Browsing by Author "Lazarova N."

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    Immobilization of trichosporon cutaneum R57 on PVA/TEOS/ MPTEOS hybrid matrices for removal of manganese ions
    (2013-10-17) Georgieva N.; Bryaskova R.; Lazarova N.; Racheva R.
    New hybrid materials based on polyvinyl alcohol (PVA), 3-mercaptopropyltriethoxysilane (MPTEOS) and tetraethoxysilane (TEOS) were prepared, using a sol-gel process. Thermogravimetric analysis (TGA) was performed to determine the thermal stability of the hybrid materials. MPTEOS, as a precursor, ensured the presence of SH-groups, thus providing additional binding places for cell immobilization. Based on good adhesive behavior, the hybrid materials were tested as matrices for immobilization of Trichosporon cutaneum R57 for removal of manganese ions from aqueous solutions. Maximum Mn2+ removal was achieved by cells immobilized onto materials with higher MPTEOS concentration. The synthesized PVA/TEOS/MPTEOS hybrid materials proved to be efficient for use in biosorption applications. © Biotechnol. & Biotechnol. Eq.
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    Lactobacillus spp. from traditional Bulgarian dairy products
    (2016-01-01) Nemska V.; Lazarova N.; Georgieva N.; Danova S.
    Over the last few years the traditional dairy products have been gaining much more popularity among scientists and consumers. They are a part of the nutritional diet of people since ancient times and are a proven source of lactic acid bacteria (LAB) with confirmed and beneficial effects on human health. LAB are the main cause of lactic acid fermentation and determine the specific properties of the resulting products. Home-made fermented dairy products are a part of the daily diet and tradition is saved in several rural regions of Bulgaria. However, the beneficial microbiota of some of them is poorly characterized. Therefore, any research aimed at the isolation and identification of LAB from traditional foods helps to define the autochthonous microbiota, which is typical for the area/product. With these aims 26 artisanal samples of 4 types Bulgarian dairy products: yoghurt, white-brined cheese, yellow cheese and curd, were collected. Their lactic microflora was studied and 74 pure cultures were isolated. They were identified as Lactobacillus spp. using classical approaches for identification. For this reason further characterization of the created collection of lactobacilli is considered perspective.
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    Phenol degradation by trichosporon cutaneum r57 in the presence of copper ions
    (2015-01-01) Lazarova N.; Valladares A.; Georgieva N.; Müller R.
    A major class of environmental toxins are the heavy metals and metal derived substances. Phenols are another widely spread pollutant in the industrial wastewaters. In real contaminated sites it is common that different organic and inorganic compounds are present as a threat for the ecosystem. Thus it is important to work on economical and environmentally friendly ways to handle the problem. The ability of some microorganisms to live in stressed conditions makes them attractive in the context of environmental biotechnology. The filamentous yeast Trichosporon cutaneum strain R57 was cultivated in batch mode on a liquid medium, with phenol as a sole carbon source, in the presence of various concentrations of Cu2+ from 0 to 0.15 mM. The growth and degradation time of the phenol under different Cu2+ ions concentrations by Tr. cutaneum cells were studied. The impact of the biomass for the process was also analysed. Degradation of phenol in the presence of Cu2+ was achieved and a relation with the cell density was observed. In the concentration range from 0.025 to 3.0 mM CuSO4.5H2O, a removal efficiency of 20 to 44 % was observed.
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    The oxidative stress response of the filamentous yeast Trichosporon cutaneum R57 to copper, cadmium and chromium exposure
    (2014-01-01) Lazarova N.; Krumova E.; Stefanova T.; Georgieva N.; Angelova M.
    Despite the intensive research in the past decade on the microbial bioaccumulation of heavy metals, the significance of redox state for oxidative stress induction is not completely clarified. In the present study, we examined the effect of redox-active (copper and chromium) and redox-inactive (cadmium) metals on the changes in levels of oxidative stress biomarkers and antioxidant enzyme defence in Trichosporon cutaneum R57 cells. This filamentous yeast strain showed significant tolerance and bioaccumulation capability of heavy metals. Our findings indicated that the treatment by both redox-active and redox-inactive heavy metal induced oxidative stress events. Enhanced concentrations of Cu2+, Cr6+ and Cd2+ caused acceleration in the production of reactive oxygen species (ROS), increase in the level of oxidatively damaged proteins and accumulation of reserve carbohydrates (glycogen and trehalose). Cell response against heavy metal exposure also includes elevation in the activities of antioxidant enzymes, superoxide dismutase and catalase, which are key enzymes for directly scavenging of ROS. Despite the mentioned changes in the stress biomarkers, T. cutaneum did not show a significant growth diminution. Probably, activated antioxidant defence contributes to the yeast survival under conditions of heavy metal stress.