Lactic Acid Metabolism Research Articles

Inhibition of ruminal bacteria involved in lactic acid metabolism by extracts from Australian plants

Ethanolic extracts, essential oils and plant secondary compounds from selected Australian plants were tested in vitro for their potential to selectively inhibit bacteria associated with lactic acid production in ruminants. A combination of agar dilution and microbroth dilution assays were used to determine the minimum inhibitory concentration (MIC) of the plant extracts against a panel of ruminal bacteria. Ethanolic extract from Eremophila glabra inhibited lactate producers and all other rumen bacteria at 1.260mg/ml, except for the ruminal lactate fermenter Megasphaera elsdenii (MIC 10mg/ml). Extracts from Acacia decurrens, A. saligna, Kennedia eximia and K. prorepens inhibited ruminal lactate producer Lactobacillus spp. only (MIC from 5 to 10mg/ml). The MIC of essential oils ranged from 0.003 to 0.020mg/ml, but the inhibitory effect was not specific to lactate producers. E. glabra was identified as the plant with the most favourable effect and purified compounds from this plant were investigated for further analysis. Seven serrulatane diterpenes were isolated by chromatography and tested against the major ruminal lactate producer Streptococcus bovis and a lactate fermenter M. elsdenii in a microbroth dilution assay. All but one of these inhibited S. bovis, with the MIC ranging from 0.320 to 1.080mg/ml, with only one compound also inhibiting M. elsdenii (MIC 1.080mg/ml). Selective inhibition of lactate producing bacteria in the rumen by some Australian plant extracts and their secondary compounds was identified and may lead to further research into the application of bioactive plants in the management of lactic acidosis in ruminants.

Effect of Triticale Dried Distillers Grains with Solubles on Ruminal Bacterial Populations as Revealed by Real Time Polymerase Chain Reaction

Real time PCR was used in this study to determine the effect of triticale dried distillers grains with solubles (TDDGS) as a replacement for grain or barley silage in finishing diets on the presence of six classical ruminal bacterial species (Succinivibrio dextrinosolvens, Selenomonas ruminantium, Streptococcus bovis, Megasphaera elsdenii, Prevotella ruminicola and Fibrobacter succinogenes) within the rumen contents of feedlot cattle. This study was divided into a step-wise adaptation experiment (112 days) that examined the effects of adaptation to diets containing increasing levels of TDDGS up to 30% (n = 4), a short-term experiment comparing animals (n = 16) fed control, 20%, 25% or 30% TDDGS diets over 28 days, and a rapid transition experiment (56 days) where animals (n = 4) were rapidly switched from a diet containing 30% TDDGS to a barley-based diet with no TDDGS. It was found that feeding TDDGS as replacement for barley grain (control vs. 20% TDDGS) decreased 16S rRNA copy numbers of starch-fermenting S. ruminantium and S. bovis (p<0.001 and p = 0.04, respectively), but did not alter 16S rRNA copy numbers of the other rumen bacteria. Furthermore, feeding TDDGS as a replacement barley silage (20% vs. 25% and 30% TDDGS) increased 16S rRNA copy numbers of S. ruminantium, M. elsdenii and F. succinogenes (p<0.001; p = 0.03 and p<0.001, respectively), but decreased (p<0.001) the 16S rRNA copy number of P. ruminicola . Upon removal of 30% TDDGS and return to the control diet, 16S rRNA copy numbers of S. ruminantium, M. elsdenii and F. succinogenes decreased (p = 0.01; p = 0.03 and p = 0.01, respectively), but S. dextrinosolvens and S. bovis increased (p = 0.04 and p = 0.009, respectively). The results suggest that replacement of TDDGS for grain reduces 16S rRNA copy numbers of starch-fermenting bacteria, whereas substitution for barley silage increases 16S rRNA copy numbers of bacteria involved in fibre digestion and the metabolism of lactic acid. This outcome supports the contention that the fibre in TDDGS is highly

The discovery of oxidative phosphorylation: a conceptual off-shoot from the study of glycolysis

