Arsenic transformation mediated by gut microbiota affects the fecundity of Caenorhabditis elegans☆
Graphical abstract
Introduction
Arsenic is widely distributed throughout the earth’s crust in a complex with pyrite that can be readily dissociated from the mineral and enters into soils and water (Finnegan and Chen, 2012). Arsenic uptake and metabolism by microorganisms result in high bioavailability to other organisms (Zhu et al., 2017). Arsenic exposure generally disrupts plant metabolism, affects the growth of soil fauna, and induces the germline apoptosis in nematodes (Wang et al., 2019). Long-term exposure to arsenic is associated with human cancers, diabetes, cardiovascular disorders and reproductive defects (Zhu et al., 2014). Toxicity of arsenic to biota depends largely on its species. Relative toxicities of several arsenicals are as follows, monomethylarsenous acid [MAs(III)] = dimethylarsenous acid [DMAs(III)] > As(III) > As(V) > monomethylarsonic acid [MAs(V)] > DMAs(V) > trimethylarsinic oxide (TMAO) (Sharma and Sohn, 2009). Arsenic biotransformation is majorly mediated by microorganisms in the environment, including As(V) reduction, As(III) oxidation, arsenic methylation, demethylation, and arsenic transport. Fungi, mouse, and humans have been found to methylate As(III) as well (Gosio, 1892; Lu et al., 2014; Gokulan et al., 2018; Chi et al., 2019).
Terrestrial invertebrates are important components of the terrestrial food web (Moriarty et al., 2009). Arsenic concentrations and species in the food chains determine arsenic toxicity to organisms at higher trophic level (Moriarty et al., 2009). Moriarty et al. (2009) find that As(V) and As(III) are the main arsenic species in the terrestrial invertebrates, while methylated arsenic, arsenobetaine, and arsenocholine are present only in trace amounts (Langdon et al., 2002; Moriarty et al., 2009). Various arsenic species in invertebrates may be from arsenic biotransformation mediated by invertebrates or their gut microbiota and enrichment via food chains (Langdon et al., 2002; Moriarty et al., 2009). Most of invertebrates including bark beetles, Drosophila melanogaster and Mamestra configurata can’t transform arsenic in vivo by themselves (Rizki et al., 2006; Morrissey et al., 2007; Reimer et al., 2010), whereas gut microbiota of them have been recently demonstrated to contribute significantly to As(V) reduction in the earthworm Metaphire sieboldin (Wang et al., 2019). In addition, it is well documented that the gut microbiota of mice play an important role in arsenic transformation and its toxic effects on the host (Chi et al., 2019). Nevertheless, limited literature has studied how the gut microbiota of invertebrates involve in the arsenic transformation. Some works demonstrate the importance of arsenic metabolism mediated by gut microbiota to the physical conditions of the hosts (Tremaroli and Bäckhed, 2012), however, interactions between arsenic biotransformation mediated by specific gut microbes and the health of terrestrial invertebrates remain to be elucidated.
Nematodes are the most abundant soil metazoa and serve an important role in the food web of soil ecosystems (Bernard, 1992). Worms can be germ-free through bleaching hatchlings and then assembled diverse gut microbiota after germ-free eggs exposed to different microbial environments (Berg et al., 2016). C. elegans is an emerging model organism for studying environmental toxicology and host-gut microbiota interaction due to its small size, easiness of laboratory maintenance, and short life cycle (Sulston et al., 1983). Germline development and reproduction of C. elegans are very sensitive to toxicant exposure (Monteiro et al., 2014), and it helps to unravel the mechanism of interaction between host physiological activity and gut microbial metabolism in the host under contaminated environments. Besides, exposure to arsenic induces oxidative stress resulting from the imbalance between radical-generating and antioxidant defense system, which represents a stressful and toxic situation of chemicals for C. elegans (Liao and Yu, 2005). Hence, reproduction and oxidative stress can be biomarkers for the healthy state of C. elegans (Liao and Yu, 2005).
Escherichia coli strains are common microbes in the gut of C. elegans and one of the most intensively used engineering bacteria (Zhang et al., 2000). The ars operon of wild type E. coli strains confers arsenical resistance via reducing As(V) and extruding As(III) (Tseng et al., 2007). E. coli strains as facultative anaerobes can potentially colonize in the gut of C. elegans and involve in arsenic transformation under anoxic environment. To unveil the effect of arsenic reduction and methylation mediated by gut microbiota on the host fecundity, three types of E. coli strains were used in this study. E. coli AW3110, which loses the ability to reduce As(V) to As(III) (Carlin et al., 1995), was used as the control. E. coli BL21 containing arsRBC was served as ArsC donor to reduce As(V). E. coli BL21M bearing arsRBC and As(III) S-adenosine methyltransferase gene (arsM) from Synechocystis sp. PCC 6803 can generate As(III) and methylated arsenic from As(V) (Xue et al., 2017). Our objectives were to i) investigate the colonization of different of E. coli strains in the gut of C. elegans; ii) identify arsenic transformation occurred in the gut of C. elegans; iii) explore the fecundity and oxidative stress level of C. elegans after being exposed to different arsenic species produced by various gut microbes.
