has been previously demonstrated that specific strains of E. coli with a modified substrate transport system can be able to attain high cell densities in batch mode, due to the very low overflow metabolism displayed. However, the large amounts of oxygen demanded can lead to microaerobic conditions after some hours of cultivation, even at small scale. Typically, the inherent problems for these cultures are the high oxygen demand and the accumulation of acetate, a metabolic byproduct that is synthesized aerobically when the glucose rate exceeds the limits.In recent years, several researches have been focused on the study of induction of plasmid DNA as well as strategies for fermentation using semi-defined mediums. These studies conceived relevant results that allow us to design a production platform for enhanced plasmid DNA. So, the main goal of this chapter is to show how the development of an experimental design directed to aromatic amino acids pathway can improve the yield of a therapeutic plasmid DNA by culture of a new strain of Escherichia coli VH33.

Engineered citrate synthase alters Acetate Accumulation in Escherichia coli

Metabolic engineering is used to improve titers, yields and generation rates for biochemical products in host microbes such as Escherichia coli. A wide range of biochemicals are derived from the central carbon metabolite acetyl-CoA, and the largest native drain of acetyl-CoA in most microbes including E. coli is entry into the tricarboxylic acid (TCA) cycle via citrate synthase (coded by the gltA gene). Since the pathway to any biochemical derived from acetyl-CoA must ultimately compete with citrate synthase, a reduction in citrate synthase activity should facilitate the increased formation of products derived from acetyl-CoA. To test this hypothesis, we integrated into E. coli C ΔpoxB twenty-eight citrate synthase variants having specific point mutations that were anticipated to reduce citrate synthase activity. These variants were assessed in shake flasks for growth and the production of acetate, a model product derived from acetyl-CoA. Mutations in citrate synthase at residues W260, A267 and V361 resulted in the greatest acetate yields (approximately 0.24 g/g glucose) compared to the native citrate synthase (0.05 g/g). These variants were further examined in controlled batch and continuous processes. The results provide important insights on improving the production of compounds derived from acetyl-CoA.

Short-term low temperature treatments of harvested wine grapes (cv. Vermentino) affect the volatile organic compound profile of the berries

In the recent years, due to the climate change and the effects of greenhouse gases average temperatures are increasing. Grapes cultivated in Mediterranean areas are exposed to high temperatures especially during the late growing season and at harvest. This may induce undesirable biochemical processes (e.g. aroma losses and oxidative reactions) with negative effects on the berry composition and specific quality traits of the resulting wine. In the present study the effect of short-term low temperature treatments on harvested grapes before vinification have been evaluated. Bunches of wine grapes cv.Vermentino have been hand-harvested and then refrigerated at 4°C and 10°C for 24 and 48 hours, while 22°C has been used as a control temperature. Grapes were analysed in terms of technological parameters (weight loss, total soluble solids, titratable acidity, pH and total polyphenols) and volatile organic compound profile by HS-SPME GC-MS. Low-temperature post-harvest treatments affect total polyphenols content of the berries and appear to reduce the heat-related aroma loss, increase the content of four volatile terpenoids and decrease the accumulation of ethyl acetate.

Effects of variety and growth year on the essential oil properties of lavender (Lavandula angustifolia Mill.) and lavandin (Lavandula x intermedia Emeric ex Loisel.)

Essential oil (EO) properties of six L. angustifolia (LA) and two L. x intermedia (LI) cultivars were evaluated during summer harvest periods of 2017 and 2018, The cultivars were grown in Dörgicse, Hungary. According to our results, the essential oil (EO) content was highly dependent on the varieties in both experimental years (2017: p < 0.0001 and 2018: p < 0.0001). In 2017, the EO content values of LI accessions were all higher than those of the LA cultivars. However, in 2018, the mean EO content value of ‘Budakalászi’ (LA) (8.2 mL/100g) exceeded that of ‘Grosso’ (LI) (7.7 mL/100g). The EO of ‘Mailette’ (LA) and ‘Budakalászi’ (LA) contained the highest linalool proportions (52.9% and 47.0%) while ‘Beate’ (LA) showed the lowest (18.1%); and this latter variety was richest in linalyl-acetate (58.9%). LI varieties produced lower linalyl acetate and total ester ratios in comparison to the LA cultivars. Concerning EO composition, only the UK varieties ‘Hidcote Blue’ (LA) and ‘Munstead’ (LA) met the requirements of the Ph. Eur.This study provided evidence that the effect of growth year on the EO content was significant only in two varieties out of the eight. However, in the more rainy year 2018, the accumulation of linalool and linalyl acetate was significantly affected in several cases, where linalool proportions decreased and linalyl acetate ratios increased.

