Nikolay Vassilev - Academia.edu (original) (raw)

Papers by Nikolay Vassilev

Frontiers in Plant Science

In the last 10-15 years, the wide application of bioformulated plant beneficial microorganisms is... more In the last 10-15 years, the wide application of bioformulated plant beneficial microorganisms is accepted as an effective alternative of chemical agro-products. Two main problems can be distinguished in their production and application: (a) economical competiveness based on the overall upstream and downstream operational costs, and (b) development of commercial products with a high soil-plant colonization potential in controlled conditions but not able to effectively mobilize soil nutrients and/or combat plant pathogens in the field. To solve the above problems, microbe-based formulations produced by immobilization methods are gaining attention as they demonstrate a large number of advantages compared to other solid and liquid formulations. This mini-review summarizes the knowledge of additional compounds that form part of the bioformulations. The additives can exert economical, price-decreasing effects as bulking agents or direct effects improving microbial survival during storage and after introduction into soil with simultaneous beneficial effects on soil and plants. In some studies, combinations of additives are used with a complex impact, which improves the overall characteristics of the final products. Special attention is paid to polysaccharide carriers and their derivates, which play stimulatory role on plants but are less studied. The mini-review also focuses on the potential difficulty in evaluating the effects of complex bio-formulations.

Process Biochemistry, 1997

ABSTRACT Olive mill waste water (OMW), supplemented or not with ammonium sulphate and rock phosph... more ABSTRACT Olive mill waste water (OMW), supplemented or not with ammonium sulphate and rock phosphate (RP), was applied as a medium in a shake-flask repeated-batch fermentation with Aspergillus niger immobilized on polyurethane sponge. Compared to other treatments, the results showed higher growth of the immobilized mycelium and significant reduction of the total phenols when the waste material was enriched with RP and ammonium sulphate (N). The immobilized fungus solubilized the RP with a maximum level of soluble P of 0·58 g/litre reached during the fourth batch cycle of the OMW+RP treatment. Depending on the medium composition, three types of treated OMW were produced which could be further used for various purposes.

Bioresource Technology, 1998

... OF MICROBIALLY TREATED OLIVE MILL WASTEWATER ON TRIFOLIUM PLANTS Nikolay Vassilev,a* Maria Va... more ... OF MICROBIALLY TREATED OLIVE MILL WASTEWATER ON TRIFOLIUM PLANTS Nikolay Vassilev,a* Maria Vassileva,a ... REFERENCES Barea, JM, Escudero, JL AzconAguilar, C. (1980). ... Effetto inquitante delle acgue reflue della lavorazione delle olive su terreno agrario. ...

Minerva, 2007

Aim. One of the challenges in the field of arbuscular mycorrhizal fungi (AM) is their cultivation... more Aim. One of the challenges in the field of arbuscular mycorrhizal fungi (AM) is their cultivation in the absence of host roots and preparation of AM-inoculants free of contaminants. The use of R i T-DNA transformed roots has permitted increased AM spore production which was further improved by using twocompartment Petri dishes. Methods. In this work, we proved possible development of Glomus intraradices in liquid media which included locust bean gum (LBG) and k-carrageenan. G. intraradices formed about 1700-2400 spores in 12 weeks. Entrapment of the AM spores was carried out directly thus avoiding the laborious "conventional" technique for spore entrapment. Results. In this work we produced beads containing k-carrageenan/AM mycelium, LBG/AM myceli-um+k-carrageenan free of AM, and LBG/AM myceli-um+k-carrageenan/AM mycelium where the spore number per bead ranged from 1 to 7, 3 to 11, and 4 to 10, respectively. Further introduction of gel-bead-AM formulations into soil-plant system demonstrated their efficiency. Particularly combinations between LBG and k-carrageenan resulted in higher level of mycorrhization, increased plant growth and phosphate acquisition compared with non-inoculated control and treatments that received free AM inoculum. Conclusion. This technique could be further improved by using other gel materials, AM fungi and/or plant growth promoting microorganisms such as nitro

