Microbial Consortiums of Putative Degraders of Low-Density Polyethylene-Associated Compounds in the Ocean

Metagenomic analysis of soil from landfill site reveals a diverse microbial community involved in plastic degradation

In this study, we have investigated microbial communities structure and function using high throughput amplicon sequencing and whole metagenomic sequencing of DNA extracted from different depths of a plastic-laden landfill site. With diverse taxonomic groups inhabiting the plastic-rich soil, our study demonstrates the remarkable adaptability of microbes to use this new substrate as a carbon source. FTIR spectroscopic analysis of soil indicated degradation of plastic as perceived from the carbonyl index of 0.16, 0.72, and 0.44 at 0.6, 0.9 and 1.2 m depth, respectively. Similarly, water contact angles of 108.7 degree, 99.7 degree, 62.7 degree, and 77.8 degree of plastic pieces collected at 0.3, 0.6, 0.9, and 1.2 m depths respectively showed increased wettability and hydrophilicity of the plastic. Amplicon analysis of 16S and 18 S rRNA revealed a high abundance of several plastic-degrading bacterial groups, including Pseudomonas, Rhizobiales, Micrococcaceae, Chaetomium, Methylocaldum, Micromonosporaceae, Rhodothermaceae and fungi, including Trichoderma, Aspergillus, Candida at 0.9 m. The co-existence of specific microbial groups at different depths of landfill site indicates importance of bacterial and fungal interactions for plastic. Whole metagenome analysis of soil sample at 0.9 m depth revealed a high abundance of genes encoding enzymes that participate in the biodegradation of PVC, polyethylene, PET, and polyurethane. Curation of the pathways related to the degradation of these materials provided a blueprint for plastic biodegradation in this ecosystem. Altogether, our study has highlighted the importance of microbial cooperation for the biodegradation of pollutants. Our metagenome-based investigation supports the current perception that consortia of fungi-bacteria are preferable to axenic cultures for effective bioremediation of the environment.

Interactions between microplastics and organic contaminants: The microbial mechanisms for priming effects of organic compounds on microplastic biodegradation

The co-presence of plastics and other organic contaminants is pervasive in various ecosystems, particularly in areas with intensive anthropogenic activities. Their interactions inevitably impact the composition and functions of the plastisphere microbiome, which in turn determines the trajectory of these contaminants. Antibiotics are a group of organic contaminants that warrant particular attention due to their wide presence in environments and significant potential to disseminate antibiotic resistance genes (ARGs) within the plastisphere. Therefore, this study investigated the impacts of sulfadiazine (SDZ), a prevalent environmental antibiotic, on the composition and function of the plastisphere microbial community inhabiting micro-polyethylene (mPE), one of the most common microplastic contaminants. Our findings indicated that the presence of SDZ increased the overall plastisphere microbial abundance and enriched populations that are capable of degrading both SDZ and mPE. The abundance of Aquabacterium, a dominant plastisphere population that is capable of degrading both SDZ and mPE, increased over the course of SDZ exposure, while another abundant mPE-degrading population, Ketobacter, remained stable. Accordingly, the removal of SDZ was enhanced in the presence of mPE. Moreover, the results further revealed that not only SDZ but also other labile organic contaminants (e.g., aniline and hexane) could accelerate mPE biodegradation through a priming effect. This investigation underscores the complex dynamics among microplastics, organic contaminants, and the plastisphere microbiome, offering insights into the environmental fate of plastic and antibiotic pollutants.

Metatranscriptomics of microbial biofilm succession on HDPE foil: uncovering plastic-degrading potential in soil communities

BACKGROUND

Although plastic pollution is increasing worldwide, very little is known about the microbial processes that take place once plastic debris is incorporated into the soil matrix. In this study, we conducted the first metatranscriptome analysis of polyethylene (PE)-associated biofilm communities in highly polluted landfill soil and compared their gene expression to that of a forest soil community within a 53-day period.

RESULTS

Our findings indicate that the microbial population present in soil contaminated with plastic debris is predisposed to both inhabit and degrade plastic surfaces. Surprisingly, the microbial community from undisturbed forest soil contained a diverse array of plastic-associated genes (PETase, alkB, etc.), indicating the presence of an enzymatic machinery capable of plastic degradation. Plastic-degrading taxa were upregulated in the early stages of biofilm formation. During the maturation of the biofilm, the alkB1/alkM transcripts, which encode PE-degrading enzymes, and transporters such as fadL, livG, livF, livH, and livM were upregulated, along with transcripts associated with the fatty acid β-oxidation pathway.

