Probiotics and gut microbiome - Prospects and challenges in remediating heavy metal toxicity

The gut microbiota: A key player in cadmium toxicity - implications for disease, interventions, and combined toxicant exposures

Cadmium (Cd) is a highly toxic heavy metal contaminant found in soil and water due to human activities such as mining and industrial discharge. Cd can accumulate in the body, leading to various health risks such as organ injuries, osteoporosis, renal dysfunction, Type 2 diabetes (T2DM), reproductive diseases, hypertension, cardiovascular diseases, and cancers. The gut is particularly sensitive to Cd toxicity as it acts as the primary barrier against orally ingested Cd. Even at low concentrations, Cd can cause oxidative stress, inflammation, and intestinal bleeding. Cd also disrupts the gut microbiota, affecting its structure, taxonomic composition, and metabolic functions. Cd exposure alters the structure of the gut microbial community, reducing diversity and upregulating certain phyla and genera. This disturbance can lead to physiological and metabolic imbalances, including disruptions in energy homeostasis, amino acid, lipid, nucleotide, and short-chain fatty acid (SCFAs) metabolism. The effects of Cd on the gut microbiota depend on the duration of exposure, the dose of Cd, and can vary based on sex and age. Cd-induced gut dysbiosis has been linked to various diseases, including diabetes, adiposity, atherosclerosis, liver damage, infections, cancer, and neurodegenerative diseases. Interventions targeting the gut microbiota, such as probiotics, specific diets, melatonin, selenium, vitamin D3, and certain compounds, have shown potential in reducing the health risks associated with Cd exposure. However, combined exposure to Cd and other toxicants, such as microplastics (MPs), heavy metals, and antibiotics, can amplify the toxicity and dysbiosis in the gut microbiota.

Interactions between environmental pollutants and gut microbiota: A review connecting the conventional heavy metals and the emerging microplastics

Growing epidemiological evidence suggests that the diverse and functional gut microbiota plays a vital role in regulating the health and disease of organisms including human. However, organisms are inevitably exposed to widespread environmental pollutants, and the interactions between their gut microbiota and pollutants are relatively underreported. The present paper considers heavy metals (HMs) and microplastics (MPs) as representatives of traditional and emerging pollutants and systematically summarizes their effects on gut microbiota and the effects of gut microbiota on pollutants. The former refers to the alterations in the gut microbiota's abundance, diversity and composition caused by pollutants, whereas the latter focuses on the changes in the metabolism of pollutants by adjusting the dominant bacteria, specific enzymes, and key genes. In particular, some fields were found to be poorly studied, including extension of research to humans, mechanistic exploration of gut microbiota's changes, and the metabolism of pollutants by gut microbiota. Accordingly, we draw attention to the development and application of in vitro test models to more accurately explore the interactions between pollutants and gut microbiota when assessing human health risks. In addition, by combining state-of-the-art biological techniques with culturomics, more gut microbiota can be identified, isolated, and cultured, which helps to confirm the relationship between pollutants and gut microbiota and the potential function of gut microbiota in pollutant metabolism. Furthermore, the phenomenon of coexposure to HMs and MPs is becoming more frequent, and their interactions with gut microbiota and the influence on human health is expected to be one of the frontier research fields in the future. The key information presented in this review can stimulate further development of techniques and methodologies for filling the knowledge gaps in the relationships between combined pollutants (HMs and MPs), gut microbiota, and human health.

Environmental Chemical-Induced Cardiometabolic Disorders: Combined Epidemiological and Experimental Evidence

Screening environmental pollutants that are harmful to the cardiometabolic status and understanding their key toxic pathways are crucial for effective clinical intervention. Based on exposure data of 46 chemicals in a nationally representative 13,286 people, logistic regression and mixture modeling were used to preliminarily identify environmental pollutants with significant impacts on 12 indicators for cardiometabolic disorders. A total of 15 chemicals were found to be associated with the integrated latent class, among which four chemicals (perfluorononanoic acid [PFNA], perfluorooctanoic acid [PFOA], thiocyanate, and thallium) also contributed significantly to the mixture effect. We constructed the adverse outcome pathways (AOPs) for nine significant toxicants in both models of individual chemicals and the mixture for each cardiometabolic disorder. Notably, fluoroalkyl substances affect multiple aspects of hyperlipidemia by activating PPARα. We performed molecular docking and in vitro experiments to verify and supplement the toxicological mechanism of PFNA. Through binding to PPARα, PFNA increased the levels of downstream molecules including CD36 (fatty acid transfer), ACSL1 (fatty acid activation), and CPT1a (intracellular transfer for β-oxidation) and ultimately promoted the accumulation of triglycerides and lipid droplets in HepG2 cells. These markers, together with key events for other metabolic phenotypes, may be potential targets for scientific research or clinical treatment.

Role of Bacillus atrophaeus B1 in gut on nicotine tolerance of the fall armyworm

The fall armyworm (FAW), Spodoptera frugiperda is one of the most destructive polyphagous herbivores. Some detoxification genes have been proved to be involved in the adaptability to host plants in FAW, while the role of its gut microbiota on the responses of host switches, and their ability to adapt to new host plants remain poorly understood. Herein, we isolated five strains of nicotine-degrading bacteria from the gut of S. frugiperda larvae, among which Bacillus atrophaeus B1 exhibited the highest nicotine tolerance. This strain showed a minimum inhibitory concentration (MIC) value of 2 g/L and a nicotine degradation rate of 46.36 %. We sequenced the complete genome of B. atrophaeus B1 and 15 candidate genes were identified maybe related to nicotine degradation, among which GE003027, GE002849, GE002602, GE000220 and GE002708 had significantly higher expression when exposed to nicotine. Non-targeted metabolomics revealed 98 differentially accumulated metabolites (DAMs) under nicotine stress, which were 72 metabolites upregulated and 26 metabolites downregulated, and the pathways most affected involved xenobiotic biodegradation and metabolism, energy metabolism, and amino acid metabolism. B. atrophaeus B1 may accumulate 2-ketoglutaric acid and γ-aminobutyric acid during degradation of nicotine, which is non-toxic to S. frugiperda, and participated in the tricarboxylic acid (TCA) cycle. Additionally, 2-ketoglutaric acid and γ-aminobutyric acid were detected both in B. atrophaeus B1 and S. frugiperda treated with nicotine. Antibiotic treatment deprived most of the gut bacteria, followed by a decrease in tolerance of S. frugiperda to nicotine, and the nicotine degradation rate was significantly increased as expected after reinfection with B. atrophaeus B1. These findings provide new insights into the bacterial metabolism of nicotine degradation and offer a theoretical basis for understanding the rapid adaptability of S. frugiperda to various host plants.

The interplay of gut microbiota and heavy metals in multiple sclerosis patients

Multiple Sclerosis (MS) is a chronic inflammatory disease characterized by central nervous system (CNS). In this study, the concentration of heavy metals was measured in stool samples of MS patients by Inductively Coupled Plasma-Mass Spectroscopy (ICP-MS) method and compared with healthy people. Also, another goal of this study is to investigate the alteration of the gut microbiome of MS patients by metagenomics technique based on the 16S rRNA gene sequencing. The IL-10 ELISA assay showed no significant differences between the serum level of the IL-10 in the patients and the control group (p = 0.510). Heavy metal measurement by ICP-MS showed significantly higher levels of arsenic (As, Mean = 32.77 μg/kg), nickel (Ni, Mean = 7.154 μg/kg), manganese (Mn, Mean = 3723 μg/kg), and zinc (Zn, Mean = 5508 μg/kg) in the stool samples of the MS group compared to the control group, while concentrations of iron (Fe, Mean = 9585 μg/kg), lead (Pb, Mean = 18.54 μg/kg), titanium (Ti, Mean = 69.69 μg/kg), and tin (Sn, Mean = 13.92 μg/kg) were significantly lower. The result of gut microbiome analysis showed an increase in the abundance of the Verrumicrobiaceae, Lachnospiraceae and Ruminococcaceae families was considerably increased in MS patients compared to the control group (p < 0.05). This study reports that high levels of heavy metals such as Ars, Ni, Mn, and Zn, deficiency of Fe, Pb, Ti, and Sn, and alteration of the gut microbiome are involved in the pathogenesis of MS. The novelty of this study lies in its multi-faceted approach to understanding MS by integrating the measurement of heavy metals in stool samples with the analysis of gut microbiome alterations, thereby providing comprehensive insights into heavy metals, the gut microbiome, and potential therapeutic avenues. This study suggests several potential applications and practical implications based on its findings regarding heavy metals, gut microbiome alterations, and IL-10 levels in MS. First, the identification of elevated levels of specific heavy metals and deficiencies in others may lead to targeted screening and monitoring, informing preventive strategies for MS patients. Additionally, the observed gut microbiome changes could facilitate the development of microbiome-based therapies, such as probiotics or dietary interventions, aimed at restoring microbial balance. Finally, exploring the interplay between heavy metals, gut microbiome, and immune response may guide the creation of novel therapeutic interventions, ultimately enhancing treatment efficacy and providing new avenues for managing MS, thereby alleviating the burden of this chronic condition.