Chem Eng Commun, 2007

Bacillus thuringiensis in entrapped in k-carrageenan was capable of producing indole-3-acetic aci... more Bacillus thuringiensis in entrapped in k-carrageenan was capable of producing indole-3-acetic acid (IAA) in the presence of rock phosphate ore (RPO). After five repeated batch fermentation experiments, an average of 6.9 mg/L IAA was recorded in the presence of 1.5 g/L RPO and 4.7 mg/L IAA in the RPO-free control. The bacterium simultaneously solubilized phosphates with a maximum soluble P of 115 mg/L and

Journal of Biotechnology, Jul 30, 1998

Spores of Aspergillus niger were encapsulated in agar, calcium alginate and k-carrageenan and fur... more Spores of Aspergillus niger were encapsulated in agar, calcium alginate and k-carrageenan and further applied in citric acid production during six repeated batch cultivations. Rock phosphate (RP) at concentrations of 3 g l − 1 and 7 g l − 1 was supplemented to the culture medium to test encapsulated-fungus solubilizing capability. The highest average citric acid productivity of 0.15 g l − 1 h − 1 was reached with alginate-bead-encapsulated A. niger on RP-free culture medium while agar seemed to be the most suitable carrier on RP-supplemented medium. Accordingly, the highest average soluble P concentration of 0.20 g l − 1 batch − 1 was obtained with agar-cell beads as compared with other encapsulated systems.

Biotechnology Letters

Summary Aspergillus terreus NRRC 1960 spores were entrapped in calcium alginate gel beads or alte... more Summary Aspergillus terreus NRRC 1960 spores were entrapped in calcium alginate gel beads or alternotely the fungal mycelium was immobilized either on Celite R-626 or in agar gel cubes, and the biocatalyst was employed both in repeated batch and in continuous ...

La Chimica E L Industria, 2003

Bacteria in Agrobiology: Stress Management, 2011

The role of plant growth-promoting rhizobacteria (PGPR) in phytoremediation strategies in trace e... more The role of plant growth-promoting rhizobacteria (PGPR) in phytoremediation strategies in trace element-contaminated soils is not well understood. It is known that these bacteria have many abilities, which characterize them as a special tool in the plant rhizosphere. They ...

Microbial biotechnology, Jan 25, 2015

A biotechnological strategy for the production of an alternative P fertilizer is described in thi... more A biotechnological strategy for the production of an alternative P fertilizer is described in this work. The fertilizer was produced through rock phosphate (RP) solubilization by Aspergillus niger in a solid-state fermentation (SSF) with sugarcane bagasse as substrate. SSF conditions were optimized by the surface response methodology after an initial screening of factors with significant effect on RP solubilization. The optimized levels of the factors were 865 mg of biochar, 250 mg of RP, 270 mg of sucrose and 6.2 ml of water per gram of bagasse. At this optimal setting, 8.6 mg of water-soluble P per gram of bagasse was achieved, representing an increase of 2.4 times over the non-optimized condition. The optimized SSF product was partially incinerated at 350°C (SB-350) and 500°C (SB-500) to reduce its volume and, consequently, increase P concentration. The post-processed formulations of the SSF product were evaluated in a soil-plant experiment. The formulations SB-350 and SB-500 inc...

Applied microbiology and biotechnology, 2015

The massive application of chemical fertilizers to support crop production has resulted in soil, ... more The massive application of chemical fertilizers to support crop production has resulted in soil, water, and air pollution at a global scale. In the same time, this situation escalated consumers' concerns regarding quality and safety of food production which, due to increase of fertilizer prices, have provoked corresponding price increase of food products. It is widely accepted that the only solution is to boost exploitation of plant-beneficial microorganisms which in conditions of undisturbed soils play a key role in increasing the availability of minerals that otherwise are inaccessible to plants. This review paper is focused on the employment of microbial inoculants and their production and formulation. Special attention is given to biotechniques that are not fully exploited as tools for biofertilizer manufacturing such as microbial co-cultivation and co-immobilization. Another emerging area includes biotechnological production and combined usage of microorganisms/active natur...

