# Microbial Depolymerization of Epoxy Resins: A Novel Approach to a Complex Challenge
###### Abstract
Comparisons with abiotic controls suggested that microbial degradation of the epoxy occurred [17], possibly by oxidation of hydroxyl to the intermediate carbonyl (aldehyde). Another study investigated the effect of a fungal consortium composed of _Aspergillus versicolor_, _Cladosporium cladosporioides_ and _Chatonium_ sp. on the quality of CFRP composites [18]. The tested fungal consortium was able to grow on and penetrate this material [18]. The fungal and bacterial microflora responsible for the deterioration of an epoxy statue was also investigated [19]. Culture-dependent and -independent techniques revealed a microbial community composed of typical rock-inhibiting microbes, algal photobitons, such as _Tebouxia_ spp., _Chloroidium ellipsoidaeum_ and _Chlorella angustoellipsoidea_, and _Cyanobacteria_, such as _Leptolynghya_ sp., _Phormidium_ sp., _Cylindrosperum stagnale_, _Hassallia byssoidea_ and _Geitlerinema_ sp. Black yeasts related to the species _Friedmanniomyces endolithcus_, _Pseudotaeniolina globosa_, _Phaeococcococc catenatus_ and _Catenulostroma germanicum_ were also detected. As previously stated, few studies focus on the microbial biodegradation potential for epoxy, and only one set out with the purpose of recycling this recalcitrant synthetic polymer. Experimental evidence demonstrated that the bacteria _Rhodococcus rhodochrous_ and _Ochrobactrum anthropi_ were able to degrade Araldiite(r) epoxy resin when incubated in co-culture [20]. These bacteria were able to use the resin as a carbon source with possible degradation pathways by oxidation of the methyls in Bisphenol A, followed by decarboxylation. Regarding the biodegradation of epoxy resins, it can be summarized that, even though the literature provides some evidence, the general microbial behavior on this substrate and the different reactions involved in the microbial degradation of epoxy are still incompletely understood. Therefore, the objective of the present research project is the evaluation of the potential of microbes (fungi and bacteria) for developing a circular management of natural resourcesfor epoxy composites. The first approach was to investigate _Gandderma adsersum_, a fungus able to degrade wood, and its depolymerization abilities for epoxy samples incubated for 1, 3, 6 and 9 months in soil microcosms. In biotechnology, microbial metabolisms involved in wood degradation are often exploited. Indeed, fungi able to degrade lignin, and cellulose possesses really efficient oxidative enzymes able to degrade recalcitrant and xenobiotic compounds, such as pesticides, synthetic polymers and chlorinated aromatic compounds [21]. Lignin is a recalcitrant and complex polymer with a heterogeneous structure, composed of three different monomeric precursors (p-coumaryl alcohol, coniferyl alcohol and synapyl alcohol). Two classes of fungal enzymes are described to be mainly responsible for lignin degradation: peroxididases (lignin peroxidase and manganese peroxidase) and lacases [22]. These enzymes, generally called phenol oxidases, enable lignin degradation by different reactions causing the cleavage of the phenolic unit of this polymer. Epoxy resins are also composed of several phenolic units. This similarity makes these enzymes and microorganisms that are able to produce it--such as _G. adsersum_--good candidates for the degradation of epoxy. The second aim of this study was to evaluate the depolymerization potential of microbes naturally present on epoxy surfaces. Hence, additional analysis of microbial colonization and potential surface modifications was performed on epoxy samples incubated for 3 months and 3 years in microbiological water. Finally, isolation and identification of microbes from these environments were also carried out. Results obtained in this study provide new information in a relatively unexplored field. In a long-term prospective, microbes that are able to degrade epoxy might help scientists to develop a more sustainable and circular management of epoxy material, decreasing soil, water and atmospheric pollution.