Major heavy metals and human gut microbiota composition: a systematic review with nutritional approach

BACKGROUND

The human gut microbiota has a critical role in several aspects of host homeostasis, such as immune development, metabolism, nutrition, and defense against pathogens during life. It can be sensitive to xenobiotics including drugs, diet, or even environmental pollutants, especially heavy metals (HMs). The findings of some previous studies are heterogeneous due to the inclusion of various types of study (human, and animal studies) and wide exposures (phthalate, bisphenol A, HMS, etc.), and no comprehensive systematic review has investigated the association between HMs exposure and human gut microbiota composition. Therefore, we carried out a systematic review of human observational studies to examine this association. PubMed, Scopus, ISI Web of Science, and Google Scholar were searched using Medical Subject Headings (MeSH) and non-MeSH terms. Eventually, 12 studies for arsenic (As), lead (Pb), mercury (Hg), and cadmium (Cd) were included in this study. No eligible study was found for Aluminium.

SHORT CONCLUSION

The findings showed exposure to HMs disturbs the composition of gut microbiota and can lead to dysbiosis. Exposure to high levels of As, Pb, and Hg increased the abundance of Collinsella as pathobionts. Evidently, it is related to leaky gut, oxidative stress, and several diseases such as inflammatory bowel disease and cancers. Probiotic treatment and nutritional strategies such as high fiber intake and following antioxidant-rich diets should be considered in terms of HMs exposure.

Salt use patterns and heavy metal urinary excretion

Background

Salt usage patterns have been associated with a risk of multiple diseases; however, their relationship with heavy metal exposure has not been extensively studied.

Methods

This study analyzed survey data from 11,574 NHANES participants. Weighted linear regression models were used to examine the relationship between the type of salt used by participants, the frequency of adding salt at the table, and the frequency of adding regular or seasoned salt to cooking or food preparation, and urinary concentrations of 10 heavy metals. Multiple sensitivity analyses were also performed.

Results

The weighted regression analysis indicated that participants' salt usage patterns were associated with an increased urinary excretion of certain heavy metals. Specifically, regarding the type of salt used, compared to regular salt, the use of salt substitutes was significantly positively correlated with urinary molybdenum (Mo) levels, while not using salt or substitutes at the table was significantly positively correlated with urinary levels of both Mo and arsenic (As). In terms of the frequency of adding regular salt at the table, frequent addition compared to rarely adding salt was significantly positively correlated with urinary levels of cadmium (Cd), and antimony (Sb), while showing a significant negative correlation with urinary Mo levels. Additionally, when examining the frequency of using regular salt during cooking or food preparation, those who occasionally or very often added regular salt had significantly higher urinary levels of barium (Ba), cesium (Cs), and thallium (Tl) compared to those who never added regular salt during cooking. These associations remained stable in sensitivity analyses.

Conclusion

Our analysis revealed that participants' salt usage patterns are associated with increased excretion of certain heavy metals, suggesting possible increased exposures to these metals. While these findings are concerning, they require validation in other populations and should be confirmed through prospective studies designed based on this hypothesis.

Analysis of the Cadmium Removal Mechanism of Human Gut Bacteria Enterococcus faecalis Strain ATCC19433 from a Genomic Perspective

Cadmium (Cd) is one of the most well-known toxic metals capable of entering the human body via the food chain, leading to serious health problems. Human gut microbes play a pivotal role in controlling Cd bioavailability and toxicity within the human gastrointestinal tract, primarily due to their capacity for Cd adsorption and metabolism. In this work, a Cd-resistant bacterial strain, Enterococcus faecalis strain ATCC19433 was isolated from human gut microbiota. Cd binding assays and comprehensive characterization analyses were performed, revealing the ability of strain ATCC19433 to remove Cd from the solution. Cd adsorption primarily occurred on the bacterial cell walls, which was ascribed to the exciting of functional groups on the bacterial surfaces, containing alkyl, amide II, and phosphate groups; meanwhile, Cd could enter cells, probably through transport channels or via diffusion. These results indicated that Cd removal by the strain was predominantly dependent on biosorption and bioaccumulation. Whole-genome sequencing analyses further suggested the probable mechanisms of biosorption and bioaccumulation, including Cd transport by transporter proteins, active efflux of Cd by cadmium efflux pumps, and mitigating oxidative stress-induced cell damage by DNA repair proteases. This study evaluated the Cd removal capability and mechanism of Enterococcus faecalis strain ATCC19433 while annotating the genetic functions related to Cd removal, which may facilitate the development of potential human gut strains for the removal of Cd.

Mitigating effect of Bifidobacterium longum CCFM1077 on nonylphenol toxicity: An integrative in vitro and in vivo analysis

Nonylphenol (NP), an endocrine-disrupting compound (EDC) with accumulative properties, poses significant risks to human health and the environment. The pivotal role of probiotics in mitigating EDC toxicity has garnered increasing attention. In this study, we assessed the protective effects of Bifidobacterium longum CCFM1077, a probiotic with outstanding in vitro NP-binding ability, against NP-induced toxicity in rats. This analysis revealed that B. longum CCFM1077 effectively promoted the NP excretion and enhanced intestinal barrier integrity. Interestingly, B. longum CCFM1077, by modulating the structure and the function of gut microbiota, increased the abundance of Turicibacter, significantly elevated the level of butyric acid, and upregulated antioxidant-related metabolic pathways, thereby alleviating brain inflammation and ultimately improving behavioral disorders. This study elucidated a strategy to alleviate NP toxicity and lays a theoretical foundation for the development of novel intestinal protection strategies. It supports environmental sustainability by offering a strategy to combat NP bioaccumulation, aligning with global initiatives to minimize the environmental impact of industrial pollutants.

Guardians of the Gut: Harnessing the Power of Probiotic Microbiota and Their Exopolysaccharides to Mitigate Heavy Metal Toxicity in Human for Better Health

Heavy metal pollution is a significant global health concern, posing risks to both the environment and human health. Exposure to heavy metals happens through various channels like contaminated water, food, air, and workplaces, resulting in severe health implications. Heavy metals also disrupt the gut's microbial balance, leading to dysbiosis characterized by a decrease in beneficial microorganisms and proliferation in harmful ones, ultimately exacerbating health problems. Probiotic microorganisms have demonstrated their ability to adsorb and sequester heavy metals, while their exopolysaccharides (EPS) exhibit chelating properties, aiding in mitigating heavy metal toxicity. These beneficial microorganisms aid in restoring gut integrity through processes like biosorption, bioaccumulation, and biotransformation of heavy metals. Incorporating probiotic strains with high affinity for heavy metals into functional foods and supplements presents a practical approach to mitigating heavy metal toxicity while enhancing gut health. Utilizing probiotic microbiota and their exopolysaccharides to address heavy metal toxicity offers a novel method for improving human health through modulation of the gut microbiome. By combining probiotics and exopolysaccharides, a distinctive strategy emerges for mitigating heavy metal toxicity, highlighting promising avenues for therapeutic interventions and health improvements. Further exploration in this domain could lead to groundbreaking therapies and preventive measures, underscoring probiotic microbiota and exopolysaccharides as natural and environmentally friendly solutions to heavy metal toxicity. This, in turn, could enhance public health by safeguarding the gut from environmental contaminants.

Fecal microbiome transplantation alleviates manganese-induced neurotoxicity by altering the composition and function of the gut microbiota via the cGAS-STING/NLRP3 pathway

Manganese (Mn) is an environmental pollutant, and overexposure can cause neurodegenerative disorders similar to Alzheimer's disease and Parkinson's disease that are characterized by β-amyloid (Aβ) overexpression, Tau hyperphosphorylation and neuroinflammation. However, the mechanisms of Mn neurotoxicity are not clearly defined. In our study, a knockout mouse model of Mn exposure combined with gut flora-induced neurotoxicity was constructed to investigate the effect of gut flora on Mn neurotoxicity. The results showed that the levels of Tau, p-Tau and Aβ in the hippocampus of C57BL/6 mice were greater than those in the hippocampus of control mice after 5 weeks of continuous exposure to manganese chloride (Mn content of 200 mg/L). Transplanted normal and healthy fecal microbiota from mice significantly downregulated Tau, p-Tau and Aβ expression and ameliorated brain pathology. Moreover, Mn exposure activated the cGAS-STING pathway and altered the cecal microbiota profile, characterized by an increase in Clostridiales, Pseudoflavonifractor, Ligilactobacillus and Desulfovibrio, and a decrease in Anaerotruncus, Eubacterium_ruminantium_group, Fusimonas and Firmicutes, While fecal microbiome transplantation (FMT) treatment inhibited this pathway and restored the microbiota profile. FMT alleviated Mn exposure-induced neurotoxicity by inhibiting activation of the NLRP3 inflammasome triggered by overactivation of the cGAS-STING pathway. Deletion of the cGAS and STING genes and FMT altered the gut microbiota composition and its predictive function. Phenotypic prediction revealed that FMT markedly decreased the abundances of anaerobic and stress-tolerant bacteria and significantly increased the abundances of facultative anaerobic bacteria and biofilm-forming bacteria after blocking the cGAS-STING pathway compared to the Mn-exposed group. FMT from normal and healthy mice ameliorated the neurotoxicity of Mn exposure, possibly through alterations in the composition and function of the microbiome associated with the cGAS-STING/NLRP3 pathway. This study provides a prospective direction for future research on the mechanism of Mn neurotoxicity.

