Biophotoelectrochemical process co-driven by dead microalgae and live bacteria.

Area of Science:

• Environmental Microbiology
• Biochemistry
• Photochemistry

Background:

• Dead microalgae typically enhance anaerobic reduction by releasing nutrients.
• The role of dead microalgae as photosensitizers in microbial reduction has not been previously explored.

Purpose of the Study:

• To investigate the photoelectric synergistic linkage between dead microalgae and extracellular electron transfer (EET)-capable bacteria.
• To demonstrate that illuminated dead microalgae can drive microbial reduction processes.

Main Methods:

• Experiments using pure cultures of Geobacter sulfurreducens with illuminated dead Raphidocelis subcapitata.
• Assays involving irradiated dead Chlorella vulgaris and Shewanella oneidensis for nitrate reduction.
• Cr(VI) reduction experiments with irradiated dead Raphidocelis subcapitata and Bacillus subtilis.
• Illumination of dead microalgae in mixed-culture lake water.

Main Results:

• Illuminated dead microalgae significantly increased the rate of anaerobic bioreduction by EET-capable bacteria.
• Photoelectrons generated from dead microalgae were transferred to bacteria, enhancing reduction of nitrate and Cr(VI).
• The phenomenon was observed in natural lake water, indicating its prevalence in post-bloom ecosystems.

Conclusions:

• Dead microalgae can act as photosensitizers, driving microbial reduction through a biophotoelectrochemical process.
• This interaction involves photoelectron transfer from inactivated microalgae to EET-capable bacteria via multiheme cytochromes.
• This overlooked process is important for understanding bioreduction energetics, especially in microalgae-rich environments.