alpha-Ketoglutarate dehydrogenase mutant of Rhizobium meliloti

Melatonin protects against diclofenac induced oxidative stress mediated myocardial toxicity in rats: A mechanistic insight

Diclofenac, a traditional non-steroidal anti-inflammatory drug, is commonly used for treating chronic pain and inflammation. Recently, a number of articles have highlighted the toxicities associated with diclofenac. The current study explores the molecular mechanism of diclofenac induced cardiac toxicity following oxidative stress. Diclofenac inhibits catalase, disrupts the redox balance in cardiac tissue, accelerates the monoamine oxidase induced hydroperoxide generation and eventually inhibits crucial mitochondrial enzyme, viz., aldehyde dehydrogenase, thereby causing myocardial injury. Melatonin, the pineal indoleamine with high antioxidative efficacy, is well known for its cardio-protective properties and its dietary consumption has profound impact on cardiac health. The present study demonstrates perhaps for the first time, that apart from ameliorating oxidative load in the cardiac tissue, melatonin also attenuates the inhibition of catalase and aldehyde dehydrogenase, and prevents stress mediated stimulation of monoamine oxidase. Moreover, favourable binding of diclofenac with melatonin may protect the myocardium from the deleterious effects of this drug. The results indicate toward a novel mechanism of protection by melatonin, having future therapeutic relevance.

RNA-Seq Provides New Insights into the Gene Expression Changes in Azoarcus olearius BH72 under Nitrogen-Deficient and Replete Conditions beyond the Nitrogen Fixation Process

Azoarcus olearius BH72 is an endophyte capable of biological nitrogen fixation (BNF) and of supplying nitrogen to its host plant. Our previous microarray approach provided insights into the transcriptome of strain BH72 under N₂-fixation in comparison to ammonium-grown conditions, which already indicated the induction of genes not related to the BNF process. Due to the known limitations of the technique, we might have missed additional differentially expressed genes (DEGs). Thus, we used directional RNA-Seq to better comprehend the transcriptional landscape under these growth conditions. RNA-Seq detected almost 24% of the annotated genes to be regulated, twice the amount identified by microarray. In addition to confirming entire regulated operons containing known DEGs, the new approach detected the induction of genes involved in carbon metabolism and flagellar and twitching motility. This may support N₂-fixation by increasing energy production and by finding suitable microaerobic niches. On the other hand, energy expenditures were reduced by suppressing translation and vitamin biosynthesis. Nonetheless, strain BH72 does not appear to be content with N₂-fixation but is primed for alternative economic N-sources, such as nitrate, urea or amino acids; a strong gene induction of machineries for their uptake and assimilation was detected. RNA-Seq has thus provided a better understanding of a lifestyle under limiting nitrogen sources by elucidating hitherto unknown regulated processes.

Grape seed flour (GSF) extends longevity by improving multi-organ dysfunction and age-associated oxidative stress and inflammation in healthy rat

According to the free radical theory of aging, accumulation of reactive oxygen species (ROS) within mitochondria throughout lifespan leads to impairment of the main biological macromolecules as DNA, lipids and proteins, which might be at the basis of premature aging. One way to test experimentally such a hypothesis consists in intervention studies using antioxidant nutrients aimed at limiting or inhibiting ROS production that should be able to reduce the aging rate and disease pathogenesis. Grape seed flour (GSF) contains high level of phytochemicals among which bioactive polyphenols exhibit numerous biological properties and beneficial health effects as antioxidant, anti-inflammatory, anti-carcinogenic, multi-organ (heart, liver, kidney, and brain among others) protective. The present study aimed at testing the ability of high dosing GSF (4 g/kg bw) used as a nutritional supplement to slow down aging and prolong lifespan of Wistar rats when administered from early life (one month-old animals) till their natural death. Data clearly show that high dose GSF extends organism longevity and healthspan by improving multi-organ damages, systemic fuelling metabolism declines, and alleviated oxidative stress and inflammation in aging rats. Our data support the extending longevity effect of grape polyphenols especially when used as high dosing nutritional supplement or as natural medicine whose appropriate galenic form as solid lipid nanoformulation, is currently under investigation.

Oleic acid as a restorative agent in alleviating adrenaline induced altered morphofunctional milieu of gastric tissue and mitochondria

The role of oleic acid as a protective antioxidant has recently been recognized. The present study is aimed to explore whether oleic acid can afford protection to rat gastric tissue when challenged with adrenaline. Sixty adult healthy male albino rats were divided into 10 groups comprising of 6 animals each. First group constituted the control. Rats of the second group were injected sub-cutaneously with adrenaline bitartrate at the dose of 0.3mg/kg body weight, every day for a period of 17 days. Rats of the third, to the sixth groups were orally fed with different doses of oleic acid (2.5, 5, 10, 20 mg/kg body weight/day) respectively. The rats of seventh to tenth groups were orally fed with doses of oleic acid as mentioned above and subsequently injected with adrenaline bitartrate at 0.3mg/kg body weight sub-cutaneously. After the treatment period, the animals were euthanized through cervical dislocation following light ether anaesthesia and gastric tissues were collected for morphological and biochemical studies. Subcutaneously administered pharmacological dose of adrenaline bitartrate caused oxidative stress inducing gastric lesion in male albino rats as evident from the altered levels of biomarkers of oxidative stress, activities of antioxidant and mitochondrial enzymes related to energy metabolism with changes in tissue morphology. Pre-treatment of rats with oleic acid dose-dependently protected against these gastric injuries induced by adrenaline indicating the potentiality of oleic acid in protecting against adrenaline induced gastric injury in male albino rats where antioxidant mechanisms appear to play a pivotal role in mediating such protection.

Okra Modulates Regulatory Enzymes and Metabolites of Glucose-Utilizing Pathways in Diabetic Rats

OBJECTIVE

Using a rat diabetes model, the authors examined how substrates and products of glycolysis and key regulatory enzymes for glycolysis, gluconeogenesis, Kreb's cycle, and glycogen metabolism react to treatment with okra diet therapy, relative to glibenclamide treatment.

METHOD

The animal grouping involved normoglycemic rats, untreated diabetic rats, and diabetic rats treated with glibenclamide, 50% w/w okra sauce, exclusive okra sauce diet, or sauce without okra. Alloxan monohydrate was the diabetogenic agent. Insulin and adiponectin were assayed with enzyme-linked immunosorbent assay (ELISA) while the metabolites and enzymes were assed using standard spectrophotometric methods.

RESULTS

The exclusive diet therapy significantly (p < 0.05) improved insulin activities after 60 days and reversed the altered adiponectin activities. Glucose-6-phosphate, fructose-6-phosphate, and fructose-1,6-bisphosphate levels were depleted during diabetes, but phosphoenolpyruvate and pyruvate accumulated during the first short phase of diabetes. Rats in the glibenclamide and 100% okra diet groups showed comparable hexokinase, phosphofructokinase, and pyruvate kinase activities relative to the normoglycemic rats, while the gluconeogenic enzymes, glucose-6-phosphatase, and fructose-1,6-bisphosphatase remained altered. The authors observed that extended treatment with glibenclamide restored the activities of all the Kreb's cycle enzymes, while succinate dehydrogenase and α-ketoglutarate dehydrogenase were nonresponsive to the okra diet therapy relative to their control levels. The glycogen stores were normalized by the exclusive diet therapy, but glycogen synthase and phosphorylase activities were unresponsive.

CONCLUSIONS

Okra diet has shown insulin-sensitizing potentials with prolonged intake during diabetes as well as the potential to reverse alterations in the major carbohydrate-metabolizing enzyme.

Activation of SIRT1/PGC 1α/SIRT3 pathway by melatonin provides protection against mitochondrial dysfunction in isoproterenol induced myocardial injury

AIMS

Preventing mitochondrial dysfunction and enhancing mitochondrial health and biogenesis is a crucial therapeutic approach to ameliorate injury following acute myocardial infarction. Although the antioxidant role of melatonin against ischemia/reperfusion injury has been reported, the exact mechanism of protection, in vivo, remains poorly understood. This study aims to identify and elaborate upon mechanism of melatonin protection of rat cardiac mitochondria against acute myocardial infarction.

MAIN METHODS

Rats were pre-treated with melatonin (10 mg/kg body weight (b.w.); intraperitoneally, i.p.) before isoproterenol bitartrate (ISO) administration (25 mg/kg body weight (b.w.) subcutaneously,s.c.) and their effect on rat heart mitochondrial structure and function was studied. Biochemical changes in activity of biomarkers of oxidative stress, antioxidant enzymes as well as Krebs' cycle enzymes were analyzed. Gene expression studies and Isothermal titration calorimetric studies with pure catalase and ISO were also carried out.

