Export Of Metabolites Research Articles

SBOannotator: a Python Tool for the Automated Assignment of Systems Biology Ontology Terms.

The number and size of computational models in biology have drastically increased over the past years and continue to grow. Modeled networks are becoming more complex, and reconstructing them from the beginning in an exchangeable and reproducible manner is challenging. Using precisely defined ontologies enables the encoding of field-specific knowledge and the association of disparate data types. In computational modeling, the medium for representing domain knowledge is the set of orthogonal structured controlled vocabularies named Systems Biology Ontology (SBO). The SBO terms enable modelers to explicitly define and describe model entities, including their roles and characteristics. Here, we present the first standalone tool that automatically assigns SBO terms to multiple entities of a given SBML model, named the SBOannotator. The main focus lies on the reactions, as the correct assignment of precise SBO annotations requires their extensive classification. Our implementation does not consider only top-level terms but examines the functionality of the underlying enzymes to allocate precise and highly specific ontology terms to biochemical reactions. Transport reactions are examined separately and are classified based on the mechanism of molecule transport. Pseudo-reactions that serve modeling purposes are given reasonable terms to distinguish between biomass production and the import or export of metabolites. Finally, other model entities, such as metabolites and genes, are annotated with appropriate terms. Including SBO annotations in the models will enhance the reproducibility, usability, and analysis of biochemical networks. SBOannotator is freely available from https://github.com/draeger-lab/SBOannotator/. Supplementary data are available at Bioinformatics online.

Ucp2 regulates neonatal cardiomyocytes proliferation through modulation of their mitochondrial metabolism

A major block to mammalian cardiac regeneration is the limited capacity of adult cardiomyocytes (CMs) to proliferate in response to injury. CMs proliferation is linked to oxidative metabolism: at birth, neonatal CMs endure a metabolic switch, with high reliance on fatty acid oxidation. This leads to increased mtROS production that has been shown to mediate their cell-cycle arrest. Thus, studying mitochondrial activity in the neonate is critical to understand constrains on CMs proliferation, regardless of their age. In this context, we focus of Ucp2, a mitochondrial carrier that plays a key role in regulation of cell fuel preferences and mtROS production. Our goal is to investigate whether Ucp2 can regulate neonatal CMs proliferation through modulation of their oxidative metabolism. Using inducible and complete Ucp2 KOs mice models together with RNAseq, flow cytometry and Seahorse analysis, we have addressed the role of Ucp2 in regulation of neonatal CMs proliferation, mtROS levels, mitochondrial biogenesis and metabolic activity. Being expressed at low levels during development, Ucp2 is upregulated from P1 to P7. Its expression then decreases to become barely detectable in the adult, thus correlating with CMs proliferative period. We show that neonatal Ucp2-/- CMs display a reduced mitochondrial respiration (OCR) that is not compensated by glycolysis. This low OCR is accompanied by a strong decrease in mitochondrial mass, together with alterations of ETC complexes expression, and to an increased reliance on glutaminolysis. In addition to decreased ATP/ADP ratio, we show that this impaired metabolic activity leads to reduction of CMs proliferation, a phenotype that is mediated by p38MAPK signaling pathway. We are currently assessing the consequences of loss of Ucp2 on neonatal heart metabolites levels and mitochondrial network. We hypothesize that Ucp2, through the export of metabolites from mitochondria to cytosol, takes part in mitochondrial retrograde signaling leading to regulation of CMs maturation and proliferation.

Stability of Floodplain Subsurface Microbial Communities Through Seasonal Hydrological and Geochemical Cycles

Riparian floodplains represent an interaction zone between the terrestrial subsurface and rivers, where regional groundwater flows, infiltration, and evapotranspiration drive mixing of water and import/export of nutrients and contaminants. These dynamics create seasonally transient redox conditions that drive biogeochemical transformations, which strongly modify groundwater quality. Microbial responses to changing hydrological conditions are perhaps the critical step connecting hydrology to geochemical transformations and groundwater quality, yet are not well understood. We aimed to address this knowledge gap by monitoring seasonal transitions at the U.S. Department of Energy legacy uranium ore processing site in Riverton, WY, through spring-summer-fall hydrological transitions. Our goal was to characterize the microbial community throughout the soil profile, down to the saturated aquifer, and observe its response to wet-dry transitions across a full season and compare to changes in geochemistry and hydrology. Next-generation sequencing was employed to identify biogeochemically-relevant microbial taxa based on the 16S rRNA gene; we found a broad diversity of microbial clades including taxa involved in sulfur and metal cycling, as well as nitrification. These data were paired with measurements of soil moisture, major nutrients and cations, and trace elements. Overall microbial community composition was dependent on soil depth or type, with seasonal effects only observed in the topsoil or subsurface aquifer. This finding indicates that microbial communities in the transiently-reduced center of the soil profile at the Riverton, WY site are remarkably stable, despite moisture and redox inversions. In addition, these communities likely impact the communities in surrounding soil horizons through export of metabolites and solutes as the water table rises and falls throughout the season.

