The identification and characterization of osmotolerant yeast isolates from chemical wastewater evaporation ponds

Ramat Hovav is a major chemical industrial park manufacturing pharmaceuticals, pesticides, and various aliphatic and aromatic halogens. All wastewater streams are collected in large evaporation ponds. Salinity in the evaporation ponds fluctuates between 3% (w/v) and saturation and pH values range between 2.0 and 10.0. We looked for microorganisms surviving in these extreme environmental conditions and found that 2 yeast strains dominate this biotope. 18S rDNA sequence analysis identified the isolates as Pichia guilliermondii and Rhodotorula mucilaginosa. Both isolates grew in NaCl concentrations ranging up to 3.5 M and 2.5 M, respectively, and at a pH range of 2-10. There was a distinct difference between the Rhodotorula and Pichia strains and S. cerevisiae RS16 that served as a control strain with respect to accumulation of osmoregulators and internal ion concentrations when exposed to osmotic stress. The Pichia and Rhodotorula strains maintained high glycerol concentration also in media low in NaCl. Utilization of various carbon sources was examined. Using a tetrazolium-based assay we show that the Rhodotorula and Pichia strains are capable of utilizing a wide range of different carbon sources including anthracene, phenanthrene, and other cyclic aromatic hydrocarbons.

Solution structure of Methylophilus methylotrophus cytochrome c": insights into the structural basis of haem-ligand detachment

Cytochrome c" from Methylophilus methylotrophus is a monohaem protein with 124 amino acid residues. The iron has two histidine ligands in the oxidised form, one of which detaches and picks up a proton when the protein is reduced. Thus, both forms are paramagnetic. The structure of the oxidised form in solution, determined from NMR data is presented. The family of structures has an average backbone rmsd value of 0.53 A, and a heavy atom rmsd value of 0.95 A, within a target function range of 32 %. This structure is related to class I cytochromes with an additional helix at the N terminus. The haem-binding site occurs in a domain essentially lacking secondary structure motifs and the axial histidinyl residues were found in an unusual near perpendicular orientation. Moreover, a disulfide bridge is present, an uncommon structural feature among c-type cytochromes. The disulfide bridge, linking cysteine residues 96 and 104, forms a loop that confers rigidity and is essential to the detachment of the axial histidine (His95) as demonstrated by chemical disruption of the S-S bond. A route for protonation of the distal histidine involving haem propionate 17 is proposed and discussed in the light of available models for complex membrane proton pumps.

Pathways for utilization of carbon reserves in Desulfovibrio gigas under fermentative and respiratory conditions

The sulfate-reducing bacterium Desulfovibrio gigas accumulates large amounts of polyglucose as an endogenous carbon and energy reserve. In the absence of exogenous substrates, the intracellular polysaccharide was utilized, and energy was conserved in the process (H. Santos, P. Fareleira, A. V. Xavier, L. Chen, M.-Y. Liu, and J. LeGall, Biochem. Biophys. Res. Commun. 195:551-557, 1993). When an external electron acceptor was not provided, degradation of polyglucose by cell suspensions of D. gigas yielded acetate, glycerol, hydrogen, and ethanol. A detailed investigation of the metabolic pathways involved in the formation of these end products was carried out, based on measurements of the activities of glycolytic enzymes in cell extracts, by either spectrophotometric or nuclear magnetic resonance (NMR) assays. All of the enzyme activities associated with the glycogen cleavage and the Embden-Meyerhof pathway were determined as well as those involved in the formation of glycerol from dihydroxyacetone phosphate (glycerol-3-phosphate dehydrogenase and glycerol phosphatase) and the enzymes that catalyze the reactions leading to the production of ethanol (pyruvate decarboxylase and ethanol dehydrogenase). The key enzymes of the Entner-Doudoroff pathway were not detected. The methylglyoxal bypass was identified as a second glycolytic branch operating simultaneously with the Embden-Meyerhof pathway. The relative contribution of these two pathways for polyglucose degradation was 2:3. 13C-labeling experiments with cell extracts using isotopically enriched glucose and 13C-NMR analysis supported the proposed pathways. The information on the metabolic pathways involved in polyglucose catabolism combined with analyses of the end products formed from polyglucose under fermentative conditions provided some insight into the role of NADH in D. gigas. In the presence of electron acceptors, NADH resulting from polyglucose degradation was utilized for the reduction of sulfate, thiosulfate, or nitrite, leading to the formation of acetate as the only carbon end product besides CO2. Evidence supporting the role of NADH as a source of reducing equivalents for the production of hydrogen is also presented.

Malate Metabolism by Desulfovibrio gigas and its Link to Sulfate and Fumarate Reduction: Purification of the Malic Enzyme and Detection of NAD(P)+ Transhydrogenase Activity

Malate metabolism was investigated in lactate grown cells of Desulfovibrio gigas ; 3 mol of malate are converted into 2 mol succinate and 1 mol acetate. The malic enzyme (L-malate:NADP+ oxidoreductase) was purified to homogeneity and partially characterized. The enzyme is monomeric with molecular weight of 45 kDa. Its spectrum has no visible absorption and the activity is stimulated by K+ and Mg2+. The presence of an NAD(P)+ transhydrogenase, the observation of partial reduction of adenylylsulfate reductase by NADH (via NADH-rubredoxin oxidoreductase) and evidence for NADH-linked fumarate reductase activity support the involvement of pyridine nucleotides in the electron pathway toward the reduction of sulfur compounds and/or fumarate. An electron transfer chain to fumarate is proposed, taking into consideration these results and the stoichiometry of end-products derived from malate dismutation.