Waste Ochre for Control of Phosphates and Sulfides in Digesters at Wastewater Treatment Plants with Enhanced Biological Phosphorus Removal

Ochre, waste iron sludge from the treatment of iron rich groundwater for potable use, makes up a significant waste problem. Furthermore, wastewater treatment plants with enhanced biological phosphorus removal and the digestion of sludge are in lack of iron for the prevention of hydrogen sulfide production and the release of phosphorous during anaerobic digestion. Thus, the addition of ochre to anaerobic digestion is a potential beneficial reuse of ochre. Sludge from wastewater treatment plants with enhanced biological phosphorus removal was used for the experiments. Batch and continuous pilot-scale tests were performed for the mesophilic digestion of primary and waste-activated sludge with different doses of ochre. Two different doses of ochre corresponding to molar ratios of 1 and 2 moles Fe3+/mole P released in the batch test resulted in 29% and 57% reductions of phosphates respectively in the sludge liquor compared to the control sludge without inhibiting the digestion process. In the pilot experiment, the dosing of ochre at both a high and low dose (molar ratios of 1.6 and 0.8 Fe3+/S2−, respectively) resulted in an immediate drop in the H2S concentration (from &gt;2000 ppm down to 570 ppm), while the control reactor still produced biogas with a high hydrogen sulfide concentration. The inhibition of the digestion process was observed (accumulation of acetate) at the higher dose. In a second pilot scale experiment, lower doses of ochre were tested continuously (1.5 and 0.75 mole Fe3+/mole Preleased) to avoid any inhibition, while evaluating the phosphate precipitation. A reduction of phosphates in sludge liquor (33% and 66% for the low and high doses respectively) was obtained.

Reducción de sulfato de un lodo aclimatado gradualmente a acetato como único donador de electrones y su potencial aplicación como inóculo en una celda de combustible microbiana

The aim of the present work was to obtain a sulfidogenic sludge capable of thriving with acetate and evaluate its potential application as a source of microorganisms in a microbial fuel cell (MFC). The results showed that sulfate (SO4-2) to sulfide (HS-) conversion increased from 74 ± 0.39 % with a fed consisting of a mixture acetate:butyrate, to 85 ± 0.34 % with a fed containing only acetate. The sulfate removal rate (SRR) was of 73.14 ± 2.08 mg SO4-2 gVSS-1 L-1 h-1 and sulfate reducing activity (SRA) 6.46 ± 1.25 mg COD-H2S gVSS-1L-1h-1 with the mixture and SRR 70.51 ± 1.58 mg SO4-2 gVSS-1 L-1 h-1 ; SRA 7.67 ± 1.00 mg COD-H2S gVSS-1 L-1 h-1 with acetate. The COD removal increased from 66 ± 0.8% with the mixture to 81 ± 0.39 %, with acetate. The open circuit voltage increased from 0.668 to 0.788 V with acetate. The results suggested that this sludge could be utilized to recover energy that could be eventually susceptible to storage for further utilization while reducing sulfate and avoiding accumulation of acetate.

Engineering Corynebacterium glutamicum for the Efficient Production of 3-Hydroxypropionic Acid from a Mixture of Glucose and Acetate via the Malonyl-CoA Pathway