Subversion of Schwann Cell Glucose Metabolism by Mycobacterium leprae

Mycobacterium leprae, the intracellular etiological agent of leprosy, infects Schwann promoting irreversible physical disabilities and deformities. These cells are responsible for myelination and maintenance of axonal energy metabolism through export of metabolites, such as lactate and pyruvate. In the present work, we observed that infected Schwann cells increase glucose uptake with a concomitant increase in glucose-6-phosphate dehydrogenase (G6PDH) activity, the key enzyme of the oxidative pentose pathway. We also observed a mitochondria shutdown in infected cells and mitochondrial swelling in pure neural leprosy nerves. The classic Warburg effect described in macrophages infected by Mycobacterium avium was not observed in our model, which presented a drastic reduction in lactate generation and release by infected Schwann cells. This effect was followed by a decrease in lactate dehydrogenase isoform M (LDH-M) activity and an increase in cellular protection against hydrogen peroxide insult in a pentose phosphate pathway and GSH-dependent manner. M. leprae infection success was also dependent of the glutathione antioxidant system and its main reducing power source, the pentose pathway, as demonstrated by a 50 and 70% drop in intracellular viability after treatment with the GSH synthesis inhibitor buthionine sulfoximine, and aminonicotinamide (6-ANAM), an inhibitor of G6PDH 6-ANAM, respectively. We concluded that M. leprae could modulate host cell glucose metabolism to increase the cellular reducing power generation, facilitating glutathione regeneration and consequently free-radical control. The impact of this regulation in leprosy neuropathy is discussed.

Acute metabolic amplification of insulin secretion in mouse islets: Role of cytosolic acetyl-CoA

ObjectiveStimulation of the ß-cell metabolism by glucose and other fuels triggers insulin release by enhancing the mitochondrial ATP production and acutely amplifies the secretory response by increase in mitochondrial export of metabolites. We aimed to narrow down the uniform final reaction steps mediating fuel-induced acute amplification of insulin secretion. Material/MethodsInsulin secretion and metabolic parameters were measured in isolated mouse islets exposed to the sulfonylurea glipizide in high concentration (closing all ATP-sensitive K+ channels) during the entire experiment. Fuel-induced effects were examined after treating the islets for one hour with medium devoid of fuels. This experimental design prevented acute amplification, but only when glucose was the sole fuel. ResultsStrong amplification of insulin secretion by α-ketoisocaproate or glucose combined with α-ketoisovalerate (supplying mitochondrial oxaloacetate) was abolished within 14min after transition to medium devoid of fuels. After transition from medium containing glucose plus α-ketoisovalerate to medium containing solely glucose or α-ketoisovalerate, amplification (strong or weak, respectively) occurred until the end of the experiment. Glucose (alone or combined with α-ketoisovalerate) increased the total acetyl-CoA content as intensely as α-ketoisocaproate. Low concentrations of α-ketoisovalerate or α-ketoisocaproate were sufficient for saturation of acetyl-CoA increase, but caused no or only weak amplification, respectively. No acetyl-CoA increases occurred in the absence of glipizide. ConclusionsGlucose and other fuels regulate acute amplification of insulin secretion by controlling the supply of acetyl-CoA to the ß-cell cytosol. Cytosolic acetyl-CoA does not amplify by serving as substrate for syntheses of metabolic intermediates, but amplifies by acting as substrate for cytosolic protein acetylation.

