NAD-independent Lactate Dehydrogenases Research Articles

A novel approach to enhance high optically active L-lactate production from food waste by landfill leachate

The recycling of food waste (FW) through anaerobic fermentation into lactic acid (LA), with two isomers L-LA and D-LA, aligns with the principles of a bio-based circular economy. However, FW fermentation is often limited by competing pathways, acidification inhibition, and trace metals deficiency. This study investigates the introduction of landfill leachate, containing buffering agents (ammonia) and trace metals, into FW fermentation. Various dosages of landfill leachate, ranging from 90 (LN-90) to 450 mg/L (LN-450) based on inclusive ammonia calculation, were employed. Results showed that LA production peaked at 43.65 ± 0.57 g COD/L in LN-180 on day 6, with a high optical activity of L-LA at 92.40 ± 1.15 %. Fermentation pathway analysis revealed that landfill leachate amendment enhances hydrolysis (as evidenced by increased activity of amylase, α-glucosidase, and protease) and glycolysis (resulting in enhanced utilization of carbohydrates and glucose). The inclusive ammonia in leachate plays a crucial role as a buffer, maintaining optimal pH conditions (5–7), thereby reducing volatile fatty acid production and thus intensifying LA orientations. The increased activity of L-lactate dehydrogenase (L-LA generation) and decreased NAD-independent lactate dehydrogenase (LA consumption) in properly dosed leachate further explained the high accumulation of L-LA. Dominance of lactic acid bacteria, including Streptococcus, Enterococcus, Klebsiella, Bifidobacterium, Bavariicoccus, and Lacticaseibacillus, accounted for 91.08% (LN-90), while inhibitory effects were observed in LN-450 (4.45%). Functional gene analysis further supported the enhanced glycolysis, L-lactate dehydrogenase, and nitrogen assimilation. Finally, a network analysis indicates a beneficial effect on the genus Enterococcus and Klebsiella by landfill leachate addition. This study demonstrates the efficiency of utilizing landfill leachate to enhance LA recycling from FW fermentation, aligning with the concept of circular economy by transforming waste into valuable resources.

Heterogeneous g-C3N4/polyaniline composites enhanced the conversion of organics into methane during anaerobic wastewater treatment

In this study, g-C3N4/PANI was prepared by in situ oxidative polymerization. Graphite-phase carbon nitride (g-C3N4) with surface defects was deposited onto the surface of conductive polyaniline (PANI) to form a p-n heterojunction. This construction aimed to create an efficient heterogeneous catalyst, increasing the surface defect level and active sites of the composite, and augmenting its capability to capture and transfer extracellular electrons under anaerobic conditions. This addresses the challenge of low efficiency in direct interspecies electron transfer between bacteria and archaea during anaerobic digestion for methane production. The results showed that the prepared g-C3N4/PANI increased the CH4 yield and CH4 production rate by 82% and 96%, respectively. Notably, the conductivity and XPS test results showed that the ratio of g-C3N4 to PANI was 0.15, and the composite exhibited favorable conductivity, with a uniform distribution of pyrrolic nitrogen, pyridinic nitrogen, and graphitic nitrogen, each accounting for approximately 30%. Furthermore, g-C3N4/PANI effectively enhanced the metabolic efficiency of intermediate products such as acetate and butyrate. Analysis of the microbial community structure revealed that g-C3N4/PANI led to a significant increase in the abundance of hydrogenotrophic methanogen Methanolinea (from 48% to 64%) and enriched Clostridium (a rise of 1%) with direct interspecies electron transfer capability. Microbial community function analysis demonstrated that the addition of g-C3N4/PANI boosted the activities of key enzymes involved in anaerobic digestion, including phosphate transacetylase (PTA), phospho-butyryl transferase (PTB), and NAD-independent lactate dehydrogenase (NNLD), by 47%, 135%, and 153%, respectively. This acceleration in enzymatic activity promoted the metabolism of acetyl-CoA, butyryl-CoA, and pyruvate. Additionally, the function of ABC transporters was enhanced, thereby improving the efficiency of material and energy exchange among microorganisms.

