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A marine bacterial community that degrades poly(ethylene
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terephthalate) and polyethylene
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Rongrong Gao
1,2,3,4
, Chaomin Sun
1,2,4*
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Key Laboratory of Experimental Marine Biology, Institute of Oceanology, Chinese
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Academy of Sciences, Qingdao, China
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2
Laboratory for Marine Biology and Biotechnology, Qingdao National Laboratory
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for Marine Science and Technology, Qingdao, China
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3
College of Earth Science, University of Chinese Academy of Sciences, Beijing,
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China
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4
Center of Ocean Mega-Science, Chinese Academy of Sciences, Qingdao, China
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11
*
Corresponding author
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Chaomin Sun Tel.: +86 532 82898857; fax: +86 532 82898857.
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E-mail address: sunchaomin@qdio.ac.cn
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Keywords: ocean, plastics, bacterial community reconstitution, degradation,
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pollution
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Running title: A marine bacterial community degrades PET and PE
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preprint (which was not certified by peer review) is the author/funder. All rights reserved. No reuse allowed without permission.
The copyright holder for thisthis version posted November 8, 2020. ; https://doi.org/10.1101/2020.11.07.372490doi: bioRxiv preprint
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Abstract
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Plastic wastes have become the most common form of marine debris and present a
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growing global pollution problem. Recently, microorganisms-mediated degradation
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has become a most promising way to accomplish the eventual bioremediation of
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plastic wastes due to their prominent degradation potentials. Here, a marine bacterial
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community which could efficiently colonize and degrade both poly (ethylene
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terephthalate) (PET) and polyethylene (PE) was discovered through a screening with
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hundreds of plastic waste associated samples. Using absolute quantitative 16S rRNA
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sequencing and cultivation methods, we obtained the abundances and pure cultures
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of three bacteria mediating plastic degradation. We further reconstituted a tailored
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bacterial community containing above three bacteria and demonstrated its efficient
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degradation of PET and PE through various techniques. The released products from
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PET and PE degraded by the reconstituted bacterial community were determined by
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the liquid chromatography-mass spectrometry. Finally, the plastic degradation process
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and potential mechanisms mediated by the reconstituted bacterial community were
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elucidated through transcriptomic methods. Overall, this study establishes a stable and
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effective marine bacterial community for PET and PE degradation and sheds light on
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the degradation pathways and associated mechanistic processes, which paves a way to
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develop a microbial inoculant against plastic wastes.
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preprint (which was not certified by peer review) is the author/funder. All rights reserved. No reuse allowed without permission.
The copyright holder for thisthis version posted November 8, 2020. ; https://doi.org/10.1101/2020.11.07.372490doi: bioRxiv preprint
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Introduction
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Plastics have been found widespread in the world’s oceans
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. It has been reported that
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about 4.8 to 12.7 million tons of plastic debris per year enter the ocean
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. Plastics in the
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marine environment are of increasing concern because of their persistence and effects
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on the oceans
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, wildlife
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, and, potentially, humans
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. An estimated one million birds
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and ten thousand marine animals die each year as a result of ingestion of or trapping
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by plastics in the oceans
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. Moreover, after weathering, mechanical wear and
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ultraviolet radiation, the large plastic may be broken into fragmentation, when it is
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smaller than 5 mm in diameter, it was commonly defined as microplastics
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. Of note,
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microplastics also negatively impact upon marine biota and can be ingested and
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accumulated along trophic webs until top predators
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.
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Among various types of plastic wastes, poly (ethylene terephthalate) (PET) and
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polyethylene (PE) constitute the major 46.5% portion of the tremendous amount of
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plastic pollution debris
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. PET is a type of semi-aromatic thermoplastic co-polymer
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resin from polyester family, which has aromatic groups heteroatoms in the main
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chain
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. PE has a carbon-carbon backbone which is solely built of carbon atoms and
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has high resistance against various degradation processes, due to non-hydrolyzable
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covalent bonds
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. Both PET and PE have properties such as lower density, long
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hydrocarbon chain, high molecular weight and tensile strength, low permeability to
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gases, durability to physical and chemical degradation, non-biodegradable
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compound
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.
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Landfilling, incineration, recycling and biodegradation are the principal strategies
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to solve the plastic waste problem
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. As an environmentally friendly alternative to
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conventional plastic waste management methods, microorganisms-mediated
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degradation is the most promising way to accomplish an eventual bioremediation of
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plastic wastes. Microbial degradation of plastics is usually an enzymatic activity that
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catalyzes the cleavage of polymer bond into monomer entity
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. Thus far, PET
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hydrolyzing activity has been reported for members of the cutinase, lipase and
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preprint (which was not certified by peer review) is the author/funder. All rights reserved. No reuse allowed without permission.