Characterization of a Cyanobacterial Outer Membrane Protein: An E. Coli Tolc Homologue from Synechocystis Sp. Pcc 6803

E. coli TolC (tolerance to colicins) represents an interesting class of outer membrane (OM) proteins, as it has an α-helical periplasmic tunnel and β-barrel membrane region, providing a conduit for export of metabolites and xenobiotics from cell interior to exterior, and import of colicin E1 (1). A TolC homologue, Slr1270 from Synechocystis 6803, cloned and expressed in E. coli, has > 40% similarity and ∼16% identity to E. coli and Pseudomonas counterparts, and has a similar domain organization. Homology modeling using Pseudomonas OprM as template modeled 93% of Slr1270 sequence. The 1581bp slr1270 gene was cloned and overexpressed in E. coli. Protein from inclusion bodies, refolded through step-wise dialysis showed major bands at ∼55kDa and >150 kDa on SDS-PAGE corresponding to the monomer and trimer respectively and ∼300 kDa on CN-PAGE. Purified protein displays a far-UV CD spectrum characteristic of E. coli TolC with > 50% α-helix, and formed channels in planar lipid bilayers with a characteristic single channel conductance of ∼50 pS in 0.1M NaCl. The intact protein mass spectrum (LC-MS) with a major peak at 54,489 probably represents a mixture of two species, the TolC product with 1-40 removed and an intact 6-His tag (calculated mass 54,457.1 Da), and a product with 1-38 removed and a 5-His tag (calculated mass 54,490.2 Da) after a single carboxypeptidase event. The small peak at 54,638 Da probably corresponds to TolC product with 1-38 removed and an intact 6-His tag (calculated mass 54,627.3 Da). Peptides 39-76 and 41-76 were recovered from trypsin digests confirming N-terminal heterogeneity. (1) Zakharov, S. D. et al. 2012. Pathways of Colicin Import: Utilization of BtuB, OmpF Porin, and the TolC Drug Export Protein, Biochem. Soc. Trans., 40, 1463-1468.

Acute metabolic amplification of insulin secretion in mouse islets is mediated by mitochondrial export of metabolites, but not by mitochondrial energy generation

ObjectiveThe β-cell metabolism of glucose and of some other fuels (e.g. α-ketoisocaproate) generates signals triggering and acutely amplifying insulin secretion. As the pathway coupling metabolism with amplification is largely unknown, we aimed to narrow down the putative amplifying signals. Materials/MethodsAn experimental design was used which previously prevented glucose-induced, but not α-ketoisocaproate-induced insulin secretion. Isolated mouse islets were pretreated for one hour with medium devoid of fuels and containing the sulfonylurea glipizide in high concentration which closed all ATP-sensitive K+ channels. This concentration was also applied during the subsequent examination of fuel-induced effects. In perifused or incubated islets, insulin secretion and metabolic parameters were measured. ResultsThe pretreatment decreased the islet ATP/ADP ratio. Whereas glucose and α-ketoisovalerate were ineffective or weakly effective, respectively, when tested separately, their combination strongly enhanced the insulin secretion. Compared with glucose, the strong amplifier α-ketoisocaproate caused less increase in NAD(P)H-fluorescence and less mitochondrial hyperpolarization. Compared with α-ketoisovalerate, α-ketoisocaproate caused greater increase in NAD(P)H-fluorescence and greater mitochondrial hyperpolarization. Neither α-ketoacid anion enhanced the islet ATP/ADP ratio during onset of the insulin secretion. α-Ketoisocaproate induced a higher pyruvate content than glucose, slowly elevated the citrate content which was not changed by glucose and generated a much higher acetoacetate content than other fuels. α-Ketoisovalerate alone or in combination with glucose did not increase the citrate content. ConclusionsIn β-cells, mitochondrial energy generation does not mediate acute metabolic amplification, but mitochondrial production of acetyl-CoA and supplemental acetoacetate supplies cytosolic metabolites which induce the generation of specific amplifying signals.

Diversity of effector genes in plant pathogenic bacteria of genus Xanthomonas

Gram-negative plant pathogenic bacteria are secreting into plant cell a special type of pathogeni city-related proteins called effectors. They are capable of suppressing plant innate immunity or stimulating synthesis and export of metabolites desired by the pathogen. We identified a number of effector-coding genes typical of xanthomonads analyzing 8 completely sequenced genomes of genus Xanthomonas. Using representative collection provided by Russian Research Institute of Phytopathology we identified genetic diversity of effector gene loci in population of Xanthomonas bacteria. Patterns of effector genes were identified for individual strains and statistic linkage between particular genes and race of the pathogen was established. For the first time several untypical effector genes were found in strains of Xanthomonas campestris pv. campestris.

