Effect of soil microbial feeding on gut microbiome and cadmium toxicity in Caenorhabditis elegans

Combining chemical analysis and toxicological methods to access the ecological risk of complex contamination in Daye Lake

As one of the nine primary non-ferrous metal smelting bases in China, Daye Lake basin was polluted due to diverse human activities. But so far the pollution status and related ecological risks of this region have not been detailly investigated. In current study, pollutants including heavy metals, polycyclic aromatic hydrocarbons (PAHs) and organochlorine pesticides (OCPs) in eight sediment samples from Daye Lake were quantified. 18S rRNA gene sequencing was employed to profile the nematode community structure within these sediments. Model organism Caenorhabditis elegans (C. elegans) were further applied for a comprehensive ecological risk assessment of Daye Lake. Notably, Cadmium (Cd) was identified as a key driver of ecological risk, reaching an index of 1287.35. At sample point S4, OCPs particularly p,p'-DDT, displayed an extreme ecological risk with a value of 23.19. Cephalobidae and Mononchida showed strong sensitivity to pollutant levels, reinforcing their suitability as robust bioindicators. The composite pollutants in sampled sediments caused oxidative stress in C. elegans, with gene Vit-2 and Mtl-1 as sensitive biomarkers. By employing the multiple analysis methods, our data can offer valuable contributions to environmental monitoring and health risk assessment for composite polluted areas.

Effects of cadmium on the intestinal health of the snail Bradybaena ravida Benson

The heavy metal cadmium (Cd) is a toxic and bioaccumulative metal that can be enriched in the tissues and organs of living organisms through the digestive tract. However, more research is needed to determine whether food-sourced Cd affects the homeostasis of host gut microflora. In this study, the snail Bradybaena ravida (Benson) was used as a model organism fed with mulberry leaves spiked with different concentrations of Cd (0, 0.052, 0.71, and 1.94 mg kg-1). By combining 16S rRNA high-throughput sequencing with biochemical characterization, it was found that there were increases in the overall microbial diversity and abundances of pathogenic bacteria such as Corynebacterium, Enterococcus, Aeromonas, and Rickettsia in the gut of B. ravida after exposure to Cd. However, the abundances of potential Cd-resistant microbes in the host's gut, including Sphingobacterium, Lactococcus, and Chryseobacterium, decreased with increasing Cd concentrations in the mulberry leaves. In addition, there was a significant reduction in activities of energy, nutrient metabolism, and antioxidant enzymes for gut microbiota of snails treated with high concentrations of Cd compared to those with low ones. These findings highlight the interaction of snail gut microbiota with Cd exposure, indicating the potential role of terrestrial animal gut microbiota in environmental monitoring through rapid recognition and response to environmental pollution.

Geroprotective potential of microbiome modulators in the Caenorhabditis elegans model

Aging is associated with cellular and physiological changes, which significantly reduce the quality of life and increase the risk for disease. Geroprotectors improve lifespan and slow the progression of detrimental aging-related changes such as immune system senescence, mitochondrial dysfunction, and dysregulated nutrient sensing and metabolism. Emerging evidence suggests that gut microbiota dysbiosis is a hallmark of aging-related diseases and microbiome modulators, such as probiotics (live bacteria) or postbiotics (non-viable bacteria/bacterial byproducts) may be promising geroprotectors. However, because they are strain-specific, the geroprotective effects of probiotics and postbiotics remain poorly understood and understudied. Drosophila melanogaster, Caenorhabditis elegans, and rodents are well-validated preclinical models for studying lifespan and the role of probiotics and/or postbiotics, but each have their limitations, including cost and their translation to human aging biology. C. elegans is an excellent model for large-scale screening to determine the geroprotective potential of drugs or probiotics/postbiotics due to its short lifecycle, easy maintenance, low cost, and homology to humans. The purpose of this article is to review the geroprotective effects of microbiome modulators and their future scope, using C. elegans as a model. The proposed geroprotective mechanisms of these probiotics and postbiotics include delaying immune system senescence, preventing or reducing mitochondrial dysfunction, and regulating food intake (dietary restriction) and metabolism. More studies are warranted to understand the geroprotective potential of probiotics and postbiotics, as well as other microbiome modulators, like prebiotics and fermented foods, and use them to develop effective therapeutics to extend lifespan and reduce the risk of debilitating aging-related diseases.