KEY FINDINGS

Melatonin was shown to reduce ISO induced oxidative stress, by stimulating superoxide dismutase activity and removing the inhibition of Krebs' cycle enzymes. Herein we report for the first time in rat model that melatonin activates the SIRT1-PGC-1α-SIRT3 signaling pathways after ISO administration, which ultimately induces mitochondrial biogenesis. Melatonin exhibited significant protection of mitochondrial architecture and topology along with increased calcium ion permeability and reactive oxygen species (ROS) generation induced by ISO. Isothermal calorimetric studies revealed that melatonin binds to ISO molecules and sequesters them from the reaction thereby limiting their interaction with catalase along with occupying the binding sites of catalase themselves.

SIGNIFICANCE

Activation of SIRT1-PGC-1α-SIRT3 pathway by melatonin along with its biophysical properties prevents ISO induced mitochondrial injury in rat heart.

Attenuation of arsenic induced high fat diet exacerbated oxidative stress mediated hepatic and cardiac injuries in male Wistar rats by piperine involved antioxidative mechanisms

The current study explored the efficacy of piperine in attenuating arsenic induced high fat diet aggravated oxidative stress mediated injury in hepatic and cardiac tissues of male Wistar rats. Oral administration of piperine significantly (p < 0.05) reduced the levels of organ specific and oxidative stress biomarkers in arsenic and high fat diet treated rat hepatic and cardiac tissues in a dose dependant manner with the dose of 60 mg/kg b.w. exhibiting maximum protection. Arsenic induced high fat diet aggravated oxidative stress mediated damages in liver and heart tissues led to decreased activities of antioxidant enzymes, ROS generation, diminished activities of Krebs' cycle and respiratory chain enzymes, collapsed mitochondrial membrane potential, mitochondrial DNA damage along with altered lipid metabolism and inflammatory cytokine levels. Histochemical and histopathological studies supported the above findings. Piperine efficiently counteracted the arsenic induced high fat diet aggravated oxidative stress mediated damages by modulating antioxidant defense mechanism along with free radical quenching ability. These findings indicate that piperine protected the arsenic induced high fat diet aggravated hepatic and cardiac injuries which underline the importance of piperine in providing a possible therapeutic regime for the amelioration of arsenic-induced high fat diet aggravated oxidative stress mediated organ damages.

Beta-estradiol protects against copper-ascorbate induced oxidative damage in goat liver mitochondria in vitro by binding with ascorbic acid

AIMS

β-Estradiol (β-E), one of the chemical forms of female gonad hormone exhibited antioxidant efficacy in biochemical system, in vitro. The aim of the study was to investigate whether any other mechanism of protection by β-E to hepatic mitochondria in presence of stressor agent i.e.,a combination of Cu²⁺ and ascorbic acid is involved.

MAIN METHODS

Freshly prepared goat liver mitochondria was incubated with stressors and 1 μM β-E and post incubated with the same concentration at 37 °C at pH 7.4. Mitochondrial viability, biomarkers of oxidative stress, activities of Krebs cycle enzymes, mitochondrial membrane potential, Ca²⁺ permeability were measured. Mitochondrial morphology and binding pattern of β-E with stressors were also studied.

KEY FINDINGS

Upon incubation of mitochondria with Cu, ascorbic acid and their combination there is a significant decline in activities of four of Krebs cycle enzymes in an uncompetitive manner with a concomitant increase in Ca²⁺ permeability and membrane potential of inner mitochondrial membrane, which is withdrawn during co-incubation with β-E, but was not reversed during post incubation with the β-E. The final studies on mitochondrial membrane morphology using scanning electron microscope also exhibited damage. Isothermal titration calorimetry data also showed the negative heat change in the mixture of β-E with ascorbic acid and also its combination with Cu²⁺.

SIGNIFICANCE

Our results for the first time demonstrated that β-E protects againstCu²⁺-ascorbate induced oxidative stress by binding with ascorbic acid. The new mechanism of binding of β-E with stress agents may have a future therapeutic relevance.

Metabolic Analyses of Nitrogen Fixation in the Soybean Microsymbiont Sinorhizobium fredii Using Constraint-Based Modeling

Nitrogen is the most limiting macronutrient for plant growth, and rhizobia are important bacteria for agriculture because they can fix atmospheric nitrogen and make it available to legumes through the establishment of a symbiotic relationship with their host plants. In this work, we studied the nitrogen fixation process in the microsymbiont Sinorhizobium fredii at the genome level. A metabolic model was built using genome annotation and literature to reconstruct the symbiotic form of S. fredii. Genes controlling the nitrogen fixation process were identified by simulating gene knockouts. Additionally, the nitrogen-fixing capacities of S. fredii CCBAU45436 in symbiosis with cultivated and wild soybeans were evaluated. The predictions suggested an outperformance of S. fredii with cultivated soybean, consistent with published experimental evidence. The reconstruction presented here will help to understand and improve nitrogen fixation capabilities of S. fredii and will be beneficial for agriculture by reducing the reliance on fertilizer applications.

Rhizobia are soil bacteria able to establish symbiosis with diverse host plants. Specifically, Sinorhizobium fredii is a soil bacterium that forms nitrogen-fixing root nodules in diverse legumes, including soybean. The strain S. fredii CCBAU45436 is a dominant sublineage of S. fredii that nodulates soybeans in alkaline-saline soils in the Huang-Huai-Hai Plain region of China. Here, we present a manually curated metabolic model of the symbiotic form of Sinorhizobium fredii CCBAU45436. A symbiosis reaction was defined to describe the specific soybean-microsymbiont association. The performance and quality of the reconstruction had a 70% score when assessed using a standardized genome-scale metabolic model test suite. The model was used to evaluate in silico single-gene knockouts to determine the genes controlling the nitrogen fixation process. One hundred forty-one of 541 genes (26%) were found to influence the symbiotic process, wherein 121 genes were predicted as essential and 20 others as having a partial effect. Transcriptomic profiles of CCBAU45436 were used to evaluate the nitrogen fixation capacity in cultivated versus in wild soybean inoculated with the microsymbiont. The model quantified the nitrogen fixation activities of the strain in these two hosts and predicted a higher nitrogen fixation capacity in cultivated soybean. Our results are consistent with published data demonstrating larger amounts of ureides and total nitrogen in cultivated soybean than in wild soybean. This work presents the first metabolic network reconstruction of S. fredii as an example of a useful tool for exploring the potential benefits of microsymbionts to sustainable agriculture and the ecosystem.

IMPORTANCE Nitrogen is the most limiting macronutrient for plant growth, and rhizobia are important bacteria for agriculture because they can fix atmospheric nitrogen and make it available to legumes through the establishment of a symbiotic relationship with their host plants. In this work, we studied the nitrogen fixation process in the microsymbiont Sinorhizobium fredii at the genome level. A metabolic model was built using genome annotation and literature to reconstruct the symbiotic form of S. fredii. Genes controlling the nitrogen fixation process were identified by simulating gene knockouts. Additionally, the nitrogen-fixing capacities of S. fredii CCBAU45436 in symbiosis with cultivated and wild soybeans were evaluated. The predictions suggested an outperformance of S. fredii with cultivated soybean, consistent with published experimental evidence. The reconstruction presented here will help to understand and improve nitrogen fixation capabilities of S. fredii and will be beneficial for agriculture by reducing the reliance on fertilizer applications.

Oleic acid protects against cadmium induced cardiac and hepatic tissue injury in male Wistar rats: A mechanistic study

AIMS

The aim of the present study was to evaluate the possible antioxidant role of oleic acid (OA) against Cd-induced injuries in the heart and liver tissues of male Wistar rats.

MAIN METHODS

Rats were treated with either vehicle (control), or OA (10 mg/kg b.w., fed orally), or Cd (0.44 mg/kg b.w., s.c.), or both (OA + Cd) for 15 days. Following completion of the treatment period, biomarkers of organ damage and oxidative stress including ROS, activities of antioxidant enzymes and their level, activities of Krebs cycle enzymes and respiratory chain enzymes were measured. Levels of interleukins (IL-1β, IL-6, IL-10), tumor necrosis factor (TNF-α) and nuclear factor kappa B (NFκB) were estimated to evaluate the state of inflammation. In addition, changes in mitochondrial membrane potential and status of cytochrome c (Cyt c) were also studied.

