Dissolved organic matter kinetically controls mercury bioavailability to bacteria.

Area of Science:

• Environmental Chemistry
• Microbiology
• Biogeochemistry

Background:

• Predicting inorganic mercury (Hg) bioavailability to bacteria is crucial for understanding the environmental fate of mercury and the production of monomethylmercury.
• Dissolved organic matter (DOM) influences mercury methylation by affecting bacterial physiology and Hg(II) speciation, thereby controlling mercury bioavailability.

Purpose of the Study:

• To assess the role of DOM in Hg(II) bioavailability to a gram-negative bacterium bioreporter under varying conditions.
• To investigate the impact of DOM concentration and mercury-DOM equilibrium on Hg(II) uptake by bacteria.

Main Methods:

• Utilized a gram-negative bacterium bioreporter to measure Hg(II) bioavailability.
• Employed defined media and natural water samples with a wide range of DOM concentrations.
• Compared Hg(II) bioavailability under oxic nonequilibrium conditions versus pseudo- and equilibrium conditions.

Main Results:

• Hg(II) bioavailability was significantly higher under nonequilibrium conditions compared to DOM-absent or pseudoequilibrium conditions.
• Hg(II) bioavailability exhibited a bell-shaped curve with increasing DOM concentrations, observed in both defined media and natural samples.
• DOM appears to facilitate Hg(II) uptake by providing shuttle molecules and altering bacterial cell wall properties.

Conclusions:

• A critical, short-lived time window (<24 h) exists where DOM facilitates Hg(II) entry into aquatic food webs.
• The majority of mercury incorporation into aquatic food webs likely occurs within hours of atmospheric deposition.
• DOM plays a complex, dual role in mercury bioavailability, acting as both a nutrient and a complexing agent that influences uptake dynamics.