The study aims to investigate zinc biosorption by strains of lactobacilli and bifidobacteria with a view to exploit them as organic matrixes for zinc dietary supplementation. Sixteen human strains of Lactobacillus and Bifidobacterium were assayed for zinc uptake. The minimum inhibitory concentration of zinc salts differed among the strains, but was never below 15？mmol？L？1. When cultured in MRS broth containing 10？mmol？L？1 ZnSO4, all the strains were capable of accumulating zinc in the range between 11 and 135？μmol？g？1. The highest amount of cell-bound zinc was obtained in L. acidophilus WC 0203. pH-controlled batch cultures of this strain revealed that zinc uptake started in the growth phase, but occurred mostly during the stationary phase. Pasteurized and viable cultures accumulated similar amount of zinc, suggesting that a nonmetabolically mediated mechanism is involved in zinc uptake. These results provide new perspectives on the specific use of probiotics, since L. acidophilus WC 0203 could function as an organic matrix for zinc incorporation. The bioavailability of Lactobacillus-bound zinc deserves to be investigated to provide a future basis for optimization of zinc supplementation or fortification. 1. Introduction Zinc is one of the metal ions essential to life. After iron, it is the second most abundant transition metal ion in living organisms, including humans [1]. Zinc is present in all the tissues, fluids, and organs within the human body, for a total body content of approximately 1.4–2.3？g. It is necessary for catalytic, structural, and regulatory functions in hundreds of enzymes and in thousands of protein domains. Enumerating and discussing the role of zinc in these functions is far beyond the aim of this study [2–5]. The recommended dietary intake for zinc varies with age and physiological status, ranging between 5 and 18？mg day？1. Severe zinc deficiency causes a number of adverse physiological consequences on the epidermal, gastrointestinal, central nervous, immune, skeletal, and reproductive systems [4, 6, 7]. It has been demonstrated that the form of the trace elements affects the intake efficiency in animals. Several studies reported that certain organic compounds of trace elements (including iron, zinc, magnesium, and selenium) are more bioavailable than the inorganic forms, possibly because the mechanisms for absorption have adapted to these kinds of nutrients during species evolution [8–12]. Moreover, in order to develop biotechnological sources of trace elements for diet supplementation, microorganisms (e.g., yeast, lactobacilli,
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