Effects of Selenium- and Zinc-Enriched Lactobacillus plantarum SeZi on Antioxidant Capacities and Gut Microbiome in an ICR Mouse Model

Abstract

Selenium and zinc are essential trace minerals for humans with various biological functions. In this study, selenium- and zinc-tolerant lactic acid bacteria (LAB) isolates were screened out from human fecal samples. Amongst three hundred LAB isolates, the Lactobacillus plantarum SeZi strain displayed the tolerance against selenium and zinc with the greatest biomass production and bioaccumulation of selenium and zinc. To further assess the characteristics of this strain, the lyophilized L. plantarum SeZi were prepared and administered to Institute of Cancer Research (ICR) mice. The mice were divided into four groups, provided with normal chow (Con), or normal chow supplemented with Na₂SeO₃ and ZnSO₄∙7H₂O (SZ), L. plantarum SeZi (Lp), or selenium- and zinc-enriched L. plantarum SeZi (SZ + Lp), respectively. After 4 weeks of oral administration, the concentrations of selenium and zinc in blood were significantly increased in the SZ + Lp group when compared to the control or SZ group (p < 0.05). The increased selenium level led to an enhanced glutathione peroxidase activity and decreased blood malondialdehyde level in the SZ + Lp group (p < 0.05). Meanwhile, the results of bacterial community and microbial metabolic pathway analysis via 16S rRNA gene amplicon sequencing showed that L. plantarum SeZi significantly promoted the utilization of selenocysteine, seleno-cystathionine and seleno-methionine in the selenocompounds metabolism. Here, the in vivo antioxidant capacities of the selenium- and zinc-enriched lactobacillus strain showed us the utilization of a unique probiotic as a Se/Zn supplement with high availability, low toxicity, and additional probiotic advantages.

Keywords: antioxidant capacities; bioaccumulation; gut microbiota; selenium; zinc.

Figure 1

The concentrations of blood selenium (A) and zinc (B) in mice after 4 weeks of administration. Data were analyzed by unpaired t-test analysis and expressed as mean ± SD. ** p < 0.01 (n = 8). Con, control; SZ, selenium and zinc supplemented; Lp, Lactobacillus plantarum SeZi; SZ + Lp, selenium- and zinc-enriched L. plantarum SeZi.

Figure 2

Glutathione peroxidase (GSH-Px) activity (A), superoxide dismutase (SOD) activity (B), and lipid oxidation product malondialdehyde (MDA) level (C) in serum of mice at the final day. Treatments with different letters (a, b, c) are significantly different at p < 0.05 (n = 8). Con, control; SZ, selenium and zinc supplemented; Lp, Lactobacillus plantarum SeZi; SZ + Lp, selenium- and zinc-enriched L. plantarum SeZi.

Figure 3

Comparison of diversity indices and microbial compositions amongst groups after 4 weeks of oral administration. Alpha-diversities of microbial communities are shown as (A) richness and (B) evenness. (C) Principal Coordinates Analysis (PCoA) plot represents beta-diversity based on Bray-Curtis dissimilarity. (D) Taxonomic profiles at the phylum level (D) and the genus level (E). Relative Abundance of taxa below 0.1% were excluded prior to analyses. Significance was accepted at * p < 0.05, ** p < 0.01 (n = 8). Con, control; SZ, selenium and zinc supplemented; Lp, Lactobacillus plantarum SeZi; SZ + Lp, selenium- and zinc-enriched L. plantarum SeZi.

Figure 4

Relative abundances of Lactobacillus (A), Adlercreutzia (B), Lactococcus (C), and Allobaculum (D) in fecal samples after 4 weeks of oral administration. Data are expressed as mean ± SD. Significance was accepted at * p < 0.05, ** p < 0.01 (n = 8). Con, control; SZ, selenium and zinc supplemented; Lp, Lactobacillus plantarum SeZi; SZ + Lp, selenium- and zinc-enriched L. plantarum SeZi.

Figure 5

Selenocompounds metabolism pathway. Related enzymes include selenocysteine lyase (EC: 4.4.1.16), cystathionine gamma-synthase (EC: 2.5.1.48), cysteine-S-conjugate beta-lyase (EC: 4.4.1.13), homocysteine methyltransferase (EC: 2.1.1.13), and methionyl-tRNA synthetase (EC: 6.1.1.10). Arrows indicate the related genes that are involved in the corresponding pathway. Error bars represent means ± SD. Significance was accepted at * p < 0.05, ** p < 0.01 (n = 8). Con, control; SZ, selenium and zinc supplemented; Lp, Lactobacillus plantarum SeZi; SZ + Lp, selenium- and zinc-enriched L. plantarum SeZi. K11717, cysteine desulfurase/selenocysteine lyase; K01760, cystathionine beta-lyase; K01874, methionyl-tRNA synthetase.

Figure 6

Detoxification process of inorganic selenium. Related enzymes include 3′-phosphoadenosine 5′-phosphosulfate synthase (EC: 2.7.7.4) and selenate reductase subunit alpha (EC: 1.97.1.9). Arrows indicate the related genes that are involved in the corresponding pathway. Error bars represent means ± SD. Significance was accepted at * p < 0.05, ** p < 0.01 (n = 8). Con, control; SZ, selenium and zinc supplemented; Lp, Lactobacillus plantarum SeZi; SZ + Lp, selenium- and zinc-enriched L. plantarum SeZi. K07310, Tat-targeted selenate reductase subunit YnfF; K07309, Tat-targeted selenate reductase subunit YnfE; K12527, putative selenate reductase; K00956, sulfate adenylyltransferase subunit 1; K00957, sulfate adenylyltransferase subunit 2; K00958, sulfate adenylyltransferase.