Lactic acid bacteria supplementation: A bioprotective approach to mitigating cadmium-induced toxicity and modulating gene expression in murine models

This study aimed to assess the effects of different strains of lactic acid bacteria, namely LeviLactobacillus brevis (AC10), Lacticaseibacillus rhamnosus (AC11), and Pediococcus acidilactici (AC15), on mice exposed to cadmium-induced oxidative stress. The study assessed weight gain, liver enzymes, antioxidant enzymes, immunoglobulin factors, lipid peroxidation, and gene expression in liver and brain of mice. The findings revealed that the AC10 and AC11 strains had a higher ability to absorb Cd as compared to AC15. The in vivo analysis demonstrated that the dietary dual supplementation of AC10 and AC11 resulted in significant (p < 0.05) improvements, including increased body weight and food intake, reduced cadmium tissue deposition, decreased lipid peroxidation, enhanced cellular antioxidant redox potential, suppressed inflammation genes in the liver and brain tissues, and improved morpho-characteristics of the jejunum in mice challenged by cadmium-induced toxicity. The multiple mechanisms of action, including heavy metal sequestration, antioxidant enhancement, and maintenance of intestinal integrity, highlight the potential of these probiotics' intervention as a viable approach to counteract the deleterious effects of cadmium exposure.

Dietary silicate minerals relieving cadmium or lead poisoning in juvenile sea cucumber, Apostichopusjaponicus

Industrial activities increase Apostichopus japonicus exposure to toxic heavy metals. This study evaluates the efficacy of three dietary silicate minerals (montmorillonite, zeolite, and kaolin) in relieving cadmium and lead toxicity in A. japonicus. Over four weeks, juvenile A. japonicus (7 - 9 g) were fed diets incorporating montmorillonite, zeolite, or kaolin, replacing sea mud at a 1:1 ratio. Experimental groups were: SM (control with sea mud), M (montmorillonite), Z (zeolite), and K (kaolin). Each group was exposed to cadmium (50 mg kg-1) or lead (100 mg kg-1) at the minimal toxic dose (MTD). Groups M and K demonstrated excellent growth performance, marked by improvements in weight gain rate (WGR), specific growth rate (SGR), feed conversion ratio (FCR), and survival rate (SR). Their coelomic fluid revealed higher enzymatic activities, such as acid phosphatase (ACP), alkaline phosphatase (AKP), catalase (CAT), and superoxide dismutase (SOD). Additionally, groups M and K showed a reduced accumulation of cadmium and lead in their tissues; group K notably excelled in mitigating intestinal tissue damage. In contrast, Group Z exhibited significantly poorer performance. In other aspects, the trends among the three experimental groups were generally similar: the activity of intestinal digestive enzymes declined, intestinal microbiota diversity decreased, and the stability of community composition increased. In summary, the supplementation of montmorillonite and kaolin effectively reduces cadmium and lead toxicity, diminishes oxidative damage, and promotes intestinal health in A. japonicus. These findings provide valuable insights for enhancing safety in A. japonicus aquaculture.

Metal(loid)-gut microbiota interactions and microbiota-related protective strategies: A review

Human exposure to metal(loid)s has dramatically increased over the past five decades, which has triggered public concern worldwide. Recently, gut microbiota has been considered a target for metal(loid)s, and some literature has reviewed the interactions between gut microbiota and heavy metal(loid)s (HMs) with high toxicity. However, whether there is an interaction between gut microbiota and metal(loid)s with essential roles or some normal functions are far from clear to date. Importantly, in addition to traditional probiotics that have been clarified to alleviate the adverse effect of HMs on the body, some novel probiotics, prebiotics, synbiotics, and postbiotics may also exhibit comparable or even better abilities of metal(loid) remediation. In this review, we mainly outline and discuss recent research findings on the metal(loid)-gut microbiota interactions and microbiota-related protective strategies.

Pollution-related changes in nest microbiota: Implications for growth and fledging in three passerine birds

Non-ferrous smelters emit toxic metals into the environment, posing a threat to wildlife health. Despite the acknowledged role of microbes in host health, the impact of such emissions on host-associated microbiota, especially in wild birds, remains largely unexplored. This study investigates the associations of metal pollution, fitness, and nest microbiota (serving as a proxy for early-life microbial environment) which may influence the nestling health and development. Our study focuses on three passerine birds, the great tit (Parus major), blue tit (Cyanistes caeruleus), and pied flycatcher (Ficedula hypoleuca), within control and metal-polluted sites around a Finnish copper-nickel smelter. The polluted sites had been contaminated with arsenic (As), cadmium (Cd), copper (Cu), nickel (Ni), and zinc (Zn). We performed bacterial 16S rRNA sequencing and metal analyses on 90 nests and monitored nestling body mass, fledging success, and various biotic and abiotic factors. Our findings revealed species-specific responses to metal exposure in terms of both fitness and nest microbiota. P. major and C. caeruleus showed sensitivity to pollution, with decreased nestling growth and fledging in the polluted zone. This was accompanied by a shift in the bacterial community composition, which was characterized by an increase in some pathogenic bacteria (in P. major and C. caeruleus nests) and by a decrease in plant-associated bacteria (within C. caeruleus nests). Conversely, F. hypoleuca and their nest microbiota showed limited responses to pollution, indicating greater tolerance to pollution-induced environmental changes. Although pollution did not correlate with nest alpha diversity or the most abundant bacterial taxa across all species, certain potential pathogens within the nests were enriched in polluted environments and negatively correlated with nestling fitness parameters. Our results suggest that metal pollution may alter the nest bacterial composition in some bird species, either directly or indirectly through environmental changes, promoting pathogenic bacteria and potentially impacting bird survival.

Cadmium exposure in infants and children: toxicity, health effects, dietary risk assessment and mitigation strategies

As a non-essential metal, cadmium (Cd) poses a significant threat to food safety and public health. This risk is particularly pronounced for infants and young children due to their high food consumption relative to body weight and immature physiological systems. This review examines the health risks associated with Cd exposure, particularly during the prenatal period through adolescence. It evaluates the prevalence of Cd-rich foods in children's diets and their intake levels across various countries. The review demonstrates that Cd exposure is associated with neurodevelopmental disorders, immune dysfunction, and cardiovascular diseases. It also highlights geographic differences in exposure, with some Asian countries, such as Thailand and China, exhibiting higher overall levels of Cd intake among children compared to other regions. This review presents several recommendations to mitigate Cd intake during early childhood, including reducing the Cd content in food, inhibiting Cd absorption, and promoting its excretion from the body. To minimize the risk of dietary Cd intake in children, it is recommended that stringent regulations of Cd limits in children's food be implemented, alongside a coordinated multi-stakeholder effort. This review provides important insights into effective public health policy development, laying the foundation for achieving broader public health goals.

Probiotics in addressing heavy metal toxicities in fish farming: Current progress and perspective

Heavy metal contamination of aquatic environments adversely affects the health of aquatic organisms and consumption of fish contaminated with heavy metals poses serious health risks to humans. Among various strategies, probiotics (living microorganisms known to have beneficial effects on the host), which have been extensively applied in the aquaculture industry, could be helpful for heavy metal detoxification and remediation. Several probiotics, including Lactobacillus strains, exhibit heavy metal binding, high heavy metal tolerance, and other beneficial characteristics for the host. Notably, numerous probiotics have been reported to bind heavy metals and excrete them from the host. Various probiotic strains (Lactobacillus, Bacillus, Lactococcus, etc.) show beneficial effects in alleviating heavy metal toxicity in cultured fish species. Certain probiotic bacteria reduce the absorption and bioavailability of heavy metals by enhancing heavy metal detoxification and sequestration while preserving gut barrier function. This review summarises the toxic effects of selected heavy metals on the health of farmed fish and discusses the role of probiotic strains in remediating the consequential exposure-induced immune toxicity and oxidative stress. Moreover, we discussed the protective strategies of probiotics against heavy metal accumulation in various tissues and gut dysbiosis in fish to alleviate heavy metal toxicity in fish farming, thereby promoting a sustainable blue economy worldwide.

Earthworm gut bacteria facilitate cadmium immobilization through the formation of CdS nanoparticles

Gut bacteria of earthworm Amynthas hupeiensis exhibit significant potential for the in-situ remediation of cadmium (Cd)-contaminated soil. However, the mechanisms by which these gut bacteria immobilize and tolerate Cd remain elusive. The composition of the gut bacterial community was characterized by high-throughput sequencing. Cd-tolerant bacteria were isolated from the gut, and their roles in Cd immobilization, as well as their tolerance mechanisms, were explored through chemical characterization and transcriptome analysis. The predominant taxa in the gut bacterial community included unclassified Enterobacteriaceae, Citrobacter, and Bacillus, which were distinctly different from those in the surrounding soil. Notably, the most Cd-tolerant gut bacterium, Citrobacter freundii DS strain, immobilized 63.61% of Cd2+ within 96 h through extracellular biosorption and intracellular bioaccumulation of biosynthetic CdS nanoparticles, and modulation of solution pH and NH4+ concentration. Moreover, the characteristic signals of CdS were also observed in the gut content of A. hupeiensis when the sterilized Cd-contaminated soil was inoculated with C. freundii. The primary pathways involved in the response of C. freundii to Cd stress included the regulation of ABC transporters, bacterial chemotaxis, cell motility, oxidative phosphorylation, and two-component system. In conclusion, C. freundii facilitates Cd immobilization both in vitro and in vivo, thereby enhancing the host earthworm's adaptation to Cd-contaminated soil.