CONCLUSIONS

In this study, we address the underlying patterns of gene expression during biofilm development in a PE-associated plastisphere in soil and address the pressing question of whether natural microbial communities have the potential to biodegrade petrochemical-based plastic in the soil environment.

Omic-driven strategies to unveil microbiome potential for biodegradation of plastics: a review

Plastic waste accumulation has lately been identified as the leading and pervasive environmental concern, harming all living beings, natural habitats, and the global market. Given this issue, developing ecologically friendly solutions, such as biodegradation instead of standard disposal, is critical. To effectively address and develop better strategies, it is critical to understand the inter-relationship between microorganisms and plastic, the role of genes and enzymes involved in this process. However, the complex nature of microbial communities and the diverse mechanisms involved in plastic biodegradation have hindered the development of efficient plastic waste degradation strategies. Omics-driven approaches, encompassing genomics, transcriptomics and proteomics have revolutionized our understanding of microbial ecology and biotechnology. Therefore, this review explores the application of omics technologies in plastic degradation studies and discusses the key findings, challenges, and future prospects of omics-based approaches in identifying novel plastic-degrading microorganisms, enzymes, and metabolic pathways. The integration of omics technologies with advanced molecular technologies such as the recombinant DNA technology and synthetic biology would guide in the optimization of microbial consortia and engineering the microbial systems for enhanced plastic biodegradation under various environmental conditions.

Engineering the mangrove soil microbiome for selection of polyethylene terephthalate-transforming bacterial consortia

Mangroves are impacted by multiple environmental stressors, including sea level rise, erosion, and plastic pollution. Thus, mangrove soil may be an excellent source of as yet unknown plastic-transforming microorganisms. Here, we assess the impact of polyethylene terephthalate (PET) particles and seawater intrusion on the mangrove soil microbiome and report an enrichment culture experiment to artificially select PET-transforming microbial consortia. The analysis of metagenome-assembled genomes of two bacterial consortia revealed that PET catabolism can be performed by multiple taxa, of which particular species harbored putative novel PET-active hydrolases. A key member of these consortia (Mangrovimarina plasticivorans gen. nov., sp. nov.) was found to contain two genes encoding monohydroxyethyl terephthalate hydrolases. This study provides insights into the development of strategies for harnessing soil microbiomes, thereby advancing our understanding of the ecology and enzymology involved in microbial-mediated PET transformations in marine-associated systems.

Potential routes of plastics biotransformation involving novel plastizymes revealed by global multi-omic analysis of plastic associated microbes

Despite increasing efforts across various disciplines, the fate, transport, and impact of synthetic plastics on the environment and public health remain poorly understood. To better elucidate the microbial ecology of plastic waste and its potential for biotransformation, we conducted a large-scale analysis of all publicly available meta-omic studies investigating plastics (n = 27) in the environment. Notably, we observed low prevalence of known plastic degraders throughout most environments, except for substantial enrichment in riverine systems. This indicates rivers may be a highly promising environment for discovery of novel plastic bioremediation products. Ocean samples associated with degrading plastics showed clear differentiation from non-degrading polymers, showing enrichment of novel putative biodegrading taxa in the degraded samples. Regarding plastisphere pathogenicity, we observed significant enrichment of antimicrobial resistance genes on plastics but not of virulence factors. Additionally, we report a co-occurrence network analysis of 10 + million proteins associated with the plastisphere. This analysis revealed a localized sub-region enriched with known and putative plastizymes-these may be useful for deeper investigation of nature's ability to biodegrade man-made plastics. Finally, the combined data from our meta-analysis was used to construct a publicly available database, the Plastics Meta-omic Database (PMDB)-accessible at plasticmdb.org. These data should aid in the integrated exploration of the microbial plastisphere and facilitate research efforts investigating the fate and bioremediation potential of environmental plastic waste.

