BIOLOGICAL TREATMENT OF MERCURY WASTES
Introduction. It would seem paradoxical that biological systems could be put to useful work treating as toxic a substance as mercury. But in limited ways and degrees this has occurred, and the successes are reviewed here.
Theory of Mercury Transformation Process(es). "Perhaps the most toxic metals are the nonessential metals such as cadmium, lead, and mercury" (7:318). Some microorganisms that encounter these metals have developed strategies to prevent entry of them into their cells or literally to pump them back out again: sequestration, active transport, or chemical transformation (7:319). The last of these (oxidation-reduction reactions) is used to reduce the mercuric ion, Hg+2 [also written as Hg(II)] to elemental, metallic mercury, Hg0, which is volatile and can thus diffuse away from a microbial cell through surrounding air or water (7:323).
Methylation of mercuric ion forms [mono]methyl mercury, CH3Hg+1, or dimethylmercury, (CH3)2Hg--10 to 100 times more toxic to organisms than inorganic mercury; but these forms can also be diffused away, by the organism (7:323). (Other metals similarly methylated are tin, lead, arsenic and selenium (7:323)).
Summers has described more fully than all others referenced here the enzymatic details of mercury "biotransformations" from one valence state to another or from one organic state to another or to inorganic, elemental mercury (9). She suggests that bacterial ability to convert both inorganic and organic mercury compounds to "less toxic , volatile elemental mercury" is general and widespread--"among the most widely found plasmid-determined bacterial phenotypes" (9:105). So, bacterial machinations with mercury, leading to its tie-up or removal, are clearly feasible. (Summers' descriptions beyond that (9) are mildly interesting but on a enzymatic, molecular level and difficult for a neophyte microbiologist to decipher.)
Experiences...