Investigation of potential biopesticides activities of microalgae derived extracts

Plant diseases are one of the major problems that significantly affect crop yield and quality in agriculture. Synthetic chemicals commonly used in the fight against these diseases can harm not only the target organisms but also the environment and other living organisms. These negative impacts have increased the search for environmentally friendly and sustainable alternatives, highlighting the importance of biopesticides. Microalgae present significant potential for both the protection and improvement of agricultural products. They are used in various agricultural applications such as breeding, foliar application, and seed treatment, producing metabolites with biopesticide effects. In this study, 32 microalgal strains from the Bursa Technical University Algae and Cyanobacteria Culture Collection (AQUAMEB) were used. The strains were isolated from freshwater, marine, and high salinity environments. After small-scale productions, the harvested microalgae were lyophilized and dried, and then extracted using various solvents (methanol, ethanol, acetone, DMSO, hexane, and methanol:water) with different extraction methods (Soxhlet, probe sonication, ultrasonic bath, and glass beads). The antimicrobial effects of these extracts were tested on bacteria and fungi using agar disk diffusion, agar well diffusion, and minimum inhibitory concentration (MIC) methods. The results showed that extracts prepared with polar solvents were more effective against gram-negative bacteria. In particular, extracts prepared with methanol and methanol-water solvents exhibited strong inhibitory activity against Escherichia coli, with MIC values detected below 0.625 mg/mL. In Salmonella typhimurium tests, a zone diameter of up to 25 mm was observed, with extracts obtained from Chlorophyta AQUAMEB-59 and Scenedesmus sp. AQUAMEB-57 being the most effective against this bacterium. However, limited activity was observed against gram-positive bacteria and fungi. The findings obtained through agar diffusion and MIC methods were consistent with each other. In conclusion, the potential of microalgae as antimicrobial agents and biopesticides is strongly supported. Microalgae can provide healthier and more effective long-term solutions in the agricultural sector by reducing antimicrobial resistance development. Furthermore, since they decompose easily in nature without leaving chemical residues, their environmental impact is minimized. However, further research is needed for the effective and widespread use of these strains in large-scale applications.