Acetate Molar Research Articles

The beneficial effect of Enterococcus faecium on the in vitro ruminal fermentation rate and extent of three typical total mixed rations in northern China

in vitro batch cultures were performed to determine the effect of Enterococcus faecium at inclusion levels of 0 (Control), 1.33, 2.67, 4, 5.33 and 6.67×106CFU/mL in culture fluids consisted of 25mL filtrated rumen fluid and 50mL buffer solution on rumen degradability, kinetics of gas production, and fermentation characteristics of 3 typical total mixed rations in northern China with different forage and/or concentrate ingredients (MF, a ration with a mixed forage combination of corn silage and alfalfa hay; CSA, a ration with a single forage of corn stalks and same concentrate in MF; CSB, a ration with same forage in CSA but concentrate ingredients different from MF and CSB). After 72h incubation, in vitro dry matter disappearance and cumulative gas production were greater in MF than CSA and CSB (P<0.001), and the fermentation characteristics varied depending on the ration incubated. Regardless of what type of ration was incubated, the in vitro dry matter disappearance, cumulative gas production, asymptotic gas production, and maximum gas production rate values were all greater in the E. faecium addition group than the control (P<0.010) and increased linearly with the augmentation of the E. faecium addition level (P<0.001). In comparison with the control, E. faecium addition slightly decreased pH, but did not alter ammonia N concentration. Microbial crude protein and total volatile fatty acid concentrations in the culture fluids were increased by the E. faecium addition (P<0.001), and molar acetate and butyrate proportions were decreased (P<0.001), but molar propionate and valerate proportions were increased (P<0.001). Methane production estimated by volatile fatty acids was decreased by E. faecium addition and fermentation efficiency was greater in the E. faecium addition in comparison with the control (P<0.001). In summary, rumen fermentation characteristics differed depending on forage ingredient and nutrient density in the rations; the E. faecium addition increased the in vitro rumen dry matter degradability and sped up the fermentation process, resulting in a remarkable increase in total VFA production (from 14.0 to 25.7%). E. faecium addition level of at least 2.67×106CFU/mL exhibited high potential for stimulating the growth of rumen microbes to increase the glucogenic propionate energy supply for host ruminants.

Interactions of alfalfa hay and sodium propionate on dairy calf performance and rumen development

The objective of this experiment was to investigate the effects of different levels of alfalfa hay (AH) and sodium propionate (Pro) added to starter diets of Holstein calves on growth performance, rumen fermentation characteristics, and rumen development. Forty-two male Holstein calves (40±2kg of birth weight) were used in a complete randomized design with a 3×2 factorial arrangement of treatments. Dietary treatments were as follows: (1) control = concentrate only; (2) Pro = concentrate with 5% sodium propionate [dry matter (DM) basis]; (3) 5% AH = concentrate + 5% alfalfa hay (DM basis); (4) 5% AH + Pro = concentrate + 5% alfalfa hay + 5% sodium propionate (DM basis); (5) 10% AH = concentrate + 10% alfalfa hay (DM basis); and (6) 10% AH + Pro = concentrate + 10% alfalfa hay + 5% sodium propionate (DM basis). All calves were housed in individual pens bedded with sawdust until 10wk of age. They were given ad libitum access to water and starter throughout the experiment and were fed 2L of milk twice daily. Dry matter intake was recorded daily and body weight weekly. Calves from the control, 10% AH, and 10% AH + Pro treatments were euthanized after wk 10, and rumen wall samples were collected. Feeding of forage was found to increase overall dry matter intake, average daily gain, and final weight; supplementing sodium propionate had no effect on these parameters. Calves consuming forage had lower feed efficiency than those on the Pro diet. Rumen fluid in calves consuming forage had higher pH and greater concentrations of total volatile fatty acids and molar acetate. Morphometric parameters of the rumen wall substantiated the effect of AH supplementation, as plaque formation decreased macroscopically. Overall, the interaction between forage and sodium propionate did not affect calf performance parameters measured at the end of the experiment. Furthermore, inclusion of AH in starter diets positively enhanced the growth performance of male Holstein calves and influenced both the macroscopic and microscopic appearances of the rumen wall. These benefits, however, were small when only sodium propionate was offered.

