The use of lactic acid bacteria to reduce mercury bioaccessibility

Fecal microbiota transplantation as an effective way in treating methylmercury-poisoned rats

Methylmercury (MeHg) can cause devastating neurotoxicity in animals and human beings. Gut microbiota dysbiosis has been found in MeHg-poisoned animals. Fecal microbiota transplantation (FMT) has been shown to improve clinical outcomes in a variety of diseases such as epilepsy, amyotrophic lateral sclerosis (ALS) and autism. The aim of this study was to investigate the effects of FMT on MeHg-poisoned rats. FMT treatment was applied to MeHg-poisoned rats for 14 days. The neurobehavior, weight changes, dopamine (DA), the total Hg and MeHg level were evaluated. Besides, the gut microbiota and metabolites change in feces were also checked. It was found that FMT helped weight gain, alleviated the neurological disorders, enhanced fecal mercury excretion and MeHg demethylation, reconstructed gut microbiome and promoted the production of gut-brain axis related-metabolites in MeHg-poisoned rats. This study elaborates on the therapeutic efficacy of FMT in treating of MeHg-poisoned rats, which sheds lights on the treatment of neurological diseases like Minamata Disease and even Parkinson's Disease.

Phosphate Uptake and Its Relation to Arsenic Toxicity in Lactobacilli

The use of probiotic lactobacilli has been proposed as a strategy to mitigate damage associated with exposure to toxic metals. Their protective effect against cationic metal ions, such as those of mercury or lead, is believed to stem from their chelating and accumulating potential. However, their retention of anionic toxic metalloids, such as inorganic arsenic, is generally low. Through the construction of mutants in phosphate transporter genes (pst) in Lactiplantibacillus plantarum and Lacticaseibacillus paracasei strains, coupled with arsenate [As(V)] uptake and toxicity assays, we determined that the incorporation of As(V), which structurally resembles phosphate, is likely facilitated by phosphate transporters. Surprisingly, inactivation in Lc. paracasei of PhoP, the transcriptional regulator of the two-component system PhoPR, a signal transducer involved in phosphate sensing, led to an increased resistance to arsenite [As(III)]. In comparison to the wild type, the phoP strain exhibited no differences in the ability to retain As(III), and there were no observed changes in the oxidation of As(III) to the less toxic As(V). These results reinforce the idea that specific transport, and not unspecific cell retention, plays a role in As(V) biosorption by lactobacilli, while they reveal an unexpected phenotype for the lack of the pleiotropic regulator PhoP.

Protective effects of oral administration of lactic acid bacteria strains against methylmercury-induced intestinal toxicity in a murine model

The utilization of lactic acid bacteria has been proposed to mitigate the burden of heavy metal exposure through processes probably involving chelation and reduced metal bioaccessibility. We evaluated the effects of daily intake of two strains of lactobacilli (Lactobacillus intestinalis LE1 or Lactobacillus johnsonii LE2) on intestinal toxicity during methylmercury (MeHg) exposure through drinking water (5 mg/L) for two months in mice. MeHg exposure resulted in inflammation and oxidative stress at the colon, as well as an increase in intestinal permeability accompanied by decreased fecal short-chain fatty acids (SCFA). The administration of the strains resulted in a differential protective effect that, based on their chelation capacity, supported the existence of additional mechanisms of action besides chelation. Both strains reduced IL-1β levels and oxidative stress, while LE1 lowered TNF-α, diminished MeHg-induced mucus over-secretion triggered by the IL-4/IL-13/STAT6 pathway, reduced intestinal permeability, and ameliorated inflammation and oxidative stress, probably by acting on the Keap1/Nrf2/ARE pathway. Administration of LE1 partially restored SCFA contents, which could be partly responsible for the positive effects of this strain in alleviating MeHg toxicity. These results demonstrate that lactobacilli strains can be useful tools in reducing the intestinal toxicity of MeHg, the main mercurial form conveyed by food.