Bacteria in Agrobiology: Stress Management, 2011

The role of plant growth-promoting rhizobacteria (PGPR) in phytoremediation strategies in trace e... more The role of plant growth-promoting rhizobacteria (PGPR) in phytoremediation strategies in trace element-contaminated soils is not well understood. It is known that these bacteria have many abilities, which characterize them as a special tool in the plant rhizosphere. They ...

Critical Reviews in Environmental Science and Technology, 2011

At the interface between the atmosphere and the earth&amp... more At the interface between the atmosphere and the earth's crust and being the substrate for natural and agricultural ecosystems, the soil is open to inputs of heavy metals from many sources. Pollution of the biosphere with toxic metals has accelerated dramatically since the beginning of the industrial revolution. In response to a growing need to address environmental contamination, many remediation

Bioresource Technology, 2000

Penicicllium variabile P16, encapsulated in agar or calcium alginate, produced gluconic acid in r... more Penicicllium variabile P16, encapsulated in agar or calcium alginate, produced gluconic acid in repeated batch shake-flask cultures. Agar-encapsulated mycelium produced 21% more gluconic acid than Ca-alginate-encapsulated fungus, and was utilized in experiments for rock phosphate solubilization. The latter was closely related to gluconic acid production, which was affected by the presence of rock phosphate. Maximum amounts of dissolved P (0.226

Applied Soil Ecology, 2010

Penicicllium variabile P16, encapsulated in agar or calcium alginate, produced gluconic acid in r... more Penicicllium variabile P16, encapsulated in agar or calcium alginate, produced gluconic acid in repeated batch shake-flask cultures. Agar-encapsulated mycelium produced 21% more gluconic acid than Ca-alginate-encapsulated fungus, and was utilized in ...

Frontiers in Plant Science

In the last 10-15 years, the wide application of bioformulated plant beneficial microorganisms is... more In the last 10-15 years, the wide application of bioformulated plant beneficial microorganisms is accepted as an effective alternative of chemical agro-products. Two main problems can be distinguished in their production and application: (a) economical competiveness based on the overall upstream and downstream operational costs, and (b) development of commercial products with a high soil-plant colonization potential in controlled conditions but not able to effectively mobilize soil nutrients and/or combat plant pathogens in the field. To solve the above problems, microbe-based formulations produced by immobilization methods are gaining attention as they demonstrate a large number of advantages compared to other solid and liquid formulations. This mini-review summarizes the knowledge of additional compounds that form part of the bioformulations. The additives can exert economical, price-decreasing effects as bulking agents or direct effects improving microbial survival during storage and after introduction into soil with simultaneous beneficial effects on soil and plants. In some studies, combinations of additives are used with a complex impact, which improves the overall characteristics of the final products. Special attention is paid to polysaccharide carriers and their derivates, which play stimulatory role on plants but are less studied. The mini-review also focuses on the potential difficulty in evaluating the effects of complex bio-formulations.

Process Biochemistry, 1997

ABSTRACT Olive mill waste water (OMW), supplemented or not with ammonium sulphate and rock phosph... more ABSTRACT Olive mill waste water (OMW), supplemented or not with ammonium sulphate and rock phosphate (RP), was applied as a medium in a shake-flask repeated-batch fermentation with Aspergillus niger immobilized on polyurethane sponge. Compared to other treatments, the results showed higher growth of the immobilized mycelium and significant reduction of the total phenols when the waste material was enriched with RP and ammonium sulphate (N). The immobilized fungus solubilized the RP with a maximum level of soluble P of 0·58 g/litre reached during the fourth batch cycle of the OMW+RP treatment. Depending on the medium composition, three types of treated OMW were produced which could be further used for various purposes.

