Ability of Trichoderma hamatum Isolated from Plastics-Polluted Environments to Attack Petroleum-Based, Synthetic Polymer Films

Kateřina Malachová,Grażyna Adamus,Michelina Soccio,Pavlína Šlosarčíková,Nadia Lotti,Zuzana Rybková,Čeněk Novotný,Fabio Fava,Vincent Verney

doi:10.3390/pr8040467

Abstract

Microorganisms colonizing plastic waste material collected in composting-, landfill-, and anaerobic digestion plants were isolated to obtain novel strains maximally adapted to the degradation of plastics due to long-term contact with plastic polymers. Twenty-six bacterial strains were isolated and identified by the 16 S rRNA method, and eighteen strains of yeasts and fungi using 18 S rRNA and the internal transcribed spacer ITS sequencing of the 18 S rRNA gene. In selected strains, the ability to degrade linear low-density polyethylene (LLDPE), low-density polyethylene (LDPE), polystyrene (PS), and polyvinyl chloride (PVC) was tested in aerobic liquid-medium cultures. An oxidative, two-step pretreatment of LLDPE and LDPE using γ- or UV-irradiation followed by a high-temperature treatment was carried out, and the pretreated plastics were also included in the degradation experiments. The respective weight losses after biodegradation by Trichoderma hamatum were: virgin and γ/T90-pretreated LLDPE (2.2 ± 1.2 and 3.9 ± 0.5%), virgin and UV/T60-pretreated LDPE (0.5 ± 0.4 and 1.3 ± 0.4%), and virgin PS (0.9 ± 0.4%). The Fourier transform infrared spectroscopy (FTIR) analysis showed that during the treatment of pretreated LLDPE, T. hamatum attacked low molecular weight LLDPE oligomers, reducing the functional groups (carbonyl C = O), which was paralleled by a slight increase of the molar mass of pretreated LLDPE and a decrease of the dispersity index, as demonstrated by gel permeation chromatography (GPC). Thermogravimetric analysis (TGA) highlighted the formation of functional groups on LLDPE due to polymer pretreatment that favored fungal attack at the polymer surface. The results provide insight into microbial consortia that spontaneously colonize the surface of plastics in various environments and their capability to attack plastic polymers.

Highlights

Research focusing on the biodegradation of recalcitrant plastic polymers brought evidence that many microorganisms are able to attack polymeric chains
Samples of plastic polymers from the following sites were used for the isolation of new bacterial and fungal strains: a compost sample from the municipal composting plant (Grenoble, France), a compost sample from the composting plant (Schendelbeke, Belgium), a sample of black mulching film removed from agricultural soil in Belgium, a plastic sample removed from soil along a highway in Belgium, a sample of sludge from the anaerobic digester at a wastewater treatment plant (Treviso, Italy), and a sample of plastics removed from a landfill (Styron plant, Schkopau, Germany)
Bacteria of the genus Bacilllus dominated in the compost, anaerobic sludge- and landfill samples, whereas no similar predominance by a single genus could be observed among the isolated fungal organisms

Summary

Introduction

Research focusing on the biodegradation of recalcitrant plastic polymers brought evidence that many microorganisms are able to attack polymeric chains. The degradation efficiency was mostly low [1,2]. There is a need to isolate highly degradative strains of bacteria and fungi and better understand the biochemistry of polymer degradation with the aim to develop efficient degradation technologies [3,4]. Polyethylene (PE) is the most common plastic, accounting for 34%. It is extremely resistant to biodegradation [1,5]. Its degradability can be enhanced by abiotic photo- and thermooxidative treatments, resulting in the production of carboxyl, hydroxyl, and carbonyl groups that can be oxidized by microbial metabolism [6,7]

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Results

Conclusion