Acid tolerance of lactate-utilizing bacteria of the order Bacteroidales contributes to prevention of ruminal acidosis in goats adapted to a high-concentrate diet.

The rapid accumulation of organic acids, particularly lactate, has been suggested as the main cause of ruminal acidosis (RA) for ruminants fed high-concentrate diets. Previous research has shown that a gradual shift from low-to high-concentrate diets within 4 to 5 weeks effectively reduces the risk for RA. However, the mechanisms remain unknown. In this study, 20 goats were randomly allocated into four groups (n=5) and fed with a diet containing a weekly increasing concentrate portion of 20%, 40%, 60%, and 80% over 28d. At d 7, 14, 21, and 28, one group (named C20, C40, C60, and C80 according to the last concentrate level that they received) was killed and the ruminal microbiome was collected. Ruminal acidosis was not detected in any of the goats during the experiment. Nonetheless, ruminal pH dropped sharply from 6.2 to 5.7 (P<0.05) when dietary concentrate increased from 40% to 60%. A combined metagenome and metatranscriptome sequencing approach identified that this was linked to a sharp decrease in the abundance and expression of genes encoding nicotinamide adenine dinucleotide (NAD)-dependent lactate dehydrogenase (nLDH), catalyzing the enzymatic conversion of pyruvate to lactate (P<0.01), whereas the expression of two genes encoding NAD-independent lactate dehydrogenase (iLDH), catalyzing lactate oxidation to pyruvate, showed no significant concomitant change. Abundance and expression alterations for nLDH- and iLDH-encoding genes were attributable to bacteria from Clostridiales and Bacteroidales, respectively. By analyzing the gene profiles of 9 metagenome bins (MAG) with nLDH-encoding genes and 5 MAG with iLDH-encoding genes, we identified primary and secondary active transporters as being the major types of sugar transporter for lactate-producing bacteria (LPB) and lactate-utilizing bacteria (LUB), respectively. Furthermore, more adenosine triphosphate was required for the phosphorylation of sugars to initiate their catabolic pathways in LPB compared to LUB. Thus, the low dependence of sugar transport systems and catabolic pathways on primary energy sources supports the acid tolerance of LUB from Bacteroidales. It favors ruminal lactate utilization during the adaptation of goats to a high-concentrate diet. This finding has valuable implications for the development of measures to prevent RA.

Platelet Lactate Production during Room Temperature Storage Promotes Bacterial Growth