Section snippets
C. elegans, bacterial strains, and plasmids
C. elegans strain (Bristol) N2 was maintained on nematode growth media (NGM) seeded with E. coli OP50 at 25 °C (Brenner, 1974). E. coli strains were grown aerobically in Luria Broth (LB) medium at 37 °C supplemented with 30 μg mL−1 chloramphenicol (for E. coli AW3110) or 50 μg mL−1 kanamycin (E. coli BL21M) as required. Information about all strains and plasmids are presented in Table S1.
Single colonies of E. coli AW3110, BL21 or BL21M were inoculated into 5 mL of LB medium consisting of the
Reproduction of C. elegans exposed to As(V)
There were no differences in brood sizes between worms pre-fed with E. coli BL21, BL21M, and inactive E. coli AW3110 after being treated with 0, 10 and 50 μM As(V) (Fig. 1a and b). Brood sizes of worms pre-fed with E. coli BL21 and BL21M were significantly (P < 0.05) lower than those pre-fed with E. coli AW3110 under exposure to 100 μM As(V) (Fig. 1a and b). No difference in brood sizes between worms pre-fed with E. coli BL21 (135.78 ± 7.70 eggs per worm) and those pre-fed with E. coli BL21M
Discussion
Interplay between host and gut microbiota in a variety of animals demonstrates the significant importance of gut microbiota to the host’s health, development, resource utilization and immune protection (Clemente et al., 2012; Erkosar and Leulier, 2014). To ensure arsenic biotransformation mediated by the gut microbiota, germ-free eggs were pre-grown on live E. coli BL21 or BL21M-seeded plates up to L4 larva stage, then transferred to inactive E. coli AW3110 and exposed to As(V). The stable
Conclusion
In this study, we employed E. coli strains BL21 and BL21M as model bacteria. Both strains successfully colonized in the gut of C. elegans and contributed a lot to As(V) reduction and DMAs formation in the gut of worms treated with As(V). The generation of As(III) and DMAs by gut microbes significantly induced the increases of VTG, GST and SOD levels which are connected with reproduction and oxidative stress defense of worms. Toxicity test further showed that arsenic biotransformation mediated
CRediT authorship contribution statement
Guo-Wei Zhou: Methodology, Investigation, Formal analysis, Visualization, Writing - original draft. Xiao-Ru Yang: Writing - review & editing, Visualization. Fei Zheng: Investigation, Writing - review & editing. Zi-Xing Zhang: Resources, Writing - review & editing. Bang-Xiao Zheng: Writing - review & editing. Yong-Guan Zhu: Conceptualization, Project administration, Writing - review & editing. Xi-Mei Xue: Methodology, Investigation, Formal analysis, Visualization, Project administration, Writing
Declaration of competing interest
We declare that we have participated sufficiently in the work to take public responsibility for the appropriateness of the experimental design and method, and the collection, analysis, and interpretation of the data. We have reviewed the final version of the manuscript and all authors have agreed to all the contents in the manuscript, including the data as presented. The authors declare no competing financial interest.
Neither the entire paper nor any part of its content has been published or
Acknowledgements
We thank Dr. Ya-Mei Wang (Xiamen University) for kindly providing the wild-type C. elegans strain N2 (Bristol) obtained from Caenorhabditis Genetics Center funded by the NIH National Center for Research Resources. This work was supported by the National Natural Science Foundation of China (41877422) and Science and Technology Project of Fujian Province (2017Y0082).
References (55)
- et al.
Exposure to inorganic arsenic can lead to gut microbe perturbations and hepatocellular carcinoma
Acta Pharm. Sin. B
(2016) - et al.
The impact of the gut microbiota on human health: an integrative view
Cell
(2012) - et al.
Transient adult microbiota, gut homeostasis and longevity: novel insights from the Drosophila model
FEBS Lett.
(2014) - et al.
Vitellogenins increase stress resistance of Caenorhabditis elegans after Photorhabdus luminescens infection depending on the steroid-signaling pathway
Microb. Infect.
(2013) - et al.
