Veneta Groudeva

The microbial community of Vetiver root and its involvement into essential oil biogenesis.

Vetiver is the only grass cultivated worldwide for the root essential oil, which is a mixture of sesquiterpene alcohols and hydrocarbons, used extensively in perfumery and cosmetics. Light and transmission electron microscopy demonstrated the presence of bacteria in the cortical parenchymatous essential oil-producing cells and in the lysigen lacunae in close association with the essential oil. This finding and the evidence that axenic Vetiver produces in vitro only trace amounts of oil with a strikingly different composition compared with the oils from in vivo Vetiver plants stimulated the hypothesis of an involvement of these bacteria in the oil metabolism. We used culture-based and culture-independent approaches to analyse the microbial community of the Vetiver root. Results demonstrate a broad phylogenetic spectrum of bacteria, including alpha-, beta- and gamma-Proteobacteria, high-G+C-content Gram-positive bacteria, and microbes belonging to the Fibrobacteres/Acidobacteria group. We isolated root-associated bacteria and showed that most of them are able to grow by using oil sesquiterpenes as a carbon source and to metabolize them releasing into the medium a large number of compounds typically found in commercial Vetiver oils. Several bacteria were also able to induce gene expression of a Vetiver sesquiterpene synthase. These results support the intriguing hypothesis that bacteria may have a role in essential oil biosynthesis opening the possibility to use them to manoeuvre the Vetiver oil molecular structure.

Isolation and Identification of Arsenic-Transforming Bacteria from Arsenic Contaminated Sites in Bulgaria

ABSTRACT Five environmental sites in Bulgaria were sampled for bacterial isolates that could transform different arsenic forms. In total, 108 bacterial strains that could grow in the presence of high concentrations of arsenic species were isolated. Only 27 from all strains show the transforming abilities. These isolates were enriched from the sediment samples, the performed classical taxonomy and analysis of the 16S rDNA gene sequence revealed them to belong to β- and γ-Proteobacteria and in particular in genera Pseudomonas, Azoarcus and Alcaligenes.

MICROBIAL TOXICITY OF ETHANOLAMINES

ABSTRACT Metal working fluids (MWFs) are used in metal working industries in processes like grinding, turning, drilling and cutting. In the presence of water the complex mixture of materials in metal working fluids will be susceptible to microbial deterioration. The control of contamination of MWFs usually is performed by the addition of different antimicrobial agents (biocides). Alkanolamines are used in metal working fluids as corrosion inhibitors but they have also antimicrobial effect. Studies of few different alkanolamines showed their antimicrobial effect to be enhanced at high pH. From the other hand, development of resistant populations occurs. The aim of this study was to evaluate the degree of toxicity of mono-, di- and triethanolamine for bacterial strains isolated from metal working fluids at different pH values and different concentration.

Bacterial Microflora of Contaminated Metalworking Fluids

ABSTRACT Metal working fluids (MWF) are commonly used in manufacturing and machining industries. There are four major classes of MWF: (i) which contain lubricant base oils without water (straight oils), (ii) composed of an aqueous oil emulsion with oil in high concentration (soluble oils) or (iii) lower concentration (semi-synthetic MWF) and (iv)formulated with no petroleum oils (synthetic fluid). Historically, microbial contamination of metal working fluids has been a problem in the metalworking industries, primarily because of potential adverse health effects and microbial growth effects on fluid quality and performance. Metalworking fluids are chemically complex mixtures. Such mixtures render MWFs potentially toxic to the environment. One solution to the disposal problem is on-site biological treatment of waste MWFs, using bioreactor systems. Bioaugmentation with selected strains may improve the opportunity to create more reproducible system. In this study the bacterial microflora of soluble oil and synthetic metalworking fluid in-use was quantified, isolated and tentatively identified. An indicator plates for dehydrogenase activity were used in attempt to demonstrate the potential of bacteria isolated from contaminated metalworking fluids to utilize hydrocarbons—a component of MWFs.

Bioleaching of a Rich-In-Carbonates Copper Ore at Alkaline pH

A rich-in- carbonates copper ore was subjected to bioleaching under alkaline pH conditions by means of different microorganisms or their metabolites. The ore contained 1.40% copper, 1.94% sulphur, 3.25% iron and 20.3% carbonates, and had a pH of 8.6 and a highly positive net neutralization potential (325 kg CaCO3/t). Copper was present mainly as different sulphide minerals (bornite, covellite, chalcopyrite). The leaching was carried out by means of the shake-flask technique at 32 oC using finely ground (minus 100 μm) ore. The following microorganisms were used to leach the sample: ammonifying bacteria (related to the genera Bacillus, Acinetocater and Vibrio); heterotrophic bacteria (Acetobacter and Pseudomonas) and fungi (Asperillus niger and Penicillium chrysogenum) producing citric acid; heterotrophic bacteria (Micrococcus, Alcaligenes and Bacillus) producing amino acids (mainly alanine); basophilic chemolithotrophic bacteria (Thiobacillus thioparus, Hallothiobacillus neapolitanus, Starkeya novella; ”silicate bacteria” (Bacillus circulans) producing organic acids and exopolysaccharides; bacteria possessing urease enzymatic activity (Corynebacterium). The best results were achieved by means of a mixed culture of urease-possessing bacteria, which under certain conditions was able to solubilize 64.4% of the copper within 30 days of leaching.