The origins of oxidative phosphorylation, initially known as aerobic phosphorylation, grew out of three research areas of muscle metabolism, creatine phosphorylation, aerobic metabolism of lactic acid in muscle, and studies on the nature and role of adenosine triphosphate (ATP). Much of this work centred round the laboratory of Otto Meyerhof, and most of those contributing to the study of aerobic phosphorylation were influenced by that laboratory: particularly Lipmann and also Ochoa. The work of Engelhardt on ATP levels in blood also appears to have been influenced by the studies of Meyerhof’s laboratory. However, with the work of Kalckar, influenced by Lipmann, biochemists began to realise the potential importance of the process. This was confirmed and extended by Belitzer and Ochoa and the theoretical contribution of Lipmann. Thus it is not easy to identify a single point that marked the initiation of studies in this field. The early work was based on the use of tissue homogenates and cells but ultimately this approach limited research possibilities. The development of techniques based on mitochondria opened up new possibilities and brought this first phase of the study of oxidative phorphorylation to a close.

Effects of selected lactic acid bacteria on the characteristics of amaranth sourdough

As the processing of amaranth in baked goods is challenging, the use of sourdough fermentation is a promising possibility to exploit the advantages of this raw material. In this study the fermentation properties of Lactobacillus plantarum, Lactobacillus paralimentarius and Lactobacillus helveticus in amaranth-based sourdough were examined in order to validate them as starter cultures. pH, total titratable acidity (TTA) and lactic/acetic acid ratio of the sourdough and sensory properties of the resulting wheat bread were evaluated using fermentation temperatures of 30 and 35 °C. While fermentation pH, TTA and lactic acid concentration showed small variations with the use of L. plantarum and L. paralimentarius, L. helveticus reached the most intensive acidification after initial adaptation to the substrate. Acetic acid production was independent of lactic acid metabolism. Furthermore, the lactic/acetic acid ratio exceeded recommendation by 10-35 times (fermentation quotient 25-82). Sensory evaluation showed no significant differences between the two fermentation temperatures but differences among the three micro-organisms. The results provide relevant information on the fermentation properties required of a customised starter for amaranth flour.

Effect of Dietary Lipid Type on the Enhancement of Swimming Endurance of Mice by L-Lactic Acid

Mice fed either a diet containing 6% lard, fish oil or Erabu sea snake lipids for 16 weeks were intraperitoneally injected L-lactic acid or glucose (25 mg/kg) following injection of physiological saline and subjected to swimming tests at 30 min after each injection. The swimming time ratio of lactic acid to saline injections was greater in mice fed sea snake lipids than those fed lard (p < 0.01) or fish oil (p < 0.05), and significantly greater than that of glucose to saline injections only in mice fed sea snake lipids (p < 0.01) but not those fed lard or fish oil. Increased endurance by injected glucose was not observed in mice fed any of the diets. These results indicate that dietary lipid type affects the endurance of mice injected with L-lactic acid, and Erabu sea snake lipids may contain factors that regulate lactic acid metabolism effectively.

Supplementing fructose-based block supplements to forage-fed cattle increases capacity for lactic acid metabolism

Acidosis is one of the more important maladies afflicting cattle fed significant amounts of grain and has enormous economic impact for feedlots, dairies, and producers of seed stock. The highest incidence of acidosis occurs when animals are being transitioned from high-roughage diets to diets containing high levels of concentrates. When grain-based diets are consumed in excess, consumed too quickly, or fed without proper adaptation, digestive end products (organic acids) can accumulate within the rumen, resulting in acidosis. Lactic acid is one of the key organic compounds that accumulates under these conditions. Coupled with the animal's limited ability to metabolize lactate, accumulation of lactic acid in the rumen lowers ruminal pH and subsequently depresses feed intake. One means of preventing acidosis is to directly populate the rumen with lactate-utilizing bacteria. Alternatively, exposure to low levels of lactate (i.e., levels insufficient to harm the animal) may stimulate development of a population of lactate-utilizing bacteria. The objective of our study was to determine if supplementing low-moisture blocks made of high fructose corn syrup could increase ruminal lactate concentrations and subsequently stimulate growth of lactate-metabolizing bacteria. If successful, this could prove useful for adapting forage-fed cattle to grain-based diets.

