A survey of intact low-density polyethylene film biodegradation by terrestrial Actinobacterial species

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ORIGINAL ARTICLE

A survey of intact low-density polyethylene film biodegradation by terrestrial Actinobacterial species Zahra Soleimani 1 & Sara Gharavi 1

&

Mohammadreza Soudi 2 & Zahra Moosavi-Nejad 1

Received: 17 April 2020 / Revised: 13 July 2020 / Accepted: 12 August 2020 # Springer Nature Switzerland AG 2020

Abstract Low-density polyethylene (LDPE) polymer is mainly used in the production of plastic bags and food packaging making up the largest volume of plastic pollutions. These polymers are potential substrates for bacteria in the bioremediation process. In this study, soil samples were collected from different plastic landfills in Iran and subsequently enriched in specific media (polyethylene as carbon source) to increase the population of LDPE-degrading bacteria. Seventeen PE-degrading bacteria, some novel, were isolated from Iranian soil samples and identified using 16S rDNA gene sequencing. These isolates were capable of degrading PE in a limited incubation period without the need for physicochemical pretreatments and comprise mostly of Actinobacteria which include the three genera of Streptomyces, Nocardia, and Rhodococcus. The isolates belonged to 17 different species of gram-positive Actinobacteria. In all, 11 species of the genus Streptomyces, 3 species of the genus Rhodococcus, and 3 species of the genus Nocardia were identified. The isolates with less than 99% 16S rRNA gene similarity to previously known species were suspected to be new species. Various analyses (weight loss, SEM, FTIR, and tensile strength test) to determine polyethylene biodegradation rate were carried out after a 60-day incubation period. Analysis of polyethylene biodegradation elucidates that Actinobacteria have a high ability for biodegradation of polyethylene-based plastics. Streptomyces sp. IR-SGS-T10 showed the highest reduction in weight of the LDPE film (1.58 mg/g/day) after 60 days of incubation without any pretreatments. Rhodococcus sp. IR-SGS-T11 shows the best reduction in the tensile property of LDPE film, while results from FTIR study for Streptomyces sp. IR-SGS-Y1 indicated a significant change in structural analysis. Keywords Biodegradation . Environmental pollution . Low-density polyethylene . Actinobacteria . Bacteria

Introduction Plastic industries have produced 8.3 billion tons of plastic up to 2017 (Geyer et al. 2017). Plastics increasingly displace other materials, especially natural ones. In addition to a number of irreplaceable applications, plastics are used incautiously and hence assumed to be one of the most serious threats to the global environment. The excessive use and disposal of these recalcitrant plastics have resulted in the deposition of greater than 348 million tons of plastic on earth in 2017 (Garside

* Sara Gharavi [email protected] 1

Department of Biotechnology, Faculty of Biological Sciences, Alzahra University, Vanak, Tehran, Iran

2

Department of Microbiology, Faculty of Biological Sciences, Alzahra University, Vanak, Tehran, Iran

2019). Lack of efficient and suitable metho