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Biotransformation mediated by microbes can affect the biogeochemical cycle of arsenic. However, arsenic biotransformation mediated by earthworm-related microorganisms has not been well explored, especially the role played by earthworm skin microbiota. Herein, we reveal the profiles of arsenic biotransformation genes (ABGs) and elucidate the microbial communities of the earthworm gut, skin, and surrounding soil from five different soil environments in China. The relative abundance of ABGs in the earthworm skin microbiota, which were dominated by genes associated with arsenate reduction and transport, was approximately three times higher than that in the surrounding soil and earthworm gut microbiota. The composition and diversity of earthworm skin microbiota differed significantly from those of the soil and earthworm gut, comprising a core bacterial community with a relative abundance of 96% Firmicutes and a fungal community with relative abundances of 50% Ascomycota and 13% Mucoromycota. In addition, stochastic processes mainly contributed to the microbial community assembly across all samples. Moreover, fungal genera such as Vishniacozyma and Oomyces were important mediators of ABGs involved in the biogeochemical cycle of arsenic. This is the first study to investigate earthworm skin as a reservoir of microbial diversity in arsenic biotransformation. Our findings broaden the current scientific knowledge of the involvement of earthworms in the arsenic biogeochemical cycle., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier B.V. All rights reserved.)

The growing contamination of arsenic and plastics has severely effects on the soil fauna health, including shifts of gut microbiota community. A few studies have focused on effects of microplastics and metal(loid) in soil and fauna gut microbiome. However, the environmental effect of nanoplastics and arsenic on the earthworm gut microbiota, especially on arsenic biotransformation in the gut, remain largely unknown. Here, a microcosm study was performed to explore the effects of nanoplastics and arsenic on the microbiota characteristics in earthworm Metaphire vulgaris gut using Illumina high throughput sequencing, and to investigate changes in the gut microbiota-mediated arsenic biotransformation genes (ABGs) by using high-throughput quantitative PCR. Our results demonstrated that the concentration of arsenic in the earthworm body tissues after exposure to arsenic and nanoplastics was significantly lower from that with arsenic alone exposure. Moreover, the clearly different bacterial community was observed in the soil compared with the earthworm gut, which was dominated by Proteobacteria, Actinobacteria, and Firmicutes at phylum level. Arsenic exposure significantly disturbed bacterial community structure in the earthworm gut, but exposure to nanoplastics did not induce gut microbiota changes. More interestingly, nanoplastics can relieve adverse effect of arsenic on the gut microbiota possibly by adsorbing arsenic. In addition, a total of 16 ABGs were detected, and predominant genes involved in arsenic reduction and transport process were observed in the earthworm guts. In short, this study provides a new picture of the effects of nanoplastics and arsenic on the gut microbiota and arsenic biotransformation in soil fauna gut., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021. Published by Elsevier B.V.)

Microplastic (MP) pollution is widespread in various ecosystems and is colonized by microbes that form biofilms with compositions and functions. However, compared with aquatic environments, the soil environment has been poorly studied in terms of the taxonomic composition of microbial communities and the factors influencing the community structure of microbes in the plastisphere. In the present study, a microcosm experiment was conducted to investigate the plastisphere bacterial communities of MP (polyvinyl chloride, PVC) in soils with different pH (4.62, 6.5, and 7.46) and arsenic (As) contents (13 and 74 mg kg -1 ). Bacterial communities in the plastisphere were dominated by Proteobacteria and Firmicutes, with distinct compositions and structures compared with soil bacterial communities. Soil pH and As content significantly affected the plastisphere bacterial communities. Constrained analysis of principal coordinates and a structural equation model demonstrated that soil pH had a stronger influence on the dissimilarity and diversity of bacterial communities than did soil As content. Soil pH affected As speciation in soil and on MP. The concentration of dimethylarsinic acid (DMA) was significantly higher on MP than that in soil, indicating that As methylation occurred on MP. These results suggest that environmental fluctuations govern plastisphere bacterial communities with cascading effects on biogeochemical cycling of As in the soil ecosystems., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

The soil protistan community makes important contributions to the ecological functions of soil. However, our knowledge of the effects of pollutants, especially plastic particles, on the soil protistan community is still very limited compared to our knowledge on other soil microbes, such as bacterial and fungi. In this study, we revealed the effects of combined and single pollution caused by arsenic (As) and microplastics/nanoplastics (MPs/NPs) on bacterial, fungal and protistan communities. Our results revealed that combined pollution through As and MPs/NPs distinctly affected the composition and structure of the soil protistan communities (P < 0.05), but in the case of bacteria, only some families were altered, and there was no impact on fungi. Changes of soil protistan communities might be mainly due to As pollution, and MPs/NPs exposure increased this detrimental effect. Further, As + MPs exposure greatly increased the abundance of soil protistan parasites, and As + NPs exposure caused an evident decrease in the abundance of soil protistan consumers (P < 0.05). These findings indicate that combined pollution by As and MPs/NPs can affect the ecological functions of soil by altering soil protistan communities. These results will help enhance our understanding of the impact of plastic particles on soil ecosystems., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