Acetate formation in the photoheterotrophic bacteriumChloroflexus aurantiacusinvolves an archaeal type ADP-forming acetyl-CoA synthetase isoenzyme I

The bacterium Chloroflexus aurantiacus excreted significant amounts of acetate during photohetero trophic growth on glucose and in resting cell suspensions. Up to 1.5 mol acetate per mol glucose were formed. In acetate-forming cells, the activities of phosphotransacetylase and acetate kinase, usually involved in acetate formation in Bacteria, could not be detected; instead, the cells contained an acetyl-CoA synthetase (ADP-forming) (ACD) (acetyl-CoA + ADP + Pi → acetate + ATP + CoA), an enzyme so far reported in prokaryotes to be specific for acetate-forming Archaea. ACD, which was induced 10-fold during growth on glucose, was purified and the encoding gene was identified as Caur_3920. The recombinant enzyme, a homotetrameric 300-kDa protein composed of 75-kDa subunits, was characterized as functional ACD. Substrate specificities and kinetic constants for acetyl-CoA/acetate and other acyl-CoA esters/acids were determined, showing similarity of the C. aurantiacus ACD to archaeal ACD I isoenzymes, which are involved in acetate formation from sugars. This is the first report of a functional ACD involved in acetate formation in the domain of Bacteria.

The impact of high dietary zinc oxide on the development of the intestinal microbiota in weaned piglets

Weaned piglets were fed diets containing 57 (low) or 2425 (high) mgkg(-1) analytical grade ZnO for a period of 5weeks. Intestinal contents were sampled in weekly intervals and analyzed for bacterial cell numbers and main bacterial metabolites. The most severe effects of high dietary zinc were observed 1week after weaning in the stomach and small intestine. Pronounced reductions were observed for Enterobacteriaceae and the Escherichia group as well as for Lactobacillus spp. and for three of five studied Lactobacillus species. The impact of high dietary zinc diminished for enterobacteria with increasing age, but was permanent for Lactobacillus species. Bifidobacteria, enterococci, streptococci, Weissella spp. and Leuconostoc spp. as well as the Bacteroides-Prevotella-Porphyromonas group were not influenced by high dietary zinc throughout the trial. High dietary zinc reduced bacterial metabolite concentrations and increased molar acetate ratios at the expense of propionate in the proximal intestine, but differences diminished in older animals. Lower lactate concentrations were observed in the high dietary zinc group throughout the feeding trial. This study has shown that the application of dietary zinc at high concentrations leads to transient and lasting effects during the development of the intestinal microbiota, affecting composition as well as metabolic activity.

Effect of forage conservation method on ruminal lipid metabolism and microbial ecology in lactating cows fed diets containing a 60:40 forage-to-concentrate ratio

The effect of forage conservation method on ruminal lipid metabolism and microbial ecology was examined in 2 complementary experiments in cows. Treatments comprised fresh chopped grass, barn-dried hay, or untreated (UTS) or formic acid-treated silage (FAS) prepared from the same grass sward. Preparation of conserved forages coincided with the collection of samples from cows offered fresh grass. In the first experiment, 5 multiparous Finnish Ayrshire cows (229d in milk) were used to compare the effects of feeding diets based on grass followed by hay during 2 consecutive 14-d periods separated by a 5-d transition during which extensively wilted grass was fed. In the second experiment, 5 multiparous Finnish Ayrshire cows (53d in milk) were assigned to 1 of 2 blocks and allocated treatments according to a replicated 3×3 Latin square design with 14-d periods to compare the effects of hay, UTS, and FAS. Cows received 7 or 9kg/d of the same concentrate in experiments 1 and 2, respectively. Conservation of grass by drying, but not ensiling, decreased forage fatty acid content primarily due to losses of 18:2n-6 and 18:3n-3. Compared with grass, feeding hay had no effect on dry matter intake (DMI), rumen pH, or fermentation characteristics, other than increasing ammonia content, but lowered whole-tract organic matter and fiber digestibility (experiment 1). Relative to hay, silage increased DMI, rumen volatile fatty acid (VFA) concentrations, and molar proportions of butyrate, and decreased molar acetate proportions (experiment 2). Compared with UTS, FAS increased DMI, had no effect on rumen ammonia or VFA concentrations, but tended to lower rumen pH and the molar ratio of lipogenic to glucogenic VFA. Conservation method had no substantial effect on ruminal or whole-tract digestibility coefficients. Compared with fresh grass and silages, hay decreased lipolysis and biohydrogenation (BH) of dietary unsaturates in the rumen, resulting in similar flows of 18:2n-6 and 18:3n-3, but lower amounts of trans-11 18:1 and Δ11,13 18:2 at the omasum. The extent of silage fermentation had minimal influence on ruminal lipid metabolism. Treatments were not associated with changes in the relative abundance of specific bacteria known to be capable of BH or rumen protozoal numbers. In conclusion, conservation method altered forage lipids, the extent of lipolysis and BH in the rumen, and the flow of fatty acids at the omasum, in the absence of substantial changes in ruminal Butyrivibrio populations.

