Fermentation Capacity as a Measure of Net Growth of Rumen Microorganisms

A simple technique for measuring the rate of fermentation of rumen microorganisms is described. It allows quick preparation and handling of the rumen sample immediately after collection. The average rate of fermentation of rumen samples collected from a lactating cow fed on alfalfa hay and concentrate in the ratio of 2:1 was very similar to the rate obtained by other methods. On the assumption that when substrate is in excess, the fermentation rate is proportional to the total microbial cells, the method was used to estimate the net growth of rumen microorganisms. The maximal fermentation rate of subsamples, taken at the beginning and after 1 hr of incubation of a sample, was measured. The results indicate a net average growth of 8% per hr, or 192% per day, in approximate agreement with rumen turnover time. The highest net growth does not necessarily coincide with the highest gas-production rate in the rumen, in part because the bicarbonate concentration in the rumen contents varies. In a cow fed on hay and concentrate, the net growth was lowest before feeding and immediately after feeding.     

Evaluation of a Method of Measuring Fermentation Rates and Net Growth of Rumen Microorganisms

The method of el-Shazly and Hungate for measuring gas production in rumen contents was slightly modified and used throughout this investigation. The variation in the fermentation rates due to samples collected separately from a sheep fed on hay was less than 2%. When samples obtained through a stomach tube were compared with samples collected through the rumen fistula, the variation was about 3%. The rates of gas and acid production were approximately similar in samples obtained from the rumen at the same time when no sodium bicarbonate was added. During in vitro incubation of whole ruminal contents, there was a highly significant correlation between the net growth rate values (obtained by using fermentation capacity as an index) and the change in concentration of viable rumen bacteria or total ciliate protozoa.     

Urea and short-chain fatty acids metabolism in Holstein cows fed a low-nitrogen grass-based diet

Three ruminally cannulated and multicatheterised lactating dairy cows were used to investigate the effect of different supplement strategies to fresh clover grass on urea and short-chain fatty acid (SCFA) metabolism in a zero-grazing experiment with 24-h blood and ruminal samplings. Fresh clover grass was cut every morning and offered from 0800 to 1500 h. Maize silage was fed at 1530 h. The three treatments, arranged in a Latin square, differed by timing of feeding rolled barley and soya-bean hulls relative to fresh clover grass. All diets had the same overall composition. Treatments were soya-bean hulls fed at 0700 h and barley fed at 1530 h (SAM), barley fed at 0700 h and soya-bean hulls fed at 1530 h (BAM), and both soya-bean hulls and barley fed at 1530 h (SBPM). The grass had an unexpectedly low content of crude protein (12.7%) and the cows were severely undersupplied with rumen degradable protein. The treatment effects were numerically small; greater arterial ammonia concentration, net portal flux of ammonia and net hepatic flux of urea during part of the day were observed when no supplementary carbohydrate was fed before grass feeding. A marked diurnal variation in ruminal fermentation was observed and grass feeding increased ruminal concentrations of propionate and butyrate. The net portal fluxes of propionate, butyrate, isovalerate and valerate as well as the net hepatic uptake of propionate, butyrate, valerate and caproate increased after feeding at 0700 h. The hepatic extraction of butyrate showed a relatively large depression with grass feeding with nadir at 1200 to 1330 h. The increased net portal absorption and the decreased hepatic extraction resulted in an approximately six-fold increase in the arterial blood concentration of butyrate. The gut entry rate of urea accounted for 70 ± 10% of the net hepatic production of urea. Saliva contributed to 14% of the total amount of urea recycled to the gut. Urea recycling to the gut was equivalent to 58% of the dietary nitrogen intake. Despite the severe undersupply of rumen degradable protein, the portal-drained viscera did not extract more than 4.3% of the urea supplied with arterial blood. This value is in line with the literature values for cows fed diets only moderately deficient in rumen degradable protein and indicates that cows maximise urea transfer across gut epithelia even when the diet is moderately deficient in rumen degradable protein.     

Defining an optimal carbon source/methionine feed strategy for growth and cephalosporin C formation by Cephalosporium acremonium.

