Phototrophic Fe(II) oxidation benefits from light/dark cycles

Area of Science:

• Microbiology
• Geochemistry
• Environmental Science

Background:

• Phototrophic Fe(II)-oxidizers link sunlight, Fe(II) oxidation, and CO2 fixation for energy and growth.
• Understanding the influence of light-dark cycles on these organisms is crucial for microbial ecology and biogeochemical processes.

Purpose of the Study:

• To investigate the impact of different light-dark cycle durations on the growth and Fe(II) oxidation rates of Chlorobium ferrooxidans KoFox.
• To compare these effects against constant light conditions.

Main Methods:

• Culturing Chlorobium ferrooxidans KoFox under constant light, short light/dark cycles (10h light/14h dark), and long light/dark cycles (2-3 days light/2-3 days dark).
• Monitoring Fe(II) oxidation rates and cell growth.
• Analyzing mineral structures using Scanning Electron Microscopy (SEM) and 57Fe Mössbauer spectroscopy.

Main Results:

• Fe(II) oxidation was completed fastest under constant light, but maximum oxidation rates were significantly higher under both short and long light-dark cycles.
• Short light-dark cycles exhibited the fastest maximum Fe(II) oxidation rates.
• Cell growth reached similar densities across all conditions, occurring in both light and dark phases.
• SEM and Mössbauer spectroscopy revealed poorly crystalline Fe(III) oxyhydroxides (e.g., ferrihydrite) regardless of light conditions.

Conclusions:

• Periods of darkness significantly influence phototrophic Fe(II)-oxidizers.
• Light-dark cycles, particularly shorter ones, can enhance Fe(II) oxidation rates compared to constant light.
• The findings provide insights into the metabolic flexibility and ecological role of these bacteria in environments with fluctuating light availability.