Systematic understanding of the potential manganese-adsorption components of a screened Lactobacillus plantarum CCFM436

Manganese (Mn) is a toxic heavy metal that has a variety of adverse effects on human health under excess exposure. Here, we screened the lactic acid bacteria Lactobacillus plantarum CCFM436, which displayed a good potential Mn adsorption capacity, from 34 isolates via the Mn binding ability, antioxidative activity and tolerance in simulated gastrointestinal solution. The Mn adsorption of L. plantarum CCFM436 was mainly accomplished by extracellular components (extracellular polysaccharides 6.50-7.22%, cell wall 26.87-43.90%, wall-membrane space, and membrane 41.48-47.51%), whereas only 8.12-18.40% of Mn was transferred into intracellular protoplast. Transmission electron microscope observation indicated that more EPS was secreted with higher levels of Mn stress. Fourier transform infrared spectroscopy showed that the carboxyl and amino groups of L. plantarum CCFM436 made the greatest contribution to the Mn adsorption ability. High performance liquid chromatography analysis indicated that the levels of amino acids (aspartic, glutamic, arginine and lysine) rich in amino/carboxyl groups decreased and cysteine increased, further favorable to tolerance the intracellular Mn stress. The manganese transport operon (mntr) and manganese transporters (mnth1/mnt2/mnt3) were identified by PCR-sequencing. Moreover, qRT-PCR analysis proved that MntH 1-3 were the potential Mn importers and negatively regulated by MntR. This study contributes our scientific understanding of the health-benefits of probiotics and provides a new potential reference in food applications against Mn toxicity.