## 4 Discussion
### Microbial Communities' Characterization
The genus _Hyphomicrobium_, from _Hyphomicrobiaceae_ family are linked to degradation of a variety of phenolic compounds [113] more specifically to NP degradation in lab-scale column soil [114] and in sludge at lab condition [115]. Based in these reports and in the presence of this genus among the \"specialist genera\" in systems doped with NP and OP in the present study, this genus probably played an important role in the NP and OP degradation. As previous mention, PCP can affect the structure of the microbial community. For instance, [PERSON] et al. [83] reported changes in aerobic granular sludge microbial community but only at PCP concentrations between 100 and 200 \(\upmu\)g\(\cdot\)g\({}^{-1}\), with no changes below 100 \(\upmu\)g\(\cdot\)g\({}^{-1}\). In the present study, the comparison of substrate exposed to doped stream water with that of control systems, indicated that several specialist genera were enriched following exposure to the chlorophenol compound, suggesting a growth benefit for target compounds biodegradation. The three more abundance genera in doped samples were: _Denitomonas (Rhodocyclaceae_ family), _Xenococcus_P PCC_7305_ (_Xenococcusaceae_ family) and _Rhodocyclaceae_uncultured (Rhodocyclaceae_ family). Members of the _Rhodocyclaceae_ family have been described to use organic pollutants as a food source [107] and have a prominent role in the degradation of aromatic compounds such as toluene [116], benzene [117], quinoline [118] and PAHs [119; 120], including pyrene [121] and phenanthrene [122]. Important genes in PAH biodegradation, PAH-specific dioxygenase genes, are found in this bacterial family [122], showing anaerobic pathway for aromatic degradation that includes the benzyl-succinate synthase genes and central benzoyl-CoA reductase in _Dechlomonas_ genus [123]. This bezoyl-CoA reductase is an important enzyme in pathway PCP degradation [124; 125]. According to [PERSON] et al. [126], the _Dechlomonas_ genus is associated with PCP anaerobic degradation process. The biodegradation of PCP can occur by different processes: hydroxylation, oxygenolysis and reductive dichloromethane [127; 128]. Moreover, the intermediates of PCP metabolism indicated that carbon ring-cleavage had taken place after dichloromethane process [126]. In the PCP degradation, two important steps for ring-cleavage, including hydroxylation and carboxylation, can occur [129]. Microorganisms belonging to the family of _Rhodocyclaceae_, i.e., _Azoarcus_ or _Thauera_ genus [130; 131] can act as the degraders into these two steps [126]. Therefore, the _Denitromonas_ genus may have had an important role in degradation of PCP in this work. The _Xenococcus_PCC_7305 from _Xenococcusaceae_ family is the cyanobacteria species with higher proportion in the group of \"specialist genera\". There is no information about the _Xenococcus_ sample (_Nostocales_ order) being associated to degradation of organic compounds. Sometimes cyanobacteria do not have a direct role in the degradation process, but cyanobacteria exudates can provide an endogenous source of growth substrates to bacteria [131], promoting degradation of contaminants. Regarding _Archaea_, which represented only 1-2% of the global microbial community, the phylum with more representation was _Thuamarchaeota_ (_Nitrososphaeria_ class). This phylum has shown an important role in nitrification process [131], as well as the capacity to aerobically degrade of crude oil [130]. However, no information is available regarding their possible role in alkylphenol and/or chlorophenol compounds degradation.