Microbes Facilitate Mineral Deposition in Bioelectrochemical Systems

Hydrothermal chimneys are striking, characteristic features of marine hydrothermal vents. These chimneys are dynamic environments occupied by a diversity of microbes whose distribution is typically concordant with mineralogy and temperature. Recent studies indicate that these chimney assemblages are conductive and present the possibility that microbial extracellular electron transfer may occur through these minerals, linking spatially separated electron donors and acceptors. Here we explore the relationships among biology, mineralogy, and electric potential in hydrothermal systems using crushed hydrothermal chimney as inoculum in high (75 degrees C) and low (30 degrees C) temperature bioelectrical systems. All experiments with live microbial communities incubated in the presence of a poised electrode resulted in enhanced mineral deposition relative to (A) a live, open circuit (not poised) electrode, or (B) dead microbial communities in the presence of a poised electrode. Microbial abundance increased in both high- and low-temperature treatments, dominated by taxa allied to the Deferribacterales on the high temperature treatment electrode, and Chromatiales and Campylobacterales on the low-temperature treatment electrodes. Here we discuss the results of these experiments and consider the implications of these observations for the role that microorganisms may play in the formation of metal-rich hydrothermal chimneys.