## 3 Results
### Comparative Analysis of the Microbial Structure
#### 3.2.2 Sediment Associated Microbial Communities  
Lake Alboraj sediment bacterial communities presented the lowest diversity regarding bacterial taxa. The sequencing clustered a total of 28 phyla, 58 classes, 94 orders, 117 families and 109 genera. Most of the genera were unknown or uncultured. At the phylum level, Proteobacteria (55%), Actinobacteria (19%) and Firmicutes (10%) comprised the overall structure, accounting for 84% of relative abundance (Figure 2). Within Proteobacteria classes, _Gammaproteobacteria_ (48%) was the dominant, which was related to sulphur cycleprocesses. Moreover, _Alphaproteobacteria_ and _Deltaproteobacteria_ (4% and 3%, respectively), which are related to nitrate reduction and sulphur cycle, completed the main phylum. In addition to the Proteobacteria members, representative of the Actinobacteria phylum, were observed. Actinobacteria, the second phylum, was almost dominated by members of _Actinobacteria_ class (17%). Firmicutes, the third most abundant phyla, was formed by _Bacilii_ members (7%).  
The most abundant family within the bacterial community (Figure 3) was _Pseudomonasaceae_, a _Gammaproteobacteria_ with 26% of the total population. _Pseudomonadaceae_ is closely reported to nitrogen cycling, including some species which have been reported to be able to perform aerobic or anaerobic denitrification processes commonly by nitrate-reduction or nitroaromatic compound degradation (i.e., fertilisers, pesticides) [34; 35]. In addition, _Burkholderiaceae_ family, with a 10% of relative abundance, has been reported to manage widespread adaptation to different ecological niches and can also perform very diverse metabolic functions (i.e., nitrogen fixation, aromatic compound catabolism) [36]. Other _Gammaproteobacteria_ member with a 9% of relative abundance was _Moraxellaceae_ family, which has saprophytic capacities. The members of this family have been described as active agents in decomposition and subsequent mineralisation of organic matter present in the environment [37]. In addition, although it is not a family related to nitrogen-cycle, some of its genera have been reported to be related to nitrate-reducing processes [38].  
The Actinobacteria relatives present in Lake Alboraj sediment clustered mainly in the recent described _Propionibacteriumae_ family, accounting 16% of relative abundance of the total. Remarkably, its metabolic properties are monospecific, however, its metabolic functionality may change whether new species were included [39]. On the other hand, a well-known _Alphaproteobacteria_ member was _Rhodobacteraceae_. This family is characterised by its metabolic multifunctionality on sulphur and carbon cycles, as well as the symbiotic association with other microorganisms [30], which makes it can be found widespread distributed throughout the lake. The noteworthy function of the family is the oxidation of sulphur, its simple compounds (sulphide, thiosulphate) or sulphate (in some cases) to obtain a carbon source [30]. Elemental sulphur is usually the end product of its metabolism. Another significant finding is the abundance of _Flarobacteriaceae_ members, which is mainly particle-associated and strongly dependent on the availability of organic matter [24; 40].