Introduction: Transfusion related sepsis is a serious concern for both military and civilian trauma centers. The primary source of bacterial contamination associated with such events is room temperature (RT) stored platelets. Due to high risk of bacterial contamination, RT stored platelets may only be administered up to 5 days post-collection. Although approved by the FDA, cold stored platelets may only be administered 3 days post-collection under current regulations. In this study, we utilized the opportunistic pathogen Acinetobacter baumannii - a reported cause of platelet contamination and important hospital acquired infection (HAI) - as a model organism to assess bacterial growth in platelets stored either at room temperature (22oC) or refrigerated (4oC), as well as determine contributors to bacterial growth.Methods: Apheresis platelets in plasma (PLT) were obtained from healthy donors using the Terumo Trima Accel Automated Blood Collection System (Terumo BCT). Platelet poor plasma (PPP) was obtained from PLT aliquots centrifuged twice at 2,500 x g for 5 min. Other PLT aliquots were stimulated with Phorbol 12-myristate 13-acetate (PMA) to generate activated platelets (aPLT). Following activation, aPLTs were pelleted through centrifugation at 2,500 x g for 5 min and the releasate (REL) was transferred to a separate container. Pelleted aPLTs were washed 3 times in sterile PBS and suspended in PPP. In some experiments aliquots of PPP were supplemented with 40 mM lactic acid. Aliquots of PLT, PPP, aPLT, and REL were transferred to pH SAFE minibags (Blood Cell Storage, Inc) and inoculated (a.k.a., contaminated) with A. baumannii clinical isolate Ci79. Minibag aliquots stored at RT were agitated using an orbital shaker set to 60 rpm while refrigerated aliquots were stored under static conditions. Bacterial growth was monitored daily through dilution plating. In some experiments, lactate levels in PLT aliquots were assessed by iSTAT (Abbott) using CG4+ test cartridges.Results: Bacterial growth progressed exponentially over the first 3 days post-collection in PLT aliquots stored at RT. However, growth was significantly (p < 0.05) reduced in PPP units (Fig. 1A). Neither platelet activation status nor released factors appeared to have any effect as no significant differences were observed in bacterial growth between contaminated PLT and aPLT units, nor between contaminated PPP and REL units (Fig. 1A). Growth progressed at a much faster rate and to a greater magnitude in the presence of live platelets (PLT and aPLT), suggesting the contribution of platelet metabolism. Thus, lactate levels were assessed in PLT units and found to mirror bacterial growth (Fig. 1B). Furthermore, addition of lactic acid to RT stored PPP restored bacterial growth (Fig. 1A). Growth remained static throughout under all treatment conditions stored refrigerated.Conclusions: Bacterial growth remained static over the 5 day post-collection observation period during cold storage. Additionally, bacterial growth at RT appeared to be related to increased production of lactate from pyruvate via NAD-dependent lactate dehydrogenase (nLDH) following glycolysis (Fig. 1C). To that end, many bacteria, including A. baumannii,as well as various Staphylococcus spp, and Streptococcus spp, possess genes encoding for NAD-independent lactate dehydrogenases (iLDH) which enable utilization of lactate as a carbon source (Fig. 1D). These data demonstrate that not only can bacterial growth be controlled through refrigeration, but RT stored platelets potentiate bacterial growth through their accelerated metabolism relative to cold storage. [Display omitted] DisclosuresNo relevant conflicts of interest to declare.

Production of chiral 2-hydroxy-carboxylates through NAD-independent lactate dehydrogenase catalyzed resolution

Production of chiral 2-hydroxy-carboxylates through NAD-independent lactate dehydrogenase catalyzed resolution

A novel biocatalyst for efficient production of 2-oxo-carboxylates using glycerol as the cost-effective carbon source.

BackgroundThe surplus of glycerol has increased remarkably as a main byproduct during the biofuel’s production. Exploiting an alternative route for glycerol utilization is significantly important for sustainability of biofuels.ResultsA novel biocatalyst that could be prepared from glycerol for producing 2-oxo-carboxylates was developed. First, Pseudomonas putida KT2440 was reconstructed by deleting lldR to develop a mutant expressing the NAD-independent lactate dehydrogenases (iLDHs) constitutively. Then, the Vitreoscilla hemoglobin (VHb) was heterologously expressed to further improve the biotransformation activity. The reconstructed strain, P. putida KT2440 (ΔlldR)/pBSPPcGm-vgb, exhibited high activities of iLDHs when cultured with glycerol as the carbon source. This cost-effective biocatalyst could efficiently produce pyruvate and 2-oxobutyrate from dl-lactate and dl-2-hydroxybutyrate with high molar conversion rates of 91.9 and 99.8 %, respectively.ConclusionsThe process would not only be a promising alternative for the production of 2-oxo-carboxylates, but also be an example for preparation of efficient biocatalysts for the value-added utilization of glycerol.