Bacterial membrane proteomics

About one quarter to one third of all bacterial genes encode proteins of the inner or outer bacterial membrane. These proteins perform essential physiological functions, such as the import or export of metabolites, the homeostasis of metal ions, the extrusion of toxic substances or antibiotics, and the generation or conversion of energy. The last years have witnessed completion of a plethora of whole-genome sequences of bacteria important for biotechnology or medicine, which is the foundation for proteome and other functional genome analyses. In this review, we discuss the challenges in membrane proteome analysis, starting from sample preparation and leading to MS-data analysis and quantification. The current state of available proteomics technologies as well as their advantages and disadvantages will be described with a focus on shotgun proteomics. Then, we will briefly introduce the most abundant proteins and protein families present in bacterial membranes before bacterial membrane proteomics studies of the last years will be presented. It will be shown how these works enlarged our knowledge about the physiological adaptations that take place in bacteria during fine chemical production, bioremediation, protein overexpression, and during infections. Furthermore, several examples from literature demonstrate the suitability of membrane proteomics for the identification of antigens and different pathogenic strains, as well as the elucidation of membrane protein structure and function.

Export of metabolites by the proteins of the DMT and RhtB families and its possible role in intercellular communication

The earlier published and new experimental data are summarized on the properties of the genes encoding the membrane proteins of the DMT family (RhtA (YbiF), EamA (YdeD), YijE, YddG, YedA, PecM, eukaryotic nucleoside phosphate sugar and hexose phosphate transporters), the RhtB/LysE family (RhtB, RhtC, LeuE, YahN, EamB (YfiK), ArgO (YggA), CmaU), as well as some other families (YicM, YdhC, YdeAB, YdhE (NorE)). These proteins are involved in the export of amino acids, purines, and other metabolites from the cell. The expression of most of the genes encoding these proteins is not induced by the substrates they transport but is controlled by the global regulation systems, such as the Lrp protein, and activated by the signal compounds involved in the intracellular communication. The level of expression, assessed in experiments on translational fusion of the corresponding bacterial genes with the beta-galactosidase gene, depends on the growth phase of the bacterial culture, composition of the medium, and some stress factors, such as pH osmolarity or decreased aeration. The efflux of normal cell metabolites is assumed to be the natural function of these proteins. This function may play a role in density-dependent behavior of cell populations (quorum sensing). It may have been enhanced in the course of evolution via specialization of these proteins in the efflux of compounds derived from metabolic intermediates and adjusted to the role of transmitters.

Relations Between Structure and Function of the Mitochondrial ADP/ATP Carrier

Import and export of metabolites through mitochondrial membranes are vital processes that are highly controlled and regulated at the level of the inner membrane. Proteins of the mitochondrial carrier family ( MCF ) are embedded in this membrane, and each member of the family achieves the selective transport of a specific metabolite. Among these, the ADP/ATP carrier transports ADP into the mitochondrial matrix and exports ATP toward the cytosol after its synthesis. Because of its natural abundance, the ADP/ATP carrier is the best characterized within MCF, and a high-resolution structure of one conformation is known. The overall structure is basket shaped and formed by six transmembrane helices that are not only tilted with respect to the membrane, but three of them are also kinked at the level of prolines. The functional mechanisms, nucleotide recognition, and conformational changes for the transport, suggested from the structure, are discussed along with the large body of biochemical and functional results.

Transport Activity of MCT1 Expressed in Xenopus Oocytes Is Increased by Interaction with Carbonic Anhydrase

Injection of carbonic anhydrase isoform II (CA) into Xenopus frog oocytes increased the rate of H+ flux via the rat monocarboxylate transporter isoform 1 (MCT1) expressed in the oocytes. MCT1 activity was assessed by changes of intracellular H+ concentration measured by pH-selective microelectrodes during application of lactate. CA-induced augmentation of the rate of H+ flux mediated by MCT1 was not inhibited by ethoxyzolamide (10 microM) and did not depend on the presence of added CO2/HCO3- but was suppressed by injection of an antibody against CA. Deleting the C terminus of the MCT1 greatly reduced its transport rate and removed transport facilitation by CA. Injected CA accelerated the CO2/HCO3(-)-induced acidification severalfold, which was blocked by ethoxyzolamide and was independent of MCT1 expression. Mass spectrometry confirmed activity of CA as injected into the frog oocytes. With pulldown assays we demonstrated a specific binding of CA to MCT1 that was not attributed to the C terminus of MCT1. Our results suggest that CA enhances MCT1 transport activity, independent of its enzymatic reaction center, presumably by binding to MCT1.