Biogenic iron compounds: XRD, Mossbauer and FTIR study

AbstractMaterials based on biogenic iron oxides, which are a product of the metabolic activities of the neutrophilic iron-oxidizing bacteria (NIOB) from Sphaerotilus-Leptothrix group, were investigated. Natural microbial probes were collected from freshwater flow from Vitosha Mountain (Bulgaria) and cultivated under laboratory conditions in respect to select suitable cultures and conditions (nutrition media) for biomaterial accumulation of biogenic oxides. Samples were studied by physicochemical methods: X-ray diffraction, Mossbauer spectroscopy and IR spectroscopy. Their phase composition and physicochemical properties were obtained. Presence of both amorphous and crystal phase (ultra- and highly dispersed particles) was proved. Iron-containing compound in the natural biomass consists of α-FeOOH. The cultivated materials have more complex composition with iron-containing ingredients as α-FeOOH, Γ-FeOOH, Γ-Fe2O3 and Fe3O4. The sample of natural biomass was tested in reaction of CO oxidation and it showed potential to be used as catalyst support.

Microbial Diversity in Heavy-Metal Polluted Waters

ABSTRACT Indigenious water microflora as well as the presence of metal- and xenobiotic biotransforming bacteria were investigated in waters near the KCM Pb-Zn smelter, South Bulgaria. Content of As, Hg, Cd, Mn, Pb, Cu and Zn exceeded in times the maximum permission standart. Absence of some microbial groups demonstrated a change in the microbial community structure in the region. Ecotoxicology test ISO/DIS 10712.2 displayed toxic environmental effect of the polluted waters, especially one of them which demonstrated 72% ofn ecotoxicity. More than 20 ecologically relevant new bacteria were cultured. Three of them demonstrated tolerance to Cd, Cu and Mn and five- a tolerance to 2,4-dichlorphenoxyacetic acid. Our result revealed that the heavy metal pollutions reduced the microbial diversity in the studied waters, are ecotoxic as well as that some of newly isolated bacteria possess a capacity for a clean-up biotechnologies in the region.

CHARACTERIZATION OF ARSENIC-TRANSFORMING BACTERIA FROM ARSENIC CONTAMINATED SITES IN BULGARIA

ABSTRACT The growth of the bacterial strains, previously isolated from arsenic contaminated sites in Bulgaria, was tested in the absence and the presence of different concentration of arsenite and arsenate. Two isolates, Pseudomonas putida K6 and Pseudomonas mendosina M3, were of particular interest because they appeared to gain metabolic energy during the arsenic transformation. After screening test for genes from aox and ars—operon, it was detected only the gene for arsH protein in strains as Ps. stutzeri and Ps. mendosina.

Bioremediation of Petroleum—Polluted Soils by Adsorptive Immobilized Corynebacterium Sp. RB—96

ABSTRACT Living cells of oil-degrading bacteria, Corynebacterium sp. RB—96, were immobilized on two different types of zeolite materials (rhodopin and rhodosorb, “Ecotech”, Sofia) by adsorption. The optimal parameters of immobilization (concentration of the carrier, time for adsorption, growth phase of the bacteria) were investigated. The biodegradation of crude oil of light and heavy type by cells immobilized on these zeolites was tested. The cells immobilized on rhodopin were better degraders then the free cells. The cells attached to rhodosorb degraded crude oil more slowly in comparison with the immobilized cells. Corynebacterium sp. RB—96 (free and adsorbed) oxidized light crude oil with preference.

Phenol degradation by environmental bacteria entrapped in cryogels

The aim of this study was to assess the capability of bacterial isolates immobilized on poly(ethylene oxide) (PEO) cryogels to degrade and utilize phenol as a sole source of carbon and energy. Two xenobiotic-degrading bacteria were isolated from industrial areas polluted with heavy metals and aromatics. Sequencing of their 16S rDNA classified them as Pseudomonas rhodesiae (denoted as KCM R5) and Bacillus subtilis (denoted as KCM RG5). The following operation parameters were used: sequencing batch process, 24 h cycle of feeding, increasing phenol concentrations from 300 to 1000 mg·L−1, volume of inflow – 250 mL, volume of outflow – from 212 to 7 mL and temperature of 28 °C. The PEO-KCM R5 biofilter was found to remove phenol at a concentration of 1000 mg·L−1, while the PEO-KCM RG5 system was unable to degrade phenol at a concentration of about 600 mg·L−1. After four weeks of biodegradation, the PEO biofilms remained compact, porous and elastic, while containing compact microbial biofilm as shown by scanning electron microscopy analysis of the cryogels. Taken together, our results demonstrate that our novel bacterial entrapment system in PEO cryogels is highly effective and sustainable for phenol degradation and can be relevant for application in the detoxification technologies of industrially polluted waters.