# Microbial Depolymerization of Epoxy Resins: A Novel Approach to a Complex Challenge
## 4 Discussion  
Overall, the results concerning the microcosms experiment are not sufficient to assess the potential of the tested fungus for the depolymerization of epoxy samples. Nevertheless, contact angle measurements showed that the fungus _G. adspersum_ might be able to decrease the hydrophobicity of the epoxy surface more efficiently than the other tested conditions (untreated, UV treated and soil). This is an interesting result; _G. adspersum_ is a withe-rot fungus, able to degrade lignin [35]. It is widely recognized that this phenolic compound is synthetized by plants for protection and structural purposes and it is composed by a strong hydrophobic meshwork [36]. However, fungi that are able to degrade lignin overcome this issue by the production of oxidative extracellular enzymes, able to attack this compound, such as peroxididases (lignin peroxidase and manganese peroxidase) and phenol oxidases (e.g., lacases). Therefore, it can be supposed that one or more of these enzymes could have partially oxidized the epoxy surface and reduced its hydrophobicity. On the other hand, the data on the microbiological water allowed us to acquire more knowledge on the underexplored field of microbial depolymerization of epoxy-related materials. Indeed, as previously described, ESEM analysis revealed an intense microbial colonization on the surface of the older epoxy samples composed of microbes with different sizes and shapes. To the best of our knowledge, this is the first description of an abundant microbial colonization of a pure epoxy material in fresh water. In fact, very little is known on the microbial colonization and depolymerization of solid epoxy materials. Experimental evidence has described microbial colonization of epoxy varnish in marine water [17], revealing that, in the presence of _Pseudomonas putida_, the corrosion resistance of the coating was lower than in the samples just with marine water. [PERSON] et al. (2015) [19] investigated the microflora responsible for the deterioration of an epoxy statue exposed to outdoor conditions. Through a culture-independent approach, _Chloorella angustoellipsoidea_ was detected. This is a green algal microorganism, often associated with lichen [19]. The size and shape of these green algae show close similarity to those detected on the surface of the epoxy samples analyzed after more than 3 years in the microbiological water. Mineral aggregates were also discovered in this water, and these could be the results of microbial metabolisms. Indeed, biogenic mineral precipitation is a common ability of microbes. For instance, [PERSON] et al. (1991) [37] reported that fungi and bacteria from desert soil were able to precipitate calcite, the most abundant CaCO\({}_{3}\) polymorph, when cultured in Ca-rich media. Experimental evidences demonstrated that bacteria isolated from cave environments were able to precipitate CaCO\({}_{3}\), producing three polymorphs--aragonite, calcite and vaterite [38]. Similarly, experimental evidence reported that some ureolytic bacteria isolated from sludge and calcareous soil precipitated crystals of CaCO\({}_{3}\) in an enzymatic reaction catalyzed by ureases and carbonic anhydrases [39; 40]. According to [PERSON] et al. (2010) [38], biogenic CaCO\({}_{3}\) formation is a fundamental defensive mechanism induced by microbes in order to prevent toxic effects and cell death provoked by excess of Ca in soil. Hence, one possible interpretation is that the microbes present in the microbiological water were precipitating CaCO\({}_{3}\) to decrease the concentration of this ion in the medium. In fact, IC analysis of the water revealed that Ca was the most abundant ion in this environment (28.6 g/L, Supplementary Table S1). However, carbonate is not the only Ca-containing mineral involved in microbial metabolisms. It is well known that microbes are able to both produce [41; 42] and dissolve [41; 43; 44] calcium oxalates.