| The formation of As2S3 in nature as the mineral orpiment
has been observed only in extreme environments, such as geothermal reservoir
fluids and hot springs, and previously was assumed to be abiotic. We now
know that certain types of bacteria can precipitate As2S3 both intra-
an extra-cellulary. Microbial precipitation of As2S3 is an example of
how biomineralization often is linked to fundamental cellular processes:
in this case, As2S3 formation is tightly coupled to the repiration of
arsenate and sulfate. In this transmission electron micrograph (cell length
approximately 2 microns), a thin section of a bacteriaum that precipitates
AS2S3 is shown. Notice how the small dark particles of As2S3 line the
inside of the cytoplasmic membrane (the site of the electron transport
chain). |
