Alexander Rapoport

• Prof., Ph.D., D.Sc.
• Principal Investigator at University of Latvia

Recent biotechnological research has contributed significantly to the continuous expansion and understanding of the mechanisms of eukaryotic cell functioning in yeast. Nevertheless, the influence of selenium on the resistance of yeast cells and the processes of anhydrobiosis requires extending the existing knowledge. Anhydrobiosis is a mechanism en...

Executive summary Microbes are all pervasive in their distribution and influence on the functioning and well‐being of humans, life in general and the planet. Microbially‐based technologies contribute hugely to the supply of important goods and services we depend upon, such as the provision of food, medicines and clean water. They also offer mechani...

Lignocellulose, the most abundant and renewable plant resource, is a complex of polymers mainly composed of polysaccharides (cellulose and hemicelluloses) and an aromatic polymer (lignin). Utilisation of lignocellulosic biomass for biotechnological applications has increased over the past few years. Xylan is the second most abundant carbohydrate in...

Anhydrobiosis is a state of living organisms during which their metabolism is reversibly delayed or suspended due to a high degree of dehydration. Yeast cells, which are widely used in the food industry, may be induced into this state. The degree of viability of yeast cells undergoing the drying process also depends on rehydration. In an attempt to...

Acetoin is an important bio-product useful in the chemical, food and pharmaceutical industries. Microbial fermentation is the major process for the production of bioacetoin, as the petroleum resources used in chemical methods are depleting day by day. Bioacetoin production using wild microorganisms is an easy, eco-friendly and economical method for...

An interesting development of biotechnology has linked microbial cell immobilisation with nanoparticles. The main task of our research was to reveal the possible influences of differently electrically charged diamond nanoparticles upon physiological characteristics of the yeast Saccharomyces cerevisiae. It was revealed that the adverse impact of th...

Studies on the chemical mechanisms of furfural formation showed the possibility to apply a new differential catalysis of hemicellulose — its depolymerisation and pentose dehydration to furfural. This change led to the increase in furfural yield and essential decrease of cellulose destruction. The lignocellulose residue that remains after the produc...

Production of carotenoids and lipids by Rhodotorula toruloides CBS 14 cultivated on wheat straw hydrolysate was investigated. An ultra-high-performance liquid chromatography (UHPLC) method for carotenoid quantification was developed and validated. Saponification effects on individual carotenoid quantification were identified, and lipid and caroteno...

The benefit of bioaugmentation of activated sludge (AS) with yeasts was tested using AS and wastewaters (WW) that originated from the chemical industry, as well as synthetic WW. A stimulating effect of Saccharomyces cerevisiae on microbial respiration intensity in AS was shown. The added yeast biomass maintained viability in AS, an inhibitory effec...

The ability of cells to adhere to substrates is an important factor for the effectiveness of biotechnologies and bioimplants. This research demonstrates that the statistical distribution of the sizes of the cells (Saccharomyces cerevisiae) attached to the substrate surface correlates with the statistical distribution of electrical potential on the...

Lentinula edodes 3565 and Ganoderma lucidum 9621 were compared for their ability to produce lignocellulolytic enzymes in submerged (SM) and surface liquid (SL) fermentation of hydrolysed colza straw lignin waste that remained after the production of furfural and bioethanol (CS lignin). Application of cultivated mushrooms to dispose of pretreated co...

Mitochondria are dynamic organelles as they continuously undergo fission and fusion. These dynamic processes conduct not only mitochondrial network morphology but also activity regulation and quality control. Saccharomyces cerevisiae has a remarkable capacity to resist stress from dehydration/rehydration. Although mitochondria are noted for their r...

Two Saccharomyces cerevisiae strains, BY4741 and BY4741-derived strain lacking the IST2 gene (ist2Δ), were used to characterise the possible role of cortical endoplasmic reticulum (ER) protein Ist2 upon cell dehydration and subsequent rehydration. For the first time, we show that not only protein components of the plasma membrane (PM), but also at...

Astrobiology is often regarded as the study of life beyond Earth, but here we consider life on Earth through an astrobiological lens. Microbiology has historically focused on various anthropocentric sub‐fields (such as fermented foods or commensals and pathogens of crop plants, livestock, and humans), but addressing key biological questions via ast...

