Microbial degradation of low-density polyethylene and synthesis of polyhydroxyalkanoate polymers

Abstract

We have characterized the ability of eight bacterial strains to utilize powdered low-density polyethylene (LDPE) plastic (untreated and without any additives) as a sole carbon source. Cell mass production on LDPE-containing medium after 21 days of incubation varied between 0.083 ± 0.015 g/L cell dry mass (cdm) for Micrococcus luteus IRN20 and 0.39 ± 0.036 g/L for Cupriavidus necator H16. The percent decrease in LDPE mass ranged from 18.9% ± 0.72% for M. luteus IRN20 to 33.7% ± 1.2% for C. necator H16. Linear alkane hydrolysis products from LDPE degradation were detected in the culture media, and the carbon chain lengths of the hydrolysis products detected varied, depending on the species of bacteria. We also determined that C. necator H16 produced short-chain-length polyhydroxyalkanoate biopolymers, while Pseudomonas putida LS46 and Acinetobacter pittii IRN19 produced medium-chain-length biopolymers while growing on polyethylene powder. Cupriavidus necator H16 accumulated poly (3-hydroxybutyrate-co-3-hydroxyvalerate) (PHB-V) polymers to 3.18% ± 0.4% of cdm. The monomer composition of the PHB-V was 94.9% ± 0.61% 3-hydroxybutyrate and 5.03% ± 0.56% 3-hydroxyvalerate. This is the first report that provides direct evidence for simultaneous bioconversion of LDPE plastic to biodegradable polyhydroxyalkanoate polymers.

Challenges with Verifying Microbial Degradation of Polyethylene

“…Figure 4a,b shows polyethylene particles (particle size of 400 µm or less) and PE films, respectively, that have used by researchers in biodegradation experiments. Figure 4c,e, respectively represent images of colonization and attachment of Sphigobacterium moltivorum and Pseudomonas putida on the surface of PE particles (with different magnifications), while Figure 4d,f shows evidence of corrosion/penetration the PE by Sphigobacterium moltivorum and Delftia tsuruhatensis [37,66].…”

“…Gas chromatography (GC) using non-polar columns has been used to determine biofragmentation and existence of saturated linear alkanes in culture media after microbial degradation of polyethylene [66]. Abrusci et al (2011) and Kyaw et al (2012) used GC-MS to detect saturated alkanes generated by microbial degradation of polyethylene [31,53].…”

“…The biodegradation process usually includes biofragmentation of the PE polymers by secreted enzymes, followed by bioassimilation of small cleavage fragments (molar mass must be less than 500 g/mol) by the microorganisms [56,66]. Many of the species shown to degrade PE are also able to consume linear n-alkanes like paraffin (C 44 H 90 , M w = 618).…”

“…However, the remaining cells may be removed by subjection the PE samples to ultra-sonication [37]. The rate of biodegradation is usually reported as the percentage of polymer weight loss per unit time of experiment as below [53,66]; % weight loss = [(initial weight − final weight)/initial weight] However, weight loss can result from consumption of low molar mass PE material and may not be a good indicator of complete biodegradation of intact to fragmented polymer chains. Also, in the case of polyethylene powder, the recovery of particles from media is not accurate, as the particles maybe easily missed, and this measurement suffers from wide-range of standard deviation in data collection.…”

Spatial structure in the “Plastisphere”: Molecular resources for imaging microscopic communities on plastic marine debris

“…Biofilms can also change the physical and chemical properties of plastic and influence further colonization by metazoan larvae (Chung et al, 2010;Hadfield, 2010). Microbes and biofilms can promote degradation of PMD (Chauhan, Agrawal, Deshmukh, Roy, & Priyadarshini, 2018;Kumari, Chaudhary, & Jha, 2019;Montazer, Habibi Najafi, & Levin, 2018;Shah, Hasan, Hameed, & Ahmed, 2008;Zettler, Mincer, & Amaral-Zettler, 2013), but they can also hinder abiotic ageing by shielding PMD from ultraviolet (UV) radiation in the surface ocean, arguably the most important and rapid abiotic process of plastic breakdown in the environment (Song et al, 2017). Moreover, biofilms can make plastic smell and taste like food to animals such as birds and fish that rely on chemoreception for food selection (Savoca, Tyson, McGill, & Slager, 2017;Savoca, Wohlfeil, Ebeler, & Nevitt, 2016).…”