Fixation of lead by lactic bacteria in liquid médium

Central Asia is known for its environmental pollution, and contaminants concentrate throughout the food chain. Thus, heavy metals as lead could be found in animal products as camel milk which is consumed in high quantity, especially in Kazakhstan. To test the detoxification effect of fermented camel milk, two stages study was performed: (i) isolation and identification of lactic bacteria (LAB) strains from fermented camel milk (shubat); (ii) quantitative lead fixation test by the isolated LAB. Identification was achieved by molecular methods (rRNA16S). The test consisted to put in presence a known quantity bacterial biomass of each of 13 strains tested with a known quantity of lead in liquid medium. Lead was added as Pb(NO3)2 at concentrations: 0, 1, 15, 30 and 50 mg/L. The concentration of unfixed lead was measured by atomic absorption spectrometry. According to results of sequencing, the majority of strains were of genus Enterococcus and Lactobacillus, secondarily Lactococcus and Leuconostoc. All tested strains fix lead, but with different capabilities. For some strains saturation phenomenon was observed: the percentage of fixed Pb decreased when the concentration of lead increased. Strains showing very high binding capacities were Enterococcus faecium, E. durans, L. kefiri and Leuconostoc mesenteroides.. (Résumé d'auteur