Challenges and strategies for preventing intestinal damage associated to mercury dietary exposure

Food represents the major risk factor for exposure to mercury in most human populations. Therefore, passage through the gastrointestinal tract plays a fundamental role in its entry into the organism. Despite the intense research carried out on the toxicity of Hg, the effects at the intestinal level have received increased attention only recently. In this review we first provide a critical appraisal of the recent advances on the toxic effects of Hg at the intestinal epithelium. Next, dietary strategies aimed to diminish Hg bioavailability or modulate the epithelial and microbiota responses will be revised. Food components and additives, including probiotics, will be considered. Finally, limitations of current approaches to tackle this problem and future lines of research will be discussed.

Lactic acid bacteria strains reduce in vitro mercury toxicity on the intestinal mucosa

A bicameral model consisting of Caco-2 and HT29-MTX intestinal epithelial cells and THP-1-derived macrophages has been used to test the ability of two strains of Lactobacillus to protect from damage caused by mercury. Exposure to 1 mg/ml mercury [Hg(II) or methyl-Hg] for seven days in this model resulted in an inflammatory and pro-oxidant response mainly driven by macrophages. This led to an impairment in the intestinal barrier, defective tight-junctions, increased permeability and mucus hypersecretion. In addition, the wound-healing capacity of the epithelial monolayer was also diminished. However, the presence of heat-killed Lactobacillus intestinalis or Lactobacillus johnsonii cells during Hg exposure reverted these effects, and most of the parameters recovered values similar to control cells. Both lactobacilli showed the capacity to bind Hg(II) and methyl-Hg under the cell culture conditions. This points to Hg sequestration as a likely mechanism that counteracted Hg toxicity. However, differences in the Hg binding capacity and in the effects between both strains suggest that other probiotic-mediated mechanisms may play a role in the alleviation of the damage elicited by Hg. These results show the potential of the bicameral intestinal epithelial model for screening of effective strains for their use in later in vivo studies.

The Influence of Binding of Selected Mycotoxin Deactivators and Aflatoxin M1 on the Content of Selected Micronutrients in Milk

Milk containing aflatoxin M1 (ATM1) in quantities above 0.05 µg/kg is considered unsuitable for consumption. It is possible to use mycotoxin deactivators that bind aflatoxin M1 and allow the further use of milk. The study aimed to examine the impact of selected mycotoxin deactivators (beta-glucan from yeast and oats, and live and dead lactic acid bacteria) on the nutritional composition of milk after binding to aflatoxin M1 intentionally added to milk. The study used consumption milk with 2.8% milk fat intentionally contaminated with aflatoxin M1. Furthermore, 0.05% and 0.1% solutions of beta-glucan from yeast and beta-glucan from oats were added to the contaminated milk, as well as live and dead lactic acid. Concentrations of Na, K, Mg, and Ca were monitored at the zero hour of binding of mycotoxin deactivators and ATM1, after 2 h of binding, and after 4 and 24 h of binding. The largest deviations were found in Na, K, and Mg, while the minimum changes were observed in Ca. Live lactic acid bacteria were found to have the least impact on micronutrients, except in Na (difference = 40, p = 0.029, GES = 0.083), where the 0.1% solution from oats had the least impact on micronutrient content. The results of this study suggest that it is best to use live lactic acid bacteria where the different duration of action regarding nutrients, with the possible exception of Na, is not relevant, which indicates that, when using this mycotoxin deactivator, milk contaminated with ATM1 can be further used.

Mitigation of potentially toxic elements in food products by probiotic bacteria: A comprehensive review

Potentially toxic elements (PTEs) as non-degradable elements (especially carcinogenic types for humans such as lead (Pb), cadmium (Cd), mercury (Hg), and arsenic (As)) are widely distributed in the environment. They are one of the most concerned pollutants that can be absorbed and accumulated in the human body, primarily via contaminated water and foods. Acute or chronic poisoning of humans to PTEs can pose some serious risks for human health even at low concentrations. In this context, some methods are introduced to eliminate or reduce their concentration. While the biological treatment by bacterial strains, particularly probiotic bacteria, is considered as an effective method for reducing or eliminating of them. The consumption of probiotics as nonpathogenic microorganisms at regular and adequate dose offer some beneficial health impacts, it can also be applied to remove PTEs in both alive and non-alive states. This review aimed to provide an overview regarding the efficacy of different types of probiotic bacteria for PTEs removal from various environments such as food, water, in vitro, and in vivo conditions.