KEY FINDINGS

Pre-treatment of rats with OA significantly protected against Cd-induced detrimental changes possibly by decreasing endogenous ROS through regulation of antioxidant defense system, inflammatory responses and activities of metabolic enzymes. Moreover, OA was also found to restore mitochondrial membrane potential possibly by regulating Cyt c leakage thereby increasing mitochondrial viability.

SIGNIFICANCE

Our results for the first time demonstrated systematically that OA provided protection against Cd-induced oxidative stress mediated injuries in rat heart and liver tissues through its antioxidant mechanism. The results raise the possibility of using OA singly or in combination with other antioxidants or diet in the treatment of situations arising due to oxidative stress and may have future therapeutic relevance.

Gallic acid protects rat liver mitochondria ex vivo from bisphenol A induced oxidative stress mediated damages

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Bisphenol A induces oxidative stress mediated liver mitochondrial damage.

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Bisphenol A induced damage is being protected when mitochondria are co-incubated with gallic acid.

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Scanning electron microscopy of mitochondrial tomography supports the biochemical observations.

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Gallic acid may be used as future remedial measure for the protection of bisphenol A induced damages of liver mitochondria.

Humans are often exposed to bisphenol A (BPA), the monomer of polycarbonate plastics and epoxy resins, through BPA contaminated drinking water, beverages and foods, packaged in polycarbonate plastic bottles and cans coated with epoxy resins due to leaching. Several research groups have reported that BPA may cause damage of mitochondria in liver, kidney, heart and brain cells by inducing oxidative stress. The antioxidant efficacy of gallic acid (GA), a polyphenol compound obtained from plants, against different toxicants induced oxidative stress has been well established. The aim of the present study was to examine the protective efficacy of GA against BPA induced oxidative damages of the rat liver mitochondria ex vivo. In our study, we have found a significant decrease in the intactness of mitochondria; a significant increase (P ≤ 0.001) in the levels of lipid peroxidation end product (i.e. malondialdehyde) and protein carbonylation product; and also a significant decrease (P ≤ 0.001) in the reduced glutathione content; when mitochondria were incubated with BPA (160 μM/ml) only. These results indicate that BPA probably causes damage to the cellular macromolecules through oxidative stress. We have observed significant counteractions (P ≤ 0.001) against BPA induced alterations in mitochondrial intactness, lipid peroxidation and protein carbonylation products formation and reduced glutathione content when mitochondria were incubated with BPA and GA (20 μg/ml/ 40 μg/ml/ 80 μg/ml) in combination in a dose-dependent manner. Gallic acid also showed significant restorations (P ≤ 0.001) of the activities of antioxidant enzymes, Krebs cycle enzymes, respiratory chain enzymes and thiolase when mitochondria were incubated with BPA and dosage of GA (20 μg/ml/ 40 μg/ml/ 80 μg/ml) in combination compared to BPA incubated mitochondria. Furthermore, GA significantly (P ≤ 0.001) counteracted the BPA induced decrease in tryptophan and NADH auto-fluroscence levels in mitochondria. This result suggests that GA protects the mitochondria probably by reducing the oxidative stress. Besides, GA protects the mitochondrial surface from BPA induced oxidative damages as viewed under the scanning electron microscope. Considering all the results, it can be concluded that GA shows potent efficacy in protecting the rat liver mitochondria ex vivo from BPA induced oxidative stress mediated damages.

Glucose and arabinose dependent mineral phosphate solubilization and its succinate-mediated catabolite repression in Rhizobium sp. RM and RS

Rhizobium sp. RM and RS are Vigna radiata root nodule isolates with the ability to solubilize tricalcium phosphate and rock phosphate under 50 mM Tris-Cl buffering conditions. Rhizobium sp. RM and RS were unique as they could produce two different organic acids, gluconic acid and oxalic acid using glucose and arabinose, respectively, which are two of the most prominent sugars present in the rhizospheric soil. However, P solubilization in these isolates was repressed in the presence of succinate resembling the phenomenon of catabolite repression. RM and RS produced 24 mM and 20 mM gluconic acid in presence of glucose which was repressed to 10 mM and 8 mM, respectively, in glucose + succinate conditions. Similarly, RM and RS produced 28 mM and 23 mM oxalic acid in arabinose containing media which was repressed to 9 mM and 8 mM, respectively, in the presence of arabinose + succinate. Results of enzyme activities indicated 66% repression of quinoprotein glucose dehydrogenase in glucose + succinate compared to glucose grown cells and 84% repression of glyoxylate oxidase in arabinose + succinate compared to arabinose grown cells. This is perhaps the first report on mechanism of P solubilization in rhizobia through utilization of two different sugars, glucose and arabinose and its repression by succinate. Succinate-mediated catabolite repression of arabinose is the unique aspect of this study.

Aqueous bark extract of Terminalia arjuna protects against cadmium-induced hepatic and cardiac injuries in male Wistar rats through antioxidative mechanisms

Cadmium (Cd) is one of the most ubiquitous toxic heavy metal in the environment. The present study was conducted to evaluate the protective role of aqueous bark extract of Terminalia arjuna (TA) against Cd induced oxidative damage in hepatic and cardiac tissues as the TA bark extract has folkloric medicinal use in the treatment of various hepatic and cardiac disorders. Male Wistar rats were divided into 4 groups. The control group was treated with normal saline as the vehicle; the second group orally administered with TA (20 mg/kg bw) daily for 15 days; the third group injected with Cd-acetate (0.44 mg/kg bw, s.c.) every alternate day for a period of 15 days; and the fourth group was administered with TA, 60 min prior to Cd treatment. The biomarkers of organ damage were significantly increased in the Cd treated groups. Besides, a significant alteration in the tissue levels of biomarkers of oxidative stress, the activities and the levels of antioxidant enzymes was observed following treatment with Cd. Additionally, some of the enzymes were found to be inhibited uncompetitively by Cd when tested in an in vitro system. Furthermore, evidence gathered from studies on the histological parameters and mitochondrial membrane potential in both the tissues argue in favour of the possible protective role of TA against Cd induced damage. Finally, gas chromatography-mass spectrometry revealed the presence of eight major bioactive phytochemicals in aqueous bark extract of TA having potent free radical scavenging property. The results indicate that the extract could protect hepatic and cardiac tissues against Cd-induced oxidative stress mediated damages through antioxidant mechanism(s).

Low molecular weight galactomannans-based standardized fenugreek seed extract ameliorates high-fat diet-induced obesity in mice via modulation of FASn, IL-6, leptin, and TRIP-Br2

Background: Obesity is a complex, chronic metabolic disorder and its prevalence is increasing throughout most of the world. Low molecular weight galactomannans-based standardized fenugreek seed extract (LMWGAL-TF) has previously shown anti-diabetic and anti-hyperlipidemic potential. Aim: To evaluate the efficacy and mechanism of action of LMWGAL-TF in treating high fat diet (HFD)-induced obesity and hyperlipidemia in mice. Materials and methods: Male C57BL/6 mice were fed the HFD for 12 weeks and were co-administered with LMWGAL-TF (10, 30 and 100 mg kg-1, p.o.). Variables measured were behavioral, biochemical, molecular and histopathological. In a separate in vitro experiment, copper-ascorbate (Cu-As)-induced mitochondrial oxidative damage was evaluated. Results: The HFD-induced increase (p < 0.001) in body weight, fat mass, lean mass, adipose tissue (brown, mesenteric, epididymal and retroperitoneal) and liver weight was significantly attenuated (p < 0.001) by LMWGAL-TF (30 and 100 mg kg-1). The HFD-induced elevated levels of serum lipid, interleukins (ILs)-6 and leptin were significantly decreased (p < 0.001) by LMWGAL-TF (30 and 100 mg kg-1). Elevated fatty acid synthase (FASn), IL-6, leptin and transcriptional regulator interacting with the PHD-bromodomain 2 (TRIP-Br2) mRNA expression in brown adipose tissue (BAT), liver, and epididymal fat were significantly down-regulated (p < 0.001) by LMWGAL-TF (30 and 100 mg kg-1). Additionally, HFD-induced histological alterations in skeletal muscle, liver, white adipose tissue (WAT) and BAT were also reduced by LMWGAL-TF. Furthermore, the Cu-As-induced alteration in mitochondria oxidative stress (lipid peroxidation, protein carbonylation, glutathione, glutathione reductase, glutathione peroxidase, isocitrate dehydrogenase and α-ketoglutarate dehydrogenase) in skeletal muscle and BAT was significantly (p < 0.001) ameliorated by LMWGAL-TF (2, 4 and 6 mg mL-1) treatment. It also reduced the Cu-As-induced mitochondrial swelling. Conclusion: LMWGAL-TF showed its beneficial effect in reducing HFD-induced obesity via down-regulation of FASn, IL-6, leptin, and TRIP-Br2 in mice.