Effects of body temperature change on the level of lactic acid and oxygen metabolism after the hypothermic cardiopulmonary bypass(CPB)

Objective To investigate the effects of body temperature change on the level of arterial blood lactic acid and oxygen metabolism after the hypothermic cardiopulmonary bypass(CPB),and to provide a basis for controlling body temperature of patients.Methods 60 patients performed the open cardiac operation under hypothermic cardiopulmonary bypass were monitored.The arterial and mixed venous blood gas,and the level of lactic acid were measured at four different rectal temperatures:37,37.5,38℃ and 38.5℃,by taking samples of arterial and venous bloods.Results The systemic arterial-venous oxygen content and oxygen extraction were increased during rewarming time.The level of arterial blood lactic acid at the rectal temperature of 37.5℃ mostly approachs the nornlal value.next is at the rectal temperature of 37℃ and 38 ℃,respectively.And the level of arterial blood laetic acid at the rectal temperature of 38.5℃ is the hilghest (hyperlactacidemia).The difference shows a statistically significance.Conclusions During the rewarming process after the hypothermic cardiopulmonary bypass(CPB),the body temperature change is a key factor influencing oxygen extraction and blood lactic acid level.The nursing staff should control the body temperature of patients with the safe range of around 37.5℃. Key words: Extracorporeal Circulation; Body Temperature Regulation; Blood Lactate; Oxygen Consumption; Nursing Care

Parkinsonism and Elevated Lactic Acid with Sertraline

Dear Editor: A few reports of sertraline-induced akathisia and dystonia are available, but reporting on sertraline-induced Parkinsonism is negligible (1). We report a case of Parkinsonism associated with sertraline use. To our knowledge, this is the first case in the literature to highlight a possible relation between selective serotonin reuptake inhibitors (SSRIs) and lactic acid metabolism. Case Report Mrs L, aged 45 years, is a married, middleclass housewife. She was premorbidly well adjusted and had no significant psychiatric or medical history and no significant family history. She presented with a 2-month history of persistent sadness, frequent crying spells, suicidal ideation, agitation, feelings of hopelessness and worthlessness, disturbed biological functioning, and weight loss of 5 kg. Her illness was precipitated by severe financial losses in her husband's business. Moreover, he had taken a large loan to start his business, and his creditors were demanding payment. Their visits to the home caused her to become markedly restless and apparently unresponsive to her surroundings for periods of 30 minutes to 2 hours. She emerged from these spells when cold water was sprinkled on her face. Mrs L was hospitalized in a private nursing home and given tablet alprazolam 0.5 mg daily and intravenous fluid with parental B complex. She was later referred to our hospital, where all medication was discontinued on admission. She was diagnosed with major depression with conversion disorder and was started on sertraline 50 mg daily and clonazepam 1 mg daily. We increased her sertraline to 100 mg daily on the fourth day of admission. The next day, she developed excessive salivation, mask-like facies, bradykinesia, cogwheel rigidity, tremors of both hands, and monotonous speech. We immediately discontinued sertraline, and she was given intramuscular promethazine 50 mg, with partial response. We sought the opinion of a neurologist on the same day, and Mrs L was given a diagnosis of possible sertaline-induced Parkinsonism. According to the Extrapyramidal Symptom Rating Scale (2), her Parkinsonism was moderately severe. We started her on trihexyphenidyl 2 mg daily, increased to 6 mg daily over a period of 7 days. She was maintained on this dosage for 10 days, and her extrapyramidal symptoms (EPS) fully remitted. However, when trihexyphenidyl was tapered to 2 mg daily, the Parkinsonism symptoms reappeared. We therefore increased the dosage of trihexyphenidyl back to 6 mg daily, with successful results. Because her symptoms reappeared, she was investigated thoroughly. Magnetic resonance imaging (MRI) of the head revealed bilateral basal ganglia focal hyperintensities without any specific lesion. She had a normal biochemical profile for blood sugar, urea, serum creatinine, calcium phosphorus, and alkaline phosphatase. …

