33
As
Arsenic
74.922
Beneficial extracellularly:
some microbes
Arsenic
Major functions in cells: (1)
- Can support chemolithoautotrophic growth in some microbes
- Electron acceptor for anaerobic respiration
- Organoarsenicals used as antibiotics in some microbes
Environmental and health impacts:
- Arsenic-contaminated water is public health issue
Response to Limitation:
- Substitute Sb for As as terminal electron acceptor (2)
Learn More!
(1) Arsenic: Electron Acceptor and Donor for Microbes
The biological role of arsenic has a complicated history. In 2011, Science published a paper claiming that there is a bacterium that uses arsenic instead of phosphorus in its DNA (Wolfe-Simon et al., 2011). The findings in the paper were later found to be false, disproving the arsenic-based-life theory.
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However, arsenic does have several biological roles. Both arsenic (As) and antimony (Sb) are commonly found as oxyanions and are subject to biologically-mediated redox reactions. Arsenate (As(V))-reducing and arsenite (As(III))-oxidizing microbes have been well studied, and play a major role in the biogeochemical cycling of As (Biswas & Sarkar, 2022). Metalloid oxidation can support chemolithoautotrophic growth: As(III) or Sb(III) can serve as an electron donor to provide reducing equivalents for the fixation of CO2 into organic matter (Deng et al., 2021).
Arsenic may also be used in Bacteria for the synthesis of organoarsenicals as antibiotics. Arsenicals have a long history in medicine, extending at least to the time of the ancient Greeks (Paul et al., 2022). The recent discovery of arsinothricin as a bacterially produced organoarsenical antibiotic provides an additional example of how As may play a beneficial role in microbes (Li et al., 2021).
(2) Substitution of Sb for As
Studies in the Stibnite Mine where both arsenic and antimony are present show that microbes will first use arsenic if available, suggesting that it is the preferred electron acceptor, possibly because of the greater electrochemical potential of the As(V)/As(III) couple compared to the Sb(V)/Sb(III) couple. However, when arsenic was depleted, the microbes in the mine were capable of utilizing antimony as an alternate terminal electron acceptor to support growth, thereby reducing the organisms' requirement for arsenic (Kulp et al., 2014).