WCMR Member, Philippe Van Cappellen discovers microbial factors that affect redox potential in nature

WCMR Member, Dr. Philippe Van Cappellen of the Ecohydrology Research group, along his co-authors, recently discovered that microbial exudates, in particular flavins, released by bacteria play a hand in the changes in trends in the redox potential observed in natural waters.

Redox electrodes are commonly and widely used to measure the redox potential (EH) of natural waters and are used to describe the types of chemistry that can occur. In this study, a time series of synthetic systems which included the bacterial strain Shewanella oneidensis MR-1, were set up to mimic water-saturated subsurface environments. Several other key components (groundwater solutes, metabolic substrates, geothite etc.) of the natural environment were added back in a stepwise manner. These key factors recreated of a full, step-wise, redox cascade similar to what is observed in natural systems.

Results showed that the presence of electroactive microbial flavins (an exudate) could be detected, even at miniscule concentrations. In this work, flavins provided a good explanation as to the low EH results observed in the presence of strong oxidants.

Most are familiar with the geochemical and physicochemical factors that affect changes in trends in redox potential but this experiment sheds light on the microbial factors at play in natural waters. The results highlight the potential role of microbes in EH measurements that would be beneficial and relevant to not only microbiologists but environmental (geo)chemists as well.

Original article (pdf)