Bioresource Technology, 1998

... OF MICROBIALLY TREATED OLIVE MILL WASTEWATER ON TRIFOLIUM PLANTS Nikolay Vassilev,a* Maria Va... more ... OF MICROBIALLY TREATED OLIVE MILL WASTEWATER ON TRIFOLIUM PLANTS Nikolay Vassilev,a* Maria Vassileva,a ... REFERENCES Barea, JM, Escudero, JL AzconAguilar, C. (1980). ... Effetto inquitante delle acgue reflue della lavorazione delle olive su terreno agrario. ...

Minerva, 2007

Aim. One of the challenges in the field of arbuscular mycorrhizal fungi (AM) is their cultivation... more Aim. One of the challenges in the field of arbuscular mycorrhizal fungi (AM) is their cultivation in the absence of host roots and preparation of AM-inoculants free of contaminants. The use of R i T-DNA transformed roots has permitted increased AM spore production which was further improved by using twocompartment Petri dishes. Methods. In this work, we proved possible development of Glomus intraradices in liquid media which included locust bean gum (LBG) and k-carrageenan. G. intraradices formed about 1700-2400 spores in 12 weeks. Entrapment of the AM spores was carried out directly thus avoiding the laborious "conventional" technique for spore entrapment. Results. In this work we produced beads containing k-carrageenan/AM mycelium, LBG/AM myceli-um+k-carrageenan free of AM, and LBG/AM myceli-um+k-carrageenan/AM mycelium where the spore number per bead ranged from 1 to 7, 3 to 11, and 4 to 10, respectively. Further introduction of gel-bead-AM formulations into soil-plant system demonstrated their efficiency. Particularly combinations between LBG and k-carrageenan resulted in higher level of mycorrhization, increased plant growth and phosphate acquisition compared with non-inoculated control and treatments that received free AM inoculum. Conclusion. This technique could be further improved by using other gel materials, AM fungi and/or plant growth promoting microorganisms such as nitro

Chem Eng Commun, 2007

Bacillus thuringiensis in entrapped in k-carrageenan was capable of producing indole-3-acetic aci... more Bacillus thuringiensis in entrapped in k-carrageenan was capable of producing indole-3-acetic acid (IAA) in the presence of rock phosphate ore (RPO). After five repeated batch fermentation experiments, an average of 6.9 mg/L IAA was recorded in the presence of 1.5 g/L RPO and 4.7 mg/L IAA in the RPO-free control. The bacterium simultaneously solubilized phosphates with a maximum soluble P of 115 mg/L and

Journal of Biotechnology, Jul 30, 1998

Spores of Aspergillus niger were encapsulated in agar, calcium alginate and k-carrageenan and fur... more Spores of Aspergillus niger were encapsulated in agar, calcium alginate and k-carrageenan and further applied in citric acid production during six repeated batch cultivations. Rock phosphate (RP) at concentrations of 3 g l − 1 and 7 g l − 1 was supplemented to the culture medium to test encapsulated-fungus solubilizing capability. The highest average citric acid productivity of 0.15 g l − 1 h − 1 was reached with alginate-bead-encapsulated A. niger on RP-free culture medium while agar seemed to be the most suitable carrier on RP-supplemented medium. Accordingly, the highest average soluble P concentration of 0.20 g l − 1 batch − 1 was obtained with agar-cell beads as compared with other encapsulated systems.

Biotechnology Letters

Summary Aspergillus terreus NRRC 1960 spores were entrapped in calcium alginate gel beads or alte... more Summary Aspergillus terreus NRRC 1960 spores were entrapped in calcium alginate gel beads or alternotely the fungal mycelium was immobilized either on Celite R-626 or in agar gel cubes, and the biocatalyst was employed both in repeated batch and in continuous ...