The effect of the method of methionine addition, growth-limiting carbon source (glucose vs sucrose), and culture growth rate on cephalosporin C production was investigated in a Cephalosporium acremonium defined medium fed batch fermentation. Batch addition of methionine, at a concentration of 3 g/L, prior to the start of a fed sucrose fermentation was found to interfere with the ability of the culture to utilize this sugar, thus limiting growth and decreasing cephalosporin C production. Batch methionine addition had no effect on glucose-limited cultures. Concurrent exponential feeding of methionine with sucrose improved both culture growth and productivity. Under the control of identical carbon source limiting feed profiles, sucrose was observed to support greater cephalosporin C production than glucose. Optimal cephalosporin C production in a C. acremonium defined medium fed batch fermentation was obtained through controlling culture growth during the rapid growth phase at a relatively low level with respect to mumax (mu approximately 0.036 h-1) until achieving a desired cell mass with a concurrent sucrose and methionine feed, followed by maintaining relatively vigorous growth (mu approximately 0.01 h-1) with sucrose for the duration of the fermentation.     

Rumen fermentation,nutrient flow to the duodenum and digestibility in bulls fed calcium soaps of rapeseed fatty acids and soya bean meal coated with calcium soaps

Three Polish Friesian bulls fitted with rumen and duodenal canulas were used in a 3 × 3 Latin square experiment to study the effect of Ca soaps of rapeseed fatty acids (CSRFA) on rumen fermentation, nutrient and fatty acid (FA) flow to the duodenum, and to investigate in vivo the possibility of using CSRFA as a means of protecting soya bean meal protein against degradation in the rumen. Treatments were (1) control, no fat (2) CSRFA, at 2% of dietary DM and (3) SBM protein coated with CSRFA (CSRFA:SBM, 1:1, wt/wt), at 4% of dietary DM. The animals were fed isonitrogenous diets, containing 45% meadow hay, 10% fodder beet and 45% concentrate mixture on a DM basis. Intake was limited to 80 g DM d⁻¹ kg^−0.75. There were no treatment effects on rumen fermentation, rumen liquid turnover rate or volume, suggesting that CSRFA were inert in the rumen. A slight decrease in ammonia concentration in the rumen fluid from the CSRFA:SBM diet and the degradability data do not confirm the protection of SBM protein by CSRFA. Treatments did not affect apparent OM digestibility in the rumen, total N and NAN (non-ammonia nitrogen) flow into the duodenum or microbial protein synthesis. However, rumen degradability of protein was increased by feeding CSRFA. Feeding CSRFA significantly increased the duodenal flows of C18:0, C18:1 and total FA, but when expressed as a percentage of intake, there were no significant treatment differences. The average duodenal flow of total FA was 81.7% of intake. Extents of biohydrogenation of unsaturated FA were decreased in diets containing CSRFA. Estimated net biohydrogenation of C18:2, C18:3 and total unsaturated C18 FA of CSRFA was 43.3, 60.4 and 59.4%, respectively. Postrumen and total tract digestibility of total and individual FA were not different between treatments     

Parameters of Rumen Fermentation in a Continuously Fed Sheep: Evidence of a Microbial Rumination Pool

