# A Snapshot of the Microbiome of a Portuguese Abandoned Gold Mining Area
## 4 Conclusions  
In summary, we conducted an analysis of the microbiome (bacterial and fungal communities) diversity, structural organization and metabolic/ecological traits in an abandoned Portuguese gold mining area with metabarcoding and bioinformatic analysis. We found that the overall microbiome diversity decreases inside the mine and the tailings contrastingly for prokaryotic and fungal communities when compared with an area without previous mining activities. Prokaryotes displayed a relatively homogeneous taxa distribution, while fungi displayed the presence of some dominant taxa. Moreover, fungi exhibit a more notorious site-specific nature with a less demarked core microbiome. The predicted bacterial metabolic profiles exhibited differences when considering the control, the tailings and mine areas, establishing a shift from carbohydrate metabolism and lignin degradation towards metabolic profiles closely associated with defense pathways and responses to environmental stress (cell cycle maintenance and repair, energy production, xenobiotic biodegradation and other secondary metabolic pathways). Moreover, the fungal community's ecological characteristics were largely dominated by saprobes. Nevertheless, the tailings also displayed multiple peculiar associations with fungi able to deal with sugar-rich and pollen substrate preferences. Thus, this work provides an initial picture of the microbiomes at these sites, and further research is necessary to gain a deeper insight into their microbial ecology and the microbiome's physiological and metabolic characteristics. For instance, further studies (e.g., cultivation-dependent methodologies) on the extremophilic consortia could be focused on the identification of metal bioremediation abilities, biosynthesis of gold nanoparticles capacities, or even in gold biorecovery strategies (e.g., [91; 92; 93; 94; 95; 96; 97; 98]). On the other hand, further studies employing additional -omics methodologies, such as metagenomics and metatranscriptomics, would also be advantageous since these could further allow gaining a deeper knowledge regarding these areas' microbiome composition, functional characterization, genomic description, metabolic potential, mobilome, resistance and community dynamics (e.g., [99]). Lastly, cultivation-dependent methods could also contribute to the description of novel species since extreme environments have been highlighted as requiring further studies in this regard (e.g., [100]). We hope this work can draw further attention to the study of Portuguese gold mining areas and promote additional research on microbes thriving in these extreme environments. The following supporting information can be downloaded at [[https://www.mdpi.com/article/10.3390/app14010226/s1](https://www.mdpi.com/article/10.3390/app14010226/s1)]([https://www.mdpi.com/article/10.3390/app14010226/s1](https://www.mdpi.com/article/10.3390/app14010226/s1)), Files S1-S6: Krona charts exhibiting the overall bacterial and fungal diversity found across the distinct samples; Figure S1: Bacteria biplot PCA results; Figure S2: Fungi biplot PCA results. Conceptualization, J.T. ; methodology, J.T., F.S. and D.S.P. ; formal analysis, J.T. ; investigation, J.T., F.S. and D.S.P. ; resources, J.P. and A.P. ; writing--original draft preparation, J.T. ; writing--review and editing, all authors; supervision, J.P. and A.P. ; funding acquisition, A.P. All authors have read and agreed to the published version of the manuscript. **Funding:** This work was carried out in the R&D Unit Centre for Functional Ecology--Science for People & the Planet (CFE) and Associate Laboratory TERRA, with references, respectively, UIDB/04004/2020 and LA/P/0092/2020, financed by FCT/MCTES through national funds (PIDDAC). The authors also thank the funding of PRR--Recovery and Resilience Plan and by the NextGeneration EU European Funds.