Enriched microbial consortia from natural environments reveal core groups of microbial taxa able to degrade terephthalate and terphthalamide

Abstract

Millions of tons of polyethylene terephthalate (PET) are produced each year, however only ~30% of PET is currently recycled in the United States. Improvement of PET recycling and upcycling practices is an area of ongoing research. One method for PET upcycling is chemical depolymerization (through hydrolysis or aminolysis) into aromatic monomers and subsequent biodegradation. Hydrolysis depolymerizes PET into terephthalate, while aminolysis yields terephthalamide. Aminolysis, which is catalyzed with strong bases, yields products with high osmolality, which is inhibitory to optimal microbial growth. Additionally, terephthalamide, may be antimicrobial and its biodegradability is presently unknown. In this study, microbial communities were enriched from sediments collected from five unique environments to degrade either terephthalate or terephthalamide by performing biweekly transfers to fresh media and substrate. 16S rRNA sequencing was used to identify the dominant taxa in the enrichment cultures which may have terephthalate or terephthalamide-degrading metabolisms and compare them to the control enrichments. The goals of this study are to evaluate (1) how widespread terephthalate and terephthalamide degrading metabolisms are in natural environments, and (2) determine whether terephthalamide is biodegradable and identify microorganisms able to degrade it. The results presented here show that known contaminant-degrading genera were present in all the enriched microbial communities. Additionally, results show that terephthalamide (previously thought to be antimicrobial) was biodegraded by these enriched communities, suggesting that aminolysis may be a viable method for paired chemical and biological upcycling of PET.

Fig 1. Observed richness for each substrate over the course of four transfers performed bi-weekly.

The overall trend shows decreasing median diversity with each transfer for each treatment. Each box represents 15 samples (5 environments x 3 replicates).

Fig 2. Unifrac Principal Coordinates Analysis of all samples.

(A) All samples from all time points and all sediments sources are displayed on a single panel to visualize larger trends in clustering, (B) Figure is shown divided into separate panels based on inoculum source and transfer number. Both panels show clustering based on Substrate (represented by color). Replicates are separate microcosm lines.

Fig 3. Taxa plot showing class level classification for the fourth (final) transfer for each substrate.

Bars show the mean relative abundance of each taxon in three replicates across all five inoculum sources. A. Mean relative abundance of each taxon across the five environments. B. Mean relative abundance of each taxon across all replicates for each environment.

Fig 4. Select highly abundant genera present at more than 10% relative abundance in at least one sample.

Y-axis shows relative abundance, box and whisker plots show distribution of data. Only data from the fourth transfer is shown. Abbreviations: terephthalamide (TA), terephthalate (TPA).

Fig 5. Differential abundance analysis showed that 47 ASVs were enriched on terephthalamide and 111 ASVs were enriched on terephthalate, relative to the rest of the data set.

Only genera which were present at >10% relative abundance in at least one sample are shown. Genera with multiple ASVs identified as differentially abundant are shown as separate boxes.

Fig 6. Relative abundance of key genera across environments and transfers by substrate.

Fig 7. High performance liquid chromatography quantification of the remaining terephthalamide in one sample from each environment and transfer.

Starting concentration was 5 g/L. Measured starting concentration is represented by the first column on the left. Each bar represents the mean of one replicate from each of the four transfers in each environment (n = 4) or the starting concentration (n = 3).

Fig 8. High performance liquid chromatography quantification of the remaining terephthalate in one sample from each environment and transfer.

Starting concentration was 10 g/L. Measured starting concentration is represented by the first column on the left. Each bar represents the mean of the three replicates in each of four transfers in each environment (n = 12) or the starting concentration (n = 3).