Safety evaluation, anti-oxidative and anti-inflammatory effects of subchronically dietary supplemented high dosing grape seed powder (GSP) to healthy rat

Grape seed powder (GSP) contains high amount of bioactive polyphenols usually used as nutritional supplement or food preservatives due to their antioxidant and scavenging properties. The purpose of the present work was to evaluate the safety of increasing dosage GSP (w/w) of 0.5%, 5%, 10% and 20% corresponding to 0.4, 4, 8 and 16 g/kg bw respectively, when administered sub-chronically to Wistar rats in a 2 month-repeated dosing oral toxicity trial. Overally GSP had no effect on food intake, decreased body weight gain without affecting brain, liver, heart or kidney relative weight. GSP did not alter haematology except an increase in platelets, slightly decreased plasma transaminases, creatinine, urea and xanthine oxidase activity, without affecting uricemia, glycemia, triglyceridemia and cholesterolemia. GSP did not affect intracellular mediators as calcium, free iron or H₂O₂, but exerted real anti-oxidative properties in the four selected organs as assessed by lower lipoperoxidation and carbonylation, higher non protein thiols and antioxidant enzyme activities as CAT, GPx and SOD. Besides GSP exerted anti-inflammatory properties as supported by lower plasma IL17 A and CRP and higher IL10 and adiponectin. Histopathologically GSP provoked the dilation of heart and kidney arterioles and increased the size of the hippocampal dentate gyrus reflecting higher neurogenesis as assessed by Ki-67 labeling. Under the experimental conditions of the current study, GSP appeared as highly safe even when administered at very high dosage and could find potential applications in a variety of biotic or abiotic stresses-induced multi-organ dysfunction.

Interaction and Regulation of Carbon, Nitrogen, and Phosphorus Metabolisms in Root Nodules of Legumes

Members of the plant family Leguminosae (Fabaceae) are unique in that they have evolved a symbiotic relationship with rhizobia (a group of soil bacteria that can fix atmospheric nitrogen). Rhizobia infect and form root nodules on their specific host plants before differentiating into bacteroids, the symbiotic form of rhizobia. This complex relationship involves the supply of C₄-dicarboxylate and phosphate by the host plants to the microsymbionts that utilize them in the energy-intensive process of fixing atmospheric nitrogen into ammonium, which is in turn made available to the host plants as a source of nitrogen, a macronutrient for growth. Although nitrogen-fixing bacteroids are no longer growing, they are metabolically active. The symbiotic process is complex and tightly regulated by both the host plants and the bacteroids. The metabolic pathways of carbon, nitrogen, and phosphate are heavily regulated in the host plants, as they need to strike a fine balance between satisfying their own needs as well as those of the microsymbionts. A network of transporters for the various metabolites are responsible for the trafficking of these essential molecules between the two partners through the symbiosome membrane (plant-derived membrane surrounding the bacteroid), and these are in turn regulated by various transcription factors that control their expressions under different environmental conditions. Understanding this complex process of symbiotic nitrogen fixation is vital in promoting sustainable agriculture and enhancing soil fertility.

Melatonin protects against lipid-induced mitochondrial dysfunction in hepatocytes and inhibits stellate cell activation during hepatic fibrosis in mice

Lipid generates reactive oxygen species (ROS) in consequence to mitochondrial fission followed by inflammation in propagating hepatic fibrosis. The interaction of SIRT1/Mitofusin2 is critical for maintaining mitochondrial integrity and functioning, which is disrupted upon excess lipid infiltration during the progression of steatohepatitis. The complex interplay between hepatic stellate cells and steatotic hepatocytes is critically regulated by extracellular factors including increased circulating free fatty acids during fibrogenesis. Melatonin, a potent antioxidant, protects against lipid-mediated mitochondrial ROS generation. Lipotoxicity induces disruption of SIRT1 and Mitofusin2 interaction leading to mitochondrial morphological disintegration in hepatocytes. Further, fragmented mitochondria leads to mitochondrial permeability transition pore opening, cell cycle arrest and apoptosis and melatonin protects against all these lipotoxicity-mediated dysfunctions. These impaired mitochondrial dynamics also enhances the cellular glycolytic flux and reduces mitochondrial oxygen consumption rate that potentiates ROS production. High glycolytic flux generates metabolically unfavorable milieu in hepatocytes leading to inflammation, which is abrogated by melatonin. The melatonin-mediated protection against mitochondrial dysfunction was also observed in high-fat diet (HFD)-fed mice through restoration of enzymatic activities associated with respiratory chain and TCA cycle. Subsequently, melatonin reduces hepatic fat deposition and inflammation in HFD-fed mice. Thus, melatonin disrupts the interaction between steatotic hepatocyte and stellate cells, leading to the activation of the latter to abrogate collagen deposition. Altogether, the results of the current study document that the pharmacological intervention with low dose of melatonin could abrogate lipotoxicity-mediated hepatic stellate cell activation and prevent the fibrosis progression.

Organic acid mediated repression of sugar utilization in rhizobia

Rhizobia are a class of symbiotic diazotrophic bacteria which utilize C4 acids in preference to sugars and the sugar utilization is repressed as long as C4 acids are present. This can be manifested as a diauxie when rhizobia are grown in the presence of a sugar and a C4 acid together. Succinate, a C4 acid is known to repress utilization of sugars, sugar alcohols, hydrocarbons, etc by a mechanism termed as Succinate Mediated Catabolite Repression (SMCR). Mechanism of catabolite repression determines the hierarchy of carbon source utilization in bacteria. Though the mechanism of catabolite repression has been well studied in model organisms like E. coli, B. subtilis and Pseudomonas sp., mechanism of SMCR in rhizobia has not been well elucidated. C4 acid uptake is important for effective symbioses while mutation in the sugar transport and utilization genes does not affect symbioses. Deletion of hpr and sma0113 resulted in the partial relief of SMCR of utilization of galactosides like lactose, raffinose and maltose in the presence of succinate. However, no such regulators governing SMCR of glucoside utilization have been identified till date. Though rhizobia can utilize multitude of sugars, high affinity transporters for many sugars are yet to be identified. Identifying high affinity sugar transporters and studying the mechanism of catabolite repression in rhizobia is important to understand the level of regulation of SMCR and the key regulators involved in SMCR.

Cellular metabolic energy modulation by tangeretin in 7,12-dimethylbenz(a) anthracene-induced breast cancer

Breast cancer is the leading cause of death among women worldwide. Chemoprevention and chemotherapy play beneficial roles in reducing the incidence and mortality of cancer. Epidemiological and experimental studies showed that naturally-occurring antioxidants present in the diet may act as anticancer agents. Identifying the abnormalities of cellular energy metabolism facilitates early detection and management of breast cancer. The present study evaluated the effect of tangeretin on cellular metabolic energy fluxes in 7,12-dimethylbenz(a) anthracene (DMBA)-induced proliferative breast cancer. The results showed that the activities of glycolytic enzymes significantly increased in mammary tissues of DMBA-induced breast cancer bearing rats. The gluconeogenic tricarboxylic acid (TCA) cycle and respiratory chain enzyme activities significantly decreased in breast cancer-bearing rats. In addition, proliferating cell nuclear antigen (PCNA) was highly expressed in breast cancer tissues. However, the activities of glycolytic enzymes were significantly normalized in the tangeretin pre- and post-treated rats and the TCA cycle and respiratory chain enzyme activities were significantly increased in tangeretin treated rats. Furthermore, tangeretin down-regulated PCNA expression on breast cancer-bearing rats. Our study demonstrates that tangeretin specifically regulates cellular metabolic energy fluxes in DMBA-induced breast cancer-bearing rats.

Diallyl disulfide ameliorates isoproterenol induced cardiac hypertrophy activating mitochondrial biogenesis via eNOS-Nrf2-Tfam pathway in rats

The beneficial effect of garlic on cardiovascular disease is well known. However, the use of raw garlic against cardiac hypertrophy is not established. In the present study we explored whether raw garlic and its compound, diallyl disulfide (DADS) could inhibit hypertrophy through H₂S and/or mitochondrial biogenesis. Cardiac hypertrophy was induced in rat by giving isoproterenol at the dose of 5 mg/kg/day subcutaneously for 14 days through alzet minipump. Aqueous garlic homogenate, DADS and NaHS (liberate H₂S) were fed to third, forth and fifth group of rats for 14 days at a dose of 250 mg/kg/day, 50 mg/kg/day, 14 µM/kg/day respectively. Garlic and DADS reduced cardiac hypertrophy markers and normalized mitochondrial ETC-complex activities, mitochondrial enzyme activites and mitochondrial biogenetic and apoptotic genes expression. Garlic and DADS enhanced eNOS and p-AKT level in rat heart along with increased NRF2 protein level and Tfam gene expression. However, normalization was not observed after administration of NaHS which generates H₂S in-vivo. In conclusion, garlic and DADS induces mitochondrial biogenesis and ameliorates cardiac hypertrophy via activation of eNOS-Nrf2-Tfam pathway in rats.

