Microbial acetone oxidation in coastal seawater

Area of Science:

• Oceanic chemistry and microbial ecology
• Atmospheric science and air-sea interactions
• Biogeochemical cycling of volatile organic compounds

Background:

• Acetone, an oxygenated volatile organic compound (OVOC), plays a role in tropospheric oxidation.
• Oceanic acetone concentrations and their loss processes, particularly microbial oxidation, are not well understood.
• Quantifying air-sea flux requires knowledge of oceanic acetone sinks.

Purpose of the Study:

• To determine if microbial oxidation to carbon dioxide (CO2) is a significant loss process for oceanic acetone.
• To quantify microbial acetone oxidation rates in a coastal marine environment.
• To assess the biological turnover time of acetone in surface waters and its implications for air-sea exchange.

Main Methods:

• Utilized 14C-labeled acetone to measure microbial oxidation to 14CO2.
• Conducted kinetic experiments to determine maximum velocity (Vmax) and Michaelis-Menten constant (Km).
• Monitored acetone loss rates and in situ concentrations over an annual cycle at a coastal station (L4).

Main Results:

• Demonstrated linear microbial acetone oxidation rates over 0.75-3.5 hours.
• Determined kinetic parameters: Vmax = 4.1 pmol L(-1) h(-1) and Km = 54 pM.
• Observed annual microbial acetone loss rates from 1.2 to 42 pmol L(-1) h(-1), with winter maxima.
• Calculated biological turnover times ranging from ~3 days (winter) to >240 days (summer).

Conclusions:

• Marine microbial oxidation of acetone to CO2 is a slow process.
• Acetone has a relatively long biological turnover time in surface waters.
• Marine microbes likely prioritize other oxygenated volatile organic compounds (OVOCs) over acetone, such as methanol and acetaldehyde.