Ethanol produced from renewable biomass, such as lignocellulosic feedstock, is one of the most promising future biofuels. In this paper, rapeseed straw was tested as an abundant and cost-effective renewable resource material for the production of cellulosic glucose. Pre-treatment of this material is an important step to improve the efficiency of su...

Anhydrobiosis is the state of life when cells are exposed to waterless conditions and gradually cease their metabolism. In this study, we determined the sequence of events in Saccharomyces cerevisiae energy metabolism during processes of dehydration and rehydration. The intensities of respiration and acidification of the medium, the amounts of phen...

Carotenoids are an essential group of compounds that may be obtained by microbiological synthesis. They are instrumental in various areas of industry, medicine, agriculture, and ecology. The increase of carotenoids’ demand at the global market is now essential. At the moment, the production of natural carotenoids is more expensive than obtaining th...

Anhydrobiosis is the state of life when cells get into waterless conditions and gradually cease their metabolism. In this study, we determined the sequence of events in Saccharomyces cerevisiae energy metabolism during processes of dehydration and rehydration. The intensities of respiration and acidification of the medium, the amounts of Phenyldica...

Currently major part of the world's energy requirements is fulfilled by fossil resources. Severe economic and environmental problems along with their limited resources are still a major issue. Long-term environmental and commercial concern has focussed into huge research in the past decades to replace fossil fuels with renewable sources of energy....

Background: Xylose transport is one of the bottlenecks in the conversion of lignocellulosic biomass to ethanol. Xylose consumption by the wild-type strains of xylose-utilizing yeasts occurs once glucose is depleted resulting in a long fermentation process and overall slow and incomplete conversion of sugars liberated from lignocellulosic hydrolysa...

Measures of microbial growth, used as indicators of cellular stress, are sometimes quantified at a single time-point. In reality, these measurements are compound representations of length of lag, exponential growth-rate, and other factors. Here, we investigate whether length of lag phase can act as a proxy for stress, using a number of model system...

Background Xylose transport is one of the bottlenecks in the conversion of lignocellulosic biomass to ethanol. Xylose consumption by the wild-type strains of xylose-utilizing yeasts occurs once glucose is depleted resulting in a long fermentation process and overall slow and incomplete conversion of sugars liberated from lignocellulosic hydrolysate...

Background Xylose transport is one of the bottlenecks in the conversion of lignocellulosic biomass to ethanol. Xylose consumption by the wild-type strains of xylose-utilizing yeasts occurs once glucose is depleted resulting in a long fermentation process and overall slow and incomplete conversion of sugars liberated from lignocellulosic hydrolysate...

Anhydrobiosis is a unique state of live organisms in which their metabolism is temporary reversibly suspended as the result of strong dehydration of their cells. This state is widely used currently during large-capacity production of active dry baker’s yeast. Other strains of the yeast Saccharomyces cerevisiae, as well as other yeast species that c...

Benzalkonium chloride (BAC) is highly abundant in wastewaters due to its wide application in household and industrial products. The aim of this research was to compare the resistance of two genetically related strains, Ogataea polymorpha (wild type) and O. polymorpha cat8Δ (recombinant strain), to enhanced concentrations of BAC (>100 mg/L) in terms...

Anhydrobiosis is a unique state of living organisms that provides the possibility of surviving conditions of extreme heat and drought with temporary and reversible suspended processes of metabolism. Beyond its ecological importance in nature, it is used for the production of viable dry microbial preparations, including active dry yeast. During the...

The possibility of using active dry microbial preparations in biotechnological processes is essential for the development of new modern industrial technologies. In this study, we show the possibility of obtaining such preparations of the genetically engineered yeast strain Ogataea (Hansenula) polymorpha with glutathione overproduction. Special pre-...

Yeast cells are able to transition into a state of anhydrobiosis (temporary reversible suspension of metabolism) under conditions of desiccation. One of the most efficient approaches for understanding the mechanisms underlying resistance to dehydration‐rehydration is to identify yeasts which are stable under such treatments, and compare them with m...