Quantifying the effect of monensin dose on the rumen volatile fatty acid profile in high-grain-fed beef cattle1

Monensin is a common feed additive used in various countries, where 1 of the associated benefits for use in beef cattle is improved efficiency of energy metabolism by the rumen bacteria, the animal, or both. Modeling fermentation-altering supplements is of interest, and thus, it is the purpose of this paper to quantify the change in VFA profile caused by monensin dose in high-grain-fed beef cattle. The developmental database used for meta-analysis included 58 treatment means from 16 studies from the published literature, and the proportional change in molar acetate, propionate, and butyrate (mol/100 mol) as well as total VFA (mM) with monensin feeding dose (mg/kg DM, concentration in the feed) was evaluated using the MIXED procedure (SAS Inst. Inc., Cary, NC) with the study treated as a random effect. The mean monensin dose in the literature database was 30.9 ± 3.70 mg/kg DM and ranged from 0.0 to 88.0 mg/kg DM. Mean DMI was 7.8 ± 0.26 kg DM/d, mean concentrate proportion of the diet was 0.87 ± 0.01, and mean treatment period was 42 ± 5.6 d. Results produced the following equations: proportional change in acetate (mol/100 mol) = -0.0634 (± 0.0323) × monensin (mg/kg DM)/100 (P = 0.068), proportional change in propionate (mol/100 mol) = 0.260 (± 0.0735) × monensin (mg/kg DM)/100 (P = 0.003), and proportional change in butyrate (mol/100 mol) = -0.335 (± 0.0916) × monensin (mg/kg DM)/100 (P = 0.002). The change in total VFA was not significantly related to monensin dose (P = 0.93). The results presented here indicate that the shift in VFA profile may be dose dependent, with increasing propionate and decreasing acetate and butyrate proportions (mol/100 mol). These equations could be applied within mechanistic models of rumen fermentation to represent the effect of monensin dose on the VFA profile in high-grain-fed beef cattle.

Hydrogen Generation in Microbial Reverse-Electrodialysis Electrolysis Cells Using a Heat-Regenerated Salt Solution

Hydrogen gas can be electrochemically produced in microbial reverse-electrodialysis electrolysis cells (MRECs) using current derived from organic matter and salinity-gradient energy such as river water and seawater solutions. Here, it is shown that ammonium bicarbonate salts, which can be regenerated using low-temperature waste heat, can also produce sufficient voltage for hydrogen gas generation in an MREC. The maximum hydrogen production rate was 1.6 m(3) H(2)/m(3)·d, with a hydrogen yield of 3.4 mol H(2)/mol acetate at a salinity ratio of infinite. Energy recovery was 10% based on total energy applied with an energy efficiency of 22% based on the consumed energy in the reactor. The cathode overpotential was dependent on the catholyte (sodium bicarbonate) concentration, but not the salinity ratio, indicating high catholyte conductivity was essential for maximizing hydrogen production rates. The direction of the HC and LC flows (co- or counter-current) did not affect performance in terms of hydrogen gas volume, production rates, or stack voltages. These results show that the MREC can be successfully operated using ammonium bicarbonate salts that can be regenerated using conventional distillation technologies and waste heat making the MREC a useful method for hydrogen gas production from wastes.