Dual role of arginine metabolism in establishing pathogenesis
Curr. Opin. Microbiol.
(2016) - et al.
Dissimilatory arsenate reductase activity and arsenate-respiring bacteria in bovine rumen fluid, hamster feces, and the termite hindgut
FEMS Microbiol. Ecol.
(2002) - et al.
Molecular characterization and expression of vitellogenin (Vg) genes from the cyclopoid copepod, Paracyclopina nana exposed to heavy metals
Comp. Biochem. Physiol. C: Toxicol. Pharmacol.
(2010) - et al.
Vitellogenin as a biomarker of exposure to estrogenic compounds in aquatic invertebrates: a review
Environ. Int.
(2008) - et al.
Effects of heavy metals on free-living nematodes: a multifaceted approach using growth, reproduction and behavioural assays
Eur. J. Soil Biol.
(2014) - et al.
Chlorhexidine resistance in Escherichia coli isolated from clinical lesions
Bakteriol. Mikrobiol. Hyg. I Abt. Orig. B
(1981)
Biochemistry of arsenic detoxification
FEBS Lett.
Aquatic arsenic: toxicity, speciation, transformations, and remediation
Environ. Int.
Effect of arsenic on growth, oxidative stress, and antioxidant system in rice seedlings
Ecotoxicol. Environ. Saf.
The embryonic cell lineage of the nematode Caenorhabditis elegans
Dev. Biol.
Assembly of the Caenorhabditis elegans gut microbiota from diverse soil microbial environments
ISME J.
Soil nematode biodiversity
Biol. Fertil. Soils
The genetics of Caenorhabditis elegans
Genetics
The ars operon of Escherichia coli confers arsenical and antimonial resistance
J. Bacteriol.
Recurrent horizontal transfer of arsenite methyltransferase genes facilitated adaptation of life to arsenic
Sci. Rep.
Gut microbiome disruption altered the biotransformation and liver toxicity of arsenic in mice
Arch. Toxicol.
The gut microbiota: a major player in the toxicity of environmental pollutants?
NPJ Biofilms Microb.
The native microbiome of the nematode Caenorhabditis elegans: gateway to a new host-microbiome model
BMC Biol.
As the worm turns: the earthworm gut as a transient habitat for soil microbial biomes
Annu. Rev. Microbiol.
Arsenic toxicity: the effects on plant metabolism
Front. Physiol.
Exposure to arsenite in CD-1 mice during juvenile and adult stages: effects on intestinal microbiota and gut-associated immune status
mBio
Action of microphytes on solid compounds of arsenic: a recapitulation
Science
Bacterial metabolism of environmental arsenic-mechanisms and biotechnological applications
Appl. Microbiol. Biotechnol.
Cited by (9)
Gut microbiota metabolize arsenolipids in a donor dependent way
2022, Ecotoxicology and Environmental SafetyCitation Excerpt :There was no significant difference observed in the water-soluble arsenical metabolites between treatments, donors or time points (p > 0.05, n = 4). Human gut bacteria can transform arsenic-containing compounds, as previously demonstrated in several in vitro and in vivo settings (Calatayud et al., 2013, 2018; van de Wiele et al., 2015; Yin et al., 2019; Zhou et al., 2020). These transformations are likely to affect the arsenic toxicity to the host (Coryell et al., 2019), with most of the literature referring to inorganic arsenic, but little is known about the role of gut microbiota in arsenolipid biotransformations and potential implications on human health.
Responses of earthworm Metaphire vulgaris gut microbiota to arsenic and nanoplastics contamination
2022, Science of the Total EnvironmentCitation Excerpt :Such as, exposure earthworm Eisenia fetida to low-level arsenic-contaminated soil for 14 days had been shown to have a significant accumulation of arsenic in earthworm hindgut (Tang et al., 2020). In addition, these studies have also indicated that As(III) was predominant form of arsenic in the worm body, suggesting a biotransformation process from As(V) in soil to As(III) in the gut that was accumulated in the body tissues (Wang et al., 2019b; Zhou et al., 2020). However, the mixture addition of nanoplastics and arsenic significantly decreased the arsenic concentrations in M. vulgaris body compared to the arsenic exposure.
Effects of Intestinal Microbiota on the Biological Transformation of Arsenic in Zebrafish: Contribution and Mechanism
2024, Environmental Science and TechnologyThe enigma of environmental organoarsenicals: Insights and implications
2022, Critical Reviews in Environmental Science and TechnologyGut homeostasis and microbiota under attack: impact of the different types of food contaminants on gut health
2022, Critical Reviews in Food Science and Nutrition
- ☆
This paper has been recommended for acceptance by Yong Sik Ok.