The role of dynamic modelling in understanding the microbial contribution to rumen function

Mechanistic models of microbial metabolism in the rumen aim at an improved understanding and integration for research purposes or at an improved prediction for practical purposes. The standard way of representing such models is the rate : state formalism. The system is defined by a number of state variables and a set of differential equations describe the change of the state variables with time. Three different types of solution to these dynamic models are distinguished, and examples of these solutions are described to illustrate the applications and contributions of dynamic modelling in the study of the rumen microbial ecosystem. Type I solutions are obtained when the system is in steady state and the differential equations are solved by setting the differentials to zero. An application of the type I solution is the indirect approach to quantifying the fibrolytic anaerobic fungi in the rumen. The solutions of the model describing the alternate life cycle of rumen fungi, with its free-swimming dispersal and particle-attached stages, appear to be consistent with ruminal and faecal observations. Type II solutions are obtained when the system is not in steady state but the differential equations can be integrated analytically. An application of this type of solution is the quantification of the growth and growth yield in batch cultures. Such models help to quantify the degradation of substrates in the rumen and to elucidate the interactions between groups of rumen micro-organisms. Type III solutions are obtained when the system is not in steady state and when the differential equations have to be solved numerically. Applications of the type III solutions are the rumen simulation models that describe substrate degradation, endproduct formation and microbial metabolism in an integrated manner. To illustrate this type III solution, a model of lactic acid metabolism in the rumen is defined, and its contribution to understanding of the paths and rates of lactic acid disappearance described. It is essential that the models are based on sound mathematical and biological principles. However, the various applications described in the paper show that models need not necessarily be complex and very detailed to contribute to better understanding.

Long-term exposure to lifelong therapies.

Three categories of highly active antiretroviral therapy (HAART)-associated major toxic effects have been identified: nucleoside-related toxic effects (e.g., neuropathy, myopathy, pancreatitis, hepatic steatosis, lactic acidosis, and possibly lipoatrophy), metabolic complications (e.g., fat redistribution, insulin resistance, and hyperlipidemia), and bone disease (e.g., osteopenia and/or osteoporosis). The toxic effects caused by nucleosides are hypothesized to be a result of mitochondrial injury and include myopathy, pancreatitis, liver failure, and lactic acidosis. Alterations in lactic acid metabolism range from common instances of asymptomatic lactic acidemia to rare occurrences of life-threatening lactic acidosis with hepatic steatosis. A metabolic syndrome consisting of lipodystrophy (i.e., fat redistribution), hyperlipidemia and insulin resistance has been observed, particularly with protease inhibitor treatment. Some additive interaction between protease inhibitors and nucleosides has also been described. The potential relationship of these metabolic abnormalities to increased risk of cardiovascular disease and diabetes has broad implications on long-term patient management. Lipodystrophy associated with HAART is generally accompanied by potentially serious abnormalities, including dyslipidemia (i.e., hypercholesterolemia and hypertriglyceridemia) and altered glucose metabolism (i.e., insulin resistance). Regimens of HAART may have adverse effects on bone metabolism, as indicated by emerging reports of osteopenia, osteoporosis, and avascular necrosis.

How anaerobic is the Wingate Anaerobic Test for humans?