The biotransformation of arsenic mediated by microorganisms plays an important role in the arsenic biogeochemical cycle. However, the fate and biotransformation of arsenic in different soil fauna gut microbiota are largely unknown. Herein the effects of arsenic contamination on five types of soil fauna were compared by examining variations in arsenic bioaccumulation, gut microbiota, and arsenic biotransformation genes (ABGs). Significant difference was observed in the arsenic bioaccumulation across several fauna body tissues, and Metaphire californica had the highest arsenic bioaccumulation, with a value of 107 ± 1.41 mg kg -1 . Arsenic exposure significantly altered overall patterns of ABGs; however, dominant genes involved in arsenic redox and other genes involved in arsenic methylation and demethylation were not significantly changed across animals. Except for M. californica, the abundance of ABGs in other animal guts firstly increased and then decreased with increasing arsenic concentrations. In addition, exposure of soil fauna to arsenic led to shifts in the unique gut-associated bacterial community, but the magnitude of these changes varied significantly across ecological groups of soil fauna. A good correlation between the gut bacterial communities and ABG profiles was observed, suggesting that gut microbiota plays important roles in the biotransformation of arsenic. Overall, these results provide a universal profiling of a microbial community capable of arsenic biotransformation in different fauna guts. Considering the global distribution of soil fauna in the terrestrial ecosystem, this finding broadens our understanding of the hidden role of soil fauna in the arsenic bioaccumulation and biogeochemical cycle., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Oral bioavailability of arsenic (As) determines levels of As exposure via ingestion of As-contaminated soil, however, the role of gut microbiota in As bioavailability has not evaluated in vivo although some in vitro studies have investigated this. Here, we made a comparison in As relative bioavailability (RBA) estimates for a contaminated soil (3913 mg As kg -1 ) using a mouse model with and without penicillin perturbing gut microbiota and metabolites. Compared to soil exposure alone (2% w/w soil in diets), addition of penicillin (100 or 1000 mg kg -1 ) reduced probiotic Lactobacillus and sulfate-reducing bacteria Desulfovibrio, enriched penicillin-resistant Enterobacter and Bacteroides, and decreased amino acid concentrations in ileum. With perturbed gut microbiota and metabolic profile, penicillin and soil co-exposed mice accumulated 2.81-3.81-fold less As in kidneys, excreted 1.02-1.35-fold less As in urine, and showed lower As-RBA (25.7-29.0%) compared to mice receiving diets amended with soil alone (56 ± 9.63%). One mechanism accounted for this is the decreased concentrations of amino acids arising from the gut microbiota shift which resulted in elevated iron (Fe) and As co-precipitation, leading to reduced As solubilization in the intestine. Another mechanism was conversion of bioavailable inorganic As to less bioavailable monomethylarsonic acid (MMA V ) and dimethylarsinic acid (DMA V ) by the antibiotic perturbed microflora. Based on in vivo mouse model, we demonstrated the important role of gut microbiota and gut metabolites in participating soil As solubilization and speciation transformation then affecting As oral bioavailability. Results are useful to better understand the role of gut bacteria in affecting As metabolism and the health risks of As-contaminated soils., (Copyright © 2021 The Author(s). Published by Elsevier Ltd.. All rights reserved.)

Combinations of metal(loid) contamination and antibiotics are considered to increase the abundance of resistance genes in the environment, whereas the combined effect of metal(loid)s and antibiotics on microbial communities and antibiotic resistance genes (ARGs) in the gut of soil fauna remains unknown. We investigated herein the alteration of ARGs and the gut microbial communities after the earthworm Metaphire sieboldi was exposed to arsenate and/or sulfamethoxazole using high-throughput quantitative PCR and Illumina sequencing analysis. Arsenic accumulation in the body tissues of arsenic-exposed earthworms exerted a significant inhibition on growth and survival. The synergistic interactions of arsenic and sulfamethoxazole increased significantly the incidence of ARGs and mobile genetic elements in the earthworm gut microbiota. In addition, co-exposure to arsenic and sulfamethoxazole altered the structure of the gut microbial communities, and the changes correlated with ARG profiles of the gut microbiota. Our results indicate that the gut of soil fauna is a neglected hotspot of antibiotic resistance.

