Effects of antibiotics on the microbial arsenic cycle in aquatic environments

Principal Investigator (Contact person)

Shigeki YAMAMURA (yshige[at]nies.go.jp) "[at] is replaced by @"

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Overall

Short summary

   We investigated the effects of antibiotics on microbial arsenate (As(V)) reduction and arsenite (As(III)) oxidation in sediments collected from a small pond and a eutrophic lake. The As(V)-reducing activities were less susceptible to chloramphenicol in aerobic conditions than in anaerobic conditions. Aerobic As(V) reduction proceeded in the presence of diverse types of antibiotics, suggesting that As-resistant bacteria are widely antibiotic-resistant. In contrast, some antibiotics (e.g., chloramphenicol) strongly inhibited aerobic As(III) oxidation. In addition, bacterial As(III) oxidase genes were scarcely amplified and Proteobacteria-related 16S rRNA genes decreased drastically in chloramphenicol-amended cultures. Erythromycin and lincomycin, which successfully target many Gram-positive bacteria, scarcely affected As(III) oxidation, although they decreased the diversity of the As(III) oxidase genes. These results indicate that aerobic As(III) oxidizers within the sediment cultures are composed mainly of Proteobacteria and are more sensitive to certain types of antibiotics than the aerobic As(V) reducers. Our results suggest that antibiotic disturbance of environmental microbial communities affects the biogeochemical cycle of As.

Summary

   Arsenic (As), a highly toxic metalloid, is distributed ubiquitously in the natural environment, but local concentrations depend upon geochemical characteristics and anthropogenic discharges. In aquatic environments, As exists mainly in two inorganic forms: arsenate (As(V)) and arsenite (As(III)), of which As(III) is the more mobile and toxic. Microbial redox transformations, i.e., As(V) reduction and As(III) oxidation, directly affect the mobility of As and play a key role in biogeochemical As cycling. This implies that the mobility and fate of As in aquatic environments can change substantially when the microflora is disturbed and the As redox cycle disrupted.
   Antibiotics, which are used extensively in stockbreeding and aquaculture as well as in human medicine, exert potentially devastating effects on microbial communities. Various antibiotics have been detected in sewage and surface water, and numerous studies over the past decade have elucidated their occurrence, fate, and effects. Previous studies have shown that bacteria can become simultaneously resistant to both antibiotics and metals including As. However, no previous studies have investigated the effect of antibiotics on As redox transformations in aquatic microflora.
   We investigated the effect of antibiotics on microbial As(V) reduction and As(III) oxidation in sediments collected from a small pond and a eutrophic lake. The As(V)-reducing activities were less susceptible to chloramphenicol in aerobic conditions than in anaerobic conditions. Aerobic As(V) reduction proceeded in the presence of diverse types of antibiotics, suggesting that As-resistant bacteria are widely antibiotic-resistant. In contrast, some antibiotics, e.g., chloramphenicol, strongly inhibited aerobic As(III) oxidation. In addition, bacterial As(III) oxidase genes were scarcely amplified and Proteobacteria-related 16S rRNA genes decreased drastically in chloramphenicol-amended cultures. Erythromycin and lincomycin, which successfully target many Gram-positive bacteria, scarcely affected As(III) oxidation, although they decreased the diversity of the As(III) oxidase genes. These results indicate that aerobic As(III) oxidizers within the sediment cultures are composed mainly of Proteobacteria and are more sensitive to certain types of antibiotics than the aerobic As(V) reducers.
   The results of this study show that susceptibility to antibiotics differs substantially between As(V) reduction and As(III) oxidation in sediment microbial communities, and that inactivation of Proteobacteria might accelerate aerobic As(V) reduction via preferential inhibition of As(III) oxidation. This suggests that introducing certain types of antibiotics (such as chloramphenicol) into aquatic environments promotes As mobilization under aerobic conditions. Antibiotic disturbance of environmental microbial communities could affect the biogeochemical cycle of As.

Publications & Link

Publications

Yamamura S., Watanabe K., Suda W., Tsuboi S., Watanabe M. (2014) Effect of Antibiotics on Redox Transformations of Arsenic and Diversity of Arsenite-Oxidizing Bacteria in Sediment Microbial Communities. Environmental Science & Technology, 48, 350-357

Yamamura S., Amachi S. (2014) Microbiology of inorganic arsenic: From metabolism to bioremediation. Journal of Bioscience and Bioengineering, 118 (1), 1-9

Yamamura S., Watanabe Mirai., Yamamoto N., Sei K., Ike M. (2009) Potential for microbially mediated redox transformations and mobilization of arsenic in uncontaminated soils. Chemosphere, 77 (2), 169-174

Yamamura S., Watanabe Mirai., Kanzaki M., Soda S., Ike M. (2008) Removal of arsenic from contaminated soils by microbial reduction of arsenate and quinone. Environ.Sci.Technol., 42 (16), 6154-6159

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