The Wingate Anaerobic Test (WAnT) is generally used to evaluate anaerobic cycling performance, but knowledge of the metabolic profile of WAnT is limited. Therefore the energetics of WAnT was analysed with respect to working efficiency and performance. A group of 11 male subjects [mean (SD), age 21.6 (3.8) years, height 178.6 (6.6) cm, body mass 82.2 (12.1) kg] performed a maximal incremental exercise test and a WAnT. Lactic and alactic anaerobic energy outputs were calculated from net lactate production and the fast component of the kinetics of post-exercise oxygen uptake. Aerobic metabolism was determined from oxygen uptake during exercise. The WAnT mean power of 683 (96.0) W resulted from a total energy output above the value at rest of 128.1 (23.2) kJ x 30 s(-1) [mean metabolic power=4.3 (0.8) kW] corresponding to a working efficiency of 16.2 (1.6)%. The WAnT working efficiency was lower (P < 0.01) than the corresponding value of 24.1 (1.7)% at 362 (41) W at the end of an incremental exercise test. During WAnT the fractions of the energy from aerobic, anaerobic alactic and lactic acid metabolism were 18.6 (2.5)%, 31.1 (4.6)%, and 50.3 (5.1)%, respectively. Energy from metabolism of anaerobic lactic acid explained 83% and 81% of the variance of WAnT peak and mean power, respectively. The results indicate firstly that WAnT requires the use of more anaerobically derived energy than previously estimated, secondly that anaerobic metabolism is dominated by glycolysis, thirdly that WAnT mechanical efficiency is lower than that found in aerobic exercise tests, and fourthly that the latter finding partly explains discrepancies between previously published and the present data about the metabolic profile of WAnT.

Expression of the Lactate Permease Gene JEN1 from the Yeast Saccharomyces cerevisiae

In Saccharomyces cerevisiae, lactate permease induction by lactic acid took place after transcription of JEN1. JEN1 transcripts were undetectable 10 min after the addition of a pulse of glucose to YP–lactic acid exponentially growing cells, while the permease activity ceased after 50 min. A value of 15.1 min was found for the half-life of JEN1 mRNA, showing the involvement of a glucose-induced mechanism of mRNA degradation. The rapid decline of the carrier activity upon glucose addition points to the existence of an irreversible carbon catabolite inactivation process. Isogenic strains, deleted in genes encoding enzymes involved in lactic acid metabolism, did not express JEN1, indicating an association of the intracellular metabolism of the acid to the transcription of the permease gene. The carbon sources capable of inducing JEN1 transcription were dependent on the strain. Distinct posttranslation mechanisms appeared to be involved in the lactate carrier activity.

The metabolic network of Lactococcus lactis: distribution of (14)C-labeled substrates between catabolic and anabolic pathways.

Lactococcus lactis NCDO 2118 was grown in a simple synthetic medium containing only six essential amino acids and glucose as carbon substrates to determine qualitatively and quantitatively the carbon fluxes into the metabolic network. The specific rates of substrate consumption, product formation, and biomass synthesis, calculated during the exponential growth phase, represented the carbon fluxes within the catabolic and anabolic pathways. The macromolecular composition of the biomass was measured to distribute the global anabolic flux into the specific anabolic pathways. Finally, the distribution of radiolabeled substrates, both into the excreted fermentation end products and into the different macromolecular fractions of biomass, was monitored. The classical end products of lactic acid metabolism (lactate, formate, and acetate) were labeled with glucose, which did not label other excreted products, and to a lesser extent with serine, which was deaminated to pyruvate and represented approximately 10% of the pyruvate flux. Other minor products, keto and hydroxy acids, were produced from glutamate and branched-chain amino acids via deamination and subsequent decarboxylation and/or reduction. Glucose labeled all biomass fractions and accounted for 66% of the cellular carbon, although this represented only 5% of the consumed glucose.

Oxygen uptake, heart rate and blood lactate concentration during a normal training session of an aerobic dance class.

