Octanoic acid helps Poterioochromonas malhamensis control toxic Microcystis sp.

This study explores the synergistic use of the mixotrophic flagellate Poterioroochromonas malhamensis and octanoic acid to effectively control harmful Microcystis sp. and prevent the resurgence of resistant strains. Poterioroochromonas malhamensis efficiently grazes on Microcystis sp., yet predation pressure can drive the evolution of resistant strains, which often re-emerge and predominate within approximately 20 days. Importantly, octanoic acid maintains its inhibitory and lethal effects against these strains, preventing their comeback. The study's key findings are as follows: (1) The concurrent application of P. malhamensis and 100 mg L^-1 octanoic acid rapidly eliminates Microcystis sp., utilizing the acid's resistance-suppressing properties to prevent regrowth. (2) A preliminary reduction of Microcystis sp. density by P. malhamensis, succeeded by a low dose of octanoic acid (12.5 mg L^-1 or higher), postpones the resurgence, presenting a cost-effective strategy. (3) In instances where P. malhamensis density is inadequate for controlling Microcystis sp. alone, a supplementary application of octanoic acid at 25 mg L^-1 daily for four days (25 mg L^-1× 4) aids P. malhamensis in eradicating Microcystis sp. The study concludes that octanoic acid fortifies the biological control by P. malhamensis and, by inhibiting and eliminating resistant Microcystis strains, introduces an innovative strategy for managing Microcystis blooms.