Combination Effects of Nitrocompounds, Pyromellitic Diimide, and 2-Bromoethanesulfonate on in Vitro Ruminal Methane Production and Fermentation of a Grain-Rich Feed

An L(16) (4(5)) orthogonal experimental design was used to evaluate combination effects of nitroethane (0-15 mM), 2-nitroethanol (0-15 mM), 2-nitro-1-propanol (0-15 mM), pyromellitic diimide (0-0.07 mM), and 2-bromoethanesulfonate (0-0.05 mM) on in vitro ruminal fermentation of a grain-rich feed. In vitro dry matter disappearance was adversely affected by these inhibitors, while cumulative gas production was not affected. Volatile fatty acid production was increased by nitroethane and 2-bromoethanesulfonate in a dose-dependent manner and was decreased by 2-nitroethanol and pyromellitic diimide. All inhibitor treatments increased the molar acetate proportion, while decreasing proportions of propionate and butyrate; hydrogen recovery was decreased by 36.9-45.2%; and methane production was reduced by 95.2-99.2%. The methanogenesis inhibition ranked: nitroethane > 2-nitroethanol > 2-nitro-1-propanol > 2-bromoethanesulfonate > pyromellitic diimide; combined concentrations of 5, 5, 5, 0.02, and 0.03 mM, respectively, gave the optimal inhibiting efficiency. These results may provide a reference to develop effective mitigation of methane emission from ruminants.

Desulfosoma profundi sp. nov., a thermophilic sulfate-reducing bacterium isolated from a deep terrestrial geothermal spring in France

A novel strictly anaerobic bacterium designated SPDX02-08(T) was isolated from a deep terrestrial geothermal spring located in southwest France. Cells (1-2×2-6μm) were non-motile, non sporulating and stained Gram negative. Strain SPDX02-08(T) grew at a temperature between 40 and 60°C (optimum 55°C), pH between 6.3 and 7.3 (optimum 7.2) and a NaCl concentration between 0 and 5g/l (optimum 2g/l). Sulfate, thiosulfate and sulfite were used as terminal electron acceptors, but not elemental sulfur, nitrate, nitrite, Fe (III) or fumarate. In the presence of sulfate, strain SPDX02-08(T) completely oxidized pyruvate, propionate, butyrate, isobutyrate, valerate, isovalerate and hexadecanoate. Stoichiometric measurements revealed a complete oxidation of part of lactate (0.125mol of acetate produced per mole lactate oxidized). Strain SPDX02-08(T) required yeast extract to oxidize formate and H(2) but did not grow autotrophically on H(2). Among the substrates tested, only pyruvate was fermented. The G+C content of the genomic DNA was 57.6mol%. Major cellular fatty acids of strain SPDX02-08(T) were iso-C(15:0), C(15:0), and C(16:0). Phylogenetic analysis of the 16S small-subunit (SSU) ribosomal RNA gene sequence indicated that strain SPDX02-08(T) belongs to the genus Desulfosoma, family Syntrophobacteraceae, having Desulfosoma caldarium as its closest phylogenetic relative (97.6% similarity). The mean DNA/DNA reassociation value between strain SPDX02-08(T) and Desulfosoma caldarium was 16.9±2.7%. Based on the polyphasic differences, strain SPDX02-08(T) is proposed to be assigned as a new species of the genus Desulfosoma, Desulfosoma profundi sp. nov. (DSM 22937(T)=JCM 16410(T)). GenBank accession number for the 16S rRNA gene sequence of strain SPDX02-08(T) is HM056226.

The modification of glucose levels and N source in the Hungate's medium to stimulate the production of fibrolytic enzymes of Anaeromyces sp. YQ3 grown on corn stalks

Hungate's method is a well-accepted protocol for the isolation or incubation of anaerobes with a roll tube technique. The aim of this study was to stimulate fungal enzyme production by optimizing the components of Hungate's medium for the growth of a rumen fungus Anaeromyces sp. YQ3. The organism was grown on corn stalks and incubated for 10 days in defined media with two glucose levels (G+, glucose in the Hungate's medium as a glucose control; G−, glucose removed in a modified Hungate's medium) and four N sources (N1: yeast extract+tryptone+(NH4)2SO4 in Hungate's medium (control); N2: yeast extract+(NH4)2SO4; N3: tryptone+(NH4)2SO4; and N4: tryptone+yeast extract). In the G− media, the recovered activities of feruloyl esterase (FAE) (P<0.0001), acetyl esterase (AE) (P=0.0065) and xylanase (P<0.0001) were decreased, while the G+ media with N1 nitrogen stimulated the production of FAE and xylanase (P<0.0001). The G− medium with N2 nitrogen increased the recovered activities of carboxymethyl cellulase (P=0.0001) and avicelase (P<0.0001), while the N3 and N4 media increased the recovered activity of AE (P=0.0015). The N4 medium was comparable to the N1 medium in stimulating the amount of recovered xylanase activity. The activities of FAE (P<0.0001), AE (P<0.0001), and xylanase (P<0.0001) showed a time-dependent increase and reached their peaks at day 10, while the avicelase activity peaked at day 8 (P=0.0071). The esterase activities (FAE and AE) were positively correlated with the enzyme activities of xylanase and carboxymethyl cellulase (r>0.48, P<0.05). After a 10-day incubation, the glucose in the Hungate's media contributed to an increase in organic matter disappearance (P<0.0001) and volatile fatty acid (VFA) concentration (P<0.0001), except for molar acetate proportions. The N4 treatment increased organic matter disappearance and total VFA concentration (P=0.0002). The change in N source did not alter molar proportions of acetate, propionate and valerate, while the N2 treatment increased molar butyrate proportion (P<0.0035), and both N2 and N3 increased the molar proportion of branched chain VFAs (P<0.0041). In summary, the glucose in the Hungate's medium is beneficial for stimulating the production of esterases and xylanase, thereby promoting fungal growth. Amending the N source in Hungate's medium brings about different yields of rumen fungal esterases and polysaccharide hydrolases that have important nutritional impacts on fibre degradation in ruminant animals.