The feed and feces of a continuously fed sheep were analyzed for carbon, hydrogen, and nitrogen, with oxygen as the remainder. The daily feed-feces weight difference was used as the reactant in an equation representing the rumen fermentation. The measured products were the daily production of volatile fatty acids (VFA), CH(4), CO(2), and ammonia. The carbon unaccounted for was assumed to be in the microbial cell material produced in the rumen and absorbed before reaching the feces. The ratio of C to H, O, and N in bacteria was used to represent the elemental composition of the microbes formed in the rumen fermentation, completing the following equation:C(20.03)H(36.99)O(17.406)N(1.345) + 5.65 H(2)O --> C(12)H(24)O(10.1) + 0.83 CH(4) VFA + 2.76 CO(2) + 0.50 NH(3) + C(4.44)H(8.88)O(2.35)N(0.785) microbial cells absorbed With C arbitrarily balanced and O balanced by appropriate addition of water, any error is reflected in the H. The H recovery was 98.5%. The turnover rate constant for rumen liquid equilibrating with polyethylene glycol (PEG) was 2.27 per day. Direct counts and volume measurements of the individual types of bacteria and protozoa in the rumen were used to calculate the total microbial cell volume in the rumen, not equilibrating with it. The dry matter in the rumen (582 g) and the nitrogen content (12.05) of the microbes in the rumen were estimated, the latter constituting 85% of the measured N in the rumen. Calculations for rumen dry matter and nitrogen turning over at the PEG rate introduce big discrepancies with other parameters; a rumination pool must be postulated. Its size and composition are estimated. Arguments are presented to support the view that dry matter and some of the microbes, chiefly the protozoa, do not leave the rumen at the PEG rate. One experiment with the same sheep fed twice daily showed significantly less production of microbial cells than did the continuous (each 2 hr) feeding. Analysis of the microbial cell yield suggests that, on the basis of 11 mg of cells per adenosine triphosphate molecule, a maximum of six adenosine triphosphate molecules could have been formed from each molecule of hexose fermented.     

Comparison of microbial fermentation of high- and low-forage diets in Rusitec, single-flow continuous-culture fermenters and sheep rumen

Eight Rusitec and eight single-flow continuous-culture fermenters (SFCCF) were used to compare the ruminal fermentation of two diets composed of alfalfa hay and concentrate in proportions of 80 : 20 (F80) and 20 : 80 (F20). Results were validated with those obtained previously in sheep fed the same diets. Rusitec fermenters were fed once daily and SFCCF twice, but liquid dilution rates were similar in both types of fermenters. Mean values of pH over the 12 h postfeeding were higher (P < 0.001) in Rusitec than in SFCCF, with diet F80 showing higher values (P < 0.001) in both types of fermenters. Concentrations of total volatile fatty acids (VFA) were higher (P < 0.001) in SFCCF than in Rusitec, and in both systems were higher (P = 0.002) for diet F20 than for diet F80. There were significant differences between systems in the proportions of the main VFA, and a fermentation system × diet interaction (P < 0.001) was detected for all VFA with the exception of valerate. No differences (P = 0.145) between the two types of fermenters were detected in dry matter (DM) digestibility, but NDF, microbial N flow and its efficiency were higher (P = 0.001) in SFCCF compared to Rusitec. Whereas pH values and VFA concentrations remained fairly stable through the day in both in vitro systems, pH dropped and VFA increased shortly after feeding in sheep rumen reaching the minimum and maximal values, respectively, about 4 h after feeding. Both in vitro systems detected differences between diets similar to those found in sheep for liquid dilution rate, pH values, DM digestibility, microbial N flow and growth efficiency. In contrast, acetate/propionate ratios were lower for diet F20 than for F80 in sheep rumen (2.73 and 3.97) and SFCCF (3.07 and 4.80), but were higher for diet F20 compared to F80 (4.29 and 3.40) in Rusitec, with values considered to be unphysiological for high-concentrate diets. In vivo NDF digestibility was affected (P = 0.017) by diet, but no differences between diets (P > 0.05) were found in any in vitro system. A more precise control of pH in both types of fermenters and a reduction of concentrate retention time in Rusitec could probably improve the simulation of in vivo fermentation.     

Production of cyclodextrin glucanotransferase from alkalophilic Bacillus sp. TS1-1: Optimization of carbon and nitrogen concentration in the feed medium using central composite design

Optimisation of nutrient feeding was developed to overcome the limitation in batch fermentation and to increase the CGTase production from Bacillus sp. TS1-1 in fed batch fermentation. Optimisation of the C/N ratio in the feed stream was conducted in a 5 l fermenter, where feeding was initiated at constant rate of 0.02 h⁻¹. In our initial screening process, the addition of nitrogen source boosted the growth of the microbes, but on the other hand reduced the CGTase production. The amount of tapioca starch and yeast extract was optimised in order to obtain a sufficient growth and thus, increased the CGTase production. Results were analysed using three-dimensional response surface plot, and the optimised values of carbon and nitrogen concentration of 3.30% (w/v) and 0.13% (w/v) were obtained, respectively. CGTase activity increased up to 80.12 U/ml, which is 13.94% higher as compared to batch fermentation (70.32 U/ml). This also led to 14.54% increment of CGTase production in fed batch culture as compared to the production before the optimisation. The CGTase activity obtained was close to the predicted value, which is 78.05 U/ml.     