La Chimica E L Industria, 2003

Bacteria in Agrobiology: Stress Management, 2011

The role of plant growth-promoting rhizobacteria (PGPR) in phytoremediation strategies in trace e... more The role of plant growth-promoting rhizobacteria (PGPR) in phytoremediation strategies in trace element-contaminated soils is not well understood. It is known that these bacteria have many abilities, which characterize them as a special tool in the plant rhizosphere. They ...

Microbial biotechnology, Jan 25, 2015

A biotechnological strategy for the production of an alternative P fertilizer is described in thi... more A biotechnological strategy for the production of an alternative P fertilizer is described in this work. The fertilizer was produced through rock phosphate (RP) solubilization by Aspergillus niger in a solid-state fermentation (SSF) with sugarcane bagasse as substrate. SSF conditions were optimized by the surface response methodology after an initial screening of factors with significant effect on RP solubilization. The optimized levels of the factors were 865 mg of biochar, 250 mg of RP, 270 mg of sucrose and 6.2 ml of water per gram of bagasse. At this optimal setting, 8.6 mg of water-soluble P per gram of bagasse was achieved, representing an increase of 2.4 times over the non-optimized condition. The optimized SSF product was partially incinerated at 350°C (SB-350) and 500°C (SB-500) to reduce its volume and, consequently, increase P concentration. The post-processed formulations of the SSF product were evaluated in a soil-plant experiment. The formulations SB-350 and SB-500 inc...

Applied microbiology and biotechnology, 2015

The massive application of chemical fertilizers to support crop production has resulted in soil, ... more The massive application of chemical fertilizers to support crop production has resulted in soil, water, and air pollution at a global scale. In the same time, this situation escalated consumers' concerns regarding quality and safety of food production which, due to increase of fertilizer prices, have provoked corresponding price increase of food products. It is widely accepted that the only solution is to boost exploitation of plant-beneficial microorganisms which in conditions of undisturbed soils play a key role in increasing the availability of minerals that otherwise are inaccessible to plants. This review paper is focused on the employment of microbial inoculants and their production and formulation. Special attention is given to biotechniques that are not fully exploited as tools for biofertilizer manufacturing such as microbial co-cultivation and co-immobilization. Another emerging area includes biotechnological production and combined usage of microorganisms/active natur...

Bacteria in Agrobiology: Stress Management, 2011

The role of plant growth-promoting rhizobacteria (PGPR) in phytoremediation strategies in trace e... more The role of plant growth-promoting rhizobacteria (PGPR) in phytoremediation strategies in trace element-contaminated soils is not well understood. It is known that these bacteria have many abilities, which characterize them as a special tool in the plant rhizosphere. They ...

Critical Reviews in Environmental Science and Technology, 2011

At the interface between the atmosphere and the earth&amp... more At the interface between the atmosphere and the earth's crust and being the substrate for natural and agricultural ecosystems, the soil is open to inputs of heavy metals from many sources. Pollution of the biosphere with toxic metals has accelerated dramatically since the beginning of the industrial revolution. In response to a growing need to address environmental contamination, many remediation

Bioresource Technology, 2000

Penicicllium variabile P16, encapsulated in agar or calcium alginate, produced gluconic acid in r... more Penicicllium variabile P16, encapsulated in agar or calcium alginate, produced gluconic acid in repeated batch shake-flask cultures. Agar-encapsulated mycelium produced 21% more gluconic acid than Ca-alginate-encapsulated fungus, and was utilized in experiments for rock phosphate solubilization. The latter was closely related to gluconic acid production, which was affected by the presence of rock phosphate. Maximum amounts of dissolved P (0.226

Applied Soil Ecology, 2010

Penicicllium variabile P16, encapsulated in agar or calcium alginate, produced gluconic acid in r... more Penicicllium variabile P16, encapsulated in agar or calcium alginate, produced gluconic acid in repeated batch shake-flask cultures. Agar-encapsulated mycelium produced 21% more gluconic acid than Ca-alginate-encapsulated fungus, and was utilized in ...