| 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-
and extra-cellularly. 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 respiration of
arsenate and sulfate. In this photo, cultures before and after the precipitation
of As2S3 can be seen. The bottle on the left shows a culture a few days
after inoculation; the bottle on the right shows a culture after two weeks.
A synthetic sample of As2S3 (Aldrich) lies between them. (see Newman et
al., 1997 Appl. Environ. Microbiol. 63:2022-2028) |