Effects of the acid–base treatment of corn on rumen fermentation and microbiota,inflammatory response and growth performance in beef cattle fed high-concentrate diet

Beef cattle are often fed high-concentrate diet (HCD) to achieve high growth rate. However, HCD feeding is strongly associated with metabolic disorders. Mild acid treatment of grains in HCD with 1% hydrochloric acid (HA) followed by neutralization with sodium bicarbonate (SB) might modify rumen fermentation patterns and microbiota, thereby decreasing the negative effects of HCD. This study was thus aimed to investigate the effects of treatment of corn with 1% HA and subsequent neutralization with SB on rumen fermentation and microbiota, inflammatory response and growth performance in beef cattle fed HCD. Eighteen beef cattle were randomly allocated to three groups and each group was fed different diets: low-concentrate diet (LCD) (concentrate : forage = 40 : 60), HCD (concentrate : forage = 60 : 40) or HCD based on treated corn (HCDT) with the same concentrate to forage ratio as the HCD. The corn in the HCDT was steeped in 1% HA (wt/wt) for 48 h and neutralized with SB after HA treatment. The animal trial lasted for 42 days with an adaptation period of 7 days. At the end of the trial, rumen fluid samples were collected for measuring ruminal pH values, short-chain fatty acids, endotoxin (or lipopolysaccharide, LPS) and bacterial microbiota. Plasma samples were collected at the end of the trial to determine the concentrations of plasma LPS, proinflammatory cytokines and acute phase proteins (APPs). The results showed that compared with the LCD, feeding the HCD had better growth performance due to a shift in the ruminal fermentation pattern from acetate towards propionate, butyrate and valerate. However, the HCD decreased ruminal pH and increased ruminal LPS release and the concentrations of plasma proinflammatory cytokines and APPs. Furthermore, feeding the HCD reduced bacterial richness and diversity in the rumen. Treatment of corn increased resistant starch (RS) content. Compared with the HCD, feeding the HCDT reduced ruminal LPS and improved ruminal bacterial microbiota, resulting in decreased inflammation and improved growth performance. In conclusion, although the HCD had better growth performance than the LCD, feeding the HCD promoted the pH reduction and the LPS release in the rumen, disturbed the ruminal bacterial stability and increased inflammatory response. Treatment of corn with HA in combination with subsequent SB neutralization increased the RS content and helped counter the negative effects of feeding HCD to beef steers.     

Feeding behavior, rumination, reticulo-ruminal fermentation and plasma volatile fatty acids, compared in goats and sheep; influence of the diet

Two-year old Alpine she-goats (n = 3) and Texel ewes (n = 3) were compared as to eating behaviour, rumination and volatile fatty acids (VFA) in rumen and blood. The animals were fed once daily with two different proportions (20 and 80%) of barley and hay. Dry matter intake was fixed at 48 g D.M/kg P0.75 per day. In similar feeding and environmental conditions, eating behaviour and rumination of goats and sheep did not differ much: the goats tended to eat faster and there were more rumination periods in the sheep. Latency time, mean duration of rumination periods, daily rumination time and circadian pattern of rumination did not differ significantly between the two species (fig. 1). With both diets we observed a higher VFA concentration and a lower acetate/propionate ratio in the rumen of the ewes; however, rumen pH was lower only in those eating the 80% barley ration (fig. 2). Blood VFA in the jugular vein did not differ between sheep and goats (fig. 3). The proportion of cereals and hay in the diets affected rumen fermentation and rumination pattern in both species. With a higher concentrate/roughage ratio, rumen and plasma VFA increased, while the pH and acetate/propionate ratio in the lumen juice, the number of rumination periods and daily rumination time decreased. When the animals were fed the 80% barley ration, there was practically no rumination in the first 9 h after the single meal. During this time, rumen pH was minimal and VFA levels in the rumen and blood were maximal.     