Lead and cadmium biosorption from milk by Lactobacillus acidophilus ATCC 4356

The food and water contamination with heavy metals is increasing due to the environmental pollutions. Lead and cadmium are the toxic heavy metals for humans that can be found in air, soil, water, and even food. Lactic acid bacteria have the ability to remove and diminish the level of heavy metals. In this study, Lactobacillus acidophilus was used to remove lead and cadmium in milk and the capability of this valuable bacterium in biosorption of these metals low concentrations (µg/L or ppb) in milk was evaluated. First, the variables on lead and cadmium removal by this bacterium have been studied by Plackett-Burman design. Then, the bioremoval process was optimized and the three main factors, the bacterium concentration, contact time, and the initial heavy metal concentration were chosen by using a central composite design. The optimum lead and cadmium bioremoval yield of 80% and 75% were observed, respectively, at 1 × 1012 CFU of L. acidophilus in milk at the 4th day and the initial ion concentration of 100 µg/L. The 3D plots analysis showed the interaction effects on metal biosorption. This study showed that L. acidophilus is a natural effective biosorbent for lead and cadmium removal from milk.

Green tea infusion reduces mercury bioaccessibility and dietary exposure from raw and cooked fish

Human exposure to mercury (Hg) and methylmercury (MeHg) through the ingestion of seafood raises human health-related concerns. In contrast, green tea has health benefits and its consumption potentially reduces bioaccessibility of dietary Hg. The present study aimed to assess the effect of green tea in total mercury (THg) and MeHg bioaccessibility in raw and cooked marine fish species commonly having high Hg levels. Preliminary results demonstrated that significantly higher reductions of bioaccessible THg were attained after the co-ingestion of green tea infusion (1 cup or more) in the oral and intestinal phases. Overall, the present findings clearly show that the co-ingestion of green tea along with seafood grilling strongly reduces THg and MeHg bioaccessibility in all fish species and consequently diminishes the probability of exceeding MeHg provisional tolerable weekly intakes through the consumption of these species with high Hg levels. Such results point out the need to better understand the beneficial/preventive role of green tea infusions and other food processing techniques in bioaccessibility reduction of other chemical contaminants present in food products. Such information is certainly useful to help consumers to wisely select their food, and to enable food safety authorities to integrate such information in risk assessment.

Protection of human intestinal epithelial cells from oxidative stress caused by mercury using lactic acid bacteria

Heavy metals are harmful to human health. Therefore, we investigated the biosorption of heavy metals by lactic acid bacteria (LAB). Of all the tested heavy metals, biosorption by LAB was highest for mercury, followed by lead, cadmium, and finally arsenic. The viability of HCT-116 cells was reduced by half in the presence of 7.5 µg/mL mercury but recovered after the addition of selected LAB strains. HCT-116 cells showed increased superoxide dismutase and catalase activities, whereas glutathione peroxidase activities decreased significantly. Addition of Lactobacillus sakei TOKAI 57m recovered all antioxidant enzyme activities. Our results suggest that this strain can be used for cellular detoxification.

