Abstract—Selenium is well known as an essential trace element since the 20th century, but it can be overdosed easily because of its toxicity. According to the present regulations [1] only the potentially most harmful, inorganic selenium salts can be added to any comestibles. Elemental selenium is considered as the least toxical of all selenium forms and in the same time supplementation with its nano-size particles has the same or better bioavailability compared to its salts. In our experiments we managed to produce nano-size (100-500nm) elemental selenium by using probiotic yogurt bacteria in a fermentation procedure. We developed the laboratory technology of product purification and recovery from bacteria. Index Terms—Antioxidant, Food Supplement, Lactic Acid Bacteria, Nanosphere, Selenium. I. INTRODUCTION A. Selenium forms in Our Environment In the geosphere there is not enough natural elemental selenium that worth to exploit with economic benefit. Usually we can find relatively large amount of elemental selenium in ores, few carbon layers of the soil and in the soils of volcanic areas. The most common selenium forms of our biosphere are the inorganic selenium salts. These salts leach easily from the soil and become available for the plants by the groundwater [2]. In alkaline environment a termodinamically stable form of selenium is the selenate ion (SeO 4 2 -). Selenates have better soluble but worse absorption properties than selenites. Selenite (SeO 3 2 -) occurs in neutral pH environment and it is less soluble compared to selenate. Selenite also has the ability to absorb to particles dynamically and can be reduced to elemental selenium (Se 0 ) by chemical or biological ways. Selenides (Se 2- ) and the selenium enriched sulphides occur in reductive or acidic environment, have weak soluble and oxidating properties, plants and animals hardly can take them up. B. Selenium forms in the Biological Systems Se proteins, synthesized by plants and animals contain Se–Met; which is the principal form of Se in cereals and other plants. Animals do not distinguish between Se–Met and its S-analogue Met. Both amino acids are incorporated in proteins via the same enzymatic pathway [3] In plants selenate is much more easily transported than selenite or organic Se [4]. Se distribution over several plant compartments depends on plant species, developmental phase, physiological condition, form, and concentration of the Se available, and the presence of other substances, Manuscript received June 13, 2011; revised June 29, 2011. The authors are with Institute of Bio and Environmental Energetics University of Debrecen, Centre for Agricultural Sciences and Engineering H-4032 Debrecen, Böszörményi út 138. Hungary eszenyipeter@agr.unideb.hu especially sulfates. Selenoproteins are common in Brazil nuts and Se-accumulating plants, like onion, garlic, species of brassica genus and mushrooms. Certain yeasts, like Saccharomyces cerevisiae, have the ability to accumulate and transform high concentration of selenium, when we add Na 2 SeO 3 to the growth medium. Similarly to plants, Se is mainly incorporated as Se–Met in their proteins. [5]. Due to its low cost and its ability to synthetize selenoproteins yeasts can be well utilized for nutritional supplementation. C. Biological Production of Nano Particles Researchers just started to recognise in the recent years the importance of the ability of certain microorganisms to produce nano-sized particles in the course of their metabolism. Many elements in trace concentrations are essential for the growth and reproduction of plants, animals and microorganisms, however these elements easily become toxic at concentrations higher than the physiological level. Scientists have shown that many plants and bacteria can actively uptake and reduce metal ions from soil and solutions. Nair and Pradeep [6] used Lactic acid bacteria in buttermilk whey to produce gold-silver composite materials. These alloy materials, in submicron dimensions, form several well-defined crystal morphologies, and this crystal growth does not affect the viability of the bacteria. Magneto-tactic bacteria, for instance, have intracellular magnetic structures, the magnetosomes, which comprise nanometer-sized, membrane-bound crystals of the magnetic iron minerals magnetite (Fe 3 O 4 ) or greigite (Fe 3 S 4 ). Magnetosomes [7] are the results of a mineralization process with biological control over the accumulation of iron and the deposition of the mineral particle with specific size and orientation within a membrane vesicle at specific locations in the cell. Moon [8]. discovered that certain thermophyl and psychrotolerant metal-reducer bacteria (Shewanella sp.; Thermoanaerobacter sp) are able to produce copious amounts of extra-cellular metal (M)-substituted magnetite nano-particles using akaganeite and dopants of dissolved form. Not only the bacteria but also the fungi are able to synthetize nano-sized products. Fungi, due to their metal accumulation and tolerant ability, were placed into the centre of attention of nano-particle production researches [9]. Their economic viability, ease in scale up in solid substrate fermentations and large-scale secretion of extracellular enzymes, makes them advantageous for nano-particle production [10]. As a new field of nanobiotechnology, besides bacteria and fungi, plants are also able to produce nano-particles. In a study scientists [10] describe that they managed to fabric gold nano-particles using live plants. In their experiment they grew Alfalfa plants in an AuCl 4 rich environment, plants absorbed the Au metal successfully, that was Elemental, Nano-Sized (100-500 nm) Selenium Production by Probiotic Lactic Acid Bacteria Péter Eszenyi, Attila Sztrik, Beáta Babka, and József Prokisch International Journal of Bioscience, Biochemistry and Bioinformatics, Vol. 1, No. 2, July 2011 148