Oxyanions of selenium and arsenic occur in waters as a consequence of
human activities, or from natural sources. These toxic elements have
biogeochemical cycles mediated by microorganisms. An important discovery
was that certain bacteria achieve anaerobic growth using selenate or
arsenate as oxidants, forming elemental selenium or arsenite. These
results have geochemical significance, and the phenomenon may be exploited
to remove these toxins from contaminated waters and soils.
We investigated Mono Lake because it has high levels of hydrothermally
derived arsenate (~ 200 μM) in its alkaline and saline waters.
Bacterial respiration of arsenate in the anoxic waters mineralizes as much
as 14 % of the lake’s annual primary production. If microbial life
existed on the volcanically active surface of Mars some 3 billion years
ago, this finding has implications for the possible types of respiration
occurring in its shrinking haloalkaline lakes.
Next: The other Doc—J.B. Phillips and the California Department of Fish and Game