ABSTRACT
This chapter provides an overall picture of the mercury cycle in the biosphere, to emphasize the role of microbial systems in this cycle, and to present what is known about the genetic and biochemical bases for the microbial transformations. Despite its relatively low concentration in the environment, mercury is one of the better understood elements which undergo a complex cycle in the biosphere. Greater than 80% of the mercury found in fish (such as tuna and swordfish) is methylated, including that in fish living in uncontaminated off-shore waters. The frequent association of mercury resistance with antibiotic-resistance plasmids in clinical isolates is somewhat curious. Since both inorganic mercury and organomercurials can be volatile, the nature of the volatile mercury was a critical question. A most important difference appears to exist in the molecular weights of the mercuric reductase enzymes.