In vitro assessment of cyanotoxins bioaccessibility in raw and cooked mussels

The oral route by ingestion of water and food contaminated with cyanotoxins is the main route of exposure to these toxins. This study addresses for the first time the bioaccessibility of some of the most common Microcystins (MC-LR, MC-RR and MC-YR) and Cylindrospermopsin (CYN) simultaneously in raw and steamed mussels spiked at 250 ng/g fresh weight of each cyanotoxin, after an in vitro digestion, including the salivary (incubation with artificial saliva, 30s), gastric (with pepsin, 2h, pH 2), duodenal (with pancreatin and bile salts, 2h, pH 6.5) and colonic phases (with lactic-acid bacteria, 48h, pH 7.2). The results obtained suggest that the potential absorption of these cyanotoxins by consumption of contaminated mussels is lower than expected. After the total effect of cooking and digestion, the mean bioaccessibility levels recorded were 24.65% (CYN), 31.51% (MC-RR), 17.51% (MC-YR) and 13.20% (MC-LR). Moreover, toxins were transferred to the steaming waters at 3.77 ± 0.24 μg L^-1 CYN, 2.29 ± 0.13 μg L^-1 MC-LR, 6.60 ± 0.25 μg L^-1 MC-RR and 3.83 ± 0.22 μg L^-1 MC-YR. These bioaccessibility results should be considered for a more accurate risk assessment related to these cyanotoxins in mussels, including the fact that the steaming waters could also represent a risk after human consumption.

Dietary Compounds To Reduce In Vivo Inorganic Arsenic Bioavailability

It is estimated that approximately 200 million people are exposed to arsenic levels above the World Health Organization provisional guideline value, and various agencies have indicated the need to reduce this exposure. In view of the difficulty of removing arsenic from water and food, one alternative is to reduce its bioavailability (the amount that reaches the systemic circulation after ingestion). In this study, dietary components [glutathione, tannic acid, and Fe(III)] were used to achieve this goal. As(III) or As(V) (1 mg/kg body weight) was administered daily to BALB/c mice, along with the dietary components, for 15 days. The results confirm the efficacy of Fe(III) and glutathione as reducers of arsenic bioavailability and tissue accumulation. Also, these treatments did not result in reductions of Ca, K, P, and Fe contents in the liver. These data suggest that use of these two compounds could be part of valid strategies for reducing inorganic arsenic exposure in chronically exposed populations.

Intestinal Methylation and Demethylation of Mercury

Mercury (Hg) is a global pollutant, which is linked with different diseases. The methylation of Hg and demethylation of methylmercury (MeHg) in the environment were extensively studied and summarized; however, the transformation of Hg in the intestine is less presented. In this review, the research progress and the perspectives on the intestinal transformation of Hg were discussed. Studies found that MeHg could be formed when exposed to inorganic Hg by the gut microbiota in aquatic organisms, terrestrial invertebrates, and mammals, etc. hgcAB genes could be used as indicators for predicting Hg methylation potential. In vitro studies using fecal specimen, intestinal contents, and the isolated intestinal microbes confirmed the intestinal demethylation of MeHg. The investigation on the effects of Hg exposure to the abundance and diversity of intestinal microbes and their metabolites could shed light on the mechanism of the toxicity of Hg, especially the neurotoxicity of MeHg, which deserves further study.

Effect of lactic acid bacteria on mercury toxicokinetics

The capacity of two LAB strains to inhibit inorganic [Hg(II)] and organic (methyl-Hg; MeHg) mercury translocation through monolayers of co-cultures of NCM460 and HT29-MTX colonic cells was evaluated. Lactobacillus casei BL23 and Lactobacillus acidophilus ATCC4356 reduced the permeability of Hg(II) and MeHg from aqueous solutions through NCM460/HT29-MTX monolayers (20-94% reduction). However, assays using the bioaccessible (soluble) Hg fraction obtained by in vitro gastrointestinal digestion of Hg-contaminated swordfish only showed a reduction (42%) with the BL23 strain. In vivo experiments carried out in mice receiving an acute dose of Hg(II) or MeHg (0.5 mg/kg body weight/day) with or without lactobacilli resulted in significant decreases of the bioavailability of MeHg with both strains and increased excretion of Hg in feces after treatment with the lactobacilli. However, Hg(II) bioavailability or excretion was not affected. Hg accumulation in liver and kidney remained similar in LAB-treated or non-treated animals. This is the first study of the impact of LAB on Hg(II) and MeHg toxicokinetics and shows that some LAB strains have potential to diminish MeHg bioavailability. Furthermore, it has established the basis for new studies on the protective effect of LAB under conditions resembling subchronic and chronic Hg exposures.