Mechanisms of isoproterenol-induced cardiac mitochondrial damage: protective actions of melatonin

Mitochondrial dysfunction due to oxidative damage is the key feature of several diseases. We have earlier reported mitochondrial damage resulting from the generation of oxidative stress as a major pathophysiological effect of isoproterenol (ISO)-induced myocardial ischemia in rats. That melatonin is an antioxidant that ameliorates oxidative stress in experimental animals as well as in humans is well established. We previously demonstrated that melatonin provides cardioprotection against ISO-induced myocardial injury as a result of its antioxidant properties. The mechanism of ISO-induced cardiac mitochondrial damage and protection by melatonin, however, remains to be elucidated in vitro. In this study, we provide evidence that ISO causes dysfunction of isolated goat heart mitochondria. Incubation of cardiac mitochondria with increasing concentrations of ISO decreased mitochondrial succinate dehydrogenase (SDH) activity, which plays a pivotal role in mitochondrial bioenergetics, as well as altered the activities of other key enzymes of the Kreb's cycle and the respiratory chain. Co-incubation of ISO-challenged mitochondria with melatonin prevented the alterations in enzyme activity. That these changes in mitochondrial energy metabolism were due to the perpetration of oxidative stress by ISO was evident from the increased levels of lipid peroxidation and decreased reduced glutathione/oxidized glutathione ratio. ISO-induced oxidative stress also altered mitochondrial redox potential and brought about changes in the activity of the antioxidant enzymes manganese superoxide dismutase and glutathione peroxidase, eventually leading to alterations in total ATPase activity and membrane potential. Melatonin ameliorated these changes likely through its antioxidant abilities suggesting a possible mechanism of cardioprotection by this indole against ISO-induced myocardial injury.

Protective effect of antioxidant rich aqueous curry leaf (Murraya koenigii) extract against gastro-toxic effects of piroxicam in male Wistar rats

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Piroxicam causes gastric ulceration through oxidative stress.

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Curry leaf extract protects against piroxicam induced gastric injury.

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Antioxidant mechanism(s) are involved in such protection.

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The extract may have future therapeutic potential.

Piroxicam (chemically 4-hydroxy-2-methyl-N-2-pyridinyl-2H-1,2-benzothiazine-3-carboxamide), a classical non-steroidal anti-inflammatory drug (NSAID) is orally administered to arthritic patients. Inhibition of prostaglandin E₂ (PGE₂) synthesis and subsequent free hydroxyl radical generation in vivo exert gastro-toxic side effects on piroxicam treatment. Leaves of curry plant are rich in antioxidants with prolific free radical scavenging activities. This led us to investigate the efficiency of the use of curry leaves in ameliorating piroxicam induced gastric damage. Piroxicam was orally (30 mg per kg body weight) administered in male albino Wistar rats to generate gastric ulcers. These rats were orally fed with graded doses of aqueous extract of curry or Murraya koenigii leaves (Cu LE) prior to piroxicam administration. Oxidative stress biomarkers, activities of antioxidant and pro-oxidant enzymes, mucin content and nature, PGE₂ level, activities of mitochondrial enzymes and histomorphology of gastric tissues were studied. Piroxicam treatment altered all the above mentioned parameters whereas, curry leaf extract pre-treated animals were protected against piroxicam induced alterations. Hence, the protective action of the antioxidant rich Cu LE was investigated to propose a new combination therapy or dietary management to arthritic patients using piroxicam.

Physiology, genetics, and biochemistry of carbon metabolism in the alphaproteobacterium Sinorhizobium meliloti

A large proportion of genes within a genome encode proteins that play a role in metabolism. The Alphaproteobacteria are a ubiquitous group of bacteria that play a major role in a number of environments. For well over 50 years, carbon metabolism in Rhizobium has been studied at biochemical and genetic levels. Here, we review the pre- and post-genomics literature of the metabolism of the alphaproteobacterium Sinorhizobium meliloti. This review provides an overview of carbon metabolism that is useful to readers interested in this organism and to those working on other organisms that do not follow other model system paradigms.

A link between arabinose utilization and oxalotrophy in Bradyrhizobium japonicum

Rhizobia have a versatile catabolism that allows them to compete successfully with other microorganisms for nutrients in the soil and in the rhizosphere of their respective host plants. In this study, Bradyrhizobium japonicum USDA 110 was found to be able to utilize oxalate as the sole carbon source. A proteome analysis of cells grown in minimal medium containing arabinose suggested that oxalate oxidation extends the arabinose degradation branch via glycolaldehyde. A mutant of the key pathway genes oxc (for oxalyl-coenzyme A decarboxylase) and frc (for formyl-coenzyme A transferase) was constructed and shown to be (i) impaired in growth on arabinose and (ii) unable to grow on oxalate. Oxalate was detected in roots and, at elevated levels, in root nodules of four different B. japonicum host plants. Mixed-inoculation experiments with wild-type and oxc-frc mutant cells revealed that oxalotrophy might be a beneficial trait of B. japonicum at some stage during legume root nodule colonization.

What determines the efficiency of N(2)-fixing Rhizobium-legume symbioses?

Biological nitrogen fixation is vital to nutrient cycling in the biosphere and is the major route by which atmospheric dinitrogen (N(2)) is reduced to ammonia. The largest single contribution to biological N(2) fixation is carried out by rhizobia, which include a large group of both alpha and beta-proteobacteria, almost exclusively in association with legumes. Rhizobia must compete to infect roots of legumes and initiate a signaling dialog with host plants that leads to nodule formation. The most common form of infection involves the growth of rhizobia down infection threads which are laid down by the host plant. Legumes form either indeterminate or determinate types of nodules, with these groups differing widely in nodule morphology and often in the developmental program by which rhizobia form N(2) fixing bacteroids. In particular, indeterminate legumes from the inverted repeat-lacking clade (IRLC) (e.g., peas, vetch, alfalfa, medics) produce a cocktail of antimicrobial peptides which cause endoreduplication of the bacterial genome and force rhizobia into a nongrowing state. Bacteroids often become dependent on the plant for provision of key cofactors, such as homocitrate needed for nitrogenase activity or for branched chain amino acids. This has led to the suggestion that bacteroids at least from the IRLC can be considered as ammoniaplasts, where they are effectively facultative plant organelles. A low O(2) tension is critical both to induction of genes needed for N(2) fixation and to the subsequent exchange of nutrient between plants and bacteroids. To achieve high rates of N(2) fixation, the legume host and Rhizobium must be closely matched not only for infection, but for optimum development, nutrient exchange, and N(2) fixation. In this review, we consider the multiple steps of selection and bacteroid development and how these alter the overall efficiency of N(2) fixation.

Melatonin protects against isoproterenol-induced alterations in cardiac mitochondrial energy-metabolizing enzymes, apoptotic proteins, and assists in complete recovery from myocardial injury in rats

The present study was undertaken to explore the protective effect of melatonin against isoproterenol bitartrate (ISO)-induced rat myocardial injury and to test whether melatonin has a role in preventing myocardial injury and recovery when the ISO-induced stress is withdrawn. Treatment for rats with ISO altered the activities of some of the key mitochondrial enzymes related to energy metabolism, the levels of some stress proteins, and the proteins related to apoptosis. These changes were found to be ameliorated when the animals were pretreated with melatonin at a dose of 10 mg/kg BW, i.p. In addition to its ability to reduce ISO-induced mitochondrial dysfunction, we also studied the role of melatonin in the recovery of the cardiac tissue after ISO-induced damage. Continuation of melatonin treatment in rats after the withdrawal of ISO treatment was found to reduce the activities of cardiac injury biomarkers including serum glutamate oxaloacetate transaminase (SGOT), lactate dehydrogenase (LDH), and cardio-specific LDH1 to control levels. The levels of tissue lipid peroxidation and reduced glutathione were also brought back to that seen in control animals by continued melatonin treatment. Continuation of melatonin treatment in post-ISO treatment period was also found to improve cardiac tissue morphology and heart function. Thus, the findings indicate melatonin’s ability to provide cardio protection at a low pharmacological dose and its role in the recovery process. Melatonin, a molecule with very low or no toxicity may be considered as a therapeutic for the treatment for ischemic heart disease.

