| Zinc is an essential trace element for the human body and plays an important role in human health.Zinc deficiency is closely related to the occurrence of various diseases.The forms of zinc supplementation mainly include inorganic zinc,organic zinc and bio-zinc,among which bio-zinc showed more beneficial effects on the absorption and relatively high bioavailability.The enrichment and transformation of zinc by microorganisms were common methods for obtaining bio-zinc,and yeast were one of the most widely used microorganisms,and the reports which related to the enrichment of zinc by lactic acid bacteria(LAB)were relatively less.LAB are a type of bacteria that are beneficial to the health of the host and are widely used in the food industry.Previous reports indicated that LAB could enrich trace elements,protect the intestinal barriers,relieve the gut inflammation and modulate immune responses.However,the protective effects on alleviation of mice colitis in zinc-enriched LAB remain unclear.In this study,the screening capacity of LAB with high zinc-enriched was evaluated by comparison of properties in vitro and the methods for the enrichment of zinc were optimized.The relationship between the ability of zinc enrichment and the surface properties of the strains was explored.Moreover,the effect of zinc-enriched LAB on the ulcerative colitis in mice was further analyzed.The main results of this study are listed as follows:Firstly,the ability of 33 strains of LAB to concentrate zinc was evaluated in zinccontaining medium and zinc-containing aqueous solution.The amount of zinc bound by strains was varied from 0.064 mg/g to 1.76 mg/g per dry biomass in zinc-containing medium and 1.31 mg/g to 19.84 mg/g per dry biomass in zinc-containing aqueous solution,respectively.The amount of zinc enriched by the strains in the aqueous solution was much higher than the bacteria medium.The most effective LAB strain in zinc-binding was Lactobacillus plantarum CCFM242,and the amount of zinc enriched was 19.84 mg/g per dry biomass.Then the conditions for the zinc binding of Lactobacillus plantarum CCFM242 in zinccontaining aqueous solution were optimized.The optimum zinc binding conditions were as follows: the initial zinc concentration was 250 mg/L,the initial pH was 5,the temperature was 37?,the incubation time was 1 h and the bacterial concentration was 4 g/L.Under this optimized condition,the amount of enriched zinc was increased to 24.8 mg/g per dry biomass.To clarify the relationship between the ability of zinc binding and the surface properties of LAB,9 strains of LAB with different abilities of zinc binding were selected according to the preliminary screening results.The surface properties of these strains were determined including hydrophobicity,self-agglutination and surface charge.Linear correlation analysis between the zinc-enriched amount and the surface properties of the strains was further evaluated.As a result,although the differences among the hydrophobicity,self-agglutination capacity and surface charge of the strains were detected,the linear correlation between the zinc-enriched ability and the surface properties of the strains was not significant.It was found that 73.81% of zinc was bound to the cell wall and 20.16% entered the protoplast by component stripping.After the masking of amino and carboxyl groups,the ability of the bacteria to enrich zinc was remarkably reduced.The effects of zinc-enriched LAB on ulcerative colitis were investigated.It was found that the zinc-enriched LAB decreased the disease activity index of mice with colitis,increased the length of colon,and decreased the activity of MPO significantly.In addition,the levels of proinflammatory cytokines including TNF-?,IL-1? and IL-6 were also down-regulated,while the level of anti-inflammatory cytokine IL-10 was up-regulated.The microbial diversity in the zincexposed group was decreased,and microbial communities related to the induction of colitis were altered by 16 S r RNA gene sequencing analysis.After intervention by zinc-enriched LAB,the diversity of intestinal microbiome was restored close to the previous level. |
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