Vinasse organic matter quality and mineralization potential, as influenced by raw material, fermentation and concentration processes

Both dilute and concentrated vinasse can be spread on agricultural fields or used as organic fertilizer. The effects of different characteristics of the original raw material on the biochemical composition of vinasse and their C and N mineralization in soil were investigated. Vinasse samples were obtained from similar industrial fermentation processes based on the growth of microorganisms on molasses from different raw material (sugar beet or sugar cane) and vinasse concentration (dilute or concentrated). The nature of the raw material used for fermentation had the greatest effect on the nature and size of the resistant organic pool. This fraction included aromatic compounds originating from the raw material or from complex molecules and seemed to be quantitatively related to acid-insoluble N. Samples derived from sugar beet were richer in N compounds and induced greater net N mineralization. The effect of evaporation varied with the nature of the raw material. Concentration led to a slight increase in the abundance of phenolic compounds, acid-insoluble fraction, and a slight decrease in the labile fraction of vinasses partly or totally derived from sugar beet. The effect of the dilute vinasse from sugar cane was greater. The concentrated vinasse had a smaller labile fraction, induced N immobilization at the beginning of incubation, and exhibited greater N concentration in the acid-insoluble fraction than the dilute vinasse.     

Influence of Oxygen and Glucose on Primary Metabolism and Astaxanthin Production by Phaffia rhodozyma in Batch and Fed-Batch Cultures: Kinetic and Stoichiometric Analysis

The influence of the oxygen and glucose supply on primary metabolism (fermentation, respiration, and anabolism) and astaxanthin production in the yeast Phaffia rhodozyma was investigated. When P. rhodozyma grew under fermentative conditions with limited oxygen or high concentrations of glucose, the astaxanthin production rate decreased remarkably. On the other hand, when the yeast grew under aerobic conditions, the astaxanthin production rate increased with increasing oxygen uptake. A kinetic analysis showed that the respiration rate correlated positively with the astaxanthin production rate, whereas there was a negative correlation with the ethanol production rate. The influence of glucose concentration at a fixed nitrogen concentration with a high level of oxygen was then investigated. The results showed that astaxanthin production was enhanced by an initial high carbon/nitrogen ratio (C/N ratio) present in the medium, but cell growth was inhibited by a high glucose concentration. A stoichiometric analysis suggested that astaxanthin production was enhanced by decreasing the amount of NADPH required for anabolism, which could be achieved by the repression of protein biosynthesis with a high C/N ratio. Based on these results, we performed a two-stage fed-batch culture, in which cell growth was enhanced by a low C/N ratio in the first stage and astaxanthin production was enhanced by a high C/N ratio in the second stage. In this culture system, the highest astaxanthin production, 16.0 mg per liter, was obtained.     

The stimulatory effect of the organic sulfur supplement, mercaptopropane sulfonic acid on cellulolytic rumen microorganisms and microbial protein synthesis in cattle fed low sulfur roughages

Two metabolism trials (experiments 1 and 2) were conducted to examine the effect of the organic S compound, sodium 3-mercapto-1-propane sulfonic acid (MPS) on feed intake, fiber digestibility, rumen fermentation and abundance of cellulolytic rumen microorganisms in cattle fed low S (<0.11%) roughages. Urea was provided in all treatments to compensate for the N deficiency (<0.6%) in the roughages. In experiment 1, steers (333 ± 9.5 kg liveweight) were fed Angleton grass (Dicanthium aristatum) supplemented with S in equivalent amounts as either MPS (6.0 g/day) or sodium sulfate (9.56 g/day). Supplementation of Angelton grass with either sulfate or MPS resulted in an apparent increase in flow of rumen microbial protein from the rumen. Sulfur supplementation did not significantly change whole tract dry matter digestibility or intake, even though sulfate and MPS supplementation was associated with an increase in the relative abundance of the fibrolytic bacteria Fibrobacter succinogenes and anaerobic rumen fungi. Ruminal sulfide levels were significantly higher in the sulfate treatment, which indicated that the bioavailability of the two S atoms in the MPS molecule may be low in the rumen. Based on this observation, experiment 2 was conducted in which twice the amount of S was provided in the form of MPS (8.0 g/day) compared with sodium sulfate (6.6 g/day) to heifers (275 ± 9 kg liveweight) fed rice straw. Supplementation with MPS compared with sulfate in experiment 2 resulted in an increase in concentration of total volatile fatty acids, and ammonia utilization without a change in feed intake or whole tract fiber digestibility even though S and N were above requirement for growing cattle in both these treatment groups. In conclusion, supplementation of an S deficient low-quality roughage diet with either MPS or sodium sulfate, in conjunction with urea N, improved rumen fermentation, which was reflected in an increase in urinary purine excretion. However, MPS appeared to have a greater effect on stimulating short-chain fatty acid production and ammonia utilization when provided at higher concentrations than sulfate. Thus, the metabolism of MPS in the rumen needs to be investigated further in comparison with inorganic forms of S as it may prove to be more effective in stimulating fermentation of roughage diets.     

