Inhibitory effects of Skeletonema costatum on mercury methylation by Geobacter sulfurreducens PCA

Algae and mercury (Hg) are ubiquitous in marine environments. In this study, we investigated the effects of a typical marine algae of diatom Skeletonema costatum on Hg methylation by an iron-reducing bacterium of Geobacter sulfurreducens (G. sulfurreducens) PCA. In the absence of Skeletonema costatum, the bacterial MeHg production rate maximized at 104.06 +/- 11.7 ng L-1 h(-1) with a high Hg level, while the highest methylation efficiency was achieved at a low Hg concentration. The existence of Skeletonema costatum greatly inhibited the capability of G. sulfurreducens PCA to methylate Hg. With the increase in algal biomass, there was a significant mitigation of MeHg formation and Hg-0 release, leaving a considerable proportion of immobilized Hg2+ species (up to 47%) associated with algal cell materials. These results suggest that marine algae are crucial in determining the bioavailability of Hg contaminants and the methylating potential of G. sulfurreducens PCA. (C) 2018 Elsevier Ltd. All rights reserved.