Toxic effects and mechanisms of chronic cadmium exposure on Litopenaeus vannamei growth performance based on combined microbiome and metabolome analysis

Cadmium (Cd) pollution seriously affects marine organisms' health and poses a threat to food safety. Although Cd pollution has attracted widespread attention in aquaculture, little is known about the toxic mechanisms of chronic Cd exposure on shrimp growth performance. The study investigated the combined effects of chronic exposure to Cd of different concentrations including 0, 75, 150, and 300 μg/L for 30 days on the growth performance, tissue bioaccumulation, intestinal microbiology, and metabolic responses of Litopenaeus vannamei. The results revealed that the growth was significantly inhibited under exposure to 150 and 300 μg/L Cd2+. The bioaccumulation in gills and intestines respectively showed an increasing and inverted "U" shaped trend with increasing Cd2+ concentration. Chronic Cd altered the intestinal microflora with a significant decrease in microbial richness and increasing trends in the abundances of the potentially pathogenic bacteria Vibrio and Maribacter at exposure to 75 and 150 μg/L Cd2+, and Maribacter at 300 μg/L. In addition, chronic Cd interfered with intestinal metabolic processes. The expressions of certain metabolites associated with growth promotion and enhanced antioxidant power, including N-methyl-D-aspartic acid, L-malic acid, guanidoacetic acid, betaine, and gluconic acid were significantly down-regulated, especially at exposure to 150 and 300 μg/L Cd2+, and were negatively correlated with Vibrio and Maribacter abundance levels. In summary, chronic Cd exposure resulted in severe growth inhibition and increased Cd accumulation in shrimp tissues. Increased levels of intestinal pathogenic bacteria and decreased levels of growth-promoting metabolites may be the key causes of growth inhibition. Harmful bacteria Vibrio and Maribacter may be associated with the inhibition of growth-promoting metabolite expression and may be involved in disrupting intestinal metabolic functions, ultimately impairing shrimp growth potential. This study sheds light on the potential toxicological mechanisms of chronic Cd inhibition on shrimp growth performance, offering new insights into Cd toxicity studies in aquaculture.

Protective effect of Lactiplantibacillus plantarum CCFM8661 against heavy metal mixture-induced liver and kidney injury in mice

Human health and the ecological balance are both gravely threatened by heavy metal pollution brought on by global industrialization. Probiotics are thought to represent a novel class of medicinal products for reducing heavy metal toxicity. Though simultaneous poisoning of numerous heavy metals is more prevalent, the majority of current studies on probiotics in the treatment of heavy metal poisoning concentrate on a single heavy metal. Thus, a mouse damage model was created in this investigation using five heavy metals (Pb, Cd, Hg, Cr, and As), and Lactiplantibacillus plantarum CCFM8661 was utilized as an intervention therapy. The oxidative stress markers, including superoxide dismutase (SOD), catalase (CAT), antioxidant capacity (T-AOC), and malondialdehyde (MDA), were evaluated in the blood, liver, and kidney tissues of mice throughout the experiment by tracking changes in body weight. Additionally, the amounts of five heavy metals were measured in the liver and kidney tissues. The alleviation of tissue damage and the detoxifying activity of L. plantarum CCFM8661 in mice with combined heavy metal intoxication were assessed by histopathological examination of liver and kidney tissues. Results revealed that during the test period, L. plantarum CCFM8661 significantly reduced the content of MDA and the contents of Pb, Cd, Hg, Cr, and As in liver and kidney tissues, while also significantly increasing weight gain and the activities of SOD, CAT, and T-AOC in mouse blood, liver, and kidney tissues compared to the model group. Mouse liver and kidney tissue damage from combined heavy metal exposure was considerably lessened by L. plantarum CCFM8661 when compared to the model group, according to H&E staining. This study demonstrates that L. plantarum CCFM8661 may be utilized as a useful intervention for the treatment of combined heavy metal poisoning by efficiently reducing the harm that heavy metals do to the body and maintaining bodily health.

The rhizosphere microbiome reduces the uptake of arsenic and tungsten by Blechnum orientale by increasing nutrient cycling in historical tungsten mining area soils

The growth of pioneer plants in metal mining area soil is closely related to their minimal uptake of toxic elements. Pioneer plants can inhibit the uptake of toxic elements by increasing nutrient uptake. However, few studies have focused on the mechanisms by which the rhizosphere microbiome affect nutrient cycling and their impact on the uptake of toxic elements by pioneer plants. In this study, we selected Blechnum orientale to investigate the potential roles of the rhizosphere microbiome in nutrient cycling and plant growth in a historical tungsten (W) mining area. Our results showed that while the arsenic (As) and W contents in the soil were relatively high, the enrichment levels of As and W in the B. orientale were relatively low. Furthermore, we found that the As and W contents in plants were significantly negatively correlated with soil nutrients (S, P and Mo), suggesting that elevated levels of these soil nutrients could inhibit As and W uptake by B. orientale. Importantly, we found that these nutrients were also identified as the most important factors shaping rhizosphere microbial attributes, including microbial diversity, ecological clusters, and keystone OTUs. Moreover, the genera, keystone taxa and microbial functional genes enriched in the rhizosphere soils from mining areas played a key role in nutrient (S, P and Mo) bioavailability, which could further increase the nutrient uptake by B. orientale. Taken together, our results suggest that rhizosphere microorganisms can improve pioneer plant growth by inhibiting toxic element accumulation via the increase in nutrient cycling in former W mining areas.

The effects of heavy metal exposure on brain and gut microbiota: A systematic review of animal studies

The gut-brain axis is a crucial interface between the central nervous system and the gut microbiota. Recent evidence shows that exposure to environmental contaminants, such as heavy metals, can cause dysbiosis in gut microbiota, which may affect the gut-brain communication, impacting aspects of brain function and behavior. This systematic review of the literature aims to evaluate whether deleterious effects on brain function due to heavy metal exposure could be mediated by changes in the gut microbiota profile. Animal studies involving exposure to heavy metals and a comparison with a control group that evaluated neuropsychological outcomes and/or molecular outcomes along with the analysis of microbiota composition were reviewed. The authors independently assessed studies for inclusion, extracted data and assessed risk of bias using the protocol of Systematic Review Center for Laboratory Animal Experimentation (SYRCLE) for preclinical studies. A search in 3 databases yielded 16 eligible studies focused on lead (n = 10), cadmium (n = 1), mercury (n = 3), manganese (n = 1), and combined exposure of lead and manganese (n = 1). The animal species were rats (n = 7), mice (n = 4), zebrafish (n = 3), carp (n = 1) and fruit fly (n = 1). Heavy metals were found to adversely affect cognitive function, behavior, and neuronal morphology. Moreover, heavy metal exposure was associated with changes in the abundance of specific bacterial phyla, such as Firmicutes and Proteobacteria, which play crucial roles in gut health. In some studies, these alterations were correlated with learning and memory impairments and mood disorders. The interplay of heavy metals, gut microbiota, and brain suggests that heavy metals can induce direct brain alterations and indirect effects through the microbiota, contributing to neurotoxicity and the development of neuropsychological disorders. However, the small number of papers under review makes it difficult to draw definitive conclusions. Further research is warranted to unravel the underlying mechanisms and evaluate the translational implications for human health.

Probiotics Pediococcus acidilactici GR-1 promotes the functional strains and remodels gut microbiota to reduce the Cr(VI) toxicity in a dual-chamber simulated intestinal system

Numerous animal studies have demonstrated the toxicity of hexavalent chromium [Cr(VI)] and the bioremediative effects of probiotics on the composition and functions of gut microbiota. Since the precise mechanisms of Cr(VI) detoxification and its interactions with human gut microbiota were unknown, a novel dual-chamber simulated intestinal (DCSI) system was developed to maintain both the stability of the simulated system and the composition of the gut microbiota. Probiotic GR-1 was found to regulate intestinal gut microbiota, thereby reducing the toxicity of Cr(VI) within the DCSI system. The results indicate that Cr(VI) levels were reduced from 2.260 ± 0.2438 μg/g to 1.7086 ± 0.1950 μg/g in the gut microbiota cell pellet, and Cr(VI) permeability decreased from 0.5521 ± 0.1132 μg/L to 0.3681 ± 0.0178 μg/L after 48 h in simulated gut fluid. Additionally, the removal rate of 1,1-Diphenyl-2-picrylhydrazyl (DPPH), reducibility (Vitamin C), and total antioxidant capacity (T-AOC) increased by 50.83%, 31.70%, and 27.56%, respectively, following probiotic treatment. The increase in antioxidant capacity correlated with total Cr removal (P < 0.05, r from -0.80 to 0.73). 16S rRNA sequencing analysis showed that gut microbiota composition was reshaped by the addition of probiotics, which regulated the recovery of the functional gut microbiota to normal levels, rather than restoring the entire gut microbiota composition for community function. Thus, this study not only demonstrates the feasibility and stability of culturing gut microbiota but also offers a new biotechnological approach to synthesizing functional communities with functional strains for environmental risk management.