Mechanistic understanding of the fermentative L‐glutamic acid overproduction by Corynebacterium glutamicum through combined metabolic flux profiling and transmembrane transport characteristics

AbstractSince the 1950s when Micrococcus glutamicus later renamed Corynebacterium glutamicum was discovered, the production of amino acids by fermentative methods has become an important aspect of industrial microbiology. Numerous studies to understand and improve the metabolic conditions leading to amino acid overproduction have been carried out. Most amino acids are currently produced by use of mutants that contain combinations of auxotrophic and regulatory mutations. L‐Glutamic acid is the amino acid produced in the greatest quantities (106 tonnes per year) and Corynebacteria are central to its industrial production. However, further improvements to strain performance are difficult to obtain by empirical optimization and a more rational approach is required. The use of metabolic flux analysis provides valuable information regarding bottlenecks in the formation of desired metabolites. Such techniques have found application in elucidating flux control, provided insight into metabolic network function and developed methods to amplify or redirect fluxes in engineered bioprocesses. Hence, branch points in biosynthesis, precursor supply in fuelling reactions and export of metabolites can be manipulated, resulting in high glutamic acid overproduction by Corynebacterium glutamicum fermentations. In this review, in addition to reviewing the state of play in metabolic flux analysis for glutamate overproduction, the metabolic pathways involved in the production of L‐glutamic acid, the mechanisms mediating its efflux and secretion as well as their manipulation to achieve higher glutamate production, are discussed. The link between metabolic flux and transmembrane transport of glutamic acid are also considered. Copyright © 2004 Society of Chemical Industry

Production and export of metabolites from liver and heart mitochondria and anaplerosis.

A method to study the export of citric acid cycle intermediates from rat liver mitochondria supplied with various individual substrates or combinations of substrates was designed to focus on the role of mitochondria in anaplerosis and cataplerosis. Under most conditions malate, citrate, and aspartate were exported in far higher amounts than isocitrate and alpha-ketoglutarate. In the presence of pyruvate alone or pyruvate in combination with most other substrates, citrate export equaled or was only slightly less than malate export. This contrasts with pancreatic islet mitochondria where citrate export is unaffected by many substrates. Malate and succinate potentiated pyruvate-induced citrate export and succinate caused massive malate export from liver mitochondria. Heart mitochondria, which possess very little or no pyruvate carboxylase, unlike liver and pancreatic islet mitochondria, did not produce malate from pyruvate. Heart mitochondria produced malate, but not citrate, from succinate. The results indicate that liver mitochondria export a larger number of metabolites from a wider range of substrates than do islet or heart mitochondria. This may reflect the multiple roles of the liver in body metabolism versus the specialized roles of the islet cell and heart.

Export of metabolites from pancreatic islet mitochondria as a means to study anaplerosis in insulin secretion

Recent evidence suggests that the mitochondrial synthesis (anaplerosis) of α-ketoglutarate or intermediates that can be converted to α-ketoglutarate, such as citrate or glutamate, are important for insulin secretion stimulated by metabolizable secretagogues. In order to focus on the productive role of mitochondria (anaplerosis) separate from the consumptive role of the cytosol (cataplerosis) in insulin secretion, pyruvate and other metabolites of insulin secretagogues were added to microgram amounts of mitochondria obtainable from rat or mouse pancreatic islets and the export of metabolites was surveyed. Cellular levels of metabolites in rat islets were also measured. The export of malate from mitochondria was the most responsive to various substrates. The export of citrate did not increase in the presence of pyruvate alone or pyruvate plus glutamate, but malate plus pyruvate caused citrate to be exported. Citrate levels in intact cells did not change with glucose. Glutamate levels did not increase in intact islets in the presence of glucose, thus not providing evidence for glutamate acting as a messenger in glucose-induced insulin secretion. The citrate level may not need to increase in order to provide increased malonyl-coenzyme A for signaling insulin secretion. Unlike many cells, insulin cells probably obtain cytosolic NADPH equivalents by exporting them from mitochondria to the cytosol via a pyruvate malate shuttle or an isocitrate shuttle. The current results suggest that the reason for anaplerosis in insulin secretion is quite complex and not fully explained by current knowledge.

Metabolite export of isolated guard cell chloroplasts of Vicia faba.

