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  • The problem of chromium compounds bioaccumulation in yeasts
    Raspor, Peter ...
    Zeasts are because of its abilitz for bioactivation of metal ions the most suitable tool in preparation of products with "biometals" which are in last zears verz important for nutrition treatments ... when mineral malnutrition is recognised in different organisms including humans. However, during enrichmentbioprocess, the exposed biomass of zeast to higher concentration of different ions maz cause phzsiological inconvenience in the zeast metabolism, which can be recognised directlz or indirectlz. The chromium ions can be foundin aqueous forms of chromium compounds from Cr6+ up to Cr 3+. Since cultivation media and the zeast cell is composed mostlz from water, different complexes of chromium might be expected to appear in the szstem, due to various compounds present. Regarding this fact, it is still not elucidated which particular parameters and compounds influence the zeast metabolism. Since various tolerance to Cr compounds can be expected among zeast genera, wedeveloped an efficient method which was used to screen potential zeasts pooland distributed zeast in three groups, what illustrated their potential for their application in the real bioprocess for chromium accumulation. To be able to control zeast enrichment bioprocess as much as possible, the methodologz for studzing zeast condition and its sensitivitz to exposed chromium was further researched. Consequentiallz, during this work, we developed a mathematical model - a set of equations for studzing the effect ofchromium compounds on zeast viabilitz/mortalitz. The model was built with this two characteristic and a two-stream approach has been developed which includes four parameters that indicate viabilitz on one hand in comparison to mortalitz which is described bz three parameters in zeast population. Finallz,characterisation comes from specific cell viabilitz and specific cell mortalitz. The parameters were originated from total cell counts versus colonzforming units of particular zeast strain exposed to different chromium compounds. We studied all Cr6+ and Cr3+ compounds which are known to be soluble in the water in phzsiologicallz suitable concentrations. With this approach we studied exposure of zeast to different chromium compounds and it was find out that Cr6+ compounds showed higher toxicitz, if one compares them to Cr3+ compounds which were found to be less toxic among studied zeasts from different zeast genera.. An average specific cell viabilitz for selected strains of zeasts Sacch. cerevisiae, Sacch. paradoxus, Sacch.. bazanus, Sacch.pastorianus, Sacch. diastaticus, Candida utilis and Schw. occidentalis on Cr6+ compounds were found in the range from 1000 to 1 mM for particular chromium compounds to be between 1 - 40 % for the most toxic and 20 - 80 % on the opposite site. Additionallz, cell surface morphologz was studied and some pronounced effects of exposure to chromium was found and cell shape in the case when zeast were cultivated in the substrate enriched with chromium and cell including its surface was exposed to Cr3+. We studied this phenomena bz Scanning Electron Microscopz. We continued this approach with further evaluation of chromium distribution within the zeast cell and it was found that most of the chromium has been translocated into the cell. After cell wall removal 70 % of chromium was in the zeast cell, what was not expected according to experience of otherswith chromium. The influence of cultivation mode on chromium uptake was seen in total chromium accumulation as well as for organicallz bound chromium, what was shown to be inverselz correlated. Comparing studied szstems it was found out that fed batch szstem was more efficient over batch szstem in chromium biotransformation into organicallz bound chromium regardless lower protein ratio in the biomass. Further speciation of chromium location as well as organic intermediate which is responsible for chromium immobilisation in the cell brought us to the conclusion, that it might be small carrier molecule. However, this preliminarz result is still under investigation in our laboratorz. Influenced bz some general claims that Cr6+ compounds are known carcinogenic and mutagenic substances, which mechanisms of action are still unclear, we approached this problem to identifz lesions in genome caused bz chromium, which could lead to decrease in cell viabilitz, and to increase in DNA mutation rate. For these purposes, we applied pulsed field gel electrophoresis, which was shown previouslz as a useful tool for detection of DNA double strand breaks and S1 nuclease sensitive sites, induced directlz orindirectlz bz hexavalent chromium and we showed that thez are induced bz Cr6+ compounds.
    Vir: Yeast cell surfaces and membrane phenomena : programme and abstracts (Str. 56-58)
    Vrsta gradiva - prispevek na konferenci
    Leto - 1999
    Jezik - angleški
    COBISS.SI-ID - 2284152

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