Glutamate, Ornithine, Arginine, Proline, and Polyamine Metabolic Interactions: The Pathway Is Regulated at the Post-Transcriptional Level

The metabolism of glutamate into ornithine, arginine, proline, and polyamines is a major network of nitrogen-metabolizing pathways in plants, which also produces intermediates like nitric oxide, and γ-aminobutyric acid (GABA) that play critical roles in plant development and stress. While the accumulations of intermediates and the products of this network depend primarily on nitrogen assimilation, the overall regulation of the interacting sub-pathways is not well understood. We tested the hypothesis that diversion of ornithine into polyamine biosynthesis (by transgenic approach) not only plays a role in regulating its own biosynthesis from glutamate but also affects arginine and proline biosynthesis. Using two high putrescine producing lines of Arabidopsis thaliana (containing a transgenic mouse ornithine decarboxylase gene), we studied the: (1) effects of exogenous supply of carbon and nitrogen on polyamines and pools of soluble amino acids; and, (2) expression of genes encoding key enzymes in the interactive pathways of arginine, proline and GABA biosynthesis as well as the catabolism of polyamines. Our findings suggest that: (1) the overall conversion of glutamate to arginine and polyamines is enhanced by increased utilization of ornithine for polyamine biosynthesis by the transgene product; (2) proline and arginine biosynthesis are regulated independently of polyamines and GABA biosynthesis; (3) the expression of most genes (28 that were studied) that encode enzymes of the interacting sub-pathways of arginine and GABA biosynthesis does not change even though overall biosynthesis of Orn from glutamate is increased several fold; and (4) increased polyamine biosynthesis results in increased assimilation of both nitrogen and carbon by the cells

Associated bacteria affect sexual reproduction by altering gene expression and metabolic processes in a biofilm inhabiting diatom

Diatoms are unicellular algae with a fundamental role in global biogeochemical cycles as major primary producers at the base of aquatic food webs. In recent years, chemical communication between diatoms and associated bacteria has emerged as a key factor in diatom ecology, spurred by conceptual and technological advancements to study the mechanisms underlying these interactions. Here, we use a combination of physiological, transcriptomic, and metabolomic approaches to study the influence of naturally coexisting bacteria, Maribacter sp. and Roseovarius sp., on the sexual reproduction of the biofilm inhabiting marine pennate diatom Seminavis robusta. While Maribacter sp. severely reduces the reproductive success of S. robusta cultures, Roseovarius sp. slightly enhances it. Contrary to our expectation, we demonstrate that the effect of the bacterial exudates is not caused by altered cell-cycle regulation prior to the switch to meiosis. Instead, Maribacter sp. exudates cause a reduced production of diproline, the sexual attraction pheromone of S. robusta. Transcriptomic analyses show that this is likely an indirect consequence of altered intracellular metabolic fluxes in the diatom, especially those related to amino acid biosynthesis, oxidative stress response, and biosynthesis of defense molecules. This study provides the first insights into the influence of bacteria on diatom sexual reproduction and adds a new dimension to the complexity of a still understudied phenomenon in natural diatom populations

From A. rhizogenes RolD to Plant P5CS: Exploiting Proline to Control Plant Development

The capability of the soil bacterium Agrobacterium rhizogenes to reprogram plant development and induce adventitious hairy roots relies on the expression of a few root-inducing genes (rol A, B, C and D), which can be transferred from large virulence plasmids into the genome of susceptible plant cells. Contrary to rolA, B and C, which are present in all the virulent strains of A. rhizogenes and control hairy root formation by affecting auxin and cytokinin signalling, rolD appeared non-essential and not associated with plant hormones. Its role remained elusive until it was discovered that it codes for a proline synthesis enzyme. The finding that, in addition to its role in protein synthesis and stress adaptation, proline is also involved in hairy roots induction, disclosed a novel role for this amino acid in plant development. Indeed, from this initial finding, proline was shown to be critically involved in a number of developmental processes, such as floral transition, embryo development, pollen fertility and root elongation. In this review, we present a historical survey on the rol genes focusing on the role of rolD and proline in plant development

Nutritional requirements for the production of dithiolopyrrolone antibiotics by Saccharothrix algeriensis NRRL B-24137