Under natural conditions yeast cells as well as other microorganisms are regularly subjected to the influence of severe drought, which leads to their serious dehydration. The dry seasons are then changed by rains and there is a restoration of normal water potential inside the cells. To survive such seasonal changes a lot of vegetative microbial cel...

This study investigates biofuel production from wheat straw hydrolysate, from which furfural was extracted using a patented method developed at the Latvian State Institute of Wood Chemistry. The solid remainder after furfural extraction, corresponding to 67.6% of the wheat straw dry matter, contained 69.9% cellulose of which 4% was decomposed durin...

We show for the first time that a recombinant strain of yeast Ogataea (Hansenula) polymorpha is at least as tolerant to dehydration-rehydration treatment as the wild type strain. It is believed that this unusual characteristic of this recombinant yeast strain is linked with its ability to overproduce glutathione. Based on plasma membrane permeabili...

Microbial cells can enter a state of anhydrobiosis under desiccating conditions. One of the main determinants of viability during dehydration-rehydration cycles is structural integrity of the plasma membrane. Whereas much is known about phase transitions of the lipid bilayer, there is a paucity of information on changes in activity of plasma membra...

The effect of temperature, time and amount of enzyme on hydrolysis of wheat straw lignocellulose remaining after furfural production was studied. The residual substrate was subjected to enzymatic hydrolysis at different temperatures — 45 °C, 50 °C and 55 °C. Hydrolysis time was 72 hours, and samples were taken every 24 hours. The maximum glucose yi...

Anhydrobiosis is a unique phenomenon of nature which gives possibility to various live organisms to survive during very hot and dry seasons of the year. It is the state in which all processes of metabolism are temporarily reversibly suspended as the result of strong dehydration of the cells. The state of anhydrobiosis is used for industrial product...

The effect of lignocellulose and lignin on growth of mycelium of mushroom Lentinula edodes and laccase activity in cultivation medium was studied. It was shown that cultivation of L. edodes mycelium in liquid nutrient medium with addition of 0.25-0.5% of kraft lignin increased mycelium biomass yield approximately two times compared with reference c...

Dehydration of yeast cells causes them to enter a state of anhydrobiosis in which their metabolism is temporarily and reversibly suspended. This unique state among organisms is currently used in the production of active dry yeasts, mainly used in baking and winemaking. In recent decades non-conventional applications of yeast dehydration have been p...

The state of anhydrobiosis is linked with the reversible delay of metabolism as a result of strong dehydration of cells, and is widely distributed in nature. A number of factors responsible for the maintenance of organisms’ viability in these conditions were revealed. This study was directed to understanding how changes in cell wall structure may i...

A new test-system was developed for rapid evaluation of the cytoprotective potential of substances which can be included in cosmetics and health care compositions. It was evaluated by changes of the viability of yeast cells after dehydration/rehydration (D/R) treatment. To check the efficiency of proposed test system we studied the effects of water...

Small and uncharged glycerol is an important molecule for yeast metabolism and osmoadaptation. Using a series of S. cerevisiae BY4741-derived mutants lacking genes encoding a glycerol exporter (Fps1p) and/or importer (Stl1p) and/or the last kinase of the HOG pathway (Hog1p), we studied their phenotypes and various physiological characteristics with...

Yeast cells are well adapted to interfacial habitats, such as the surfaces of soil or plants, where they can resist frequent fluctuations between wet and dry conditions. Saccharomyces cerevisiae is recognized as an anhydrobiotic organism, and it has been the subject of numerous studies that aimed to elucidate this ability. Extensive data have been...

Anhydrobiosis is a unique state of living organisms when metabolism is temporarily and reversibly delayed in response to the extreme desiccation of cells. Production of dry active preparations of yeast grown under anaerobic conditions is not currently possible since preparations are extremely sensitive to the dehydration procedure, in spite they co...

We have demonstrated that a thermotolerant yeast strain (Saccharomyces cerevisiae TS1) is much more resistant to dehydration-rehydration treatments than a mesophilic strain of S. cerevisiae. Yeast resistance to dehydration-rehydration was found to be similar in cells from exponential and stationary growth phases. Under controlled rehydration condit...