Reducing methylmercury accumulation in fish using Escherichia coli with surface-displayed methylmercury-binding peptides

Seafood consumption is widely considered as the primary route for human exposure to the neurotoxin methylmercury (MeHg) that is produced by certain anaerobic microorganisms and can bioaccumulate to high concentration levels in natural aquatic food webs. In this study, a novel methylmercury-binding peptide with seven amino acids was displayed on the cell surfaces of Escherichia coli strain W-1, which was isolated from fish feces and fused with ice nucleation protein. These cells exhibited high affinity and selectivity toward methylmercury. They efficiently removed more than 96% of 12 μM methylmercury, and accumulation of methylmercury in the engineered strain was four times higher than that in the wild type. Transmission electron microscopy confirmed methylmercury accumulation on cell membranes. Carassius auratus was fed by engineered bacteria, which showed a decrease in methylmercury concentration in muscles of about 36.3 ± 0.7%; whereas an increase in methylmercury concentration was observed in the feces (36.7 ± 0.8%) in comparison to the control group. The engineered strain in the gut captured methylmercury and prevented it's absorption by muscles, while some bacteria with methylmercury were excreted in the feces. The surface-engineered E. coli effectively protected fish from methylmercury contamination.

Bioremediation and Electricity Generation by Using Open and Closed Sediment Microbial Fuel Cells

The industrial contamination of marine sediments with mercury, silver, and zinc in Penang, Malaysia was studied with bio-remediation coupled with power generation using membrane less open (aerated) and closed (non-aerated) sediment microbial fuel cells (SMFCs). The prototype for this SMFC is very similar to a natural aquatic environment because it is not stimulated externally and an oxygen sparger is inserted in the cathode chamber to create the aerobic environment in the open SMFC and no oxygen supplied in the closed SMFC. The open and closed SMFCs were showed the maximum voltage generation 300.5 mV (77.75 mW/m²) and 202.7 mV (45.04 (mW/m²), respectively. The cyclic voltammetry showed the oxidation peak in open SMFCs at +1.9 μA and reduction peak at -0.3 μA but in closed SMFCs oxidation and reduction peaks were noted at +1.5 μA and -1.0 μA, respectively. The overall impedance (anode, cathode and solution) of closed SMFCs was higher than open SMFCs. The charge transfer impedance showed that the rates of substrate oxidation and reduction were very low in the closed SMFCs than open SMFCs. The Nyquist arc indicated that O₂ act as electron acceptor in the open SMFCs and CO₂ in the closed SMFCs. The highest remediation efficiency of toxic metals [Hg (II) ions, Zn (II) ions, and Ag (I) ions] in the open SMFCs were 95.03%, 86.69%, and 83.65% in closed SMFCs were 69.53%, 66.57%, and 65.33%, respectively, observed during 60–80 days. The scanning electron microscope and 16S rRNA analysis showed diverse exoelectrogenic community in the open SMFCs and closed SMFCs. The results demonstrated that open SMFCs could be employed for the power generation and bioremediation of pollutants.

Polyphosphate in Lactobacillus and Its Link to Stress Tolerance and Probiotic Properties

The synthesis of the inorganic polymer polyphosphate (poly-P) in bacteria has been linked to stress survival and to the capacity of some strains to sequester heavy metals. In addition, synthesis of poly-P by certain strains of probiotic lactobacilli has been evidenced as a probiotic mechanism due to the homeostatic properties of this compound at the intestinal epithelium. We analyzed the link between poly-P synthesis, stress response, and mercury toxicity/accumulation by comparing wild-type strains of Lactobacillus and their corresponding mutants devoid of poly-P synthesis capacity (defective in the poly-P kinase, ppk, gene). Results showed that resistance to salt (NaCl) and acidic (pH 4) stresses upon ppk mutation was affected in Lactobacillus casei, while no effect was observed in two different Lactobacillus plantarum strains. Inorganic [Hg(II)] and organic (CH₃Hg) mercury toxicity was generally increased upon ppk mutation, but no influence was seen on the capacity to retain both mercurial forms by the bacteria. Notwithstanding, the culture supernatants of ppk-defective L. plantarum strains possessed a diminished capacity to induce HSP27 expression, a marker for cell protection, in cultured Caco-2 cells compared to wild-type strains. In summary, our results illustrate that the role of poly-P in stress tolerance can vary between strains and they reinforce the idea of probiotic-derived poly-P as a molecule that modulates host-signaling pathways. They also question the relevance of this polymer to the capacity to retain mercury of probiotics.