Significance of probiotics in remodeling the gut consortium to enhance the immunity of Caenorhabditis elegans

In the recent past, Caenorhabditis elegans has emerged as one of the leading nematode models for studying host-microbe interactions on molecular, cellular, or organismal levels. In general, morphological and functional similarities of the gut of C. elegans with respect to that of human has brought in speculations on the study of the intestinal microbiota. On the other hand, probiotics have proved their efficacy in metabolism, development, and pathogenesis thereby inducing an immune response in C. elegans. Nurturing C. elegans with probiotics has led to immunomodulatory effects in the intestinal microbiota, proposing C. elegans as one of the in vivo screening criteria to select potential probiotic bacteria for host health-promoting factors. The major prospect of these probiotics is to exert longevity toward the host in diverse environmental conditions. The extent of research on probiotic metabolism has shed light on mechanisms of the immunomodulatory effect exerted by the nematode model. This review discusses various aspects of the effects of probiotics in improving the health and mechanisms involved in conferring immunity in C. elegans.

Research Advances on the Adverse Effects of Nanomaterials in a Model Organism, Caenorhabditis elegans

Along with the rapid development of nanotechnology, the biosafety assessment of nanotechnology products, including nanomaterials (NMs), has become more and more important. The nematode Caenorhabditis elegans is a valuable model organism that has been widely used in the field of biology because of its excellent advantages, including low cost, small size, short life span, and highly conservative genomes with vertebral animals. In recent years, the number of nanotoxicological researchers using C. elegans has been growing. According to these available studies, the present review classified the adverse effects of NMs in C. elegans into systematic, cellular, and molecular toxicity, and focused on summarizing and analyzing the underlying mechanisms of metal, metal oxide, and nonmetallic NMs causing toxic effects in C. elegans. Our findings provide insights into what further studies are needed to assess the biosafety of NMs in the ecosystem using C. elegans. Environ Toxicol Chem 2021;40:2406-2424. © 2021 SETAC.

Metabolic regulation in soil microbial succession and niche differentiation by the polymer amendment under cadmium stress

Cadmium (Cd) contamination seriously threatens the agricultural production, so exploring the response of soil microenvironment to amendments in Cd-contaminated soils is of importance. In this study, the mechanism of remediation of Cd-contaminated soil using the polymer amendment was studied in cotton flowering stage. The results showed that the concentration of Cd in cotton root and various Cd forms in Cd-contaminated soils were obviously high. High concentration of Cd, especially exchangeable Cd, could seriously affect the soil microenvironment. The root growth of cotton could be promoted, the carbon and nitrogen concentration and storage in soil were increased by 21.72-50.00%, while the exchangeable Cd concentration in soil were decreased by 41.43%, after applying the polymer amendment. In addition, the polymer amendment affected the soil microbial niche, increased the relative abundance of soil bacteria (Flaviaesturariibacter, Rubellimicrobium, and Cnuella), fungi (Verticillium and Tricharina), actinomycetes (Blastococcus and Nocardioides), and fungivores nematodes (Aphelenchus), and improved soil microbial metabolic functions (metabolism of nucleotides and carbohydrates). Therefore, this polymer amendment could be used to remediate severe Cd-contaminated soils, and the changes in the microbial and nematode communities help us understand the detoxification mechanism of the polymer amendment in Cd-contaminated soils.

Alternative model organisms for toxicological fingerprinting of relevant parameters in food and nutrition

In the field of (food) toxicology, there is a strong trend of replacing animal trials with alternative methods for the assessment of adverse health effects in humans. The replacement of animal trials is not only driven by ethical concerns but also by the number of potential testing substances (food additives, packaging material, contaminants, and toxicants), which is steadily increasing. In vitro 2D cell culture applications in combination with in silico modeling might provide an applicable first response. However, those systems lack accurate predictions of metabolic actions. Thus, alternative in vivo models could fill the gap between cell culture and animal trials. In this review, we highlight relevant studies in the field and spotlight the applicability of alternative models, including C. elegans, D. rerio, Drosophila, HET-CAM and Lab-on-a-chip.

