Bacteria mediate methylation of iodine in marine and terrestrial environments

Methyl iodide (CH,I) plays an important role in the natural iodine cycle an d participates in atmospheric ozone destruction. However, the main source o f this compound in nature is still unclear. Here we report that a wide vari ety of bacteria including terrestrial and marine bacteria are capable of me thylating the environmental level of iodide (0.1 muM). Of the strains teste d, Rhizobium sp, strain MRCD 19 was chosen for further analysis, and it was found that the cell extract catalyzed the methylation of iodide with S-ade nosyl-L-methionine as the methyl donor. These results strongly indicate tha t bacteria contribute to iodine transfer from the terrestrial and marine ec osystems into the atmosphere.