This study was performed with the goal of revealing if the dehydration procedure used in our new immobilisation method noticeably decreases the viability of yeast cells in immobilised preparations. Various yeasts were used in this research: Saccharomyces cerevisiae cells that were rather sensitive to dehydration and had been aerobically grown in an...

The yeast Saccharomyces cerevisiae was shown to be extremely sensitive to dehydration-rehydration treatments when stationary phase cells were subjected to conditions of severe oxygen limitation, unlike the same cells grown in aerobic conditions. The viability of dehydrated anaerobically grown yeast cells never exceeded 2 %. It was not possible to i...

One of the most important topics of modern biotechnology is linked with the problem of obtaining of bioethanol and other valuable compounds from the renewable resources. Latvian scientists developed completely new unique technology of simultaneous production of furfural and bioethanol from hardwood. This technology is based on new way for the obtai...

The current study evaluated a newer method, which includes a dehydration step, of immobilising Saccharomyces cerevisiae L-77 and Saccharomyces cerevisiae L-73 onto hydroxylapatite and chamotte ceramic supports. Efficiency of cell immobilisation on chamotte was significantly higher than hydroxylapatite. Immobilised yeast preparations were investigat...

Yeasts grow at very different potassium concentrations adapting their intracellular cation levels to changes in the external environment. Potassium homeostasis is maintained with the help of several transporters mediating the uptake and efflux of potassium with various affinities and mechanisms. In the model yeast S. cerevisiae, two uptake systems,...

The influence of sodium chloride (NaCl) treatment on the antifungal activity of the bacterium Pseudomonas aurantiaca, a producer of biopesticide for vegetable plants, was investigated. It was shown that an increase in the NaCl concentration in incubation solutions from 1 M to 3 M led to a significant increase in the antifungal activity of this bact...

Hydroxyapatite (HAP) ceramics was tested for the first time for the possibility of being used as a new carrier for the immobilisation of yeast cells that are both model organisms for eukaryotic cell investigations and producers, which is important in classical and modern biotechnological processes. It was shown that under typical immobilisation con...

The influence of calcium and magnesium ions on resistance to dehydration in the yeast, Saccharomyces cerevisiae, was investigated. Magnesium ion availability directly influenced yeast cells' resistance to dehydration and, when additionally supplemented with calcium ions, this provided further significant increase of yeast resistance to dehydration....

We have found that incubation in lactose solutions (0.75 M) of yeast culture Saccharomyces cerevisiae sensitive to dehydration damage increased the stability of the cells during dehydration. Simultaneously with this increase in viability, a decrease in plasma membrane permeability during rehydration was seen. Using Fourier transform infrared spectr...

Dehydration of microorganisms, rendering them anhydrobiotic, is often an efficient method for the short and long term conservation of different strain-producers. However, some biotechnologically important recombinant bacterial strains are extremely sensitive to conventional treatment. We describe appropriate conditions during dehydration of the rec...

Yeast is known to experience in natural and industrial conditions cycles of dehydration–rehydration. Several molecular mechanisms can be triggered in response to this and other environmental stressors and to rescue yeast cells of the cytotoxic effect. Since heat shock proteins constitute one of the most important systems of the response to stress w...

Human cells are the eukaryotic ones. Simulation of wide-spectrum electromagnetic radiation influence on eu-karyotic cells was performed with yeast which is usually used now in molecular biological and medical biological investigations as the ideal model of eukaryotic system. The aim of the research was to observe possible induced alterations of the...

Human cells are the eukaryotic ones. Simulation of wide-spectrum electromagnetic radiation influence on eukaryotic cells was performed with yeast which is usually used now in molecular biological and medical biological investigations as the ideal model of eukaryotic system. The aim of the research was to observe possible induced alterations of the...

The presented material concerns the theoretical basis for obtaining high-quality active dry biopreparations. It deals with the present understanding of anabiosis, contains data on yeast resistance against dehydration and the limits for preserving the viability of microorganisms in anabiosis. The process of water transport in yeast biomass during de...