Net nutrient absorption and liver metabolism in lactating dairy cows fed supplemental dietary biotin

The effect of feeding supplemental biotin on net absorption and metabolism of nutrients by the portal-drained viscera (PDV; the gut, pancreas, spleen and associated fat) and liver of lactating dairy cows was measured. Three cows in early to mid-lactation catheterised for measurements of net nutrient absorption and metabolism by the PDV and liver were fed a total-mixed ration with or without supplemental biotin at 20 mg/day using a switch-back design (ABA v. BAB) with three 2-week periods. There were no effects of feeding biotin on dry matter intake (22.2 kg/day), milk yield (29.5 kg/day) or milk composition. There was also no effect of feeding biotin on net release of glucose by the liver, net liver removal of glucose precursors (propionate, alanine, lactate) or net liver release of β-hydroxybutyrate. Feeding biotin increased net PDV release of ammonia. Reasons for the response are not certain, but a numerical increase in net PDV release of acetate suggests that rumen or hindgut fermentation was altered. Results of the present study do not support the hypothesis that supplemental biotin increases liver glucose production in lactating dairy cows.     

Stoichiometry of carbohydrate fermentation and microbial growth efficiency in a continous culture of mixed rumen bacteria

Summary A population of mixed rumen bacteria was maintained in a chemostat at four different dilution rates, with glocose as the growth limiting carbon and energy substrate. Increasing the dilution rate shifted the proportions of end products: methane decreased and propionate increased. Fermentation and hydrogen balances were calculated from the fermentation end products. Values were similar to earlier ones from batch incubations of rumen contents. This suggests that theoretical overall reaction schemes for carbohydrate fermentation in the rumen, proposed earlier, are also valid in continuous culture.A positive correlation between dilution rate and microbial growth efficiency (gN_inc./kg OM_f was observed, confirming earlier work.Apparently conflicting results of chemostat work and recent in vivo experiments are discussed.     

Effects of Changes in Feed Level, Starvation, and Level of Feed After Starvation Upon the Concentration of Rumen Protozoa in the Ovine

Four rumen fistulated sheep were used in five experiments to investigate the effect of feed level upon the concentration of rumen ciliate protozoa. The sheep were fed once daily 650 g of a pelleted diet composed of corn cobs, 45%; alfalfa meal, 35%; oats, 12.5%; cane molasses, 5%; urea, 0.4%; and vitamins and minerals, 2%. The concentration of protozoa reached minimum and maximum values at 5 and 22.5 h after feeding, respectively. Thus, to estimate apparent generation rates, concentrations of protozoa were determined at 5 and 20 h postfeeding. Apparent generation rate/h = natural log of ([concentration of protozoa at 20 h divided by concentration at 5 h] divided by the time interval, [T20 to T5]). Alteration of the feed to protozoa ratio by starvation and by changing the level of feed (200 to 900 g/day) showed that as the ratio of feed to protozoa increased, generation rate increased. Measurements of liquid turnover rates in the rumen showed that turnover rate decreased as feed level decreased. Turnover rate was near zero when the sheep were starved. Small quantities of soluble substrates, added directly to the rumen of starved sheep, maintained the protozoal population when rumen turnover was minimal. Furthermore, as rumen turnover rate increased with increased levels of feed, the effect of substrate on maintaining the protozoal population was negated. Thus, at high feed levels, turnover rate may be the dominant factor controlling the establishment and concentration of protozoa in the rumen.     