The amino acid and humic acid requirements of Saccharothrix algeriensis NRRL B-24137 for growth and production of the dithiolopyrrolone antibiotics were studied in a semi-synthetic medium (SSM). Nature and concentration of amino acids and humic acid strongly influenced the growth and dithiolopyrrolone specific production. The highest value of thiolutin (acetyl-pyrrothine) specific production was obtained in the presence of 1 g/l humic acid (336 mg/g DCW), and in the presence of 5mM l-cystine (309 mg/g DCW) as compared to 19 mg/g DCW obtained with the control. Furthermore, thiolutin production was increased about six-fold, four-fold and three-fold in the presence of l-proline, l-glutamic acid and dl-histidine, respectively. In contrast,the production of thiolutin was reduced by addition of other amino acids such as l-glutamine, dl-ethionine, l-methionine and l-arginine. The highest value of isobutyryl-pyrrothine production was obtained in the presence of 2,6-diaminopimelic acid and l-lysine (7.8 and 1.0 mg/g DCW, respectively). However, the highest value of butanoyl-pyrrothine production was obtained in the presence of humic acid (6.6 mg/g DCW), followed by l-cysteine and l-proline (3.6 and 3.2 mg/g DCW, respectively). In addition, the maximum specific production of senecioyl-pyrrothine (29 mg/g DCW) and tigloyl-pyrrothine (21 mg/g DCW) was obtained in the presence of humic acid. We found that, except for isobutyryl-pyrrothine, production of all dithiolopyrrolones was favoured by addition of l-proline. The maximum specific production was obtained with l-proline at concentrations of 2.50mM for thiolutin (133mg/gDCW),1.25mMfor senecioyl-pyrrothine, tigloyl-pyrrothine and butanoyl-pyrrothine production (29, 23 and 3.9 mg/gDCW, respectively). Production of all dithiolopyrrolones strongly decreased as the l-methionine or dl-ethionine concentration was increased in the culture medium

Medium alkalization due to carbon metabolism is largely responsible for inhibition of bacterial growth by Vibrio cholerae supernatants

Vibrio cholerae is the causative agent of the diarrheal disease cholera. Many Vibrio species secrete antimicrobial factors, though the identity of such a factor has not been determined for any V. cholerae strain. Such an antimicrobial factor could be relevant to pathogenesis of cholera, which disrupts the intestinal microbiome. In this study, we investigated the antimicrobial effects of supernatant from 72 hour old cultures of V. cholerae C6706 on Shigella flexneri CFS100. Inhibition of S. flexneri growth was found to be dependent on the alkaline pH of the supernatant. A 1:1 mixture of pH-adjusted supernatant and LB was found to inhibit S. flexneri growth at alkaline but not neutral pH, as was pH-adjusted LB alone. In minimal medium, elevation of supernatant pH by V. cholerae was dependent on nutritional factors, and this elevation of medium pH also correlated with increased S. flexneri growth inhibition. Though medium alkalization in LB is often attributed to amino acid catabolism and the consequent production of ammonia, supplementation of V. cholerae cultures in minimal medium with amino acids had a weaker effect on alkalization and inhibition than did supplementation with selected carbon sources. This suggests that some feature of carbon metabolism causes medium alkalization and the resultant antimicrobial activity. Several V. cholerae mutants in potentially relevant pathways were screened for alkalization and S. flexneri growth inhibition, but none had any effect.Complicating this picture is the finding that V. cholerae grown under microaerobic conditions produce a less alkaline supernatant with stronger S. flexneri growth inhibition. The significance of this is unknown.Molecular Bioscience

Metabolomic profiling and stable isotope labelling of Trichomonas vaginalis and Tritrichomonas foetus reveal major differences in amino acid metabolism including the production of 2-hydroxyisocaproic acid, cystathionine and S-methylcysteine