3-Hydroxypropionic acid (3-HP) has been recognized as one of the top value-added building block chemicals, due to its numerous potential applications. Over the past decade, biosynthesis of 3-HP via the malonyl-CoA pathway has been increasingly favored because it is balanced in terms of ATP and reducing equivalents, does not require the addition of costly coenzymes, and can utilize renewable lignocellulosic biomass. In this study, gene mcr encoding malonyl-CoA reductase from Chloroflexus aurantiacus was introduced into Corynebacterium glutamicum ATCC13032 to construct the strain Cgz1, which accumulated 0.30 g/L 3-HP. Gene ldhA encoding lactate dehydrogenase was subsequently deleted to eliminate lactate accumulation, but this decreased 3-HP production and greatly increased acetate accumulation. Then, different acetate utilization genes were overexpressed to reuse the acetate, and the best candidate Cgz5 expressing endogenous gene pta could effectively reduce the acetate accumulation and produced 0.68 g/L 3-HP. To enhance the supply of the precursor acetyl-CoA, acetate was used as an ancillary carbon source to improve the 3-HP production, and 1.33 g/L 3-HP could be produced from a mixture of glucose and acetate, with a 2.06-fold higher yield than from glucose alone. Finally, to inhibit the major 3-HP competing pathway-fatty acid synthesis, 10 μM cerulenin was added and strain Cgz5 produced 3.77 g/L 3-HP from 15.47 g/L glucose and 4.68 g/L acetate with a yield of 187 mg/g substrate in 48 h, which was 12.57-fold higher than that of Cgz1. To our best knowledge, this is the first report on engineering C. glutamicum to produce 3-HP via the malonyl-CoA pathway. The results indicate that the innocuous biosafety level I microorganism C. glutamicum is a potential industrial 3-HP producer.

Improvement of Streptococcus suis glutamate dehydrogenase expression in Escherichia coli through genetic modification of acetate synthesis pathway.

Escherichia coli generates acetate as an undesirable by-product that has several negative effects on protein expression, and the reduction of acetate accumulation by modifying genes of acetate synthesis pathway can improve the expression of recombinant proteins. In the present study, the effect of phosphotransacetylase (pta) or/and acetate kinase (ackA) deletion on glutamate dehydrogenase (GDH) expression was investigated. The results indicated that the disruptions of pta or/and ackA decreased the acetate accumulation and synthesis of per gram cell, and increased cell density, and GDH expression and synthesis of per gram cell. The pta gene was more important for acetate formation than the ackA gene. Using the strain with deletions of pta-ackA (SSGPA) for GDH expression, acetate accumulation (2·61gl-1 ) and acetate synthesis of per gram cell (0·229gg-1 ) were lowest, decreasing by 28·29 and 41·43% compared with those of the parental strain (SSG) respectively. The flux of acetate synthesis (6·6%) was decreased by 72·15% compared with that of SSG, and the highest cell density (11·38gl-1 ), GDH expression (2·78mgml-1 ), and GDH formation of per gram cell (0·2442mgmg-1 ) were obtained, which were 1·22-, 1·43- and 1·17-times higher than the parental strain respectively. SIGNIFICANCE AND IMPACT OF THE STUDY: Significance and Impact of the Study: Acetate is the key undesirable by-product in Escherichia coli cultivation, and both biomass and production of desired products are increased by the reduction of acetate accumulation. In the present study, the strains with deletions of pta or/and ackA were constructed to reduce the acetate accumulation and improve the GDH expression, and the highest expression level of GDH was obtained using the strain with lesion in pta-ackA that was 1·17-times higher than that of the parental strain. The construction strategy of recombinant E. coli for decreasing the acetate excretion can be used for high expression level of other desired products.

Failure to Maintain Acetate Homeostasis by Acetate-Activating Enzymes Impacts Plant Development.

The metabolic intermediate acetyl-CoA links anabolic and catabolic processes and coordinates metabolism with cellular signaling by influencing protein acetylation. In this study we demonstrate that in Arabidopsis (Arabidopsis thaliana), two distinctly localized acetate-activating enzymes, ACETYL-COA SYNTHETASE (ACS) in plastids and ACETATE NON-UTILIZING1 (ACN1) in peroxisomes, function redundantly to prevent the accumulation of excess acetate. In contrast to the near wild-type morphological and metabolic phenotypes of acs or acn1 mutants, the acs acn1 double mutant is delayed in growth and sterile, which is associated with hyperaccumulation of cellular acetate and decreased accumulation of acetyl-CoA-derived intermediates of central metabolism. Using multiple mutant stocks and stable isotope-assisted metabolic analyses, we demonstrate the twin metabolic origins of acetate from the oxidation of ethanol and the nonoxidative decarboxylation of pyruvate, with acetaldehyde being the common intermediate precursor of acetate. Conversion from pyruvate to acetate is activated under hypoxic conditions, and ACS recovers carbon that would otherwise be lost from the plant as ethanol. Plastid-localized ACS metabolizes cellular acetate and contributes to the de novo biosynthesis of fatty acids and Leu; peroxisome-localized ACN1 enables the incorporation of acetate into organic acids and amino acids. Thus, the activation of acetate in distinct subcellular compartments provides plants with the metabolic flexibility to maintain physiological levels of acetate and a metabolic mechanism for the recovery of carbon that would otherwise be lost as ethanol, for example following hypoxia.