Aerobic metabolism of carbon reserves by the "obligate anaerobe" Desulfovibrio gigas

The sulfate-reducing bacterium, Desulfovibrio gigas, is shown by in vivo 31P-NMR to be capable of generating NTP from the utilization of internal carbon reserves both in anaerobic and in aerobic conditions. Acetate, glycerol and ethanol are the major end-products, but the production of alcohols decreases strongly when oxygen is present. When the glycolytic pathway is inhibited with fluoride, NTP levels decrease drastically but can be remarkably restored when an electron acceptor, such as oxygen, is provided. Our data are in favour of a NADH-linked electron transfer chain enabling transfer of reducing power derived from polyglucose to oxygen which provides this so-called "strict anaerobe" with the capability of surviving to oxic environments.

Purification and characterization of an NADH-rubredoxin oxidoreductase involved in the utilization of oxygen by Desulfovibrio gigas

An NADH--rubredoxin oxidoreductase previously isolated from Desulfovibrio gigas [LeGall, J. (1968) Ann. Inst. Pasteur 114, 109-115] has now been fully purified and further characterized. It contains two subunits of 27 kDa and 32 kDa. With two mid-point redox potentials of -295 mV and -325 mV, this FMN- and FAD-containing protein can induce the specific reduction of D. gigas rubredoxin. In contrast, rubredoxins from the other Desulfovibrio species or desulforedoxin from D. gigas show very low reaction rates with the same enzyme. The phylogenetic significance of the narrow specificity of the enzyme toward the rubredoxin from the same organism is discussed. The purified enzyme has NADH oxidase activity with H2O2 as a final product of O2 reduction. The reaction is half-inhibited by 4.2 microM p-chloromercuribenzoate, whereas cyanide and azide are not significant inhibitors in this reaction. The role of this protein as a part of the enzymic equipment that allows the formation of ATP in the presence of oxygen from the degradation of carbon reserves is discussed.

Rubredoxin oxidase, a new flavo-hemo-protein, is the site of oxygen reduction to water by the "strict anaerobe" Desulfovibrio gigas

A rubredoxin-oxygen oxidoreductase, a homodimer with a molecular weight of 43 kDa per monomer, was found to be a component of an electron transfer chain that couples the reduction of oxygen to water with NADH oxidation. This FAD-containing protein appears to contain a new type of heme group. The electron transfer chain is not inhibited by cyanide and azide. In contrast, CO decreases NADH oxidation rate and also induces release of the prosthetic groups from the native terminal reductase.

Structure determination of a novel cyclic phosphocompound isolated from Desulfovibrio desulfuricans

The structure of a novel diphosphodiester compound recently detected in Desulfovibrio desulfuricans cells [Santos, Fareleira, Pedregal, LeGall & Xavier (1991) Eur. J. Biochem. 201, 283-287] was fully elucidated using a combination of n.m.r. techniques in aqueous and in methanolic solutions. The novel metabolite was identified as 3-methyl-1,2,3,4-tetrahydroxybutane-1,3-cyclic bisphosphate, and the minimum energy conformation is presented. The two chiral centres have the relative configuration RS.

In vivo 31P-NMR studies of Desulfovibrio species. Detection of a novel phosphorus-containing compound

The phosphorus metabolism of sulfate-reducing bacteria was, for the first time, probed by in vivo 31P NMR. A novel phosphoric anhydride diester compound was detected in Desulfovibrio desulfuricans ATCC 27774 at intracellular concentrations up to 5 mM. The compound has been extracted and partially purified by anion-exchange chromatography and analysed by 31P, 13C and 1H NMR. These studies show that the novel phosphorus-containing compound is formed by five carbon atoms and is probably cyclic, with a Mr of approximately 300. Various Desulfovibrio strains were examined in vivo for the presence of this phosphorus-containing compound. Detectable amounts of the novel metabolite were found in D. desulfuricans ATCC 27774 when grown on lactate/sulfate, lactate/thiosulfate or pyruvate/sulfate. The phosphorus-containing compound was not detected when this strain of D. desulfuricans was grown on lactate/nitrate or pyruvate; neither was it detected in two other strains which, like D. desulfuricans ATCC 27774, have the capability of utilizing nitrate as a terminal electron acceptor.

In vivo 31P- and 13C-NMR studies of ATP synthesis and methane formation by Methanosarcina barkeri

Carbon and phosphorus metabolism of cell suspensions of Methanosarcina barkeri strain MS (DSM 800), grown on methanol, were probed in vivo by NMR. The experimental conditions, which involved thick cell suspensions, did not significantly affect the efficiency of the rate of methanol uptake by cells. Following exposure to methanol an acidification of both the intracellular and the extracellular spaces was observed and a gradient of 0.5 pH units across the cytoplasmic membrane was determined from the 31P-NMR data. High levels of intracellular ATP up to 4 mM were detected. The ADP concentration determined in a suspension of starved cells was only 2 mM, suggesting that a significant amount of ADP may be immobilized and is thus not detectable by NMR. In the presence of the protonophore, 3,3',4',5-tetrachlorosalicylanilide, the proton gradient was dissipated and the synthesis of ATP stopped. The inhibitor of the ATP synthase, N,N'-dicyclohexylcarbodiimide, was rather inefficient in inhibiting ATP synthesis. High concentrations of N,N'-dicyclohexylcarbodiimide (corresponding to 300 nmol/mg protein-1) were required to decrease the ATP content by approximately 60%, and, under these conditions, formation of acetyl phosphate was detected. However, the methanol consumption rate was not affected.