• Stomatal opening is caused by guard cell swelling due to an accumulation of osmotica. We investigated the release of carbon from guard cell chloroplasts as a source for the production of organic osmotica. • Photosynthetically active chloroplasts were isolated from guard cell protoplasts of Vicia faba. Export of metabolites into the surrounding medium was analyzed by silicone oil filtering centrifugation and spectrophotometrically by coupled metabolite assays. Effects of external oxaloacetate and 3-phosphoglycerate on photosynthetic electron transport were examined by recording chlorophyll fluorescence. • In the light, guard cell chloroplasts exported triose phosphates, glucose, maltose and hexose phosphates. The presence of phosphate in the medium was essential for the release of phosphorylated compounds and also strongly enhanced the export of glucose and maltose. Total efflux of carbon from illuminated guard cell chloroplasts was on average 486 µatom C (mg Chl)-1 h-1 , which was significant with respect to the carbon requirement for stomatal opening. • Metabolites released by illuminated guard cell chloroplasts originated predominantly from starch breakdown. Photosynthetic electron transport provided redox power for the reduction of oxaloacetate and 3-phosphoglycerate.

The export of metabolites from mitochondria and anaplerosis in insulin secretion

Combinations of insulin secretagogue-derived metabolites were added to microgram amounts of mitochondria obtained from rat and mouse pancreatic islets and the INS-1 cell line, and the export of citric acid cycle intermediates was surveyed to study anaplerosis in insulin secretion. Cellular levels of metabolites were also measured. In mitochondria from all three tissues, malate production was the most responsive to various substrates. The export of citrate and isocitrate in the presence of pyruvate and most other substrates was small and their levels in intact cells did not change with any secretagogue, except in INS-1 cells where citrate increased slightly. Changes in α-ketoglutarate and glutamate export from mitochondria and levels in intact cells indicate that glutamate can be consumed as a fuel secretagogue, but it is not likely produced as a messenger in insulin secretion. The citrate level may not need to increase in order to provide increased malonyl-CoA for signaling insulin secretion. Unlike some cells, insulin cells probably obtain cytosolic NADPH equivalents by exporting them from mitochondria to the cytosol via a pyruvate malate shuttle or an isocitrate shuttle. Only fuels that can enhance anaplerosis via pyruvate or α-ketoglutarate can be insulin secretagogues.

Expression of substrate-specific transporters encoded by Plasmodium falciparum in Xenopus laevis oocytes

When the malarial parasite Plasmodium falciparum multiplies in erythrocytes it dramatically increases uptake of essential metabolic precursors (nucleosides, nucleobases and glucose) and export of lactic acid by undefined mechanisms. The first evidence is provided here, by a detailed study in Xenopus laevis oocytes, that several specific nutrient transporters are the product of P. falciparum genes. We report the expression of nucleoside, nucleobase, hexose and monocarboxylate transport systems in Xenopus oocytes when injected with mRNA isolated from asexual stages of developing P. falciparum parasites. Their properties are distinct from transport events occurring at the infected erythrocyte membrane or the electrophysiologically identified channel localised to the parasitophorous vacuolar membrane. These novel transporters are substrate-specific and stereoselective, and represent a key regulatory step in the acquisition and export of metabolites by intraerythrocytic P. falciparum.

The blood-brain barrier: morphology, molecules, and neurothelin.

The blood-brain barrier (BBB) is a complex structure formed by vascular endothelial cells, which serve to stabilize the homeostasic processes that are essential for neural functioning. The barrier relies on tight junctions between neighboring endothelial cells and a highly restricted passage of blood-borne components through the endothelial lining. Selective transport mechanisms guarantee the essential import and export of metabolites through the BBB into and out of the neural microenvironment. The dual functions of barrier and carrier depend on distinct proteins, some of which have been characterized in detail.

The Effects of Sublethal Concentrations of Zinc, Cadmium and Mercury on Euglena. Growth and Pigments

Summary Results are presented to demonstrate the effects of sub-lethal concentrations of ZInC chloride (ZnCl 2 ), cadmium chloride (CdCl 2 ) and mercuric chloride (HgCl 2 ) on Euglena gracilis . All three heavy metals adversely effect cell division and especially cell movement, however the dry weight and protein content of the cells are little effected. There is a remarkable relative and absolute gain in dry matter and protein of metal-treated cells per cell number, and this may be due to the difference between the export of metabolites out of metal-treated and control cells since there are no metal-induced changes in cell dimensions. The three heavy metals caused destruction of chlorophyll, marked enhancement of protochlorophyll levels, lowering of both the chlorophyll a/b and pheophytin a/b ratios, and increased the carotenoid/chlorophyll ratios. These observations are interpreted in terms of the action of metals on the reductive and oxidative steps in the biosynthetic pathway of pigments.