The copyright holder for thisthis version posted November 8, 2020. ; https://doi.org/10.1101/2020.11.07.372490doi: bioRxiv preprint
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esterase
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. PE, as one of the most abundant plastics in the ocean, shows obvious signs
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of degradation when incubated with specific microorganisms under controlled
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laboratory conditions
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. However, as compared to the extensive studies about PET-
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degrading bacteria and enzymes
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, the researches about PE degradation
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mediated by microorganisms lag well behind and the degradation efficiency using a
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single strain or enzyme is still too low to meet the industrial applications requirements.
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Alternatively, using microbial community to degrade PE might be a good choice
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given their inherent multiple robust function among synergistic effect of different
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species
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. Actually, the construction of artificial microbial consortia has opened a new
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horizon in environment bioremediation in terms of removing hard biodegradable
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harmful compounds
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.
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Herein, a marine bacterial community efficiently degrading both PET and PE
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was obtained by a large-scale screening. Three bacteria driving plastic degradation
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were isolated and reconstituted to an artificial bacterial community with a similar
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degradation capability to that of the original bacterial flora. The degradation effects
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and possible products of PET and PE treated by this reconstituted bacterial
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community were further clarified by various techniques. Lastly, the potential
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degradation process and associated enzymes were disclosed through transcriptomics
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methods.
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Results
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Discovery of a marine bacterial community efficiently degrading both PET and
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PE. To obtain potential marine bacteria degrading PET or PE, we collected about 300
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sediment samples contaminated by plastic debris from different locations of a bay of
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China. Using these samples, we initiated to screen microorganisms that could use
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plastic drink bottles (whose main component is PET) or commercial PE bags as major
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carbon sources for growth. With that, a distinct consortium derived from one of the
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plastic debris samples could efficiently colonize on both PET (Supplementary Fig. 1b)
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and PE films (Supplementary Fig. 1d). Scanning electronic microscopy (SEM)
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The copyright holder for thisthis version posted November 8, 2020. ; https://doi.org/10.1101/2020.11.07.372490doi: bioRxiv preprint
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observation confirmed that the consortium could evidently colonize on PET
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(Supplementary Fig. 1f) and PE films (Supplementary Fig.1i). Of note, these
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colonizers formed an obvious biofilm layer and closely interacted each other with
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filament-like structures on PET (Supplementary Fig. 1g) and PE films
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(Supplementary Fig.1j). After removing the microbial layer from the films, significant
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morphological changes in both PET (Supplementary Figs. 2b-2d) and PE films were
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observed by SEM, especially for PE which showed large amount of heavy cracks and
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deep holes in the surface and even the inside of the film (Supplementary Figs. 2f-2h).
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Given the fact that most commercial plastics contain various additives (such as
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dyes, plasticizer, antistatic agents etc.), it is necessary to make sure that the
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consortium indeed degraded the plastics rather than the additives. We thus repeated
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the degradation test by the above consortium with the PET and PE films without any
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additives. Consistently, both PET and PE films were evidently degraded after 4 weeks
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treatment by the consortium even observed by eyes (Figs. 1b, 1d), and the four
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corners of both films lost sharp morphology as that shown in the control (Figs. 1a, 1c).
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Similar to the results obtained with the additive-containing plastics, SEM observation
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revealed that the consortium could efficiently colonize on the surface of films (Figs.
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1f, 1i) and caused obvious degradation by forming pits, cracks or holes in the surface
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and inside of PET (Fig. 1g) and PE film (Fig. 1j). Similar to additive-containing
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plastics, the consortium prefers to degrade pure PE than PET. Overall, we conclude
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that this consortium could efficiently degrade both PET and PE, and is worthy of
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further study.
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Isolation of the key degraders and reconstitution of the functional community
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capable of plastic degradation. To figure out the composition and dynamics of the
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above microbial community during the course of plastics degradation, we performed
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an absolute quantitative analysis of 16S rRNA sequences on this microbial flora. The
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growth curve of this microbial flora showed that it took about 10 h to enter the
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stationary phase and kept a stable population quantity after 7 d- or even longer
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preprint (which was not certified by peer review) is the author/funder. All rights reserved. No reuse allowed without permission.
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