Effect of replacing solvent-extracted canola meal with high-oil traditional canola, high-oleic acid canola, or high-erucic acid rapeseed meals on rumen fermentation, digestibility, milk production, and milk fatty acid composition in lactating dairy cows

The objective of this experiment was to investigate the effects of replacing conventional, solvent-extracted canola meal (control; CTRL) with high oil content; conventional, mechanically extracted canola meal (CMEC); high-oleic, low polyunsaturated fatty acid (FA) canola meal (HOLL); and high-erucic acid, low-glucosinolate rapeseed meal (RPS) on rumen function, digestibility, milk production, and milk FA composition in lactating dairy cows. The experimental design was a replicated 4×4 Latin square with 8 lactating dairy cows. Four of the cows were ruminally cannulated. All oilseed meals were included at approximately 12 to 13% of dietary dry matter (DM). Crude protein and fat concentrations (% of DM) of the meals were 43 and 3.1%, 32.8 and 16.1%, 45.2 and 13.7%, and 34.3 and 17.9% for CTRL, CMEC, HOLL, and RPS, respectively. All diets were formulated to supply net energy of lactation in excess of requirements. The CMEC and RPS diets were predicted to be about 1% deficient in metabolizable protein. Relative to the CTRL, inclusion of high-oil seed meals in the diet lowered ruminal acetate concentration and the molar acetate:propionate ratio and decreased DM intake. Milk yield generally followed DM intake and was lower for CMEC and RPS than the CTRL. Treatments had no effect on milk composition, other than an increase in milk urea nitrogen concentration for HOLL. Fat-corrected milk (3.5%) feed efficiency was increased by HOLL and RPS compared with CTRL. Urinary urea nitrogen losses were increased by HOLL, which, as a consequence, increased the ammonia-emitting potential of manure. The ratio of milk N-to-N intake was greater for CMEC and RPS. Replacing solvent-extracted canola meal with the high-oil meal decreased milk fat 12:0, 14:0, 16:0, and total saturated FA content and enhanced cis-9 18:1 and total monounsaturated FA concentrations. Relative to the CTRL, canola increased total trans FA in milk, whereas inclusion of HOLL in the diet increased trans-11 18:1 and cis-9, trans-11 CLA content. The RPS increased milk fat cis-13 22:1 content from 0.07 to 2.33g/100g of FA. In conclusion, HOLL or RPS, which are likely to come from small-scale biodiesel plants where oil is cold pressed without hexane extraction, fed at levels at or above 12 to 13% of dietary DM may decrease feed intake and milk production, but can be used to alter milk FA composition in lactating dairy cows.

Ruminal digestibility and fermentation characteristics in vitro of fenugreek and alfalfa hay combination with or without the inoculation of Neocallimastix sp. YAK11

