Screening and selection of microorganisms for oil-based plastics biodegradation

Oil-based plastics have raised severe environmental and health concerns because they accumulate due to their refractoriness to biological degradation. Consequently, the search for an efficient biological technique for their treatment is a current challenge. Several authors have reported microorganisms and specific enzymes capable of breaking down these polymers, but their number is quite limited and inefficient in most cases. Therefore, there is an urgent need to enlarge the resources available for that purpose. Twentyseven microorganisms (bacteria and fungi) isolated from composting and olive mill wastewater sludges (OMWs) were used for this study. Microorganisms were tested for the expression of lignin-degrading enzymes (laccase, oxidase, and polyphenoloxidase) as well as esterases (lipase, cutinases, and polyurethanase). The microorganisms isolated from composting and OMWs covered the full spectrum of enzymatic activities tested, however, the highest proportion of microorganisms bearing most enzymatic activities came from composting. The most frequently expressed enzymatic activities in composting isolates were related to lignin metabolism while isolates from OMWs mainly expressed esterases. Thus, microorganisms isolated from composting are considered the most suitable candidates for the biodegradation of oil-based plastics due to the wide range of enzymes produced. Among them, two fungi Rhodotorula RHM1, Aspergillus RHM15 and the bacteria Bacillus RBM2 were chosen because they showed the greatest range of enzymatic activities, including lipases, cutinases and ligninases. Therefore, composting could be considered as a source of functionally efficient microorganisms to use them as biotechnological tools for biodegradation of recalcitrant xenobiotics compounds, such as oil-based plastics.