Use of rhizosphere microorganisms in the biodegradation of PLA and PET polymers in compost soil

This work examines biodegradational changes in two types of polymer - biodegradable (polylactide, PLA) and conventional (polyethylene terephthalate, PET) - which have similar uses in industry. The main objective of this project was to select rhizosphere bacteria and fungi that were plant growth promoting microorganisms (PGPM) to accelerate the biodegradation of PLA and PET in soil in which selected plant species were cultivated. A pot experiment was conducted to evaluate polymer biodegradation in compost soil in which three plant species were cultivated: rape (Brassica napus), miscanthus (Miscanthus x giganteus), and willow (Salix viminalis). Plant growth was additionally stimulated by inoculation with two bacterial (Arthrobacter sulfonivorans, Serratia plymuthica) or two fungal strains (Clitocybe sp., Laccaria laccata). The strains used in the experiment were selected for their hydrolytic activity and their ability to grow in vitro on plastics. In the case of the bacteria, the ability to create a biofilm on both types of studied polymers was identified. Biodegradation changes in the plastics were assessed based on changes in both their surface structure and physical and chemical properties after a 6-month incubation in the soil. Biodegradation of the analysed sheets was most rapid in the presence of the S. plymuthica and L. laccata strains. The presence of PLA in the inoculated soil lowered the soil pH and increased its redox potential as well as increased the abundance of fungi and bacteria in the soil. The experiment confirmed the stimulating effect of the S. plymuthica and L. laccata strains on plant biomass.