Inability to catabolize galactose leads to increased ability to compete for nodule occupancy in Sinorhizobium meliloti

A mutant unable to utilize galactose was isolated in Sinorhizobium meliloti strain Rm1021. The mutation was found to be in a gene annotated dgoK1, a putative 2-keto-3-deoxygalactonokinase. The genetic region was isolated on a complementing cosmid and subsequently characterized. Based on genetic and bioinformatic evidence, the locus encodes all five enzymes (galD, dgoK, dgoA, SMc00883, and ilvD1) involved in the De Ley-Doudoroff pathway for galactose catabolism. Although all five genes are present, genetic analysis suggests that the galactonase (SMc00883) and the dehydratase (ilvD1) are dispensable with respect to the ability to catabolize galactose. In addition, we show that the transport of galactose is partially facilitated by the arabinose transporter (AraABC) and that both glucose and galactose compete with arabinose for transport. Quantitative reverse transcription-PCR (qRT-PCR) data show that in a dgoK background, the galactose locus is constitutively expressed, and the induction of the ara locus seems to be enhanced. Assays of competition for nodule occupancy show that the inability to catabolize galactose is correlated with an increased ability to compete for nodule occupancy.

C(4)-dicarboxylate transport mutants of Rhizobium trifolii form ineffective nodules on Trifolium repens

Mutants of Rhizobium trifolii strain 7012 defective in C(4)-dicarboxylate transport were isolated by using a selective procedure based on pH indicator media. The mutant strains CR7098 and CR7099 failed to grow on or transport succinate, fumarate, or malate, but grew at wild-type rates on several other carbon sources. The C(4)-dicarboxylate transport system was inducible in strain 7012, but was expressed constitutively in four out of five succinate-positive revertants of strain CR7098. In the fifth CR7098 revertant (strain CR8008) the system was inducible. However, in contrast to strain 7012, strain CR8008 failed to use the C(4)-dicarboxylates in the presence of a second carbon source. Revertants of strain CR7099 were similar to strain 7012. Both strains CR7098 and CR7099 nodulated white and red clover at a rate similar to that of strain 7012, but nodules formed by the mutant strains were white and ineffective. Microscopic examination showed that the pattern of development of white clover nodules formed by strain CR7098 was similar to that observed with nodules formed by strain 7012, except that large amounts of starch accumulated in bacteroid-filled cells and senescence occurred earlier. Revertant strains were effective, except for strain CR8008, which formed ineffective nodules. The results show that a supply of C(4)-dicarboxylates to bacteroids is essential for nitrogen fixation in clover nodules. However, rhizobia within plant cells must also utilize other carbon sources to support growth and division.

Further examination of presumptive Rhizobium trifolii mutants that nodulate Glycine max

Two recent reports described the isolation of derivatives of a Rhizobium trifolii strain that had gained the ability to nodulate Glycine max and Vigna radiata and that had demonstrated altered patterns of carbon source utilization, free-living nitrogen fixation, and hydrogen uptake. More extensive characterization of these strains now supports the conclusion that these strains are R. japonicum and are not derived from the putative parent R. trifolii.

Optimization of L-malic acid production by Aspergillus flavus in a stirred fermentor

Effects of various nutritional and environmental factors on the accumulation of organic acids (mainly L-malic acid) by the filamentous fungus Aspergillus flavus were studied in a 16-L stirred fermentor. Improvement of the molar yield (moles acid produced per moles glucose consumed) of L-malic acid was obtained mainly by increasing the agitation rate (to 350 rpm) and the Fe(z+) ion concentration (to 12 mg/L) and by lowering the nitrogen (to 271 mg/L) and phosphate concentrations (to 1.5 mM) in the medium. These changes resulted in molar yields for L-malic acid and total C(4) acids (L-malic, succinic, and fumaric acids) of 128 and 155%, respectively. The high molar yields obtained (above 100%) are additional evidence for the operation of part of the reductive branch of the tricarboxylic acid cycle in L-malic acid accumulation by A. flavus. The fermentation conditions developed using the above mentioned factors and 9% CaCO(3) in the medium resulted in a high concentration (113 g/L L-malic acid from 120 g/L glucose utilized) and a high overall productivity (0.59 g/L h) of L-malic acid. These changes in acid accumulation coincide with increases in the activities of NAD(+)-malate dehydrogenase, fumarase, and citrate synthase.

Deletion of citrate synthase restores growth of Sinorhizobium meliloti 1021 aconitase mutants

The symbiotic nitrogen-fixing bacterium Sinorhizobium meliloti 1021 encodes only one predicted aconitase (AcnA) in its genome. AcnA has a significant degree of similarity with other bacterial aconitases that behave as dual proteins: enzymes and posttranscriptional regulators of gene expression. Similar to the case with these bacterial aconitases, AcnA activity was reversibly labile and was regained upon reconstitution with reduced iron. The aconitase promoter was active in root nodules. acnA mutants grew very poorly, had secondary mutations, and were quickly outgrown by pseudorevertants. The acnA gene was stably interrupted in a citrate synthase (gltA) null background, indicating that the intracellular accumulation of citrate may be deleterious for survival of strain 1021. No aconitase activity was detected in this mutant, suggesting that the acnA gene encodes the only functional aconitase of strain 1021. To uncover a function of AcnA beyond its catalytic role in the tricarboxylic acid cycle pathway, the gltA acnA double mutant was compared with the gltA single mutant for differences in motility, resistance to oxidative stress, nodulation, and growth on different substrates. However, no differences in any of these characteristics were found.

Effects of indole-3-acetic acid on Sinorhizobium meliloti survival and on symbiotic nitrogen fixation and stem dry weight production

We evaluated the effects of the main auxin phytohormone, indole-3-acetic acid (IAA), on the central metabolism of Sinorhizobium meliloti 1021. We either treated S. meliloti 1021 wild-type cells with 0.5 mM IAA, 1021+, or use a derivative, RD64, of the same strain harboring an additional pathway for IAA biosynthesis (converting tryptophan into IAA via indoleacetamide). We assayed the activity of tricarboxylic acid cycle (TCA) key enzymes and found that activity of citrate synthase and alpha-ketoglutarate dehydrogenase were increased in both 1021+ and RD64 as compared to the wild-type strain. We also showed that the intracellular acetyl-CoA content was enhanced in both RD64 and 1021+ strains when compared to the control strain. The activity of key enzymes, utilizing acetyl-CoA for poly-beta-hydroxybutyrate (PHB) biosynthesis, was also induced. The PHB level measured in these cells were significantly higher than that found in control cells. Moreover, 4-week-long survival experiments showed that 80% of 1021 cells died, whereas 50% of RD64 cells were viable. Medicago truncatula plants nodulated by RD64 (Mt-RD64) showed an induction of both acetylene reduction activity and stem dry weight production.

Functional characterization of the Sinorhizobium meliloti acetate metabolism genes aceA, SMc00767, and glcB

The genes encoding malate synthase (glcB) and isocitrate lyase (aceA) and a 240-bp open reading frame (SMc00767) located downstream of aceA were isolated and functionally characterized in Sinorhizobium meliloti. Independent and double interposon mutants of each gene were constructed, and the corresponding phenotypes were analyzed. aceA mutants failed to grow on acetate, and mutants deficient in SMc00767 were also affected in acetate utilization. In contrast, mutants deficient in glcB grew on acetate similar to wild-type strain Rm5000. Complementation experiments showed that aceA and SMc00767 gene constructs were able to restore the growth on acetate in the corresponding single mutants. aceA-glcB, aceA-SMc00767, and glcB-SMc00767 double knockouts were also unable to grow on acetate, but this ability was recovered when the wild-type aceA-glcB or aceA-SMc00767 loci were introduced into the double mutants. These data confirm the functional role of aceA and SMc00767 and show that glcB, in the absence of SMc00767, is required for acetate metabolism. Isocitrate lyase and malate synthase activities were measured in strain Rm5000, the mutant derivatives, and complemented strains. aceA and glcB were able to complement the enzymatic activity lacking in the corresponding single mutants. The enzymatic activities also showed that SMc00767 represses the activity of isocitrate lyase in cells grown on acetate. Gene fusions confirmed the repressor role of SMc00767, which regulates aceA expression at the transcriptional level. Comparison of the transcriptional profiles of the SMc00767 mutant and wild-type strain Rm5000 showed that SMc00767 represses the expression of a moderate number of open reading frames, including aceA; thus, we propose that SMc00767 is a novel repressor involved in acetate metabolism in S. meliloti. Genetic and functional analyses indicated that aceA and SMc00767 constitute a functional two-gene operon, which is conserved in other alpha-proteobacteria. Alfalfa plants infected with the aceA and glcB mutants were not impaired in nodulation or nitrogen fixation, and so the glyoxylate cycle is not required in the Rhizobium-legume symbiosis.