Biotransformation of Pb and As from sewage sludge and food waste by black soldier fly larvae: Migration mechanism of bacterial community and metalloregulatory protein scales

The accumulation and transformation of lead (Pb) and arsenic (As) during the digestion of sewage sludge (SS) by black soldier fly larvae (BSFL) remain unclear. In this study, we used 16 s rRNA and metagenomic sequencing techniques to investigate the correlation between the microbial community, metalloregulatory proteins (MRPs), and Pb and As migration and transformation. During the 15-day test period, BSFL were able to absorb 34-48 % of Pb and 32-45 % of As into their body. Changes in bacterial community abundance, upregulation of MRPs, and redundancy analysis (RDA) results confirmed that ZntA, EfeO, CadC, ArsR, ArsB, ArsD, and ArsA play major roles in the adsorption and stabilization of Pb and As, which is mainly due to the high contribution rates of Lactobacillus (48-59 %) and Enterococcus (21-23 %). Owing to the redox reaction, the regulation of the MRPs, and the change in pH, the Pb and As in the BSFL residue were mainly the residual fraction (F4). The RDA results showed that Lactobacillus and L.koreensis could significantly (P < 0.01) reduce the reducible fraction (F2) and F4 of Pb, whereas Firmicutes and L.fermentum can significantly (P < 0.05) promote the transformation of As to F4, thus realizing the passivation Pb and As. This study contributes to the understanding of Pb and As in SS adsorbed by BSFL and provides important insights into the factors that arise during the BSFL-mediated migration of Pb and As.

Potential effects of individual and combined exposure to tetraconazole and cadmium on zebrafish from the perspective of enantioselectivity and intestinal microbiota

As the wide use of pesticides, they could form combined pollution with heavy metals, which would affect their environmental behaviors and toxic effects. Particularly, the effects would be more intricate for chiral pesticides. In this study, the accumulation and dissipation trends of tetraconazole enantiomers in zebrafish were investigated by individual and combined exposure of cadmium (Cd) and tetraconazole (including racemate and enantiomers) after confirming the absolute configuration of tetraconazole enantiomer. For the enantiomer treatments, Cd enhanced the accumulation of S-(+)-tetraconazole, but declined the concentrations of R-(-)-tetraconazole in zebrafish. The dissipation half-lives of tetraconazole enantiomers were extended by 1.65-1.44 times after the combined exposure of Cd and enantiomers. The community richness and diversity of intestinal microbiota were reduced in all treatments, and there were significant differences in R + Cd treatment. There was synergistic effect between Cd and S-(+)-tetraconazole for the effects on the relative abundances of Fusobacteria, Firmicutes, Proteobacteria, Actinobacteria, and Bacteroidetes. For R-(-)-tetraconazole, Cd mainly exhibited antagonistic effects. In the combined exposure of Cd and S-(+)-tetraconazole, the relative abundance changes of Cetobacterium (Fusobacteria, increase) and Edwardsiella (Proteobacteria, decrease) might affect the carbohydrate metabolism and energy metabolism, and led to the increase of S-(+)-tetraconazole bioaccumulation concentration. In the combined exposure of Cd and R-(-)-tetraconazole, Cd could increase the relative abundance of Edwardsiella (Proteobacteria), and affect the amino acid metabolism, which might reduce the bioaccumulation concentration of R-(-)-tetraconazole. This study reported for the first time that the abundance of intestinal microbiota in zebrafish might affect the bioaccumulation and dissipation of tetraconazole enantiomers, and would provide new insight for the study of combined pollutions.

Simultaneous removal of caesium and strontium using different removal mechanisms of probiotic bacteria

When radioactive materials are released into the environment due to nuclear power plant accidents, they may enter into the body, and exposing it to internal radiation for long periods of time. Although several agents have been developed that help excrete radioactive elements from the digestive tract, only one type of radioactive element can be removed using a single agent. Therefore, we considered the simultaneous removal of caesium (Cs) and strontium (Sr) by utilising the multiple metal removal mechanisms of probiotic bacteria. In this study, the Cs and Sr removal capacities of lactobacilli and bifidobacteria were investigated. Observation using an electron probe micro analyser suggested that Cs was accumulated within the bacterial cells. Since Sr was removed non metabolically, it is likely that it was removed by a mechanism different from that of Cs. The amount of Cs and Sr that the cells could simultaneously retain decreased when compared to that for each element alone, but some strains showed only a slight reduction in removal. For example, Bifidobacterium adolescentis JCM1275 could simultaneously retain 55.7 mg-Cs/g-dry cell and 8.1 mg-Sr/g-dry cell. These results demonstrated the potentials of utilizing complex biological system in simultaneous removal of multiple metal species.

Pollution characteristics and release mechanism of microplastics in a typical end-of-life vehicle (ELV) recycling base, East China

Microplastics (MPs) is a novel and significant pollution due to its eco-environmental hazards and ubiquity. In end-of-life vehicle (ELV) recycling base, MPs are widely distributed but have rare reported in scientific literature. In this study, a comprehensive analysis of MPs was conducted in a typical ELV recycling base. MPs were found in all samples at different sampling sites and environmental mediums. A total of 34 polymer types were detected by μ-FTIR, and the main polymers include PE-PP, ABS, polyester resin, nylon, and PEU plastic. MPs were released from the crushing, tearing, and breaking of plastic parts in ELVs. They were in high content in ground dust, with the abundance of 737-29,021 p/5 g D (the average abundance of 5552 ± 6435 p/5 g D). The abundance, shape, color, and size of MPs are related with functional areas of ELV recycling. Heavy metals could be adsorbed on MPs, and their contents on MPs have a significant correlation with those in the corresponding dust samples. At last, some specific MPs control measures, such as changing transportation mode, using dust-proof cloths, and equipping dust removal equipment, have been put forward.

Bioaccessibility of lead and cadmium in soils around typical lead-acid power plants and their effect on gut microorganisms

Potentially toxic elements (Pb and Cd) contamination of soil can adversely affect human health. Moreover, these metal ions interact with the gut microbiota after entering the human digestive system. Based on the physiologically based extraction test and the simulator of human intestinal microbial ecosystem, the bioaccessibility of Pb and Cd in soils contaminated with lead-acid power plants was assessed. The gastric stage exhibited the greatest average bioaccessibility of lead and cadmium (63.39% and 57.22%), followed by the small intestinal stage (6.86% and 36.29%); due to gut microorganisms, the bioaccessibility of lead and cadmium was further reduced in the colon stage (1.86% and 4.22%). Furthermore, to investigate soil contamination's effects on gut microbes, 16S rRNA high-throughput sequencing was used to identify the gut microbial species after the colon period. Due to Pb and Cd exposure, the relative abundance of Firmicutes and unidentified_Bacteria decreased, while the relative abundance of Proteobacteria, Synergistota, and Bacteroidota increased. The relationship between environmental factors and the number of microbial species in the gut was also examined using Spearman correlation analysis. Pb and Cd exposure has been found to affect the composition and structure of the gut microbiota.

Contribution of serum elements to blood pressure during pregnancy by impacting gut microbiota: A prospective cohort study

Exposure to environmental elements can alter gut microbiota, further affecting host health. Exploring the interrelationships among element exposure, gut microbiota and blood pressure (BP) during pregnancy, as well as the mediating roles of gut microbiota, is warranted, which holds implications for maternal and offspring health. In a prospective cohort study between 2017-2018, 733 pregnant women were included. The serum elements and gut microbiota during the second trimester were assessed, and BP was collected during the second and third trimester and before delivery. Fourteen associations were identified between serum elements and BP, including positive associations of zinc (Zn) and thallium (Tl) with systolic BP during the second trimester. Rubidium (Rb) showed a positive association with Pielou's evenness. Serum elements, such as Tl and Rb, were significantly associated with the relative abundance of bacteria and co-abundance groups (CAGs). Alpha diversity was negatively associated with BP levels and trajectories. Moreover, 15 associations between gut microbiota and BP were shown. Finally, mediation analysis confirmed that CAG2 and Pielou's evenness mediated the associations of Tl and Rb with BP, respectively. We concluded that serum elements can contribute to BP changes during pregnancy through gut microbiota, suggesting gut microbiota-targeted approach as a potential intervention.

Glycemic Changes Related to Arsenic Exposure: An Overview of Animal and Human Studies

BACKGROUND

Arsenic (As) is a risk factor associated with glycemic alterations. However, the mechanisms of action and metabolic aspects associated with changes in glycemic profiles have not yet been completely elucidated. Therefore, in this review, we aimed to investigate the metabolic aspects of As and its mechanism of action associated with glycemic changes.

METHODS

We searched the PubMed (MEDLINE) and Google Scholar databases for relevant articles published in English. A combination of free text and medical subject heading keywords and search terms was used to construct search equations. The search yielded 466 articles; however, only 50 were included in the review.

RESULTS

We observed that the relationship between As exposure and glycemic alterations in humans may be associated with sex, smoking status, body mass index, age, occupation, and genetic factors. The main mechanisms of action associated with changes induced by exposure to As in the glycemic profile identified in animals are increased oxidative stress, reduced expression of glucose transporter type 4, induction of inflammatory factor expression and dysfunction of pancreatic β cells.

CONCLUSIONS

Therefore, As exposure may be associated with glycemic alterations according to inter-individual differences.

