FIG. 1.

Observed MeHg production by pure cultures of DIRB, expressed as the percentage of added inorganic Hg methylated. “Other electron acceptors” refers to cultures that were grown with either nitrate or fumarate as an electron acceptor; “iron medium” refers to cultures grown with Fe(III) citrate as an electron acceptor (see Table 1). Significant differences (P < 0.05) in MeHg production in cultures relative to matched abiotic controls are indicated by stars. Error bars represent the standard deviations for three separately prepared tubes for each sample. Culture and growth conditions that were not assayed for MeHg production are labeled “NT” (not tested).