Photodynamic therapy against cyanobacteria

Area of Science:

• Environmental Science
• Aquatic Ecology
• Toxicology

Background:

• Cyanobacterial blooms pose significant ecological and health risks.
• Controlling cyanobacteria often involves chemical treatments, necessitating research into effective and selective agents.
• Reactive oxygen species (ROS) are explored for their potential algicidal properties.

Purpose of the Study:

• To evaluate the efficacy of photosensitizers and hydrogen peroxide as sources of ROS for limiting cyanobacterial growth.
• To compare the toxicity of singlet oxygen-producing compounds versus hydrogen peroxide on various algal and cyanobacterial species.

Main Methods:

• Algal toxicity tests were conducted in microplates.
• Tested compounds included 12 phthalocyanines, tetraphenol porphyrine, methylene blue (singlet oxygen producers), and hydrogen peroxide (ROS source).
• Assays were performed on three green algae species (Pseudokirchneriella subcapitata, Scenedesmus quadricauda, Chlorella kessleri) and three cyanobacteria species (Synechococcus nidulans, Microcystis incerta, Anabaena sp.).

Main Results:

• Photosensitizers and singlet oxygen demonstrated high toxicity towards certain phytoplankton species.
• The green alga Scenedesmus quadricauda exhibited high sensitivity (EC50 = 0.07 mg/L) to singlet oxygen producers.
• Hydrogen peroxide was approximately 10 times more toxic to cyanobacteria than to the tested green alga.

Conclusions:

• Singlet oxygen-producing compounds can be highly effective against specific phytoplankton, including some cyanobacteria.
• Hydrogen peroxide shows greater toxicity towards cyanobacteria compared to green algae.
• Compounds generating hydroxyl radicals appear more promising for managing cyanobacterial blooms than those producing singlet oxygen.