The aim of this research was to investigate the physiological responses and, in particular, the participation of lactic acid anaerobic metabolism in aerobic dance, which is claimed to be pure aerobic exercise. In contrast to previous studies, that have put subjects in very unfamiliar situations, the parameters were monitored in the familiar context of gymnasium, practice routine and habitual instructor. A group of 30 skilled fairly well-trained women performed their usual routine, a combination of the two styles: low (LI) and high impact (HI), and were continuously monitored for heart rate (HR) and every 8 min for blood lactate concentration ([La-]b). Of the group, 15 were tested to determine their maximal aerobic power (VO2max) using a cycle-ergometer. They were also monitored during the routine for oxygen uptake (VO2) by a light telemetric apparatus. The oxygen pulses of the routine and of the corresponding exercise intensity in the incremental test were not statistically different. The mean values in the exercise session were: peak HR 92.8 (SD 7.8)% of the subject's maximal theoretical value, peak VO2 99.5 (SD 12.4)% of VO2max, maximal [La-]b 6.1 (SD 1.7) mmol x l(-1), and mean 4.8 (SD 1.3) mmol x l(-1). Repeated measures ANOVA found statistically significant differences between the increasing [La-]b values (P < 0.001). In particular, the difference between the [La-]b values at the end of the mainly LI phase and those of the LI-HI combination phase, and the difference between the samples during the combination LI-HI phase were both statistically significant (both P = 0.002 and P = 0.002). The similar oxygen pulses confirmed the validity of the present experiment design and the reliability of HR monitoring in this activity. The HR, VO2 and, above all, the increase of [La-]b to quite high values, showing a non steady state, demonstrated the high metabolic demand made by this activity that involved lactic acid metabolism at a much higher level than expected.

CITRULLINE MALATE EFFECTS ON THE AEROBIC-ANAEROBIC THRESHOLD AND IN POST-EXERCISE BLOOD LACTATE RECOVERY

880 Citrulline malate (CM) is a pharmacological compound which has been reported to influence lactic acid metabolism. The main purposes of this study were to evaluate the CM effects on the: (a) aerobic-anaerobic threshold; (b) blood lactate accumulation; (c) 30min post-exercise blood lactate recovery. Two male groups (G1 and G2) of senior basketball players ingested CM over a period of 13 days. During this time G1 (n=15) ingested between 6-9 ampoule/day and G2 (n=15) 3 ampoule/day. Each oral ampoule contained 10ml of solute at 50% CM 2.0g. The aerobic-anaerobic threshold (W4), using as criteria the workload corresponding to a blood lactate concentration of 4mmol/L, was used to evaluate the subject's aerobic capacity. Two maximal exercise tests in cycle-ergometer (increments of 40W/5min) were conducted before and after CM ingestion. Samples of capillary blood were taken from the ear lobe after each step and during recovery and analysed in an YSI-1500 Sport. The t test of independent and repeated measures was used. Statistical analysis within group concerning the W4 showed significant (p<0.05) improvements only in G1. Additionally, 27% of the G1 elements were able to achieve an higher maximal workload in the 2nd test. No further significant results were observed on the other physiological research parameters. The substantial improvements in G1 and the lack of similar results in G2 suggests that an higher ingestion of CM is likely to induce a physiological effect concerning improvements in aerobic capacity.

Production of lactic acid and energy metabolism in vascular smooth muscle: effect of dichloroacetate.

Vascular smooth muscle metabolism is characterized by substantial production of lactic acid even under fully oxygenated conditions. The role the aerobic production of lactate plays in the energetics of smooth muscle is obscure and was investigated in this study. Helical strips of porcine carotid arteries were incubated in medium containing 1 mM dichloroacetate (DCA), an agent that stimulates pyruvate dehydrogenase and promotes the oxidation of glucose. Lactate production in resting muscle was decreased in the presence of DCA (0.033 +/- 0.006 vs. 0.111 +/- 0.014 mumol.g-1.min-1, P < 0.02), indicating diversion of glucose metabolism from lactate production to enhanced glucose oxidation. This was associated with reduction in the level of ATP+phosphocreatine (PCr) (0.99 +/- 0.01 vs. 1.40 +/- 0.09 mumol/g, P < 0.05) and cataplerosis of the tricarboxylic acid (TCA) cycle. Contraction by KCl was also associated with reduced lactate production in the presence of DCA (0.086 +/- 0.017 vs. 0.20 +/- 0.002 mumol.g-1.min-1, P < 0.01), but ATP+PCr normalized, and there was anaplerosis of the TCA cycle. Glycogen in control arteries declined by approximately 1.3 mumol/g over 30 min K+ contraction but was unchanged in the presence of DCA. By calculation, the glycogen spared could be accounted for by the quantity of glucose diverted from lactate production to glucose oxidation during contraction. It is concluded that the aerobic production of lactate is a mechanism affording optimal coordination and modulation of glucose supply and oxidative energy production with energy demand.