Fermentation characteristics of 5 combinations of fenugreek ( Trigonella foenum-graecum L., FH) and alfalfa ( Medicago sativa L., AH) hay in ratios (FH:AH) ranging from 100:0 to 0:100 were studied in response to inocula of either rumen fluids (RF) or rumen fluids plus a fungal culture of Neocallimastix sp. YAK11 (RFF). For the RFF treatment, the forage combinations were anaerobically incubated with fungal culture and Menke's medium for the first 24 h and then incubated with the stratified rumen fluids for 72 h. The value of the in vitro dry matter disappearance did not differ between RF and RFF. Cumulative gas production (ml/g DM) was fitted to an exponential model: GP t = GP max×(1 − e − c×time ); the maximum gas production (GP max) was lower in RFF than in RF (P<0.01), but the rate constant c showed no difference. Molar proportions of CO 2, CH 4, and H 2 were similar in both treatments. The pH values were lower for RFF than RF (P<0.01). Concentrations of ammonia N and total volatile fatty acids (VFA) did not differ between RF and RFF. In VFA pattern, molar proportions of propionate and valerate did not differ between RF and RFF. Molar proportion of acetate was greater in RFF than in RF (P<0.05), while molar butyrate and branch-chained volatile fatty acids proportions were lower in RFF than RF (P<0.01). Fibrolytic activities of carboxymethyl cellulase, avicelase, ferulic acid esterase, and acetyl esterase were similar between RF and RFF, but xylanase activity was greater in RFF than in RF (P<0.01). Regardless of the ratios of FH to AH in the forage combinations, the fungal inoculation at the inclusion level used did not alter the in vitro digestibility, but increased the molar acetate proportion and decreased the molar proportions of butyrate, branch-chained volatile fatty acids and maximum gas production.

Description of Anaerobaculum hydrogeniformans sp. nov., an anaerobe that produces hydrogen from glucose, and emended description of the genus Anaerobaculum

A novel anaerobic, moderately thermophilic, NaCl-requiring fermentative bacterium, strain OS1T, was isolated from oil production water collected from Alaska, USA. Cells were Gram-negative, non-motile, non-spore-forming rods (1.7-2.7×0.4-0.5 µm). The G+C content of the genomic DNA of strain OS1T was 46.6 mol%. The optimum temperature, pH and NaCl concentration for growth of strain OS1T were 55 °C, pH 7 and 10 g l(-1), respectively. The bacterium fermented D-fructose, D-glucose, maltose, D-mannose, α-ketoglutarate, L-glutamate, malonate, pyruvate, L-tartrate, L-asparagine, Casamino acids, L-cysteine, L-histidine, L-leucine, L-phenylalanine, L-serine, L-threonine, L-valine, inositol, inulin, tryptone and yeast extract. When grown on D-glucose, 3.86 mol hydrogen and 1.4 mol acetate were produced per mol substrate. Thiosulfate, sulfur and L-cystine were reduced to sulfide, and crotonate was reduced to butyrate with glucose as the electron donor. 16S rRNA gene sequence analysis indicated that strain OS1T was related to Anaerobaculum thermoterrenum (99.7 % similarity to the type strain), a member of the phylum Synergistetes. DNA-DNA hybridization between strain OS1T and A. thermoterrenum DSM 13490T yielded 68 % relatedness. Unlike A. thermoterrenum, strain OS1T fermented malonate, maltose, tryptone, L-leucine and L-phenylalanine, but not citrate, fumarate, lactate, L-malate, glycerol, pectin or starch. The major cellular fatty acid of strain OS1T was iso-C15:0 (91 % of the total). Strain OS1T also contained iso-C13:0 3-OH (3 %), which was absent from A. thermoterrenum, and iso-C13:0 (2 %), which was absent from Anaerobaculum mobile. On the basis of these results, strain OS1T represents a novel species of the genus Anaerobaculum, for which the name Anaerobaculum hydrogeniformans sp. nov. is proposed. The type strain is OS1T (=DSM 22491T=ATCC BAA-1850T). An emended description of the genus Anaerobaculum is also given.

Enhancement of biohydrogen producing using ultrasonication

Ultrasonication was evaluated as a pretreatment for biological hydrogen production from glucose in batch studies, in comparison with heat-shock pretreatment, acid pretreatment, and base pretreatment. The optimized sonication energy for hydrogen production using anaerobic digester sludge was 79 kJ/gTS. Sonication with temperature control (less than 30 °C) increased volumetric hydrogen production by 120% over the untreated sludge, and by 40% over the heat-shock and acid pretreated sludge, with a marginal (∼10%) increase in hydrogen production rate. Upon comparing the molar hydrogen yield in sonicated sludge with and without temperature control, the deleterious effect of heat on some hydrogen producers as reflected by a 30% decrease in yield to 1.03 mol H 2/mol glucose is evident. Sonication with temperature control affected a 45% increase in molar hydrogen yield to 1.55 mol H 2/mol glucose over heat-shock pretreatment at 70 °C for 30 min and acidification to pH 3.0 for 24 h at 4 °C. Sonication with temperature control produced a biomass yield of 0.13 g VSS/g COD, as compared to 0.24 g VSS/g COD for the untreated sludge. The hydrogen yield increased linearly with the molar acetate to butyrate ratio and decreased linearly with the biomass yield.