Xenobiotic metabolism and transport in Caenorhabditis elegans

Caenorhabditis elegans has emerged as a major model in biomedical and environmental toxicology. Numerous papers on toxicology and pharmacology in C. elegans have been published, and this species has now been adopted by investigators in academic toxicology, pharmacology, and drug discovery labs. C. elegans has also attracted the interest of governmental regulatory agencies charged with evaluating the safety of chemicals. However, a major, fundamental aspect of toxicological science remains underdeveloped in C. elegans: xenobiotic metabolism and transport processes that are critical to understanding toxicokinetics and toxicodynamics, and extrapolation to other species. The aim of this review was to initially briefly describe the history and trajectory of the use of C. elegans in toxicological and pharmacological studies. Subsequently, physical barriers to chemical uptake and the role of the worm microbiome in xenobiotic transformation were described. Then a review of what is and is not known regarding the classic Phase I, Phase II, and Phase III processes was performed. In addition, the following were discussed (1) regulation of xenobiotic metabolism; (2) review of published toxicokinetics for specific chemicals; and (3) genetic diversity of these processes in C. elegans. Finally, worm xenobiotic transport and metabolism was placed in an evolutionary context; key areas for future research highlighted; and implications for extrapolating C. elegans toxicity results to other species discussed.

Interactions with a Complex Microbiota Mediate a Trade-Off between the Host Development Rate and Heat Stress Resistance

Animals and plants host diverse communities of microorganisms, and these microbiotas have been shown to influence host life history traits. Much has been said about the benefits that host-associated microbiotas bestow on the host. However, life history traits often demonstrate tradeoffs among one another. Raising Caenorhabditis elegans nematodes in compost microcosms emulating their natural environment, we examined how complex microbiotas affect host life history traits. We show that soil microbes usually increase the host development rate but decrease host resistance to heat stress, suggesting that interactions with complex microbiotas may mediate a tradeoff between host development and stress resistance. What element in these interactions is responsible for these effects is yet unknown, but experiments with live versus dead bacteria suggest that such effects may depend on bacterially provided signals.

Neuronal ERK MAPK signaling in response to low-dose nanopolystyrene exposure by suppressing insulin peptide expression in Caenorhabditis elegans

The responses of different organs are important for organisms against the toxicity of environmental toxicants. So far, the neuronal response to nanoplastic exposure and the underlying mechanisms are still largely unclear. Due to the sensitivity to environmental exposures, we here employed Caenorhabditis elegans as an animal model to examine the role of ERK MAPK signaling pathway in the neurons to regulate the response to nanopolystyrene (100 nm). Nanopolystyrene exposure in the range of μg/L could significantly increase expressions of genes (lin-45, mek-2, and mpk-1) encoding ERK MAPK signaling pathway. Nanopolystyrene at the predicted environmental concentration of 1 μg/L could only significantly increase the mpk-1 expression. Meanwhile, RNAi knockdown of any of these genes caused a susceptibility to nanopolystyrene toxicity. ERK/MPK-1 acted in the neurons to regulate the response to nanopolystyrene. Moreover, three genes (ins-4, ins-39, and daf-28) encoding insulin peptides were identified as the downstream targeted genes of neuronal mpk-1 in regulating the response to nanopolystyrene. In nanopolystyrene exposed nematodes, neuronal RNAi knockdown of ins-4, ins-39, or daf-28 decreased expression of intestinal daf-2 encoding insulin receptor and increased expression of intestinal daf-16 encoding FOXO transcriptional factor. Therefore, the neuronal ERK MAPK signaling responded to nanopolystyrene by modulating the insulin signaling-mediated communication between neurons and intestine in nematodes. Our findings are helpful for understanding the molecular basis of neuronal response to nanopolystyrene in organisms.