Cooking and co-ingested polyphenols reduce in vitro methylmercury bioaccessibility from fish and may alter exposure in humans

Fish consumption is a major pathway for mercury exposure in humans. Current guidelines and risk assessments assume that 100% of methylmercury (MeHg) in fish is absorbed by the human body after ingestion. However, a growing body of literature suggests that this absorption rate may be overestimated. We used an in vitro digestion method to measure MeHg bioaccessibility in commercially-purchased fish, and investigated the effects of dietary practices on MeHg bioaccessibility. Cooking had the greatest effect, decreasing bioaccessibility on average to 12.5±5.6%. Polyphenol-rich beverages also significantly reduced bioaccessibility to 22.7±3.8% and 28.6±13.9%, for green and black tea respectively. We confirmed the suspected role of polyphenols in tea as being a driver of MeHg's reduced bioaccessibility, and found that epicatechin, epigallocatechin gallate, rutin and cafeic acid could individually decrease MeHg bioaccessibility by up to 55%. When both cooking and polyphenol-rich beverage treatments were combined, only 1% of MeHg remained bioaccessible. These results call for in vivo validation, and suggest that dietary practices should be considered when setting consumer guidelines for MeHg. More realistic risk assessments could promote consumption of fish as a source of fatty acids, which can play a protective role against cardiovascular disease.

Use of lactic acid bacteria and yeasts to reduce exposure to chemical food contaminants and toxicity

Chemical contaminants that are present in food pose a health problem and their levels are controlled by national and international food safety organizations. Despite increasing regulation, foods that exceed legal limits reach the market. In Europe, the number of notifications of chemical contamination due to pesticide residues, mycotoxins and metals is particularly high. Moreover, in many parts of the world, drinking water contains high levels of chemical contaminants owing to geogenic or anthropogenic causes. Elimination of chemical contaminants from water and especially from food is quite complex. Drastic treatments are usually required, which can modify the food matrix or involve changes in the forms of cultivation and production of the food products. These modifications often make these treatments unfeasible. In recent years, efforts have been made to develop strategies based on the use of components of natural origin to reduce the quantity of contaminants in foods and drinking water, and to reduce the quantity that reaches the bloodstream after ingestion, and thus, their toxicity. This review provides a summary of the existing literature on strategies based on the use of lactic acid bacteria or yeasts belonging to the genus Saccharomyces that are employed in food industry or for dietary purposes.

In vitro evaluation of dietary compounds to reduce mercury bioavailability

Mercury in foods, in inorganic form [Hg(II)] or as methylmercury (CH₃Hg), can have adverse effects. Its elimination from foods is not technologically viable. To reduce human exposure, possible alternatives might be based on reducing its intestinal absorption. This study evaluates the ability of 23 dietary components to reduce the amount of mercury that is absorbed and reaches the bloodstream (bioavailability). We determined their effect on uptake of mercury in Caco-2 cells, a model of intestinal epithelium, exposed to Hg(II) and CH₃Hg standards and to swordfish bioaccessible fractions. Cysteine, homocysteine, glutathione, quercetin, albumin and tannic reduce bioavailability of both mercury species. Fe(II), lipoic acid, pectin, epigallocatechin and thiamine are also effective for Hg(II). Some of these strategies also reduce Hg bioavailability in swordfish (glutathione, cysteine, homocysteine). Moreover, extracts and supplements rich in these compounds are also effective. This knowledge may help to define dietary strategies to reduce in vivo mercury bioavailability.