# Microbial Depolymerization of Epoxy Resins: A Novel Approach to a Complex Challenge
## 4 Discussion
Oxalic acid is indeed a low molecular weight organic acid, frequently produced by microorganisms, with diverse roles in the microbial world, such as fungal wood degradation [45], microbial minerals weathering [46; 47], nutrients acquisition [47], metal tolerance [48; 49] and pathogenicity [50; 51]. Further analysis should precisely identify the chemical composition of these crystals, but their presence close and/or inside the discovered microbial biofilms suggest that this microbiome is active. This hypothesis is also supported by the abundant presence of biofilm on the surface of the analyzed samples, as well as the colonization of new samples incubated for three months in the same environment. Aiming to study the microbial composition of this microbiome and to obtain pure culture of microbes potentially able to depolymerize epoxy resin, isolation in selective media was performed. Four different microbes were identified. The first one was the fungus _T. hazardous_; organisms belonging to this genus are characterized by the ability to grow in different environments. This fungus was previously isolated from plants [52; 53], wet and flatlands [54] and marine environments [55; 56]. Some species of the genus _Trichoderma_ are studied for their abilities in biodegradation of organic pollutants such as cyanide [57], pesticides [56; 58], polycyclic aromatic hydrocarbons [59] and poly(lactic acid) [60]. The second one was _Aspergillus claudustus_, fungi belonging to this species can also be found both in outdoor [61; 62] and indoor environments [63; 64]. Strains of _A. calidoustus_ find applications in degradation of biodegradable plastics [65] and petroleum [66]. ER-BacA and ER-BacB were both identified as _Variovorax_ sp., and they had 99.61% sequence identity between each other. These bacteria are interesting because they have been described in several biodegradation applications. Some examples of compounds degraded by bacteria belonging to the _Variovorax_ genus are phytates [67], insecticides [68], arsenite [69] and m-nitrophenol [70]. The last bacterial isolate (ER-BacD) was identified as _Methylovestilis_ sp. This bacterium belongs to a recently discovered genus [71] and only three different species have been described so far. The bacteria belonging to this genus are characterized by the capacity to grow and feed on either single or multi-carbon sources such as organic acids, alcohols, aromatic compounds, methanol and methylamine [72]. Some examples of compounds biodegraded by isolates of the _Methylovestilis_ genus are methanol [73], ammonia-containing molecules [74] and herbicides [75]. The results of the phylogenetic analysis revealed that the closest strain to ER-BacD was _M. discipulorum_ FAM1, with a 99.62% of sequence identity, the first ever strain identified as _M. discipulorum_ that is able to grow in the presence of phenol, methoxyphenol and naphthalene [72]. Epoxy resins are composed of phenolic monomers. Therefore, the isolated strain of _M. discipulorum_ could be one of the microbes responsible for the surface modifications observed on the epoxy. It is well known that culturable microbes represent only a minimal fraction of the microbial world. Therefore, to obtain more complete information on the overall composition of the discovered microbial community, phylogenetic and metagenomic approaches, such as next-generation sequencing, should also be undertaken. In conclusion, the detected morphological modifications (holes and cracks) on the surface below the microbial cells also support the hypothesis that this microbial community is active and could be responsible for these modifications. This would imply that one or more microbes were able to partially depolymerize the epoxy. These are encouraging results, which would be strengthened by further research. In particular, the metabolic ability and the depolymerization capacity and pathways of pure cultures of isolated microbes, as well as of _G.