The peculiarities of succinic acid production from rapeseed oil by Yarrowia lipolytica yeast

The process of succinic acid (SA) production represents the combination of microbial synthesis of α-ketoglutaric acid from rapeseed oil by yeast Yarrowia lipolytica VKM Y-2412 and subsequent decarboxylation of α-ketoglutaric acid by hydrogen peroxide to SA that leads to the production of 69.0 g l^?1 of SA and 1.36 g l^?1 of acetic acid. SA was isolated from the culture broth filtrate in a crystalline form. The SA recovery from the culture filtrate has certain difficulties due to the presence of residual triglycerides of rapeseed oil. The effect of different methods of the culture filtrate treatment and various sorption materials on the coagulation of triglycerides was studied, and as a result, the precipitation of residual triglycerides by acetone was chosen. The subsequent isolation procedures involved the decomposition of H₂O₂ in the filtrate followed by filtrate bleaching and acidification with a mineral acid, evaporation of filtrate, and SA extraction with ethanol from the residue. The purity of crystalline SA isolated from the culture broth filtrate achieved 97.6–100 %. The product yield varied from 62.6 to 71.6 % depending on the acidity of the supernatant.     

Investigation of the effect of biologically active threo-Ds-isocitric acid on oxidative stress in Paramecium caudatum

The effect of biologically active form (threo-Ds-) of isocitric acid (ICA) on oxidative stress was studied using the infusorian Paramecium caudatum stressed by hydrogen peroxide and salts of some heavy metals (Cu, Pb, Zn, and Cd). ICA at concentrations between 0.5 and 10?mM favorably influenced the infusorian cells with oxidative stress induced by the toxicants studied. The maximal antioxidant effect of ICA was observed at its concentration 10?mM irrespective of the toxicant used (either H₂O₂ or heavy metal ions). ICA was found to be a more active antioxidant than ascorbic acid. Biologically active pharmaceutically pure threo-Ds-ICA was produced through cultivation of the yeast Yarrowia lipolytica and isolated from the culture liquid in the form of crystalline monopotassium salt with a purity of 99.9%.     

Characterization and stress-protective action of <Emphasis Type="Italic">Saccharomyces cerevisiae</Emphasis> extracellular peptide factors on propionic acid bacteria

Protective effect of Saccharomyces cerevisiae exometabolites (RF₁ and RF₂) on seven strains of propionic acid bacteria under exposure to bile salts and acid stress was studied. RF₂ had a stronger protective effect than RF₁. Comparison of the analytical profiles of RF₁ and RF₂, separated by RP-HPLC, showed that nearly 80% of RF₁ components were present in RF₂. Separation of S. cerevisiae RF₁ into individual components by means of semi-preparative RP-HPLC was used for structural characterization of the active component of the RF₁ fraction. It was found to contain two pentapeptides (<1 kDa) with identical amino acid sequences (¹Gly-Pro-Tre-Gly-Pro⁵), differing in one hexose residue. The RF₂ separation method based on three-stage liquid chromatography at low and high pressure was developed, which involved analytical high-pressure gel chromatography. The use of the latter method made it possible to separate high-molecular components and perform enrichment of low-molecular peptides. Peptide origin of the RF₂ active substances with molecular masses allegedly below 300 Da was confirmed.     

The production of succinic acid by yeast Yarrowia lipolytica through a two-step process

The production of α-ketoglutaric acid by yeast Yarrowia lipolytica VKMY-2412 from ethanol and its subsequent chemical conversion to succinic acid (SA) were investigated. A highly effective and environmentally friendly process of α-ketoglutaric acid production was developed using a special pH-controlling strategy, in which the titration of the culture broth with KOH in the acid-formation phase was minimal, that allowed accumulation of only low amounts of inorganic wastes in the course of SA recovery. The culture broth filtrate containing α-ketoglutaric acid (88.7 g l^?1) was directly employed for SA production; the amount of SA produced comprised 71.7 g l^?1 with the yield of 70 % from ethanol consumed. SA was isolated from the culture broth filtrate in a crystalline form with the purity of 100 %. The yield of isolated SA was as high as 72 % of its amount in the culture broth filtrate. The antimicrobial and nematocidic effects of SA of microbial origin on pathogenic organisms that cause human and plant diseases were revealed for the first time.     

Effect ofγ-irradiated carbohydrates on isolated synaptic membranes

The effect of-irradiated solutions of carbohydrates, mainly glucose, upon Na⁺, K⁺-ATPase and lipid peroxidation in rat brain synaptosomal membranes was studied. The membrane damage by irradiated glucose was enhanced in the presence of Fe²⁺ and was diminished when a free-radical scavenger (BHT) or metal chelators (EDTA, EGTA) were present. It is suggested that a key element in the free-radical membrane damage by irradiated carbohydrates is an Fe²⁺-complex of some species of the radiolysis products. Participation of radiotoxins of carbohydrate origin in radiobiological effects is discussed.     