Marine plastisphere selectively enriches microbial assemblages and antibiotic resistance genes during long-term cultivation periods

Several studies have focused on identifying and quantifying suspended plastics in surface and subsurface seawater. Microplastics (MPs) have attracted attention as carriers of antibiotic resistance genes (ARGs) in the marine environment. Plastispheres, specific biofilms on MP, can provide an ideal niche to spread more widely through horizontal gene transfer (HGT), thereby increasing risks to ecosystems and human health. However, the microbial communities formed on different plastic types and ARG abundances during exposure time in natural marine environments remain unclear. Four types of commonly used MPs (polyethylene (PE), polypropylene (PP), polystyrene (PS), and polyvinyl chloride (PVC)) were periodically cultured (46, 63, and 102 d) in a field-based marine environment to study the co-selection of ARGs and microbial communities in marine plastispheres. After the first 63 d of incubation (p < 0.05), the initial 16S rRNA gene abundance of microorganisms in the plastisphere increased significantly, and the biomass subsequently decreased. These results suggest that MPs can serve as vehicles for various microorganisms to travel to different environments and eventually provide a niche for a variety of microorganisms. Additionally, the qPCR results showed that MPs selectively enriched ARGs. In particular, tetA, tetQ, sul1, and qnrS were selectively enriched in the PVC-MPs. The abundances of intl1, a mobile genetic element, was measured in all MP types for 46 d (5.22 × 10-5 ± 8.21 × 10-6 copies/16s rRNA gene copies), 63 d (5.90 × 10-5 ± 2.49 × 10-6 copies/16s rRNA gene copies), and 102 d (4.00 × 10-5 ± 5.11 × 10-6 copies/16s rRNA gene copies). Network analysis indicated that ARG profiles co-occurred with key biofilm-forming bacteria. This study suggests that the selection of ARGs and their co-occurring bacteria in MPs could potentially accelerate their transmission through HGT in natural marine plastics.

Degradation of low-density polyethylene by the bacterium Rhodococcus sp. C-2 isolated from seawater

Low-density polyethylene (LDPE), which accounts for 20% of the global plastic production, is discharged in great quantities into the ocean, threatening marine life and ecosystems. Marine microorganisms have previously been reported to degrade LDPE plastics; however, the exploration of strains and enzymes that degrade LDPE is still limited. Here, an LDPE-degrading bacterium was isolated from seawater of the Changjiang Estuary, China and identified as Rhodococcus sp. C-2, the relative abundance of which was dramatically enhanced during PE-degrading microbial enrichment. The strain C-2 exhibited the degradation of LDPE films, leading to their morphological deterioration, reduced hydrophobicity and tensile strength, weight loss, as well as the formation of oxygen-containing functional groups in short-chain products. Sixteen bacterial enzymes potentially involved in LDPE degradation were screened using genomic, transcriptomic, and degradation product analyses. Thereinto, the glutathione peroxidase GPx with exposed active sites catalyzed the LDPE depolymerization with the cooperation of its dissociated superoxide anion radicals. Furthermore, an LDPE degradation model involving multiple enzymes was proposed. The present study identifies a novel PE-degrading enzyme (PEase) for polyethylene bioremediation and promotes the understanding of LDPE degradation.

Metagenomic exploration of microbial and enzymatic traits involved in microplastic biodegradation

Agricultural mulch films are frequently applied to achieve high yield, resulting in large quantities of microplastic (MP) pollution in agroecosystem. However, studies focusing specifically on the diversity of MP-degrading enzymes and related microbial communities have yet to be conducted. Here, we established a soil microcosmic incubation with addition of 5% (w/w) conventional (low-density polyethylene (LDPE)) and biodegradable (blend of polylactic acid (PLA) and polybutylene adipate terephthalate (PBAT)) MPs for incubation 90 days. The DNA samples extracted from soils and plastisphere of MPs were examined by metagenomics and genome binning methods, specifically targeting carbohydrate-active enzymes (CAZymes) and plastic-degrading enzymes (PDZymes). The results revealed that plastisphere of MPs exhibited significantly distinct patterns of CAZymes and PDZymes from soils, and abundances of all examined exoenzymes were higher in plastisphere than those in soils. Plastisphere of LDPE-MPs selectively enriched proteases and alkane monooxygenase (alkB), and required families of carbohydrate-binding module (CBM) to increase the binding of CAZymes with MPs. Dissimilarly, diverse CAZymes with high abundances were observed in the plastisphere of PBAT-PLA MPs and esterases were important indicative PDZymes for PBAT-PLA degradation. The enriched exoenzymes in plastisphere of LDPE-MPs were mainly assigned to Actinobacteria while Proteobacteria with higher abundance in plastisphere of PBAT-PLA MPs containing most indicative exoenzymes. Moreover, a high-quality genome classified as Amycolatopsis japonica was reconstructed and found to contain one or more gene copies of indicative exoenzymes for polyethylene. Two novel genomes classified as Sphingomonas were selectively enriched in plastisphere of PBAT-PLA MPs and contained diverse genes encoding degrading exoenzymes. Taken together, our study highlighted the CAZymes and PDZymes can be exploited as potent microbial strategies for solving MPs pollution in croplands.