Ubiquitous contamination of microplastics and arsenic in soil ecosystems can induce many health issues to nontarget soil organisms, and will also cause many potential threats to the gut bacterial communities of soil fauna. However, the changes in the gut bacterial communities of soil fauna after exposure to both microplastics and arsenic remain unknown. In this study, the toxicity and effects on the gut microbiota of earthworm Metaphire californica caused by the combined exposure of microplastics and arsenic were examined by using arsenic species analysis and high throughput sequencing of gut microbiota. Results showed that total arsenic and arsenic species in the earthworm gut and body tissues after exposure to combination of microplastics with arsenate (As(V)) were significantly different from that treated with As(V) alone. Microplastics lessened the accumulation of total arsenic and the transformation rate of As(V) to arsenite (As(III)). Microplastics alleviated the effect of arsenic on the gut microbiota possibly via adsorbing/binding As(V) and lowering arsenic bioavailability, thus prevented the reduction of As(V) and accumulation of total arsenic in the gut which resulted in a lower toxicity on the earthworm. The study broadens our understanding of the ecotoxicity of microplastics with other pollutants on the soil animals and on their gut microbiota., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Arsenic biotransformation mediated by gut microbiota can affect arsenic bioavailability and microbial community. Arsenic species, arsenic biotransformation genes (ABGs), and the composition of gut microbial community were characterized after the earthworm Metaphire sieboldi was cultured in soils spiked with different arsenic concentrations. Arsenite (As(III)) was the major component in the earthworm gut, whereas arsenate (As(V)) was predominant in the soil. A total of 16 ABGs were quantified by high-throughput quantitative polymerase chain reaction (HT-qPCR). Genes involved in arsenic redox and efflux were predominant in all samples, and the abundance of ABGs involved in arsenic methylation and demethylation in the gut was very low. These results reveal that the earthworm gut can be a reservoir of microbes with the capability of reducing As(V) and extruding As(III) but with little methylation of arsenic. Moreover, gut microbial communities were dominated by Actinobacteria, Firmicutes, and Proteobacteria at the phylum level and were considerably different from those in the surrounding soil. Our work demonstrates that exposure to As(V) disturbs the gut microbiota of earthworms and provides some insights into arsenic biotransformation in the earthworm gut.

Increasing biochar is applied to the metal(loid) contaminated soil. However, effects of biochar on the soil-plant-earthworm-bacteria ecosystem, especially on the gut microbes of soil animals, remain largely unknown and require further research. Here, sewage sludge biochar (SSBC) and rice straw biochar (RSBC) were used in metal(loid) contaminated soils to investigate the available metal(loid) change in soils and the impact on the metal(loid) bioaccumulation in the plant and earthworm. Moreover, effects of biochar amendments on the gut bacteria of earthworms were determined by using high throughput sequencing. Our results showed that RSBC amendments had a significant suppression on the availability of cadmium, but significantly increased arsenic availability in soils (P < 0.05). Compared with the control, the significant reduction of arsenic and cadmium accumulation was observed in plant with biochar amendments. High metal(loid) concentrations were observed in the body tissues of earthworms, in which the highest bioaccumulation factor of cadmium was 18.12 in Metaphire. californica. The earthworm gut bacteria, with high abundances of Firmicutes (39.36%), Actinobacteria (23.69%) and Proteobacteria (13.02%), was significantly different from the microbe from the soil. RSBC had more significant effect on the bacterial community of earthworm gut than SSBC. Taken together, this work indicated thatbiochar amendments could decrease concentrations of arsenic and cadmium in plant, reduce the potential risk of metal(loid)s into the food chain, and shed light on the biogeochemical behaviour of biochar in the soil-plant-earthworm-bacteria ecosystems. Image 1 • Biochar amendments reduced concentrations of available cadmium, and increased available arsenic concentrations in soils. • Decreased accumulations of arsenic and cadmium in plant were observed after the biochar addition. • The earthworms accumulated large amounts of metal(loid)s, especially cadmium, from contaminated soils. • Rice straw biochar amendments had a stronger impact on bacterial communities of the earthworm gut than sewage sludge biochar. [ABSTRACT FROM AUTHOR]

It is well established that arsenic (As) pollution has a severe threat to food security and soil non-target organisms, however, its influences on soil fauna gut microbiota are poorly understood. The gut microbiota of soil fauna play an important role in host health and nutrient cycling. Here, we used dietary exposure to investigate the effects of As on the mortality and gut microbiota of two model soil collembolans (Folsomia candida and Onychiurus yodai) and determine the accumulation of As in collembolan body tissues. The results showed that, although As exposure did not induce the mortality of the two species, dose dependence of As accumulation was indeed detected in their body tissues. Oral As exposure (500 μg g−1 yeast) significantly altered the community structure (P < 0.05) of F. candida gut microbiota and reduced its diversity (by more than 20%; P < 0.05) compared to the control; however, no significant effects were observed in O. yodai gut microbiota. The two collembolan species possess significantly different gut microbiota (P < 0.05), which may partly explain the differences of the two collembolan gut microbiota response to As exposure. We further found that the genera Ochrobactrum , Geobacter and Staphylococcus were sensitive to As exposure in F. candida (P < 0.05), but these bacteria were low abundance and not altered in O. yodai. Moreover, the relative abundance of these bacteria was significantly correlated with As bioaccumulation in F. candida body tissues (P < 0.05, R2 > 0.6). Higher As bioaccumulation factor was also found in O. yodai body tissues compared to the F. candida. These results indicate that collembolan gut microbiota present a species-specific response to As and may be a more sensitive indicator than the mortality of collembolan. Image 1 • Collembolans F. candida and O. yodai possess different gut microbiota. • Effects of As on diversity and structure of gut microbiota are species-specific. • Diversity of gut microbiota is a more sensitive indicator for As than mortality. [ABSTRACT FROM AUTHOR]