This study examined the Cr(VI), Cu(II), Zn(II), Cd(II), Pb(II) sorption by intact and dehydrated Candida utilis cells. The anion [Cr2O7]2− and cation Me2+ sorption kinetics was investigated in both single- and dual-metal situations. Uptake of chromate anions occurred much more slowly singularly than with metal cations. A combination of Pb or Cu and...

The Cr(VI) sorption kinetics by intact and dehydrated Candida utilis cells were studied. Yeast dehydration led to enhanced Cr(VI) sorption activity by cells during the first 15–20 min of rehydration. In experiments with K2Cr2O7 as a chromium source, [Cr2O7]2− was converted into [CrO4]2− during incubation with dehydrated biomass. An effect of the co...

The osmotolerant yeast Debaryomyces hansenii is highly resistant to dehydration stress and this tolerance was more pronounced for cells taken from the exponential growth phase than from the stationary phase. Growth of D. hansenii in medium containing 10% (w v−1) NaCl, resulted in an additional increase in cellular resistance to dehydration, which w...

An effect of chromium(VI) ions on the growth and bioaccumulation properties of growing cells of Candida Utilis was studied. Molasses media for yeast growth containing 20 g glucose l−1 and 50+500 mg Cr(VI) l−1 were used in batch cultivation. Addition of 100 mg Cr(VI) l−1 resulted in a threefold decrease in the cell concentration, as compared with th...

The intensification of biosynthesis of fructooligosaccharides in the presence of high salt concentrations was observed during sucrose (10%) fermentation by Zymomonas mobilis 113S. A 0.6 M NaCl concentration led to an increase of oligosaccharide productivity by 3.5-fold. Sorbitol formation was increased in the presence of 0.16 M NaCl and was inhibit...

The immobilization of yeast Saccharomyces cerevisiae, their growth and ethanol production were investigated using untreated and modified stainless steel wire spheres (WS) as carriers. The carrier surface was modified by oxidation, by treatment with titanium (IV) chloride (TiCl4) or by γ-aminopropyltrietoxysilane (AS) in an attempt to raise the effi...

The effects of dehydration/rehydration on two strains of Saccharomyces cerevisiae: S600, a metabolically engineered xylose-utilising strain, and H158, the non-xylose-utilising host strain; and on the naturally xylose-utilising yeast Pachysolen tannophilus CBS 4044, were compared after glucose and xylose utilisation respectively. The yeast strains d...

Intracellular substances released into the medium during rehydration of dry yeast cells can significantly improve the quality of a synthetic medium. Acceleration of yeast growth in this medium and increased yield of biomass are observed simultaneously. The change in the molecular arrangement of intracellular membranes as a result of the strong dehy...

Anhydrobiosis is one of the most interesting phenomena of nature showing practically unlimited potentials of live organisms to survive extreme conditions of environment. Its investigations gave a lot of new information for the better understanding of water significance for the maintenance of cell viability. Using yeast cells as a simple and very co...

Different species of yeast exhibit noticeable differences in their ability to sorb Cr(VI). The sorption ability of dehydrated cells is considerably higher than that of intact cells and optimal sorption of chromium takes place at physiological (30°C) or elevated (45°C) temperatures.

When studying the dehydration effect of the eukaryotic cells on the structural and functional characteristics of the cytoplasmic membrane, it was established that serious rearrangements of its molecular organization showing up in a drastic increase in the permeability properties occurred in the yeast when the range of residual humidities of the ord...

Addition to the nutrient medium of the extracts of camomile, nettle, mint, or Saint-John's-wort to a concentration of 0.5-4% was established to activate the yeast growth. The maximum effect was recorded on the addition of the extracts to the poor "water" medium. The extracts of camomile and Saint-John's-wort were shown to inhibit the alcohol dehydr...

The effect of dehydration on the cytoplasmic membrane of yeast cells was studied using the method of spin labels. In the course of dehydration, the thermoinduced transition of lipids from the solid to a liquid-crystalline state was found to occur at a higher temperature as compared with native membranes.

From 26 to 43% of RNA undergoes degradation in yeast cells when they pass into the state of anabiosis. Most of the degradation was found to occur at the first stage of cell dehydration when free water was removed from the cells. The mechanism of RNA degradation is supposed to involve enzyme-catalysed processes which are realised in the cell at the...