Organoarsenical Biotransformations by Shewanella putrefaciens

Area of Science:

• Environmental microbiology
• Biogeochemistry
• Arsenic metabolism

Background:

• Microbial roles in the global arsenic biogeocycle are critical.
• Focus has been on inorganic arsenic redox cycling, with organoarsenical transformations less understood.
• Environmental pollutants include various organoarsenicals.

Purpose of the Study:

• To characterize organoarsenical biotransformations in the environmental microbe Shewanella putrefaciens.
• To elucidate the microbial degradation pathways of organoarsenical compounds.

Main Methods:

• Aerobic growth conditions were used to study S. putrefaciens.
• Analysis of methylarsenate (MSMA) reduction and demethylation.
• Investigation of C-As bond cleavage in aromatic arsenicals.
• Study of thiolation reactions on methylated arsenicals.
• Analysis of nitro group reduction in nitarsone and roxarsone.

Main Results:

• S. putrefaciens reduced MSMA to methylarsenite (MAs(III)) and demethylated MAs(III) to As(III).
• The microbe cleaved C-As bonds in trivalent aromatic arsenicals like roxarsone, nitarsone, and phenylarsenite.
• Methylated arsenicals were thiolated, forming more toxic metabolites.
• Nitro groups of nitarsone and roxarsone were reduced, yielding specific amino derivatives.

Conclusions:

• Shewanella putrefaciens exhibits diverse organoarsenical biotransformation capabilities.
• These findings provide a comprehensive understanding of how environmental pollutants like organoarsenicals are degraded.
• The study highlights the microbe's role in the arsenic biogeocycle.