α-Ketoglutaric Semialdehyde Dehydrogenase Isozymes Involved in Metabolic Pathways of D-Glucarate, D-Galactarate, and Hydroxy-L-proline

Azospirillum brasilense possesses an alternative pathway of l-arabinose metabolism in which alpha-ketoglutaric semialdehyde (alphaKGSA) dehydrogenase (KGSADH) is involved in the last step, the conversion of alphaKGSA to alpha-ketoglutarate. In the preceding studies, we identified a set of metabolic genes of the l-arabinose pathway including the KGSADH gene (Watanabe, S., Kodaki, T., and Makino, K. (2006) J. Biol. Chem. 281, 2612-2623; Watanabe, S., Kodaki, T., and Makino, K. (2006) J. Biol. Chem. 281, 28876-28888; Watanabe, S., Shimada, N., Tajima, K., Kodaki, T., and Makino, K. (2006) J. Biol. Chem. 281, 33521-33536). Here, we describe that A. brasilense possesses two different KGSADH isozymes from l-arabinose-related enzyme (KGSADH-I); that is, d-glucarate/d-galactarate-inducible KGSADH-II and hydroxy-l-proline-inducible KGSADH-III. They were purified homogeneously from A. brasilense cells grown on d-galactarate or hydroxy-l-proline, respectively. When compared with KGSADH-I, amino acid sequences of KGSADH-II and KGSADH-III were significantly similar but not totally identical. Physiological characterization using recombinant enzymes revealed that KGSADH-II and KGSADH-III showed similar high substrate specificity for alphaKGSA and different coenzyme specificity; that is, NAD(+)-dependent KGSADH-II and NADP(+)-dependent KGSADH-III. In the phylogenetic tree of the aldehyde dehydrogenase (ALDH) superfamily, KGSADH-II and KGSADH-III were poorly related to the known ALDH subclasses including KGSADH-I. On the other hand, ALDH-like ycbD protein involved in d-glucarate/d-galactarate operon from Bacillus subtilis is closely related to the methylmalonyl semialdehyde dehydrogenase subclass but not A. brasilense KGSADH isozymes. To estimate the correct function, the corresponding gene was expressed, purified, and characterized. Kinetic analysis revealed the physiological role as NADP(+)-dependent KGSADH. We conclude that three different types of KGSADH appeared in the bacterial evolutional stage convergently. Furthermore, even the same pathway such as l-arabinose and d-glucarate/d-galactarate metabolism also evolved by the independent involvement of KGSADH.

Sinorhizobium meliloti pSymB carries genes necessary for arabinose transport and catabolism

Arabinose is a known component of plant cell walls and is found in the rhizosphere. In this work, a previously undeleted region of the megaplasmid pSymB was identified as encoding genes necessary for arabinose catabolism, by Tn5-B20 random mutagenesis and subsequent complementation. Transcription of this region was measured by beta-galactosidase assays of Tn5-B20 fusions, and shown to be strongly inducible by arabinose, and moderately so by galactose and seed exudate. Accumulation of [(3)H]arabinose in mutants and wild-type was measured, and the results suggested that this operon is necessary for arabinose transport. Although catabolite repression of the arabinose genes by succinate or glucose was not detected at the level of transcription, both glucose and galactose were found to inhibit accumulation of arabinose when present in excess. To determine if glucose was also taken up by the arabinose transport proteins, [(14)C]glucose uptake rates were measured in wild-type and arabinose mutant strains. No differences in glucose uptake rates were detected between wild-type and arabinose catabolism mutant strains, indicating that excess glucose did not compete with arabinose for transport by the same system. Arabinose mutants were tested for the ability to form nitrogen-fixing nodules on alfalfa, and to compete with the wild-type for nodule occupancy. Strains unable to utilize arabinose did not display any symbiotic defects, and were not found to be less competitive than wild-type for nodule occupancy in co-inoculation experiments. Moreover, the results suggest that other loci are required for arabinose catabolism, including a gene encoding arabinose dehydrogenase.

Identification and Characterization of l-Arabonate Dehydratase, l-2-Keto-3-deoxyarabonate Dehydratase, and l-Arabinolactonase Involved in an Alternative Pathway of l-Arabinose Metabolism

Azospirillum brasiliense possesses an alternative pathway of L-arabinose metabolism, different from the known bacterial and fungal pathways. In the preceding articles, we identified and characterized L-arabinose-1-dehydrogenase and alpha-ketoglutaric semialdehyde dehydrogenase, which catalyzes the first and final reaction steps in this pathway, respectively (Watanabe, S., Kodaki, T., and Makino, K. (2006) J. Biol. Chem. 281, 2612-2623 and Watanabe, S., Kodaki, T., and Makino, K. (2006) J. Biol. Chem. 281, 28876-28888). We here report the remaining three enzymes, L-arabonate dehydratase, L-2-keto-3-deoxyarabonate (L-KDA) dehydratase, and L-arabinolactonase. N-terminal amino acid sequences of L-arabonate dehydratase and L-KDA dehydratase purified from A. brasiliense cells corresponded to those of AraC and AraD genes, which form a single transcriptional unit together with the L-arabinose-1-dehydrogenase gene. Furthermore, the L-arabinolactonase gene (AraB) was also identified as a component of the gene cluster. Genetic characterization of the alternative L-arabinose pathway suggested a significant evolutional relationship with the known sugar metabolic pathways, including the Entner-Doudoroff (ED) pathway and the several modified versions. L-arabonate dehydratase belongs to the ILVD/EDD family and spectrophotometric and electron paramagnetic resonance analysis revealed it to contain a [4Fe-4S](2+) cluster. Site-directed mutagenesis identified three cysteine ligands essential for cluster coordination. L-KDA dehydratase was sequentially similar to DHDPS/NAL family proteins. D-2-Keto-3-deoxygluconate aldolase, a member of the DHDPS/NAL family, catalyzes the equivalent reaction to L-KDA aldolase involved in another alternative L-arabinose pathway, probably associating a unique evolutional event between the two alternative L-arabinose pathways by mutation(s) of a common ancestral enzyme. Site-directed mutagenesis revealed a unique catalytic amino acid residue in L-KDA dehydratase, which may be a candidate for such a natural mutation.

A Novel α-Ketoglutaric Semialdehyde Dehydrogenase

Azospirillum brasilense possesses an alternative pathway of l-arabinose metabolism, which is different from the known bacterial and fungal pathways. In a previous paper (Watanabe, S., Kodaki, T., and Makino, K. (2006) J. Biol. Chem. 281, 2612-2623), we identified and characterized l-arabinose 1-dehydrogenase, which catalyzes the first reaction step in this pathway, and we cloned the corresponding gene. Here we focused on the fifth enzyme, alpha-ketoglutaric semialdehyde (alphaKGSA) dehydrogenase, catalyzing the conversion of alphaKGSA to alpha-ketoglutarate. alphaKGSA dehydrogenase was purified tentatively as a NAD(+)-preferring aldehyde dehydrogenase (ALDH) with high activity for glutaraldehyde. The gene encoding this enzyme was cloned and shown to be located on the genome of A. brasilense separately from a gene cluster containing the l-arabinose 1-dehydrogenase gene, in contrast with Burkholderia thailandensis in which both genes are located in the same gene cluster. Higher catalytic efficiency of ALDH was found with alphaKGSA and succinic semialdehyde among the tested aldehyde substrates. In zymogram staining analysis with the cell-free extract, a single active band was found at the same position as the purified enzyme. Furthermore, a disruptant of the gene did not grow on l-arabinose. These results indicated that this ALDH gene was the only gene of the NAD(+)-preferring alphaKGSA dehydrogenase in A. brasilense. In the phylogenetic tree of the ALDH family, alphaKGSA dehydrogenase from A. brasilense falls into the succinic semialdehyde dehydrogenase (SSALDH) subfamily. Several putative alphaKGSA dehydrogenases from other bacteria belong to a different ALDH subfamily from SSALDH, suggesting strongly that their substrate specificities for alphaKGSA are acquired independently during the evolutionary stage. This is the first evidence of unique "convergent evolution" in the ALDH family.

