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Biosynthesis of quantum dots (CdTe) and their effects on soil organisms

Quantum dots (QDs) are relatively homogeneous group of nanoparticles and can be modified and synthesized in different ways [1], which include electron beam irradiation, polyol-hydrolysis method, chemical precipitation method, photochemical synthesis, ?-radiation route or microwave-assisted aqueous synthesis and many others [2, 3]. They may be modified in various ways and even their potential toxic properties are dependent on these modifications [1, 4]. Their negative effect was found in bacteria, algae, invertebrates, fish and but also in some mammals [5-7]. One of the newest options for QDs synthesis is biosynthesis, sometimes also referred to as green synthesis that makes it possible to reduce the potential toxicity of these nanoparticles [8-12]. Some of the organisms are caplable of QDs biosynthesis, such as Escherichia coli [10, 13-15], Rhodobacter sphaeroides [16], Klebsiella pneumoniae [17], Klebsiella aerogenes [18], Gluconoacetobacter xylinus [19], yeasts [20] such as Saccharomyces cerevisiae [21] Schizosaccharomyces pombe [22], Torulopsis species [23], Rhodosporidium diobovatum [12], and Fusarium oxysporum [24, 25].

Although these organisms can produce different types of QDs (ZnS, PDS, CdS and CdSe), CdTe is one of the most commonly biosynthesized QDs [26]. The most commonly studied QD biosynthesis is of CdTe and CdS using recombinant E. coli expressing the particular metal-binding proteins, such as phytochelatin and / or metallothionein, glutathione and other proteins [10, 13-15]. Besides the above mentioned organisms, plants are applicable for the green synthesis, where their extract is used as the reducing agent [27-29]. The biosynthesis has also been described in animals. Rats [9, 30], mice [31], and earthworms [32] are able to produce nanoparticles. The biosynthesis in animals is very highly rated and is an assumption for use in various sectors [33, 34]. Green synthesis is made possible by the ability of an organisms to resist heavy metals [35]. It was found that during the biosynthesis of CdTe in organisms, the gene expression of the metal binding proteins such as metallothionein and phytochelatin is increased [8, 10, 15]. Studies also show that oxidative stress and other negative effects on organisms exposed to the action of a heavy metal can be reduced through the biosynthesis. Without the biosynthesis in the body of organisms in the presence of Cd(II), lysosomal membrane stability may be disturbed, changes in gene expression can occure, oxidative stress may increase, growth, sexual development, cocoon production and hatchability and juvenile viability can be reduced, and the mortality may increase [36, 37]. It is known that soil represent a major sink for contaminants in the environment. The contamination level is dependent on both the exposure to contaminants, and the biology and ecology of organisms in the soil [38, 39]. As an indicator of soil quality, collembola (Folsomia candida), an arthropod occurring in soils around the world, can be used. This organism is used as the standard test organism for ecotoxicological tests [40-42]. Another good test soil organisms such as earthworms may be used in this case [43, 44].

The aim of this work was to observe the effect of QDs on collembolans reproduction and the possibilities and influence of biosynthesis both in terms of microorganisms (E. coli), and animals earthworm (Eisenia fetida). Conclusion CdTe QDs belong to the toxic QDs group due to its cadmium content. Compared to the cadmium itself however, these QDs are more toxic to organisms than in the case with cadmium ions, which confirms that 28EC50 of CdTe QDs is 72.4 µmol L-1, which is a value much lower than that of cadmium itself. This may not be the case, if these QDs are the product of defensive mechanism against heavy metals. This tolerance is determined by the ability of biosynthesis and by the defense mechanism of the organism. There are different mechanisms by which the microorganisms and soil organisms can biosynthesize QDs using the same substance. E. coli acts probably only as a source of substances that allow the synthesis of QDs. QDs therefore are the byproduct of defense mechanisms. The biosynthesis in earthworms is very likely its own defense mechanism, as is clear from our results.

Práce je spojená s projektem CEITEC CZ.1.05/1.1.00/02.0068.

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