Abstract
Epoxy resins are among the most important polymeric substances in the thermosetting category with a critical role in composite materials. These resins Epoxy resins from petroleum-derived monomers have exceptional characteristics, including tensile strength, elevated stiffness, and outstanding electrical strength, which makes them a preference material in industrial sectors such as aerospace, construction, and automotive. However, their highly crosslinked structure severely limits reprocessing and recycling options, leading to environmental accumulation. Addressing this challenge, the EU-funded ESTELLA project (Project No. 101058371, Call: HORIZONCL4-2021-RESILIENCE-01-11) explores the potential microbial degradation of epoxy resins.
As a first approach in the EU-funded ESTELLA Project, different bacteria associated to a milled commercial epoxy matrix (HexFlow® RTM 6) were isolated. These bacteria were identified via MALDI-TOF MS (Bruker Biotyper) characterization, and their taxonomic classification was confirmed by 16S rDNA sequencing. One bacterium that was repetitively isolated from different epoxy resins samples was identified as Pseudomonas putida ULE23_002. The whole genome sequencing of this strain using MiniON and Illumina technologies revealed that it is composed of a circular chromosome of 6.59 Mb containing 6,065 putative coding sequences and with a GC content of 61.8%. Isogenic P. putida strain was cultured in a minimal medium containing samples of milled RTM 6 resin as only possible carbon and energy sources. Surprisingly, this strain survived for more than two months of incubation.
However, no significative increase in the CFUs from the culture was observed. On the other hand, scanning electron microscopy of the solid RTM 6 particles showed cells attached to the surface forming a biofilm. The adaptation and survival mechanisms of this strain on the epoxy substrate are being analyzed using multi-omics approaches, including label-free proteomics and transcriptomics (RNAseq).
Our findings shed light on the strain’s unique metabolic strategies to cope with and possibly degrade recalcitrant epoxy compounds. These results pave the way toward bio-assisted recycling processes for thermoset composites, highlighting the role of environmental isolates with metabolic flexibility.