## 4 Discussion  
Composing is an important process that ensures the recycling of organic matter and its transformation into a stable matrix that can be used as soil amendment. This approach complies with the principles of circular bioeconomy, which is the basis of the development of the EU in the foreseeable future. The presence of plant nutrients in the sludge, makes composting even more valuable as a recycling technology. Here we applied the NGS method to characterize fungal communities of thermophilic and mesophilic habitats of biodegradable waste and sewage sludge during composting. Fungi are the microbes having great importance for organic matter decomposition and transformation in nature, and thus are involved in nutrient cycling and solubilization [4; 26]. The role of fungi involved in 'organics' decomposition is thought to be mostly restricted to the early decomposition stages because most endophytic fungi obviously depend on readily available sugars or easily degradable compounds such as cellulose [27]. _Chaetomidium arxii_ and _Chaetomium globosum_ have been analyzed to release different extracellular enzymes such as amylases, cellulases, esterases, lipases, proteases (gelatin and caseinase), pectinases, and cuticles [28]. Those saprophytic fungi primarily reside on plants, soil, straw, and dung. Endophyte _Chaetomium globosum_ assists in the cellulose decomposition of plant cells [29]. Figure 8: FCoA plot of metagenomic data based on Euclidean distance matrices of microbiomes of compost samples from thermophilic and mesophilic phases. Figure 7: Rarefaction curves of sequencing data from the samples, counting the number of OTUs in both compost samples. We found higher \(\beta\)-glucosidase activity in mesophilic habitats than in thermophilic ones (Figure 3), but at the same time a higher rate of respiration in thermophiles. [PERSON] and collaborators found a lower transcriptional efficiency and lower fungal \(\beta\)-glucosidaseasome abundance in thermophilic habitats compared to the bacterial communities [30]. [PERSON] and co-authors (2017) reported on \(\beta\)-glucosidase gene representation in the bacterial phyla _Firmicutes_, _Actinobacteria_, and _Proteobacteria_ and in fungal _Ascomycota_[31]. We found _Ascomycota_ and _Basidinycota_ as the predominant phyla in both phases. These results are consistent with previous studies [32; 33; 34]. Thermophilic enzymes are favorable for the hydrolysis of isoflavye glycosides since high temperatures enhance the mass transfer rate, reduce the substrate viscosity, and reduce the risk of contamination [35]. In addition, _Sarcinomyces petricola_ is amongst the most stress-resistant yeast known [36], and constitutive melanin synthesis from 1,8-dihydroxy naphthalene (1,8-DHN) monomers confers passive resistance toward environmental exposure to solar irradiation, dryness, temperature and pH extremes, hyperosmolarity, and even ionizing radiations [37]. Many of those fungi possess secondary metabolites, i.e. cell membrane-associated carotenoids and intracellular mycosporines and mycosporine-like amino acids. Most likely, adaptation to unfavorable conditions, active metabolism under mesophilic conditions, and a passive transport mechanism contribute to their distribution in the composted sludge. Current results showed higher fungal diversity of mesophilic species compared with the thermophilic phase.This is in accordance with previous investigations reported in the literature [8]. In addition, we found similar patterns of diversity between thermophilic and mesophilic fungi [4]. When the community succession passing to the thermophilic phase the dominance is taken over by the bacteria, especially in the late part of the phase. Early studies showed _Penicillium_ and _Aspergillus_ as the most dominant fungi during composing [38; 39]. The functionality of microorganisms' systems is closely related to the nature of organic compounds, their stability and properties at the given temperature and pH.