Adenosine Triphosphate in the Bovine Rumen During Maximum Nutrient Supply and Starvation

The concentration of adenosine triphosphate (ATP) in rumen fluid from heifers fed high levels of nutrients continuously and after 12–24 h starvation has been determined in order to examine the influence of different physiological conditions. The conventional parameters for characterizing the rumen fermentation have been applied to control the effect of a different nutrient supply. The mean concentration of ATP, determined by the luciferin-luciferase assay, was 55.3 mg ATP/l rumen fluid in a heifer fed continuously, twice as much as found in a starved heifer. The mean ratio of biomass/ATP changed from 683 at the high level of energy intake to 1208 in the period of starvation. Consequently, the concentration of ATP in the rumen micro-organisms is markedly influenced by nutritional conditions. Finally, the applicability of ATP determinations in rumen microbiology is discussed.     

一株瘤胃源乳酸利用菌的分离鉴定及其体外代谢特性

【目的】从饲喂高精料的本地山羊瘤胃内分离到一株利用乳酸并能产生大量丙酸的菌株L9,并进一步研究了该菌在调控瘤胃微生物发酵中的作用。【方法】采用厌氧培养技术,结合形态、生理生化特性和16SrRNA基因序列分析结果。【结果】该菌株被鉴定为反刍兽新月形单胞菌（Selenomonas ruminantium）。该菌株体外代谢特性研究表明,L9可利用乳酸作为唯一碳源,该菌在24h内可对90mmol／L的乳酸完全降解。体外摸拟瘤胃急性酸中毒的发酵试验结果表明,以淀粉为底物时,与对照组相比,添加菌株L9可显著降低瘤胃微生物体外培养体系中乳酸浓度,提高pH值,提高总挥发性脂肪酸和丙酸浓度,并显著降低乙酸与丙酸的浓度比（P〈0．05）。【结论】结果显示,菌株L9是一株可代谢乳酸,促进丙酸生成,提高总挥发性脂肪酸浓度的有益瘤胃细菌。     

Effect of plant oils and organic acids on rumen fermentation in vitro

We determined the effect of plant oils (rapeseed, sunflower, linseed) and organic acids (aspartic and malic) on the fermentation of diet consisting of hay, barley and sugar beet molasses. Rumen fluid was collected from two sheep (Slovak Merino) fed with the same diet twice daily. Mixed rumen microorganisms were incubated in fermentation fluid, which contained rumen fluid and Mc Dougall's buffer. All supplemented diets significantly increased pH, molar proportion of propionate, and numerically decreased methane production. Lactate production was also decreased significantly (except with malate). Incorporation of plant oils into aspartate- and malate-treated incubations negated the decrease of butyrate, lactate and the increase of pH and ammonia with malate treatment, as well asin vitro dry matter digestibility and pH with aspartate treatment. The effect of combined additives on methane production and molar proportion of propionate was lower compared with additives supplemented separately. Combination of additives had no additive effect on rumen fermentation. All additives decreased total protozoan counts in rumen fluid.     

Patterns of RNA synthesis in batch and cyclic fed-batch cultures of tylosin-producingStreptomyces fradiae

Ribonucleic acid (RNA) synthesis was studied in batch and cyclic fed-batch cultures of tylosin-producingStreptomyces fradiae. In batch culture, net RNA synthesis increased with increasing growth rate then decreased as the fermentation progressed. A cyclic response pattern of net RNA synthesis was observed when glucose and glutamate solutions were cyclically fed to the batch culture; RNA synthesis rate increased sharply to a maximum level following the feeding cycles then decreased to lower values between the maxima. Data obtained from an extended cyclic fed-batch culture showed that cyclic feeding of the key nutrients allowed RNA and tylosin syntheses to continue during a period when such activities had ceased in the control batch culture.