Effect of pH on glucose and starch fermentation in batch and sequenced-batch mode with a recently isolated strain of hydrogen-producing Clostridium butyricum CWBI1009

This paper reports investigations carried out to determine the optimum culture conditions for the production of hydrogen with a recently isolated strain Clostridium butyricum CWBI1009. The production rates and yields were investigated at 30 °C in a 2.3 L bioreactor operated in batch and sequenced-batch mode using glucose and starch as substrates. In order to study the precise effect of a stable pH on hydrogen production, and the metabolite pathway involved, cultures were conducted with pH controlled at different levels ranging from 4.7 to 7.3 (maximum range of 0.15 pH unit around the pH level). For glucose the maximum yield (1.7 mol H 2 mol −1 glucose) was measured when the pH was maintained at 5.2. The acetate and butyrate yields were 0.35 mol acetate mol −1 glucose and 0.6 mol butyrate mol −1 glucose. For starch a maximum yield of 2.0 mol H 2 mol −1 hexose, and a maximum production rate of 15 mol H 2 mol −1 hexose h −1 were obtained at pH 5.6 when the acetate and butyrate yields were 0.47 mol acetate mol −1 hexose and 0.67 mol butyrate mol −1 hexose.

Significance of Biological Hydrogen Oxidation in a Continuous Single-Chamber Microbial Electrolysis Cell

A single-chamber microbial electrolysis cell (MEC) that used a high density of nonmetal-catalyst carbon fibers as the anode achieved high volumetric current densities from 1470 +/- 60 to 1630 +/- 50 A/m(3) for a hydraulic retention time of 1.6-6.5 h. The high current density was driven by a large anode surface area and corresponded to a volumetric chemical oxygen demand (COD)-removal rate of 27-49 kg COD/m(3).d. Observed H(2) harvesting rates were from 2.6 +/- 0.10 to 4.3 +/- 0.46 m(3) H(2)/m(3).d, but the H(2) production rates computed from the current densities were 16.3-18.2 m(3) H(2)/m(3).d. Tracking all significant electron sinks (residual acetate, H(2), CH(4), biomass, and soluble microbial products (SMP)) in the single-chamber MEC showed that H(2) reoxidation by anode-respiring bacteria recycled H(2) between the cathode and the anode, and this caused the large discrepancy in H(2) production and harvest rates. H(2) recycle accounted for 62-76% of observed current density, and this made the observed Coulombic efficiency 190-310% at steady state. Consequently, the cathodic conversion efficiency was only 16-24%. The current density added by H(2) recycle also increased the applied voltage from approximately 0.6 V to approximately 1.5 V for the highest H(2) harvest rate (4.3 m(3) H(2)/m(3).d). CH(4) generation consistently occurred in the continuous single-chamber MEC, and its electron fraction of consumed acetate was 7-25%. Because of methane formation and biomass/SMP accumulation, the overall H(2) recovery was moderate at 1.8-2.0 mol of H(2)/mol of acetate in the MEC. Thus, this study illustrates that a single-chamber MEC with a high anode surface area can generate high volumetric rates for COD removal and H(2) generation, but H(2) recycle and methanogenesis present significant challenges for practical application.

Strategy for enhancing photo-hydrogen production yield by repeated fed-batch cultures

Abstract In order to obtain the high H 2 yield, photo-hydrogen production by Rhodopseudomonas faecalis strain RLD-53 in fed-batch culture using acetate as the sole carbon was studied. In repeated fed-batch culture, biomass increased rapidly from 0.05 to 0.65 g/l within 120 h, with the specific maximal growth rate estimated 0.68 × 10 −3 g/h. After 120 h, biomass increased slowly and after each time feeding biomass increased slightly. The specific cumulative H 2 volumes in each phase were 2791.3, 1161.7, 1445.5 and 840.6 ml H 2 /l-culture, respectively. The average H 2 yield was 3.17 mol H 2 /mol acetate based on the whole process while the average substrate conversion efficiency reached 79.3%. Specific maximum H 2 production rate and H 2 content was 37.2 ml H 2 /l/h and 95.5%, respectively. The results demonstrated the repeated fed-batch mode obtained higher efficiency for hydrogen production, feeding acetate concentration and control of pH were important to fed-batch culture hydrogen production.