Low-molecular-weight aromatic acids mediated the adsorption of Cd2+ onto biochars: effects and mechanisms

Low-molecular-weight aromatic acids (LWMAAs), a ubiquitous organic substance in natural systems, are important in controlling the environmental fate of potentially toxic metals. However, little is known about the effects of LWMAAs on the interactions between biochars and potentially toxic metals. Herein, the influences of three aromatic acids, including benzoic acid (BA), p-hydroxy benzoic acid (PHBA), and syringic acid (SA), on the adsorption of Cd2+ onto biochars generated at three different pyrolysis temperatures under acidic and neutral conditions were examined. Generally, the adsorption ability of biochars for Cd2+ improved with the increase of pyrolysis temperature, which was ascribed to the increased inorganic element contents (e.g., P, S, and Si) and aromaticity, increasing the complexation between mineral anions and metal ions, and the enhanced cation-π interaction. Interestingly, aromatic acids considerably inhibited the adsorption of Cd2+ onto biochars, which was mainly ascribed to multi-mechanisms, including competition of LWMAA molecules and metal ions for adsorption sites, the pore blocking effect, the weakened interaction between mineral anions and Cd2+ induced by the adsorbed aromatic acids, and the formation of water-soluble metal-aromatic acid complexes. Furthermore, the inhibitory effects of LWMAAs on Cd2+ adsorption intensively depended on the aromatic acid type and followed the order of SA > PHBA > BA. This trend was related to the differences in the physicochemical features (e.g., the octanol/water partition coefficient (log Kow) and molecular size) of diverse LMWAAs. The results of this study demonstrate that the effects of coexisting LMWAAs should not be ignored when biochars are applied in soil remediation and wastewater treatment.

The Involvement of Lactic Acid Bacteria and Their Exopolysaccharides in the Biosorption and Detoxication of Heavy Metals in the Gut

Heavy metal pollution has become one of the most important global environmental issues. The human health risk posed by heavy metals encountered through the food chain and occupational and environmental exposure is increasing, resulting in a series of serious diseases. Ingested heavy metals might disturb the function of the gut barrier and cause toxicity to organs or tissues in other sites of the body. Probiotics, including some lactic acid bacteria (LAB), can be used as an alternative strategy to detoxify heavy metals in the host body due to their safety and effectiveness. Exopolysaccharides (EPS) produced by LAB possess varied chemical structures and functional properties and take part in the adsorption of heavy metals via keeping the producing cells vigorous. The main objective of this paper was to summarize the roles of LAB and their EPS in the adsorption and detoxification of heavy metals in the gut. Accumulated evidence has demonstrated that microbial EPS play a pivotal role in heavy metal biosorption. Specifically, EPS-producing LAB have been reported to show superior absorption, tolerance, and efficient abatement of the toxicity of heavy metals in vitro and/or in vivo to non-EPS-producing species. The mechanisms underlying EPS-metal binding are mainly related to the negatively charged acidic groups and unique steric structure on the surface of EPS. However, whether the enriched heavy metals on the bacterial cell surface increase toxicity to local mammal cells or tissues in the intestine and whether they are released during excretion remain to be elucidated.

metaProbiotics: a tool for mining probiotic from metagenomic binning data based on a language model

Beneficial bacteria remain largely unexplored. Lacking systematic methods, understanding probiotic community traits becomes challenging, leading to various conclusions about their probiotic effects among different publications. We developed language model-based metaProbiotics to rapidly detect probiotic bins from metagenomes, demonstrating superior performance in simulated benchmark datasets. Testing on gut metagenomes from probiotic-treated individuals, it revealed the probioticity of intervention strains-derived bins and other probiotic-associated bins beyond the training data, such as a plasmid-like bin. Analyses of these bins revealed various probiotic mechanisms and bai operon as probiotic Ruminococcaceae's potential marker. In different health-disease cohorts, these bins were more common in healthy individuals, signifying their probiotic role, but relevant health predictions based on the abundance profiles of these bins faced cross-disease challenges. To better understand the heterogeneous nature of probiotics, we used metaProbiotics to construct a comprehensive probiotic genome set from global gut metagenomic data. Module analysis of this set shows that diseased individuals often lack certain probiotic gene modules, with significant variation of the missing modules across different diseases. Additionally, different gene modules on the same probiotic have heterogeneous effects on various diseases. We thus believe that gene function integrity of the probiotic community is more crucial in maintaining gut homeostasis than merely increasing specific gene abundance, and adding probiotics indiscriminately might not boost health. We expect that the innovative language model-based metaProbiotics tool will promote novel probiotic discovery using large-scale metagenomic data and facilitate systematic research on bacterial probiotic effects. The metaProbiotics program can be freely downloaded at https://github.com/zhenchengfang/metaProbiotics.

Tailored bacteria tackling with environmental mercury: Inspired by natural mercuric detoxification operons

Mercury (Hg) and its inorganic and organic compounds significantly threaten the ecosystem and human health. However, the natural and anthropogenic Hg environmental inputs exceed 5000 metric tons annually. Hg is usually discharged in elemental or ionic forms, accumulating in surface water and sediments where Hg-methylating microbes-mediated biotransformation occurs. Microbial genetic factors such as the mer operon play a significant role in the complex Hg biogeochemical cycle. Previous reviews summarize the fate of environmental Hg, its biogeochemistry, and the mechanism of bacterial Hg resistance. This review mainly focuses on the mer operon and its components in detecting, absorbing, bioaccumulating, and detoxifying environmental Hg. Four components of the mer operon, including the MerR regulator, divergent mer promoter, and detoxification factors MerA and MerB, are rare bio-parts for assembling synthetic bacteria, which tackle pollutant Hg. Bacteria are designed to integrate synthetic biology, protein engineering, and metabolic engineering. In summary, this review highlights that designed bacteria based on the mer operon can potentially sense and bioremediate pollutant Hg in a green and low-cost manner.

Possible modulating functions of probiotic Lactiplantibacillus plantarum in particulate matter-associated pulmonary inflammation

Pulmonary disease represents a substantial global health burden. Increased air pollution, especially fine particulate matter (PM2.5) is the most concerned proportion of air pollutants to respiratory health. PM2.5 may carry or combine with other toxic allergens and heavy metals, resulting in serious respiratory allergies and anaphylactic reactions in the host. Available treatment options such as antihistamines, steroids, and avoiding allergens/dust/pollutants could be limited due to certain side effects and immense exposure to air pollutants, especially in most polluted countries. In this mini-review, we summarized how PM2.5 triggers respiratory hyperresponsiveness and inflammation, and the probiotic Lactiplantibacillus plantarum supplementation could minimize the risk of the same. L. plantarum may confer beneficial effects in PM2.5-associated pulmonary inflammation due to significant antioxidant potential. We discussed L. plantarum's effect on PM2.5-induced reactive oxygen species (ROS), inflammatory cytokines, lipid peroxidation, and DNA damage. Available preclinical evidence shows L. plantarum induces gut-lung axis, SCFA, GABA, and other neurotransmitter signaling via gut microbiota modulation. SCFA signals are important in maintaining lung homeostasis and regulating intracellular defense mechanisms in alveolar cells. However, significant research is needed in this direction to contemplate L. plantarum's therapeutic potential in pulmonary allergies.

The neonatal gut microbiome and global health

The role of gut microbiome in health, a century-old concept, has been on the center stage of medical research recently. While different body sites, disease conditions, and populations have been targeted, neonatal and early infancy appear to be the most suitable period for such interventions. It is intriguing to note that, unlike traditional use in diarrhea and maintenance of gastrointestinal health, microbiome-mediating therapies have now addressed the most serious medical conditions in young infants such as necrotizing enterocolitis and neonatal sepsis. Unfortunately, almost all new endeavors in this space have been carried out in the Western world leaving behind millions of neonates that can benefit from such manipulations while serving as a large resource for further learning. In this review, an attempt has been made to quantify the global burden of neonatal morbidity and mortality, examples presented on interventions that have failed as a result of drawing from studies conducted in the West, and a case made for manipulating the neonatal gut microbiome to address the biggest killers in early life. A brief comparative analysis has been made to demonstrate the differences in the gut microbiota of North and South and a large clinical trial of synbiotics conducted by our group in a South Asian setting has been presented. Although challenging, the value of conducting such global health research is introduced with an intent to invite medical scientists to engage in well-planned, scientifically robust research endeavors. This can bring about innovation while saving and serving the most vulnerable citizens now and protecting them from the negative health consequences in the later part of their lives, ultimately shaping a resilient and equitable world as pledged by 193 United Nations member countries in 2015.

Specific dietary fibers prevent heavy metal disruption of the human gut microbiota in vitro

Heavy metal exposure is a growing concern due to its adverse effects on human health, including the disruption of gut microbiota composition and function. Dietary fibers have been shown to positively impact the gut microbiota and could mitigate some of the heavy metal negative effects. This study aimed to investigate the effects of different heavy metals (As, Cd and Hg in different concentrations) on gut microbiota in the presence and absence of different dietary fibers that included fructooligosaccharides, pectin, resistant starch, and wheat bran. We observed that whereas heavy metals impaired fiber fermentation outcomes for some fiber types, the presence of fibers generally protected gut microbial communities from heavy metal-induced changes, especially for As and Cd. Notably, the protective effects varied depending on fiber types, and heavy metal type and concentration and were overall stronger for wheat bran and pectin than other fiber types. Our findings suggest that dietary fibers play a role in mitigating the adverse effects of heavy metal exposure on gut microbiota health and may have implications for the development of dietary interventions to reduce dysbiosis associated with heavy metal exposure. Moreover, fiber-type specific outcomes highlight the importance of evidence-based selection of prebiotic dietary fibers to mitigate heavy metal toxicity to the gut microbiota.