Efficient Production of Pyruvate from DL-Lactate by the Lactate-Utilizing Strain Pseudomonas stutzeri SDM

BackgroundThe platform chemical lactate is currently produced mainly through the fermentation of sugars presented in biomass. Besides the synthesis of biodegradable polylactate, lactate is also viewed as a feedstock for the green chemistry of the future. Pyruvate, another important platform chemical, can be produced from lactate through biocatalysis.Methodology/Principal FindingsIt was established that whole cells of Pseudomonas stutzeri SDM catalyze lactate oxidation with lactate-induced NAD-independent lactate dehydrogenases (iLDHs) through the inherent electron transfer chain. Unlike the lactate oxidation processes observed in previous reports, the mechanism underlying lactate oxidation described in the present study excluded the costliness of the cofactor regeneration step and production of the byproduct hydrogen peroxide.Conclusions/SignificanceBiocatalysis conditions were optimized by using the cheap dl-lactate as the substrate and whole cells of the lactate-utilizing P. stutzeri SDM as catalyst. Under optimal conditions, the biocatalytic process produced pyruvate at a high concentration (48.4 g l−1) and a high yield (98%). The bioconversion system provides a promising alternative for the green production of pyruvate.

Pyruvate producing biocatalyst with constitutive NAD-independent lactate dehydrogenases

Production of pyruvate from lactate through biocatalysis is a valuable process for its simple composition of reaction system and convenience of recovery. Biocatalyst with lactate-induced NAD-independent lactate dehydrogenases (iLDHs) can effectively catalyze lactate into pyruvate. To reduce the cost of biocatalyst preparation caused by indispensable lactate addition, the mutants with constitutive iLDH of Pseudomonas sp. XP-M2 were screened. Mutant XP-LM exhibited high iLDHs activities in minimal salt medium with cheap substrate glucose as the carbon source. The biocatalyst (8.2 g dry cell weight l −1) containing 169.8 U l −1 l-iLDH was prepared with 20 g 1 −1 glucose. The cost-effective biocatalyst prepared from the mutant XP-LM could efficiently catalyze lactate into pyruvate with high yield (0.961 mol mol −1). Based on the different thermostability of d-iLDH and l-iLDH in the biocatalyst, whole cells of the strain might also have the potential in production of pyruvate and d-lactate from racemic lactate.

Efficient Production of 2-Oxobutyrate from 2-Hydroxybutyrate by Using Whole Cells of Pseudomonas stutzeri Strain SDM

2-Oxobutyrate is an important intermediate in the chemical, drug, and food industries. Whole cells of Pseudomonas stutzeri SDM, containing NAD-independent lactate dehydrogenases, effectively converted 2-hydroxybutyrate into 2-oxobutyrate. Under optimal conditions, the biocatalytic process produced 2-oxobutyrate at a high concentration (44.4 g liter(-1)) and a high yield (91.5%).

Evolutionary History of d-Lactate Dehydrogenases: A Phylogenomic Perspective on Functional Diversity in the FAD Binding Oxidoreductase/Transferase Type 4 Family

Lactate dehydrogenases which convert lactate to pyruvate are found in almost every organism and comprise a group of highly divergent proteins in amino acid sequence, catalytic properties, and substrate specificity. While the L-lactate dehydrogenases are among the most studied enzymes, very little is known about the structure and function of D-lactate dehydrogenases (D-LDHs) which include two discrete classes of enzymes that are classified based on their ability to transfer electrons and/or protons to NAD in NAD-dependent lactate dehydrogenases (nLDHs), and FAD in NAD-independent lactate dehydrogenases (iLDHs). In this study, we used a combination of structural and phylogenomic approaches to reveal the likely evolutionary events in the history of the recently described FAD binding oxidoreductase/transferase type 4 family that led to the evolution of D-iLDHs (commonly referred as DLD). Our phylogenetic reconstructions reveal that DLD genes from eukaryotes form a paraphyletic group with respect to D-2-hydroxyglutarate dehydrogenase (D2HGDH). All phylogenetic reconstructions recovered two divergent yeast DLD phylogroups. While the first group (DLD1) showed close phylogenetic relationships with the animal and plant DLDs, the second yeast group (DLD2) revealed strong phylogenetic and structural similarities to the plant and animal D2HGDH group. Our data strongly suggest that the functional assignment of the yeast DLD2 group should be carefully revisited. The present study demonstrates that structural phylogenomic approach can be used to resolve important evolutionary events in functionally diverse superfamilies and to provide reliable functional predictions to poorly characterized genes.