The Nucleotide Sequence of the rep Gene of Cyanobacterial Plasmid pSM1

The nucleotide sequence was established for the rep gene of plasmid pSM1 isolated from cyanobacteriumPlectonema boryanum CALU 465. Both nucleotide sequence and the encoded amino acid sequences showed 98% homology to the corresponding sequences of small plasmids pPF1, pGL3, pPBS1, pBLX, and pPB1. An active center was identified in the replicative protein sequences.     

Enhanced α-ketoglutaric acid production and recovery in Yarrowia lipolytica yeast by effective pH controlling

The replacement of chemical synthesis by environmentally friendly energy-efficient technologies for production of valuable metabolites is a principal strategy of developing biotechnological industry all over the world. In the present study, we develop a method for α-ketoglutaric acid (KGA) production from rapeseed oil with the use of Yarrowia lipolytica yeast. Sixty strains of Y. lipolytica yeasts were tested for their ability to produce KGA, and the strain Y. lipolytica 212 (Y. lipolytica VKM Y-2412) was selected as a promising KGA producer. Using a three-stage pH controlling, in which pH was 4.5 in the growth phase, then since 72 to 144 h, pH was maintained at 3.5 and in the later phase of acid production, the titration by KOH was switch off, selected strain produced 106.5 g l^?1 of KGA with mass yield of 0.95 g g^?1. KGA in the form of monopotassium salt was isolated from the culture broth and purified. The isolation procedure involved separation of biomass, extraction of residual triglycerides, filtrate bleaching, and acidification with mineral acid (to pH 2.8–3.4), concentration, precipitation of mineral salts, and crystallization of the product. The purity of KGA isolated from the culture filtrate reached 99.1 %.     

New recombinant strains of the yeast <Emphasis Type="Italic">Yarrowia lipolytica</Emphasis> with overexpression of the aconitate hydratase gene for the obtainment of isocitric acid from rapeseed oil

The yeast Yarrowia lipolytica is capable of high-intensity synthesis (overproduction) of citric (CA) and isocitric (ICA) acids under nitrogen limitation. The ratio of the synthesized acids depends on the producing strains used and the expression level of the aconitate hydratase gene (ACO1). Recombinant variants with overexpression of the multicopy ACO1 gene have been obtained based on the natural ICA-producing strain Y. lipolytica 672. A recombinant strain Y. lipolytica 20, which has an isocitrate-citrate ratio shifted towards ICA (2.3: 1) as compared to the parental strain (1.1: 1), has been selected. Culturing of the 20 variant in a 10 L reactor has resulted in the production of 72.6 g/L of ICA and 29.0 g/L of CA with a ratio of 2.5: 1. This makes it possible to regard Y. lipolytica 20 as a promising producer for the development of an industrial process for isocitrate production.     

Larvae of Chironomids (Insecta,Diptera) Encountered in the Mantle Cavity of Zebra Mussels,Dreissena polymorpha (Bivalvia,Dreissenidae)

The paper includes data on species composition of chironomid larvae which were encountered in the mantle cavity of zebra mussels (Dreissena polymorpha) within 7 waterbodies in the Republic of Belarus. All were found to be free‐living species commonly present in periphyton and/or benthos. A long‐term study of the seasonal dynamics of these larvae in Dreissena did not reveal any typical pattern. Our data suppose that chironomids do not have an obligate association with zebra mussels and possibly enter their mantle cavity inadvertently. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Isocitric acid production from rapeseed oil by Yarrowia lipolytica yeast

Production of d _S-threo-isocitric acid (ICA) by yeast meets serious difficulties since it is accompanied by a simultaneous production of citric acid (CA) in significant amounts that reduces the yield of desired product. In order to develop an effective process of ICA production, 60 yeast strains of different genera (Candida, Pichia, Saccharomyces, Torulopsis, and Yarrowia) were tested for their ability to produce ICA from rapeseed oil; as a result, wild-type strain Yarrowia lipolytica VKM Y-2373 and its mutant Y. lipolytica 704-UV4-A/NG50 were selected as promising ICA producers. The effects of temperature, pH, aeration, and concentrations of rapeseed oil, iron, and itaconic acid on ICA production by selected strains were studied. Under optimal conditions (pH 6.0; aeration 50–55 %; rapeseed oil concentration of 20–60 gl^?1, iron ion concentration of 1.2 mg l^?1, and itaconic acid amount of 30 mM), selected strains of Y. lipolytica produced predominantly ICA with a low amount of a by-product, CA.