Trichomonas vaginalis and Tritrichomonas foetus are pathogens that parasitise, respectively, human and bovine urogenital tracts causing disease. Using LC-MS, reference metabolomic profiles were obtained for both species and stable isotope labelling with D-[U-13C6] glucose was used to analyse central carbon metabolism. This facilitated a comparison of the metabolic pathways of T. vaginalis and T. foetus, extending earlier targeted biochemical studies. 43 metabolites, whose identities were confirmed by comparison of their retention times with authentic standards, occurred at more than 3-fold difference in peak intensity between T. vaginalis and T. foetus. 18 metabolites that were removed from or released into the medium during growth also showed more than 3-fold difference between the species. Major differences were observed in cysteine and methionine metabolism in which homocysteine, produced as a bi-product of trans-methylation, is catabolised by methionine γ-lyase in T. vaginalis but converted to cystathionine in T. foetus. Both species synthesise methylthioadenosine by an unusual mechanism, but it is not used as a substrate for methionine recycling. T. vaginalis also produces and exports high levels of S-methylcysteine, whereas only negligible levels were found in T. foetus which maintains significantly higher intracellular levels of cysteine. 13C-labeling confirmed that both cysteine and S-methylcysteine are synthesised by T. vaginalis; S-methylcysteine can be generated by recombinant T. vaginalis cysteine synthase using phosphoserine and methanethiol. T. foetus contained higher levels of ornithine and citrulline than T. vaginalis and exported increased levels of putrescine, suggesting greater flux through the arginine dihydrolase pathway. T. vaginalis produced and exported hydroxy acid derivatives of certain amino acids, particularly 2-hydroxyisocaproic acid derived from leucine, whereas negligible levels of these metabolites occurred in T. foetus

Genes of different catabolic pathways are coordinately regulated by Dal81 in Saccharomyces cerevisiae

Yeast can use a wide variety of nitrogen compounds. However, the ability to synthesize enzymes and permeases for catabolism of poor nitrogen sources is limited in the presence of a rich one. This general mechanism of transcriptional control is called nitrogen catabolite repression. Poor nitrogen sources, such as leucine, γ-aminobutyric acid (GABA), and allantoin, enable growth after the synthesis of pathway-specific catabolic enzymes and permeases. This synthesis occurs only under conditions of nitrogen limitation and in the presence of a pathway-specific signal. In this work we studied the temporal order in the induction of AGP1, BAP2, UGA4, and DAL7, genes that are involved in the catabolism and use of leucine, GABA, and allantoin, three poor nitrogen sources. We found that when these amino acids are available, cells will express AGP1 and BAP2 in the first place, then DAL7, and at last UGA4. Dal81, a general positive regulator of genes involved in nitrogen utilization related to the metabolisms of GABA, leucine, and allantoin, plays a central role in this coordinated regulation.Fil: Palavecino Ruiz, Marcos Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química Biológica de la Facultad de Ciencias Exactas y Naturales. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química Biológica de la Facultad de Ciencias Exactas y Naturales; ArgentinaFil: Correa Garcia, Susana Raquel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química Biológica de la Facultad de Ciencias Exactas y Naturales. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química Biológica de la Facultad de Ciencias Exactas y Naturales; ArgentinaFil: Bermudez Moretti, Mariana. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química Biológica de la Facultad de Ciencias Exactas y Naturales. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química Biológica de la Facultad de Ciencias Exactas y Naturales; Argentin

Highlights of recent progress in plant lipid research

Raw fossil material reserves are not inexhaustible and as prices continue to raise it is necessary to find new sources of alternative and renewable energy. Oils from oleaginous field crops (sunflower and rape) with properties close to those of fossil fuel could constitute an alternative source of energy for the production of raw materials. This is the context in which the 18th International Symposium on Plant lipids (ISPL) was held in Bordeaux from 20th to 25th July 2008 at “La Cité Mondiale”. The 18th ISPL gathered 270 researchers from 33 countries. Sixty nine oral communications and 136 posters were presented during the 12 sessions of the Symposium. The sessions have covered all the different aspects of the Plant Lipid field including: Surface lipids: suberin, cutin and waxes, Fatty acids, Glycerolipids, Plant lipids as renewable sources of energy, Seed oils and bioengineering of metabolic pathways, Lipid catabolism, Models for lipid studies: lower plants, micro-organisms and others, Modifications of proteins by lipids, Sphingolipids, sterols and isoprenoids, Lipid signaling and plant stress responses, Lipid trafficking and membrane dynamics, New methods and technologies: functional lipidomics, fluxome, modelling