Greater Biofilm Formation and Increased Biodegradation of Polyethylene Film by a Microbial Consortium of Arthrobacter sp. and Streptomyces sp.

Ya-Nan Han,Feng-Min Li,Min Wei,Chao-Li Guo,Fang Han,Dong Wang,Yu-Jie Zhong,Zhong-Kui Xie,Chao Fang,Xiao-Yan Shi

doi:10.3390/microorganisms8121979

Abstract

The widespread use of polyethylene (PE) mulch films has led to a significant accumulation of plastic waste in agricultural soils. The biodegradation of plastic waste by microorganisms promises to provide a cost-effective and environmentally-friendly alternative for mitigating soil plastic pollution. A large number of microorganisms capable of degrading PE have been reported, but degradation may be further enhanced by the cooperative activity of multiple microbial species. Here, two novel strains of Arthrobacter sp. and Streptomyces sp. were isolated from agricultural soils and shown to grow with PE film as a sole carbon source. Arthrobacter sp. mainly grew in the suspension phase of the culture, and Streptomyces sp. formed substantial biofilms on the surface of the PE film, indicating that these strains were of different metabolic types and occupied different microenvironments with contrasting nutritional access. Individual strains were able to degrade the PE film to some extent in a 90-day inoculation experiment, as indicated by decreased hydrophobicity, increased carbonyl index and CO2 evolution, and the formation of biofilms on the film surface. However, a consortium of both strains had a much greater effect on these degradation properties. Together, these results provide new insights into the mechanisms of PE biodegradation by a microbial consortium composed of different types of microbes with possible metabolic complementarities.

Highlights

Agricultural mulch film is widely used to cover cultivated fields, where it promotes higher soil temperatures [1], better soil moisture conservation [2], effective weed suppression [3], and increased crop yields [4]
The enrichment and preliminary screen for bacteria capable of degrading PE film was performed by incubating soil plastic residues in minimal liquid medium supplemented with Unpretreated plastic film (UPF) powder as the sole carbon source
These isolates were further grown for another 90 days in the presence of UPF, and their effects on plastic film degradation properties such as weight loss, water contact angle (WCA), and carbonyl index were determined

Summary

Introduction

Agricultural mulch film is widely used to cover cultivated fields, where it promotes higher soil temperatures [1], better soil moisture conservation [2], effective weed suppression [3], and increased crop yields [4]. Its excellent physical and mechanical properties and affordable price make plastic mulch film the most indispensable and highly consumed product [5,6], with an estimated 1.25−1.4 million tons of film applied annually in China [7,8]. Most plastic mulch film in China is made primarily of polyethylene (PE) with superior properties such as high molecular weight (>30 kDa), 3D structure, and hydrophobicity, but these properties make PE highly resistant to degradation [9]. The government has established waste film recycling laws, but thin and ultra-thin agricultural mulch films are rarely recycled in practice. Plastic film residues remain quasi-permanently in the soil [12], a situation that is not compatible with sustainable agricultural practices. It is essential to develop an efficient method to degrade such plastics

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