Identification of rare microbial colonizers of plastic materials incubated in a coral reef environment

Plastic waste accumulation in marine environments has complex, unintended impacts on ecology that cross levels of community organization. To measure succession in polyolefin-colonizing marine bacterial communities, an in situ time-series experiment was conducted in the oligotrophic coastal waters of the Bermuda Platform. Our goals were to identify polyolefin colonizing taxa and isolate bacterial cultures for future studies of the biochemistry of microbe-plastic interactions. HDPE, LDPE, PP, and glass coupons were incubated in surface seawater for 11 weeks and sampled at two-week intervals. 16S rDNA sequencing and ATR-FTIR/HIM were used to assess biofilm community structure and chemical changes in polymer surfaces. The dominant colonizing taxa were previously reported cosmopolitan colonizers of surfaces in marine environments, which were highly similar among the different plastic types. However, significant differences in rare community composition were observed between plastic types, potentially indicating specific interactions based on surface chemistry. Unexpectedly, a major transition in community composition occurred in all material treatments between days 42 and 56 (p < 0.01). Before the transition, Alteromonadaceae, Marinomonadaceae, Saccharospirillaceae, Vibrionaceae, Thalassospiraceae, and Flavobacteriaceae were the dominant colonizers. Following the transition, the relative abundance of these taxa declined, while Hyphomonadaceae, Rhodobacteraceae and Saprospiraceae increased. Over the course of the incubation, 8,641 colonizing taxa were observed, of which 25 were significantly enriched on specific polyolefins. Seven enriched taxa from families known to include hydrocarbon degraders (Hyphomonadaceae, Parvularculaceae and Rhodobacteraceae) and one n-alkane degrader (Ketobacter sp.). The ASVs that exhibited associations with specific polyolefins are targets of ongoing investigations aimed at retrieving plastic-degrading microbes in culture.

Call for biotechnological approach to degrade plastic in the era of COVID-19 pandemic

Plastic pollution is a global issue and has become a major concern since Coronavirus disease (COVID)-19. In developing nations, landfilling and illegal waste disposal are typical ways to dispose of COVID-19-infected material. These technologies worsen plastic pollution and other human and animal health problems. Plastic degrades in light and heat, generating hazardous primary and secondary micro-plastic. Certain bacteria can degrade artificial polymers using genes, enzymes, and metabolic pathways. Microorganisms including bacteria degrade petrochemical plastics slowly. High molecular weight, strong chemical bonds, and excessive hydrophobicity reduce plastic biodegradation. There is not enough study on genes, enzymes, and bacteria-plastic interactions. Synthetic biology, metabolic engineering, and bioinformatics methods have been created to biodegrade synthetic polymers. This review will focus on how microorganisms' degrading capacity can be increased using recent biotechnological techniques.

Assembly strategies for polyethylene-degrading microbial consortia based on the combination of omics tools and the "Plastisphere"

Numerous microorganisms and other invertebrates that are able to degrade polyethylene (PE) have been reported. However, studies on PE biodegradation are still limited due to its extreme stability and the lack of explicit insights into the mechanisms and efficient enzymes involved in its metabolism by microorganisms. In this review, current studies of PE biodegradation, including the fundamental stages, important microorganisms and enzymes, and functional microbial consortia, were examined. Considering the bottlenecks in the construction of PE-degrading consortia, a combination of top-down and bottom-up approaches is proposed to identify the mechanisms and metabolites of PE degradation, related enzymes, and efficient synthetic microbial consortia. In addition, the exploration of the plastisphere based on omics tools is proposed as a future principal research direction for the construction of synthetic microbial consortia for PE degradation. Combining chemical and biological upcycling processes for PE waste could be widely applied in various fields to promote a sustainable environment.