Hsueh, S. W. | Search bioRxiv

bioRxiv2025

Mesophilic compostability of polylactic acid and the associated microbiome as revealed by metagenomics

Polylactic acid (PLA), the most popular bioplastic, has high sustainability potential as it is bio-sourced and also harbors biodegradability. A form of its biodegradability is via composting, and it was previously established that thermophilic temperatures are needed for PLA breakdown in composts. Here we report the development of composts that have overcome the temperature requirement needed for PLA composting. Our mesophilic composts exhibited clear PLA biodegradability, and this is due to specific biological activity enriched in our material. To investigate the nature of this mesophilic activity, we conducted metagenomics analysis to reveal the microbial composition and enzyme-coding potential associated with PLA biodegradation. These efforts revealed multiple enzyme subtypes with strong enrichment on PLA surfaces in our trained composts, and the top candidate was a type of hydro-lyase, an enzyme that can cleave carbon-carbon and carbon-oxygen bonds, both present in the chemical structure of PLA, in the absence of water. Hydro-lyases represent a novel class of enzymes that could facilitate PLA degradation, and our results point to the model that the combinatorial action of multiple types of enzymes is what drives PLA biodegradation and how the temperature barrier for PLA composting is overcome.

microbiology↗

bioRxiv2022

Polystyrene-colonizing bacteria are enriched for long-chain alkane degradation pathways

One of the most promising strategies for the management of plastic waste is microbial biodegradation, but efficient degraders for many types of plastics are still lacking, including for polystyrene (PS). Genomics has emerged as a powerful tool for mining environmental microbes that may have the ability to degrade different types of plastics. In this study, we use 16S sequencing to analyze the microbiomes for multiple PS samples collected from sites with different vegetation in Taiwan to reveal potential common properties between species that have exhibit growth advantages on PS surfaces. Phylum enrichment analysis identified Cyanobacteria and Deinococcus-Thermus as being the most over-represented groups on PS, and both phyla include species known to reside in extreme environments and could encode unique enzymes that grant them properties suitable for colonization on PS surfaces. Investigation of functional enrichment in PS-enriched species highlighted carbon metabolic pathways, especially those related to hydrocarbon degradation. This is corroborated by the finding that genes encoding long-chain alkane hydroxylases such as AlmA are more prevalent in the genomes of PS-associated bacteria. Our analyses illustrate how plastic in the environment support the colonization of different microbes compared to surrounding soil. In addition, our results point to the possibility that alkane hydroxylases could confer growth advantages of microbes on PS.

microbiology↗