P02 | Bacteria isolated from edible bivalve mollusks in the Adriatic Sea with potential for biodegradation of microplastics

Purpose. Microplastics (MPs, < 5mm) are increasingly detected in marine organisms, particularly in edible bivalve mollusks, and their trophic transfer along the food chain poses a growing threat to ecosystem and animal health. MPs provide a substrate for colonization by microorganisms capable of degrading them, particularly Pseudomonas spp. However, this decomposition phenomenon requires further investigation. This study aims to develop a readily reproducible microbiological screening method in the laboratory to evaluate the biodegradation capacity of MPs by bacterial strains isolated from bivalve mollusks in the Adriatic Sea. Methods. Two reference strains, Pseudomonas aeruginosa and Pseudomonas putida, known for their degrading activity on low-density polyethylene (LDPE), were initially used to standardize the screening protocol, which was then used to test 3 strains of P. putida and 3 strains of P. aeruginosa isolated from edible bivalve mollusks from the Adriatic Sea. The method, called Clear Zone, is based on inoculating the microbial strain into a medium containing plastic as the sole carbon source. The formation of a clear zone of lysis around the inoculum is an indicator of the bacteria using the plastic material as a nutrient substrate. Two different soil formulations were tested: one containing polyethylene glycol (PEG) and the other containing LPDE particles, both evaluated with and without the addition of yeast extract (0.1%). After incubation, staining with Coomassie blue was performed, and bacteria that produced a blue area against a dark background were considered positive. Results. The formulation containing PEG and yeast extract proved to be the most effective in highlighting the biodegradation zones. Of the 6 strains tested, 2 strains of P. putida and one strain of P. aeruginosa confirmed their microplastic degradation potential. Conclusions. The results obtained from the experiment allowed for the standardization of a rapid, reproducible, and sensitive protocol for selecting bacteria capable of biodegrading MPs. Additionally, 3 strains of Pseudomonas, isolated from edible bivalve mollusks in the Adriatic Sea, have been identified as potentially capable of biodegrading MPs absorbed by filter-feeding marine organisms. The next phase will consist of confirming the biodegradation activity of these bacteria in experimental systems, at a laboratory scale, that reproduce a contaminated marine habitat, both with free MPs in the water and with MPs inside bivalve mollusks. This work was funded by the Ministry of Health (RF201912370587; RC0042019; RC0072023).