A new patient with α-ketoglutaric aciduria and progressive extrapyramidal tract disease

A 4.5-year-old boy with chronic progressive encephalopathy is described. The clinical presentation initially included seizures and hypotonia which later evolved into severe extrapyramidal disease and dementia. The gas chromatography/mass spectrometry (GC/MS) analysis of urine indicated that alpha-ketoglutarate was increased 210 times and aconitic acid 80 times. No disturbance of acid/base balance, lactic acid or ammonia metabolism accompanied this clinical picture. The fibroblasts contained 29% of normal alpha-ketoglutarate dehydrogenase activity, while the activity of another mitochondrial marker enzyme, glutamate dehydrogenase, was normal. The neuroimaging studies revealed bilateral striatal necrosis. The clinical and biochemical findings were almost identical to two previously reported patients. Experience with this patient emphasizes the need for detailed organic acid biochemical investigation in any progressive encephalopathy and that extrapyramidal tract signs should evoke the possibility of alpha-ketoglutaric aciduria, among other 'neurologic organic acidemias'.

Rumen fermentation patterns in sheep receiving silages of different chemical composition supplemented with concentrates rich in starch or in digestible fibre

SUMMARYIn each of two experiments, eight silages supplemented with concentrates containing a high proportion of either starch or digestible fibre were given to rumen-cannulated sheep. The silages constituted c. 65% of the total dry matter and differed widely in chemical composition, reflecting differences in the extent of fermentation in the silo.Rumen pH was lower (P &lt; 0·01 and P &lt; 0·001 for Expts 1 and 2 respectively) and the concentration of total volatile fatty acids (VFA) in the rumen was higher (P &lt; 0·001 for Expt 2) for the starchy concentrate. Silages differed in their effects on ruminal proportions of acetate (P &lt; 0·001 and P &lt; 0·01 for Expts 1 and 2 respectively) and, inversely, of propionate (P &lt; 0·001 for Expt 1). There was evidence of a strong relationship between the molar proportion of propionate in the rumen and the concentration of lactic acid in the silage. The results indicate that the production of propionate during the metabolism of silage lactic acid by the rumen microbial population was the predominant influence on rumen fermentation pattern.It is suggested that this relationship is the basis of some of the differences in milk production reported for silages showing restricted as opposed to extensive fermentation.

Utilization of Lactic Acid by Fusarium oxysporum var. lini : Regulation of Transport and Metabolism

Lactic acid was transported in Fusarium oxysporum var. lini ATCC 10960 by a saturable transport system that had a half-saturation constant of 56.6 +/- 7.5 muM and a maximum velocity of 0.61 +/- 0.10 mmol h g (dry weight) at 26 degrees C and pH 5.0. This transport system was inducible and was not expressed in the presence of a repressing substrate. Evidence is presented that the anionic form lactate was taken up by the cells. Propionic, acetic, pyruvic, and bromoacetic acids but not succinic acid competitively inhibited the transport of lactic acid. Bromoacetic acid, which was not metabolized, was taken up to a steady-state level when intracellular and extracellular concentrations were identical, indicating that the transport system was not accumulative. The enzymatic activity that was physiologically more relevant in the metabolism of lactic acid was lactate: ferricytochrome c oxidase. This enzyme did not exhibit stereospecifity and was induced by lactic acid.

Fourth symposium on lactic acid bacteria Genetics, metabolism and applications

Fourth symposium on lactic acid bacteria Genetics, metabolism and applications