Membrane-bound l- and d-lactate dehydrogenase activities of a newly isolated Pseudomonas stutzeri strain

Pseudomonas stutzeri SDM was newly isolated from soil, and two stereospecific NAD-independent lactate dehydrogenase (iLDH) activities were detected in membrane of the cells cultured in a medium containing DL-lactate as the sole carbon source. Neither enzyme activities was constitutive, but both of them might be induced by either enantiomer of lactate. P. stutzeri SDM preferred to utilize lactate to growth, when both L-lactate and glucose were available, and the consumption of glucose was observed only after lactate had been exhausted. The Michaelis-Menten constant for L-lactate was higher than that for D-lactate. The L-iLDH activity was more stable at 55 degrees C, while the D-iLDH activity was lost. Both enzymes exhibited different solubilization with different detergents and different oxidation rates with different electron acceptors. Combining activity staining and previous proteomic analysis, the results suggest that there are two separate enzymes in P. stutzeri SDM, which play an important role in converting lactate to pyruvate.

Aerobic glycerol catabolism by Pediococcus pentosaceus isolated from wine

Glycerol catabolism was studied in Pediococcus pentosaceus N 5p isolated from wine, growing on different glycerol concentrations in aerobic conditions. Enzymatic activities of the glycerol kinase and glycerol dehydrogenase pathways were detected but the levels demonstrated allow to establish that glycerol was mainly degraded by glycerol kinase pathway. The highest levels of the activities of this pathway were expressed at the lowest concentration of glycerol, decreasing with the increase in glycerol concentration in the growth media. Glycerol was transformed in d-lactate, acetate, diacetyl and 2,3-butanediol. The enzymatic activities involved in the formation of these products were also modulated by glycerol. NAD-dependent lactate dehydrogenases were not affected by glycerol. Diacetyl reductase and acetoin reductase were inhibited by glycerol, whereas NAD-independent lactate dehydrogenases, NADH oxidase as CoA-independent acetaldehyde dehydrogenase, and acetate kinase were stimulated. The behavior of the enzymatic activities was in conformity with the fermentation balances; we propose a probable pathway for glycerol catabolism in P. pentosaceus N 5p.

Hypoxia/Anoxia as Signaling for Increased Alcohol Dehydrogenase Activity in Saffron (Crocus sativus L.) Corm

Alcohol dehydrogenase, NAD-dependent lactate dehydrogenase, and NAD-independent lactate dehydrogenase activities were investigated in corms cultivated in normoxic and hypoxic/anoxic conditions. Depending on the developmental stage, hypoxia/anoxia was a signal for increase in either alcohol dehydrogenase or NAD-dependent lactate dehydrogenase. NAD-independent lactate dehydrogenase contributed to the recycling of lactate, thus preventing acidosis.

Major role of NAD-dependent lactate dehydrogenases in aerobic lactate utilization in Lactobacillus plantarum during early stationary phase.

NAD-independent lactate dehydrogenases are commonly thought to be responsible for lactate utilization during the stationary phase of aerobic growth in Lactobacillus plantarum. To substantiate this view, we constructed single and double knockout mutants for the corresponding genes, loxD and loxL. Lactate-to-acetate conversion was not impaired in these strains, while it was completely blocked in mutants deficient in NAD-dependent lactate dehydrogenase activities, encoded by the ldhD and ldhL genes. We conclude that NAD-dependent but not NAD-independent lactate dehydrogenases are involved in this process.