Ecophysiology and the energetic benefit of mixotrophic Fe(II) oxidation by various strains of nitrate-reducing bacteria

In order to assess the importance of nitrate-dependent Fe(II) oxidation and its impact on the growth physiology of dominant Fe oxidizers, we counted these bacteria in freshwater lake sediments and studied their growth physiology. Most probable number counts of nitrate-reducing Fe(II)-oxidizing bacteria in the sediment of Lake Constance, a freshwater lake in Southern Germany, yielded about 10(5) cells mL(-1) of the total heterotrophic nitrate-reducing bacteria, with about 1% (10(3) cells mL(-1)) of nitrate-reducing Fe(II) oxidizers. We investigated the growth physiology of Acidovorax sp. strain BoFeN1, a dominant nitrate-reducing mixotrophic Fe(II) oxidizer isolated from this sediment. Strain BoFeN1 uses several organic compounds (but no sugars) as substrates for nitrate reduction. It also reduces nitrite, dinitrogen monoxide, and O(2), but cannot reduce Fe(III). Growth experiments with cultures amended either with acetate plus Fe(II) or with acetate alone demonstrated that the simultaneous oxidation of Fe(II) and acetate enhanced growth yields with acetate alone (12.5 g dry mass mol(-1) acetate) by about 1.4 g dry mass mol(-1) Fe(II). Also, pure cultures of Pseudomonas stutzeri and Paracoccus denitrificans strains can oxidize Fe(II) with nitrate, whereas Pseudomonas fluorescens and Thiobacillus denitrificans strains did not. Our study demonstrates that nitrate-dependent Fe(II) oxidation contributes to the energy metabolism of these bacteria, and that nitrate-dependent Fe(II) oxidation can essentially contribute to anaerobic iron cycling.

Isolation of anoxygenic photosynthetic bacteria from Songkhla Lake for use in a two-staged biohydrogen production process from palm oil mill effluent

We are developing a process to produce biohydrogen from palm oil mill effluent. Part of this process will involve photohydrogen production from volatile fatty acids under low light conditions. We sought to isolate suitable bacteria for this purpose from Songkhla Lake in Southern Thailand. Enrichment for phototrophic bacteria from 34 samples was conducted providing acetate as a major carbon source and applying culturing conditions of anaerobic-low light (3000 lux) at 30 °C. Among the independent isolates from these enrichments 19 evolved hydrogen with productivities between 4 and 326 ml l −1 d −1 . Isolate TN1 was the most efficient producer at a rate of 1.85 mol H 2 mol acetate −1 with a light conversion efficiency of 1.07%. The maximum hydrogen production rate for TN1 was determined to be 43 ml l −1 h −1 . Environmentally desirable features of photohydrogen production by TN1 included the absence of pH change in the cultures and no detectable residual CO 2 .

The fermentation stoichiometry of Thermotoga neapolitana and influence of temperature, oxygen, and pH on hydrogen production

The hyperthermophilic bacterium, Thermotoga neapolitana, has potential for use in biological hydrogen (H(2)) production. The objectives of this study were to (1) determine the fermentation stoichiometry of Thermotoga neapolitana and examine H(2) production at various growth temperatures, (2) investigate the effect of oxygen (O(2)) on H(2) production, and (3) determine the cause of glucose consumption inhibition. Batch fermentation experiments were conducted at temperatures of 60, 65, 70, 77, and 85 degrees C to determine product yield coefficients and volumetric productivity rates. Yield coefficients did not show significant changes with respect to growth temperature and the rate of H(2) production reached maximum levels in both the 77 degrees C and 85 degrees C experiments. The fermentation stoichiometry for T. neapolitana at 85 degrees C was 3.8 mol H(2), 2 mol CO(2), 1.8 mol acetate, and 0.1 mol lactate produced per mol of glucose consumed. Under microaerobic conditions H(2) production did not increase when compared to anaerobic conditions, which supports other evidence in the literature that T. neapolitana does not produce H(2) through microaerobic metabolism. Glucose consumption was inhibited by a decrease in pH. When pH was adjusted with buffer addition cultures completely consumed available glucose.