Formation of volatile organic compounds during the fermentation of maize as affected by sealing time and silage additive use

ABSTRACTThe study investigated the production of volatile organic compounds during the fermentation of maize containing 26.8% dry matter (DM). Forage was ensiled without additive or treated with 2 ml/kg of a chemical silage additive (SA) containing per litre 257 g sodium benzoate, 134 g potassium sorbate and 57 g ammonium propionate, and either sealed immediately or with a delay of 24 h. During the fermentation process, DM-losses, fermentation pattern (including ethyl lactate [EL] and ethyl acetate [EA]) and yeast numbers were determined. Delayed sealing and no SA resulted in highest DM losses with significant interactions between sealing time (ST) and SA on all sampling days (p < 0.001). The effects on organic acid production were variable depending on storage length. Ethanol production was affected by ST and SA, but promptly sealed silage treated with SA had consistently the lowest concentrations. Higher ethanol content during fermentation was associated with higher DM losses, as reflected by a strongly linear, positive relationship (R2 = 0.70, p < 0.001). Compared with promptly sealed silage, the counts of yeasts were higher after delayed sealing during the first 7 d of storage (p < 0.001). Moreover, SA reduced yeast numbers compared with untreated silage (p < 0.01). EL concentrations increased throughout storage, whereas EA acetate accumulation was very rapid and intense already during the early stages of fermentation and peaked on d 34. The differences in concentrations and accumulation pattern between EL and EA, especially during the early fermentation phases, make evident that their synthesis was facilitated by different pathways and reactions, respectively.

Effects of dissimilatory iron reduction on acetate production from the anaerobic fermentation of waste activated sludge under alkaline conditions

Anaerobic digestion of waste activated sludge (WAS) to produce acetate has recently attracted growing interest, while the slow hydrolytic acidification of sludge and the consumption of acetate by methanogens both decrease the yield of acetate. In this study, Fe3O4 was added to a WAS anaerobic digester under alkaline conditions (pH = 10). The concentration of short-chain fatty acids (SCFA) during WAS anaerobic fermentation was found to be affected positively by Fe3O4. The maximal SCFA production of the Fe3O4-added digester was 3619.4 mg/L, while the maximal SCFA production in the control was 2899.7 mg/L. The increase of SCFA with Fe3O4 was mainly resulted from the increase in acetate accumulation (accounting for 90%), because Fe3O4 stimulated dissimilatory iron reduction (DIR) that participated in the decomposition of complex organics and the transformation of pronionate and butyrate into acetate. Further investigation showed that each step of hydrolytic-acidification process was promoted except the homoacetogenesis. The activity of enzymes and abundance of microbes relevant to hydrolysis and acidification were in agreement with the above results.

Application of fermentation process control to increase l-tryptophan production in Escherichia coli.

In this study, process engineering and process control were applied to increase the production of l-tryptophan using Escherichia coli Dmtr/pta-Y. Different dissolved oxygen (DO) and pH control strategies were applied in l-tryptophan production. DO and pH were maintained at [20% (0-20 hr); 30% (20-40 hr)] and [7.0 (0-20 hr), 6.5 (20-40 hr)], respectively, which increased l-tryptophan production, glucose conversion percentage [g (l-tryptophan)/g (glucose)], and transcription levels of key genes for tryptophan biosynthesis and tryptophan biosynthesis flux, and decreased the accumulation of acetate and transcription levels of genes related to acetate synthesis and acetate synthesis flux. Using E. coli Dmtr/pta-Y with optimized DO [20% (0-20 hr); 30% (20-40 hr)] and pH [7.0 (0-20 hr), 6.5 (20-40 hr)] values, the highest l-tryptophan production (52.57 g/L) and glucose conversion percentage (20.15%) were obtained. The l-tryptophan production was increased by 26.58%, the glucose conversion percentage was increased by 22.64%, and the flux of tryptophan biosynthesis was increased to 21.5% compared with different conditions for DO [50% (0-20 hr), 20% (20-40 hr)] and pH [7.0].

