## 4 Discussion
Moreover, several studies have shown that many bacterial species of Bacillus (B. pumilus, B. licheniformis, keratinocyte Bacillus cereus), Sporocytophaga (S. myxococcus), Cytophaga (C. hutchinsonii), Pseudomonas (P. fluorescens var.cellulosa), Clostridium (C. cellulolytica), and Pandorae (P. norimbergensis) can also use cellulose as a source of carbon and produce cellulase for its degradation [5; 7; 51; 58]. Indeed, many species of Flavobacterium may be involved in the degradation of recalcitrant molecules (like lignocellulosic compounds) of organic matter [57]. In addition, actinomycetes are essential agents in the degradation of lignocellulosic; their ability to degrade cellulose and lignin is not as great as that of fungi, but they are involved in the decomposition of cellulosic compounds present in organic matter [35]. Indeed, NGS demonstrated that in the compost samples, there were many species belonging to the Actinobacteria phylum capable of degrading cellulose compounds. Among them, many species of _Micromonospora_ (_M. melanospora_) and thermophilic filamentous bacteria _Thermobifida_ (_T. fusca_ and _T. cellulolytica_) which possess cellulose and lignin degrading capabilities were recorded. They equally use cellulose for growth [7; 59]. Various strains of _Cellulomonas_ (_C. flavigena_ and _C. uda_) were reported to produce high yields of cellulase on cellulosic substrates: at least six endoglucanases and one exoglucanase. In addition, several species of _Streptomyces_, such as _S. reticul_ and _S. thermocarboxylus_, are able to degrade cellulose and hemicelluloses by oxidizing and solubilizing lignin components [60]. The study of microbial communities by NGS makes it possible to highlight the role they play in the transformations of cellulase activity which occur throughout the process, and has made it possible to explain the evolution of this activity in relation to the microbial concentration obtained. Indeed, the evolution of the microbial activity of compost C revealed a relative abundance of microflora compared to fungi, which confirms the NGS results; therefore, the production of cellulase could be owing not only to fungi but also to bacteria and actinomycetes. This global identification by NGS of the microbial community allows us to understand the progress of organic matter degradation. This technique makes it possible to identify several kinds of microorganisms that are involved in cellulose degradation by the production of cellulases, as well as acid/alkaline phosphatases involved in phosphate solubilization. Phosphate is an essential nutrient for plant growth. In the environment, it is found in two major forms: inorganic phosphate (Pi) that is mainly complexed with other minerals such as iron (Fe) and aluminum (Al), calcium (Ca), and magnesium (Mg), and organic phosphate (Po), which is largely immobilized in organic matter and decomposition residues. However, not all phosphate is in a bioavailable form for the roots [8]; indeed, plants are only able to assimilate H\({}_{2}\)PO\({}_{4}\)\({}^{-}\)[61]. Composting is considered to be a treatment based on the activities of the two main classes of microorganisms, bacteria and fungi. They have an ability to solubilize phosphate via their enzymatic system (acid and alkaline phosphatases). Moreover, several studies in this context have shown that phosphatase activities are clearly related to the respiratory patterns of microorganisms [8; 62]. In fact, it was shown that an increase in the concentration of phosphates is related to organic matter degradation, which is mainly owing to the activity of microorganisms throughout the duration of the treatment [8; 63]; this could explain the important phosphatase activities at the beginning and then their decrease, which is in agreement with statistical analysis showing that the phosphatase activity is positively correlated with the microbiota activity (Table 4).