Effect of pH on metabolic pathway shift in fermentation of xylose by Clostridium tyrobutyricum

The effect of pH (between 5.0 and 6.3) on butyric acid fermentation of xylose by Clostridium tyrobutyricum was studied. At pH 6.3, the fermentation gave a high butyrate production of 57.9 g l −1 with a yield of 0.38–0.59 g g −1 xylose and a reactor productivity up to 3.19 g l −1 h −1. However, at low pHs (<5.7), the fermentation produced more acetate and lactate as the main products, with only a small amount of butyric acid. The metabolic shift from butyrate formation to lactate and acetate formation in the fermentation was found to be associated with changes in the activities of several key enzymes. The activities of phosphotransbutyrylase (PTB), which is the key enzyme controlling butyrate formation, and NAD-independent lactate dehydrogenase (iLDH), which catalyzes the conversion of lactate to pyruvate, were higher in cells producing mainly butyrate at pH 6.3. In contrast, cells at pH 5.0 had higher activities of phosphotransacetylase (PTA), which is the key enzyme controlling acetate formation, and lactate dehydrogenase (LDH), which catalyzes the conversion of pyruvate to lactate. Also, PTA was very sensitive to the inhibition by butyric acid. Difference in the specific metabolic rate of xylose at different pHs suggests that the balance in NADH is a key in controlling the metabolic pathway used by the cells in the fermentation.

Cloning and analysis of the L-lactate utilization genes from Streptococcus iniae.

The presence of lactate oxidase was examined in eight Streptococcus species and some related species of bacteria. A clone (pGR002) was isolated from a genomic library of Streptococcus iniae generated in Escherichia coli, containing a DNA fragment spanning two genes designated lctO and lctP. We show that these genes are likely to be involved in the L-lactic acid aerobic metabolism of this organism. This DNA fragment has been sequenced and characterized. A comparison of the deduced amino acid sequence of LctP protein demonstrated that the protein had significant homology with the L-lactate permeases of other bacteria. The amino acid sequence of the LctO protein of S. iniae also showed a strong homology to L-lactate oxidase from Aerococcus viridans and some NAD-independent lactate dehydrogenases, all belonging to the family of flavin mononucleotide-dependent alpha-hydroxyacid-oxidizing enzymes. Biochemical assays of the gene products confirm the identity of the genes from the isolated DNA fragment and reveal a possible role for the lactate oxidase from S. iniae. This lactate oxidase is discussed in relation to the growth of the organism in response to carbon source availability.

Glucose and lactate metabolism by Actinomyces naeslundii.

Actinomyces are among the predominant bacteria in the oral microflora. This review discusses the glucose and lactate metabolism of Actinomyces naeslundii and its ecological significance in dental plaque. This bacterium has the Embden-Meyerhof-Parnas (EMP) pathway as the main route to degrade glucose. The EMP pathway-derived metabolic intermediates, phosphoenolpyruvate (PEP) and pyruvate, are further converted into different end-products, depending on the environment. Under anaerobic conditions in the absence of bicarbonate, the pyruvate is converted into lactate by a lactate dehydrogenase. In the presence of bicarbonate, the PEP is combined with bicarbonate and then converted into succinate through the succinate pathway, while the pyruvate is converted into formate and acetate through the pyruvate formate-lyase pathway. Under aerobic conditions, the pyruvate liberates acetate and CO2 through a pathway initiated by a pyruvate dehydrogenase. A. naeslundii strains also degrade lactate, aerobically, to acetate and CO2 through the conversion of lactate into pyruvate by a NAD-independent lactate dehydrogenase. These strains also synthesize glycogen from a glycolytic intermediate, glucose 6-phosphate. Besides atmospheric conditions and bicarbonate, the intracellular reduction-oxidation potential, carbohydrate concentration, and environmental pH also modulate the metabolism of A. naeslundii. Some of the phosphorylating enzymes involved in A. naeslundii metabolism--e.g., GTP/polyphosphate (PPn)-dependent glucokinase, pyrophosphate (PPi)-dependent phosphofructokinase, UDP-glucose pyrophosphorylase, and GDP/IDP-dependent PEP carboxykinase--are unique to A. naeslundii and have not been found in other oral bacteria. The utilization of PPn and PPi as phosphoryl donors, together with glycogen synthesis and lactate utilization, could contribute to the efficient energy metabolism found in A. naeslundii. Through this flexible and efficient metabolic capacity, A. naeslundii can adapt to fluctuating environments and compete with other bacteria in dental plaque. Further, this bacterium may modify the dental plaque environment and promote the microbial population shifts in dental plaque.