Rational Design of Orally Administered Cascade Nanozyme for Inflammatory Bowel Disease Therapy

Inflammatory bowel disease (IBD) affects millions of individuals worldwide annually. Enteric reactive oxygen species (ROS) play critical roles in the physiology and pathology of IBD. Nanozymes hold great promise for the treatment of IBD because of their exceptional ability to regulate redox homeostasis during ROS-related inflammation. However, the rapid development of orally administered, acid-tolerant, antioxidant nanozymes for IBD therapy is challenging. Here, a nine-tier high-throughput screening strategy is established to address the multifaceted IBD treatment demands, including intrinsic stability, radioactivity, solubility, gut microbiome toxicity, biomimetic elements, intermediate frontier molecular orbitals, reaction energy barriers, negative charges, and acid tolerance. Ni3 S4 is selected as the best matching material from 146 323 candidates, which exhibits superoxide dismutase-catalase bienzyme-like activity and is 3.13- and 1.80-fold more active than natural enzymes. As demonstrated in a mouse model, Ni3 S4 is stable in the gastrointestinal tract without toxicity and specifically targets the diseased colon to alleviate oxidative stress. RNA and 16S rRNA sequencing analyses show that Ni3 S4 effectively inhibits the cellular pathways of pro-inflammatory factors and restores the gut microbiota. This study not develops a highly efficient orally administered cascade nanozyme for IBD therapy and offers a next-generation paradigm for the rational design of nanomedicine through data-driven approaches.

Responses of the gut microbiota to environmental heavy metal pollution in tree sparrow (Passer montanus) nestlings

Gut microbiota plays a critical role in regulating the health and adaptation of wildlife. However, our understanding of how exposure to environmental heavy metals influences the gut microbiota of wild birds, particularly during the vulnerable and sensitive nestling stage, remains limited. In order to investigate the relationship between heavy metals and the gut microbiota, we analyzed the characteristics of gut microbiota and heavy metals levels in tree sparrow nestlings at different ages (6, 9 and 12-day-old). The study was conducted in two distinct areas: Baiyin (BY), which is heavily contaminated with heavy metals, and Liujiaxia (LJX), a relatively unpolluted area. Our result reveled a decrease in gut microbiota diversity and increased inter-individual variation among nestlings in BY. However, we also observed an increase in the abundance of bacterial groups and an up-regulation of bacterial metabolic functions associated with resistance to heavy metals toxicity in BY. Furthermore, we identified a metal-associated shift in the relative abundance of microbial taxa in 12-day-old tree sparrow nestlings in BY, particularly involving Aeromonadaceae, Ruminococcaceae and Pseudomonadaceae. Moreover, a significant positive correlation was found between the body condition of tree sparrow nestlings and the abundance of Bifidobacteriaceae in BY. Collectively, our findings indicate that the gut microbiota of tree sparrow nestlings is susceptible to heavy metals during early development. However, the results also highlight the presence of adaptive responses that enable them to effectively cope with environmental heavy metal pollution.

Recent Review on Selected Xenobiotics and Their Impacts on Gut Microbiome and Metabolome

As it is well known, the gut is one of the primary sites in any host for xenobiotics, and the many microbial metabolites responsible for the interactions between the gut microbiome and the host. However, there is a growing concern about the negative impacts on human health induced by toxic xenobiotics. Metabolomics, broadly including lipidomics, is an emerging approach to studying thousands of metabolites in parallel. In this review, we summarized recent advancements in mass spectrometry (MS) technologies in metabolomics. In addition, we reviewed recent applications of MS-based metabolomics for the investigation of toxic effects of xenobiotics on microbial and host metabolism. It was demonstrated that metabolomics, gut microbiome profiling, and their combination have a high potential to identify metabolic and microbial markers of xenobiotic exposure and determine its mechanism. Further, there is increasing evidence supporting that reprogramming the gut microbiome could be a promising approach to the intervention of xenobiotic toxicity.

Environmental impact assessment of active dumpsite in Ondo City, Nigeria: geochemical and geophysical approaches

An assessment of the heavy metal levels associated with municipal waste in the vicinity of the Pele dumpsite, Ondo State, Nigeria, has been undertaken with the view of evaluating the environmental hazards associated with the dumpsite. A total of 23 composite soil samples were collected, measured, and analyzed for six toxic metals, and three dipole-dipole profiles were occupied within the study area. Six different pollution indices were used to evaluate the soil pollution level and ecological risk associated with the dumpsite. The 2D electrical resistivity method was used to delineate the extent of the pollution plume. The mean concentration (in µg/g) of the metals followed a descending order as Zn (75.78) > Cu (37.09) > Pb (25.96) > Cr (6.77) > Ni (5.43) > Cd (0.38). The geoaccumulation indexes revealed Cu (0.56-2.88), Pb (0.49-2.52), and Zn (0.58-2.37) as low to moderate pollutants, while Cd (1.70-6.80) was classified as a moderate-to-considerable high-level pollutant. The ecological assessment indicated moderate risk at most of the sampling points. The 2D resistivity model revealed the weathered layer, which makes up the primary aquifer units, had relatively low resistivity zones, indicating the influence of leachates from the dumpsite, and the vertical expanse of leachate movement was evaluated to be > 25 m. The existence of this pollution plume poses threat to the ecosystem and the health of the surrounding population. Proper management is recommended to resolve this probable ecosystem and health issue.

Regulation of gut bacteria in silkworm (Bombyx mori) after exposure to endogenous cadmium-polluted mulberry leaves

Soil cadmium (Cd) pollution presents a severe pollution burden to flora and fauna due to its non-degradability and transferability. The Cd in the soil is stressing the silkworm (Bombyx mori) out through a soil-mulberry-silkworm system. The gut microbiota of B.mori are reported to shape host health. However, earlier research had not reported the effect of endogenous Cd-polluted mulberry leaves on the gut microbiota of B.mori. In the current research, we compared the phyllosphere bacteria of endogenous Cd-polluted mulberry leaves at different concentrations. The investigation of the gut bacteria of B.mori fed with the mulberry leaves was done to evaluate the impact of endogenous Cd- polluted mulberry leaves on the gut bacteria of the silkworm. The results revealed a dramatic change in the gut bacteria of B.mori whereas, the changes in the phyllosphere bacteria of mulberry leaves in response to an increased Cd concentration were insignificant. It also increased the α-diversity and altered the gut bacterial community structure of B. mori. A significant change in the abundance of dominant phyla of gut bacteria of B.mori was recorded. At the genus level, the abundance of Enterococcus, Brachybacterium and Brevibacterium group related to disease resistance, and the abundance of Sphingomonas, Glutamicibacter and Thermus related to metal detoxification was significantly increased after Cd exposure. Meanwhile, there was a significant decrease in the abundance of the pathogenic bacteria Serratia and Enterobacter. The results demonstrated that endogenous Cd-polluted mulberry leaves caused perturbations in the gut bacterial composition of B.mori, which may driven by Cd content rather than phyllosphere bacteria. A significant variation in the specific bacterial community indicated the adaptation of B. mori gut for its role in heavy metal detoxification and immune function regulation. The results of this study help to understand the bacterial community associated with endogenous Cd-polluted resistance in the gut of B.mori, which proves to be a novel addition in describing its response in activating the detoxification mechanism and promoting its growth and development. This research work will help to explore the other mechanisms and microbiota associated with the adaptations to mitigate the Cd pollution problems.

Heavy metals (HMs) pollution in the aquatic environment: Role of probiotics and gut microbiota in HMs remediation

The presence of heavy metals (HMs) in aquatic ecosystems is a universal concern due to their tendency to accumulate in aquatic organisms. HMs accumulation has been found to cause toxic effects in aquatic organisms. The common HMs-induced toxicities are growth inhibition, reduced survival, oxidative stress, tissue damage, respiratory problems, and gut microbial dysbiosis. The application of dietary probiotics has been evolving as a potential approach to bind and remove HMs from the gut, which is called "Gut remediation". The toxic effects of HMs in fish, mice, and humans with the potential of probiotics in removing HMs have been discussed previously. However, the toxic effects of HMs and protective strategies of probiotics on the organisms of each trophic level have not been comprehensively reviewed yet. Thus, this review summarizes the toxic effects caused by HMs in the organisms (at each trophic level) of the aquatic food chain, with a special reference to gut microbiota. The potential of bacterial probiotics in toxicity alleviation and their protective strategies to prevent toxicities caused by HMs in them are also explained. The dietary probiotics are capable of removing HMs (50-90%) primarily from the gut of the organisms. Specifically, probiotics have been reported to reduce the absorption of HMs in the intestinal tract via the enhancement of intestinal HM sequestration, detoxification of HMs, changing the expression of metal transporter proteins, and maintaining the gut barrier function. The probiotic is recommended as a novel strategy to minimize aquaculture HMs toxicity and safe human health.

Single and combined effects of microplastics and cadmium on the sea cucumber Apostichopus japonicus

Microplastic pollution of the ocean has received extensive attention as plastic pollution increases globally, but the potential ecological risks caused by microplastic interactions with trace metals still require further research. In this study, Apostichopus japonicus was used to explore the individual and combined toxicities of cadmium (Cd) and microplastics and their effects on growth, Cd tissue accumulation, digestive enzymes, and gut microbes. The body weight gain and specific growth rate of animals exposed to a combination of high concentrations of Cd and microplastics decreased. The addition of high concentrations of cadmium to the diet led to an increase in cadmium content in the respiratory tree, digestive tract and body wall. Amylase, lipase and trypsin decreased to different degrees in the group treated with high concentrations of Cd/microplastics. Firmicutes were significantly reduced across multiple treatment groups, with the order Lactobacillales being the most significantly affected. Cd is the pollutant causing the greatest negative impact, but the presence of microplastics undoubtedly increases its toxicity.