Leaching of organic carbon from grassland soils under anaerobiosis

The projected increase of extreme precipitation and freeze-thawing events may lead to frequent occurrence of anaerobiosis in upland soils, which has significant impacts on biogeochemical processes affecting soil carbon loss. However, compared to mineralization, the impacts of anaerobiosis (potentially accompanied by fermentation) on soil organic carbon (SOC) leaching is limited. Here we conducted microcosm and intact soil column incubation experiments to examine processes influencing SOC leaching from four typical Chinese grassland soils under simulated anaerobiosis. Compared to aerobiosis, non-fermenting anaerobiosis increased the pH, dissolved phenol concentrations and aromaticity of soil leachates. In contrast, fermenting anaerobiosis induced acetate accumulation, lowered pH, stimulated phenol oxidative activity and generally decreased aromaticity in soil leachates in both microcosm and soil column experiments relative to aerobiosis. Both anaerobiosis potentially induced a strong release of dissolved organic carbon (DOC) accompanied by iron and nitrate reduction, especially with fermentation. However, DOC in soil leachates decreased in alpine subsoils under fermentation relative to aerobiosis. This interesting phenomenon was mainly attributed to (i) minimal iron reduction and dissolution in the alpine subsoils and (ii) enhanced DOC oxidation by elevated phenol oxidative activity in the fermentation relative to aerobiosis treatments. These results collectively indicate that anaerobiosis may increase SOC leaching and its magnitude is dependent on the extent of iron reduction and pH variations. Fermentation-enhanced release of ferrous iron and acetate may have an even stronger influence on the downstream biogeochemistry. Hence, temporary anaerobiosis warrants better recognition and investigation in the Mongolian (relative to Qinghai-Tibetan) grasslands that show high soil iron reduction potentials and are predicted to experience increased extreme precipitation in the future.

Microbial Community Rearrangements in Power-to-Biomethane Reactors Employing Mesophilic Biogas Digestate

The biological conversion of hydrogen (H2) and carbon dioxide (CO2) to methane (CH4), is accomplished by the hydrogenotrophic methanogens (HM). HMs are difficult to cultivate in pure culture, but they are readily available in the mixed culture of effluents from the anaerobic degradation of organic matter, i.e. the fermentation effluent of biogas plants. The rate-limiting step in the work of CH4-forming microbial communities is the low solubility of H2 in the aqueous environment. In our approach, the simple fed-batch fermentation technique was selected to supply the gaseous substrates for the microbial community at laboratory scale and mesophilic temperature. Periodically withdrawn samples were analyzed for process parameters and the microbial communities were studied using Terminal Restriction Fragment Length Polymorphism (T-RFLP) of the mcrA gene and Ion Torrent whole metagenome DNA sequencing. The metagenome data were evaluated by both read-based and genome-centric bioinformatics tools. The rearrangements in the mixed microbial communities, triggered by switching the operating conditions to biological power-to-biomethane (bio-P2M), have been established. The production rates were 6.30 mL CH4 L-1 h-1 during the acclimation phase and 9.21 mL CH4 L-1 h-1 by the fully adapted community, respectively. The diversity of the anaerobic microbiota decreased as the bio-P2M process progressed. Feeding the community with H2 apparently promoted the abundance of several genera, in particular Candidatus Cloacimonas and Herbinix. The diversity of the Archaea community decreased considerably upon daily feeding with H2 and CO2. The predominant Archea genus was Methanobacterium in every reactor, Methanothrix persisted for the first 4 weeks, while the initially less abundant genus Methanoculleus gained advantage during the adaptation to the sustained bio-P2M process. The accumulation of acetate indicated a strong involvement of homoacetogenic bacteria.