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= Arsenic-Oxidizing Bacteria = Arsenic-Oxidizing bacteria are a group of microorganisms that are capable of increasing the oxidation states of arsenic in arsenic-containing compounds. They play an important role in the biogeochemical cycling of arsenic in the environment, including the soil, water, and sediment. Arsenic is present in the environmental water sources in many forms, with two of the more prevalent forms being As(III) and As(V). Both forms of arsenic are toxic, but As(III) is nearly 100 times more toxic and more mobile in water, and thus poses great environmental risks. Through their metabolic processes, arsenic-oxidizing bacteria can take the more toxic As(III) and form As(V) in the environment. This ability to decrease toxic As(III) makes arsenic-ozidizing bacteria a critical player in the environmental bioremediation efforts to reduce arsenic toxicity in waste water, ground water, soil, and sediment.

Bioremediation
Arsenic-oxidizing bacteria play a significant role in bioremediation efforts to reduce toxic arsenic concentrations in the environment. The oxidation of arsenic functions as environmental bioremediation since As(V) isn’t as toxic or mobile as As(III). Furthermore, the use of microbial metabolism as bioremediation is efficient, low cost, and environmentally friendly, as secondary pollution from these metabolic processes is minimal. A study conducted in 2023 measured the change in concentration of As(III) from polluted water sources in the presence of various arsenic-oxidizing bacterium, and found that the bacterial strains, Acinetobacter gandensis and Delftiatsuruhatensis are strong oxidizers of As(III), and successfully reduced As(III) present in the polluted groundwater samples. The arsenic-oxidizing capabilities of bacteria allow these particular strains to be a promising alternative to chemical oxidizers used for the treatment of heavy-metal polluted waters.

Metabolism
Arsenic-oxidizing bacteria contribute to the bioavailability of arsenic in the environment, due to their metabolic capabilities. As(III)-oxidizing bacteria utilize As(III) as the electron donor during cellular respiration for their electron transport chain. Although different bacteria utilize different metabolic processes, the overall oxidation of As(III) is conserved. The removal of two electrons from As(III) generates the oxidized As(V) as a byproduct, which is a less toxic form of arsenic in the environment. Through the process of aerobic respiration, Bacillus arsenoxydans, is capable of oxidizing As(III) to As(V), in order to generate energy. Another bacterium found in 2000, utilizes As(III) as the electron donor, O2 as the final electron acceptor for the electron transport chain used during respiration. Furthermore, these microorganisms are not only capable of using As(III) as an electron donor, but instead, are directly influenced by the concentrations of As(III) present in their environments. Higher concentrations of As(III) directly correlate with the increase in expression of genes used for carbon fixation, nitrogen fixation, and sulfate reduction. The influence of enviornmental arsenic on bacterial usage of other elements in the environment allow for these bacteria to play a vital role in the biogeochemical cycling of not just arsenic, but carbon, nitrogen, and sulfur as well.

Taxonomy
There are two broad groups of arsenic-oxidizing bacteria: Chemolitoautotrophic Arsenite Oxidizers and Heterotrophic Arsenite Oxidizers. Chemolithoautotrophic bacteria utilize carbon dioxide present in the environment as their carbon source for their metabolic processes. Heterotrophic bacteria utilize organic forms of carbon for metabolism. In terms of arsenic-oxidation capabilities, both groups utilize a key enzyme As(III) oxidase to catalyze the oxidation of As(III) into As(V). Sequencing bacterial 16srRNA allowed for scientists to find the presence of As(III) oxidase in many bacterial strains, indicated their potential to be arsenic-oxidizers.