A novel approach to Lactiplantibacillus plantarum: From probiotic properties to the omics insights

Lactiplantibacillus plantarum (previously known as Lactobacillus plantarum) strains are one of the lactic acid bacteria (LAB) commonly used in fermentation and their probiotic and functional properties along with their health-promoting roles come to the fore. Food-derived L. plantarum strains have shown good resistance and adhesion in the gastrointestinal tract (GI) and excellent antioxidant and antimicrobial properties. Furthermore, many strains of L. plantarum can produce bacteriocins with interesting antimicrobial activity. This probiotic properties of L. plantarum and existing in different niches give a great potential to have beneficial effects on health. It is also has been shown that L. plantarum can regulate the intestinal microbiota composition in a good way. Recently, omics approaches such as metabolomics, secretomics, proteomics, transcriptomics and genomics try to understand the roles and mechanisms of L. plantarum that are related to its functional characteristics. This review provides an overview of the probiotic properties, including the specific interactions between microbiota and host, and omics insights of L. plantarum.

Cascading effects of Pb on the environmental and symbiotic microbiota and tadpoles' physiology based on field data and laboratory validation

Heavy metal pollution poses a serious threat to ecosystems. Currently, there is a lack of field data that would enable us to gain a systematic understanding of the influences of heavy metals on aquatic ecosystems, especially the interactions between environments and animals. We studied the relationships between the variations in heavy metal concentrations (10 species including Pb in sediments and surface water), the community structure of environmental and symbiotic microbiota, and the gut traits of Bufo gargarizans tadpoles across 16 sampling sites on the Chengdu Plain through rigorous statistical analysis and laboratory validation. The results show that heavy metal concentrations, especially the Pb concentration of the sediment, are linked to the variations in sediment and tadpoles' gut microbiomes but not to water microbiota. For the sediment microbiota, Pb causes a trade-off between the proportions of Burkholderiales and Verrucomicrobiae and affects the methane, sulfide, and nitrate metabolisms. For tadpoles, a high sediment Pb content leads to a low abundance of gut aerobic bacteria and a large relative gut weight under both field and laboratory conditions. In addition, Pb promotes the growth of B. gargarizans tadpoles under laboratory conditions. These effects seem to be beneficial to tadpoles. However, a high Pb content leads to a low abundance of probiotic bacteria (e.g., Verrucomicrobiae, Eubacteriaceae, and Cetobacterium) and a high abundance of pathogenic bacteria in the gut and environment, suggesting potential health risks posed by Pb. Interestingly, there is a causal relationship between Pb-induced variations in sediment and symbiotic microbiotas, and the latter is further linked to the variation in relative gut weight of tadpoles. This suggests a cascading effect of Pb on the ecosystem. In conclusion, our results indicate that among the heavy metals, the Pb in sediment is a critical factor affecting the aquatic ecosystem through an environment-gut-physiology pathway mediated by microbiota.

Lactobacillus fermentum HNU312 alleviated oxidative damage and behavioural abnormalities during brain development in early life induced by chronic lead exposure

Lead exposure is a global public health safety issue that severely disrupts brain development and causes damage to the nervous system in early life. Probiotics and gut microbes have been highlighted for their critical roles in mitigating lead toxicity. However, the underlying mechanisms by which they work yet to be fully explored. Here, we designed a two-stage experiment using the probiotic Lactobacillus fermentum HNU312 (Lf312) to uncover how probiotics alleviate lead toxicity to the brain during early life. First, we explored the tolerance and adsorption of Lf312 to lead in vitro. Second, the adsorption capacity of the strain was determined and confirmed in vivo. The shotgun metagenome sequencing showed lead exposure-induced imbalance and dysfunction of the gut microbiome. In contrast, Lf312 intake significantly modulated the structure of the microbiome, increased the abundance of beneficial bacteria and short-chain fatty acids (SCFAs)-producing bacteria, and upregulated function-related metabolic pathways such as antioxidants. Notably, Lf312 enhanced the integrity of the blood-brain barrier by increasing the levels of SCFAs in the gut, alleviated inflammation in the brain, and ultimately improved anxiety-like and depression-like behaviours induced by lead exposure in mice. Subsequently, the effective mechanism was confirmed, highlighting that Lf312 worked through integrated strategies, including ionic adsorption and microbiota-gut-brain axis regulation. Collectively, this work elucidated the mechanism by which the gut microbiota mitigates the toxic effects of lead in the brain and provides preventive measures and intervention measures for brain damage due to mass lead poisoning in children.

What happens to gut microorganisms and potential repair mechanisms when meet heavy metal(loid)s

Heavy metal (loid) pollution is a significant threat to human health, as the intake of heavy metal (loid)s can cause disturbances in intestinal microbial ecology and metabolic disorders, leading to intestinal and systemic diseases. Therefore, it is important to understand the effects of heavy metal (loid)s on intestinal microorganisms and the necessary approaches to restore them after damage. This review provides a summary of the effects of common toxic elements, such as lead (Pb), cadmium (Cd), chromium (Cr), and metalloid arsenic (As), on the microbial community and structure, metabolic pathways and metabolites, and intestinal morphology and structure. The effects of heavy metal (loid)s on metabolism are focused on energy, nitrogen, and short-chain fatty acid metabolism. We also discussed the main solutions for recovery of intestinal microorganisms from the effects of heavy metal (loid)s, namely the supplementation of probiotics, recombinant bacteria with metal resistance, and the non-toxic transformation of heavy metal (loid) ions by their own intestinal flora. This article provides insight into the toxic effects of heavy metals and As on gut microorganisms and hosts and provides additional therapeutic options to mitigate the damage caused by these toxic elements.

Dietary lead modulates the mouse intestinal microbiome: Subacute exposure to lead acetate and lead contaminated soil

The effect of dietary lead on the intestinal microbiome has not been fully elucidated. To determine if there was an association between microflora modulation, predicted functional genes, and Pb exposure, mice were provided diets amended with increasing concentrations of a single lead compound, lead acetate, or a well characterized complex reference soil containing lead, i.e. 6.25-25 mg/kg Pb acetate (PbOAc) or 7.5-30 mg/kg Pb in reference soil SRM 2710a having 0.552 % Pb among other heavy metals such as Cd. Feces and ceca were collected following 9 days of treatment and the microbiome analyzed by 16 S rRNA gene sequencing. Treatment effects on the microbiome were observed in both feces and ceca of mice. Changes in the cecal microbiomes of mice fed Pb as Pb acetate or as a constituent in SRM 2710a were statistically different except for a few exceptions regardless of dietary source. This was accompanied by increased average abundance of functional genes associated with metal resistance, including those related to siderophore synthesis and arsenic and/or mercury detoxification. Akkermansia, a common gut bacterium, was the highest ranked species in control microbiomes whereas Lactobacillus ranked highest in treated mice. Firmicutes/Bacteroidetes ratios in the ceca of SRM 2710a treated mice increased more than with PbOAc, suggestive of changes in gut microbiome metabolism that promotes obesity. Predicted functional gene average abundance related to carbohydrate, lipid, and/or fatty acid biosynthesis and degradation were greater in the cecal microbiome of SRM 2710a treated mice. Bacilli/Clostridia increased in the ceca of PbOAc treated mice and may be indicative of increased risk of host sepsis. Family Deferribacteraceae also was modulated by PbOAc or SRM 2710a possibly impacting inflammatory response. Understanding the relationship between microbiome composition, predicted functional genes, and Pb concentration, especially in soil, may provide new insights into the utility of various remediation methodologies that minimize dysbiosis and modulate health effects, thus assisting in the selection of an optimal treatment for contaminated sites.

Probiotics ameliorate growth retardation of glyphosate by regulating intestinal microbiota and metabolites in crucian carp (Carassius auratus)

Glyphosate (GLY) contamination widely occurred in aquatic environments including aquaculture systems and raised hazard to aquatic organisms such as fish. Probiotics have been reported to alleviate contaminants-induced toxicity. However, whether probiotics could reduce the health risk of GLY to fish remain unknown. Here we investigated the impacts of GLY on crucian carp (Carassius auratus) by focusing on the protective roles of two commonly used aquaculture probiotics, Bacillus coagulans (BC) and Clostridium butyricum (CB). Exposure to GLY significantly caused growth retardation and reduced visceral fat and intestinal lipase activity in crucian carp. 16S rRNA sequencing indicated that dysbiosis of Bacteroidetes at phylum level and Flavobacterium at genus level might be primarily responsible for GLY-induced negative growth performance. High throughput targeted quantification for metabolites revealed that GLY changed intestinal metabolites profiles, especially the reduced bile acids and short-chain fatty acids. However, the addition of BC or CB effectively attenuated the adverse effects above by remodeling the gut microbiota composition and improving microbial metabolism. The present study provides novel evidence for ameliorating the harmful effects of GLY on fish species by adding probiotics, which highlights the potential application of probiotics in reducing the health risks of GLY in aquatic environment.