NAD-independent lactate and butyryl-CoA dehydrogenases of Clostridium acetobutylicum P262.

Clostridium acetobutylicum P262 cells that were growing on lactate and acetate had an NAD-independent lactate dehydrogenase(iLDH) activity of 200 nmol mg protein-1 min-1. Ammonium sulfate precipitation and DEAE cellulose caused a 35-fold purification. Gel filtration indicated that the iLDH had a molecular weight of approximately 55 kDa, but two bands were always observed. Phenyl sepharose could not separate the two proteins, and hydroxyapatite caused a complete loss of activity. The semi-purified iLDH had a Vmax of 13,000 nmol mg protein-1 min-1 and a Km value of 3.5 mM for D-lactate. The Vmax and Km values for L-lactate were 300 nmol mg protein-1 min-1 and 0.7 mM. The iLDH had a pH optimum of 7.5, was not activated by fructose-1,6-bisphosphate (FDP), and could be coupled to either 3-(4,5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide (MTT) or dichlorophenol-indophenol (DCPIP), but not methyl viologen (MV) or benzyl viologen (BV). The iLDH did not have strong absorbance between 500 and 300 nm, and trichloroacetic acid or acid ammonium sulfate extracts had virtually no fluorescence at 450 nm. The crude extracts also had MTT-linked butyryl-CoA dehydrogenase activity (60 nmol mg protein-1 min-1). The NAD-independent butyryl-CoA dehydrogenase eluted from DEAE-cellulose as two fractions. The yellow fraction was extremely unstable, but the green fraction could be stored for short periods of time at 5 degrees C. The green-colored butyryl-CoA dehydrogenase had strong absorption at 450 nm, and gel filtration indicated that it had a molecular weight of 90 kDa. The NAD-independent butyryl-CoA dehydrogenase could be coupled to MTT, DCPIP, or MV, but not BV. Because the NAD-independent lactate and butyryl-CoA dehydrogenase could both be linked to low potential carriers, these two enzymes may function as oxidation-reduction system in vivo.

Catabolic pathway for aerobic degradation of lactate by Actinomyces naeslundii.

The aerobic metabolism of lactate by oral Actinomyces was studied. Six of 7 strains of Actinomyces naeslundii increased their growth in the presence of lactate under aerobic conditions. Washed cells grown on lactate aerobically degraded lactate and pyruvate to acetate with a concomitant consumption of oxygen. In the presence of catalase, the molar ratios of oxygen consumed to acetate produced were 1 for lactate degradation and 0.5 for pyruvate degradation. The enzymatic activities found in cell extracts revealed that lactate could be converted to pyruvate by NAD-independent lactate dehydrogenase (iLDH) and further to acetyl CoA by pyruvate dehydrogenase (PDH). The acetyl CoA formed could be metabolized into acetate by phosphotransacetylase (PTA) and acetate kinase (AK) with the formation of ATP. These results indicate that A. naeslundii metabolizes lactate into acetate by the sequential enzymatic reactions iLDH, PDH, PTA and AK and that hydrogens produced by iLDH and PDH are transferred to oxygen. The activity of lactate degradation and oxygen consumption may modify the environmental conditions of dental plaque.

The role of an NAD-independent lactate dehydrogenase and acetate in the utilization of lactate by Clostridium acetobutylicum strain P262

The role of an NAD-independent lactate dehydrogenase and acetate in the utilization of lactate by Clostridium acetobutylicum strain P262