Identification of the Missing Links in Prokaryotic Pentose Oxidation Pathways

The pentose metabolism of Archaea is largely unknown. Here, we have employed an integrated genomics approach including DNA microarray and proteomics analyses to elucidate the catabolic pathway for D-arabinose in Sulfolobus solfataricus. During growth on this sugar, a small set of genes appeared to be differentially expressed compared with growth on D-glucose. These genes were heterologously overexpressed in Escherichia coli, and the recombinant proteins were purified and biochemically studied. This showed that D-arabinose is oxidized to 2-oxoglutarate by the consecutive action of a number of previously uncharacterized enzymes, including a D-arabinose dehydrogenase, a D-arabinonate dehydratase, a novel 2-keto-3-deoxy-D-arabinonate dehydratase, and a 2,5-dioxopentanoate dehydrogenase. Promoter analysis of these genes revealed a palindromic sequence upstream of the TATA box, which is likely to be involved in their concerted transcriptional control. Integration of the obtained biochemical data with genomic context analysis strongly suggests the occurrence of pentose oxidation pathways in both Archaea and Bacteria, and predicts the involvement of additional enzyme components. Moreover, it revealed striking genetic similarities between the catabolic pathways for pentoses, hexaric acids, and hydroxyproline degradation, which support the theory of metabolic pathway genesis by enzyme recruitment.

Cloning, Expression, and Characterization of Bacterial l-Arabinose 1-Dehydrogenase Involved in an Alternative Pathway of l-Arabinose Metabolism

Azospirillum brasiliense converts L-arabinose to alpha-ketoglutarate via five hypothetical enzymatic steps. We purified and characterized L-arabinose 1-dehydrogenase (EC 1.1.1.46), catalyzing the conversion of L-arabinose to L-arabino-gamma-lactone as an enzyme responsible for the first step of this alternative pathway of L-arabinose metabolism. The purified enzyme preferred NADP+ to NAD+ as a coenzyme. Kinetic analysis revealed that the enzyme had high catalytic efficiency for both L-arabinose and D-galactose. The gene encoding L-arabinose 1-dehydrogenase was cloned using a partial peptide sequence of the purified enzyme and was overexpressed in Escherichia coli as a fully active enzyme. The enzyme consists of 308 amino acids and has a calculated molecular mass of 33,663.92 Da. The deduced amino acid sequence had some similarity to glucose-fructose oxidoreductase, D-xylose 1-dehydrogenase, and D-galactose 1-dehydrogenase. Site-directed mutagenesis revealed that the enzyme possesses unique catalytic amino acid residues. Northern blot analysis showed that this gene was induced by L-arabinose but not by D-galactose. Furthermore, a disruptant of the L-arabinose 1-dehydrogenase gene did not grow on L-arabinose but grew on D-galactose at the same growth rate as the wild-type strain. There was a partial gene for L-arabinose transport in the flanking region of the L-arabinose 1-dehydrogenase gene. These results indicated that the enzyme is involved in the metabolism of L-arabinose but not D-galactose. This is the first identification of a gene involved in an alternative pathway of L-arabinose metabolism in bacterium.

Insertion of transposon Tn5tac1 in the Sinorhizobium meliloti malate dehydrogenase (mdh) gene results in conditional polar effects on downstream TCA cycle genes

To isolate Sinorhizobium meliloti mutants deficient in malate dehydrogenase (MDH) activity, random transposon Tn5tac1 insertion mutants were screened for conditional lethal phenotypes on complex medium. Tn5tac1 has an outward-oriented isopropyl-beta-D-thiogalactopyranoside (IPTG)-inducible promoter (Ptac). The insertion in strain Rm30049 was mapped to the mdh gene, which was found to lie directly upstream of the genes encoding succinyl-CoA synthetase (sucCD) and 2-oxoglutarate dehydrogenase (sucAB and lpdA). Rm30049 required IPTG for wild-type growth in complex media, and had a complex growth phenotype in minimal media with different carbon sources. The mdh:: Tn5tacl insertion eliminated MDH activity under all growth conditions, and activities of succinyl-CoA synthetase, 2-oxoglutarate dehydrogenase, and succinate dehydrogenase were affected by the addition of IPTG. Reverse-transcriptase polymerase chain reaction (RT-PCR) studies confirmed that expression from Ptac was induced by IPTG and leaky in its absence. Alfalfa plants inoculated with Rm30049 were chlorotic and stunted, with small white root nodules, and had shoot dry weight and percent-N content values similar to those of uninoculated plants. Cosmid clone pDS15 restored MDH activity to Rm30049, complemented both the mutant growth and symbiotic phenotypes, and was found to carry six complete (sdhB, mdh, sucCDAB) and two partial (IpdA, sdhA) tricarboxylic acid cycle genes.

Microaerophilic bacteria transduce energy via oxidative metabolic gearing

Heterotrophic microaerophilic bacteria, a diverse and ubiquitous group, are specialized for growth in O2 limited environments. Until recently, microaerophilic bacteria have been grouped with obligate aerobic organisms whose metabolic rates slow in response to physiological O2 limitation. In contrast, microaerophilic bacteria are adapted to maintain essentially constant turnover of primary energy substrates in response to a wide range of physiological O2. This capacity, oxidative metabolic gearing, allows microaerophilic bacteria to maintain catabolic enzymes, substrates, and cofactors at high steady-state levels. Oxidative metabolic gearing is thus adaptive, as it allows microaerophilic bacteria to respond to changes in physiological O2 relatively rapidly when compared to aerobic, anaerobic, or facultative microorganisms.

Citrate synthase mutants of Sinorhizobium fredii USDA257 form ineffective nodules with aberrant ultrastructure

The tricarboxylic acid (TCA) cycle plays an important role in generating the energy required by bacteroids to fix atmospheric nitrogen. Citrate synthase is the first enzyme that controls the entry of carbon into the TCA cycle. We cloned and determined the nucleotide sequence of the gltA gene that encodes citrate synthase in Sinorhizobium fredii USDA257, a symbiont of soybeans (Glycine max [L.] Merr.) and several other legumes. The deduced citrate synthase protein has a molecular weight of 48,198 and exhibits sequence similarity to citrate synthases from several bacterial species, including Sinorhizobium meliloti and Rhizobium tropici. Southern blot analysis revealed that the fast-growing S. fredii strains and Rhizobium sp. strain NGR234 contained a single copy of the gene located in the bacterial chromosome. S. fredii USDA257 gltA mutant HBK-CS1, which had no detectable citrate synthase activity, had diminished nodulation capacity and produced ineffective nodules on soybean. Light and electron microscopy observations revealed that the nodules initiated by HBK-CS1 contained very few bacteroids. The infected cells contained large vacuoles and prominent starch grains. Within the vacuoles, membrane structures that appeared to be reminiscent of disintegrating bacteroids were detected. The citrate synthase mutant had altered cell surface characteristics and produced three times more exopolysaccarides than the wild type produced. A plasmid carrying the USDA257 gltA gene, when introduced into HBK-CS1, was able to restore all of the defects mentioned above. Our results demonstrate that a functional citrate synthase gene of S. fredii USDA257 is essential for efficient soybean nodulation and nitrogen fixation.

The glcB locus of Rhizobium leguminosarum VF39 encodes an arabinose-inducible malate synthase

In the course of a study conducted to isolate genes upregulated by plant cell wall sugars, we identified an arabinose-inducible locus from a transcriptional fusion library of Rhizobium leguminosarum VF39, carrying random insertions of the lacZ transposon Tn5B22. Sequence analysis of the locus disrupted by the transposon revealed a high similarity to uncharacterized malate synthase G genes from Sinorhizobium meliloti, Agrobacterium tumefaciens, and Mesorhizobium loti. This enzyme catalyzes the condensation of glyoxylate and acetyl-CoA to yield malate and CoA and is thought to be a component of the glyoxylate cycle, which allows microorganisms to grow on two carbon compounds. Enzyme assays showed that a functional malate synthase is encoded in the glcB gene of R. leguminosarum and that its expression is induced by arabinose, glycolate, and glyoxylate. An Escherichia coli aceB glcB mutant, complemented with the R. leguminosarum PCR-amplified gene, recovered malate synthase activity. A very similar genome organization of the loci containing malate synthase and flanking genes was observed in R. leguminosarum, S. meliloti, and A. tumefaciens. Pea plants inoculated with the glcB mutant or the wild-type strain showed no significant differences in nitrogen fixation. This is the first report regarding the characterization of a mutant in one of the glyoxylate cycle enzymes in the rhizobia.