# A Snapshot of the Microbiome of a Portuguese Abandoned Gold Mining Area
## 1 Introduction
As for fungi, studies have mainly focused on the community structure associated with soil, boreal species colonizing mine tailings, the arsenic impact on the molecular diversity of arbuscular mycorrhizal and filamentous fungi, and some heavy metal tolerance traits (e.g., arsenic resistance) [28; 29; 31; 34]. Nonetheless, there is still a lack of studies simultaneously focusing on prokaryotic and fungal communities in these settings. Furthermore, given that numerous mines experience flooding during and after operations, the knowledge in these cases is notably much more constrained [39]. Additionally, the settings in these areas can also lead to the formation of acid mine drainage (AMD) ecosystems. These are a result of the slow oxidation of pyrite and other sulfide minerals exposed to air and oxygenated water, being often accelerated by microorganisms with oxidation abilities [40; 41]. When these minerals are exposed to oxygen and water through mining activities, they can undergo chemical reactions (oxidation and hydrolysis) that produce sulfuric acid. Similarly to general gold mine scenarios, while numerous studies on AMD bacteria and archaea are available, few have been conducted focusing on fungi, particularly with modern molecular biology techniques [40; 41]. During the past years, the development, optimization and implementation of DNA-based methods to study microbial communities has revolutionized modern microbiology and microbiome analysis. The application of high-throughput sequencing (HTS) next-generation sequencing (NGS) approaches has deeply expanded the possibility to extensively characterize microbial communities [42; 43; 44; 45; 46; 47; 48] while also contributing to understanding their metabolic functions and their active byproducts in a particular environmental context. During the last decade, Portuguese areas long known to be rich in Au, silver (Ag), Cu Zn, iron (Fe), W and lithium (Li) have been the focus of a fresh wave of interest. Nonetheless, so far, the study of the structural and functional microbiomes of Portuguese gold-rich areas has been largely neglected. Abandoned mining areas are recognized as extreme environments due to the consequences of auriferous removal, including increased concentrations of heavy metals, metalloids and other toxic elements. Flooded mines also pose additional challenges for microbial proliferation since the availability of organic matter, oxygen and light in these settings is often limited [39]. As there is still no record of the structural and functional microbiomes of Portuguese gold-rich areas, the aim of this work was to gather information regarding the bacterial and fungal communities in an abandoned gold mining area across areas without a history of mining activities, the mine tailings and the flooded mine interior. For that, we employed culture-independent methodologies (Illumina MiSeq(r) (Illumina, San Diego, CA, USA) 165 rRNA gene and Internal Transcribed Spacer 2 subregion targeted metabarcoding sequencing) coupled with differential bioinformatic analysis to profile these communities and their functional/ecological traits at various locations of the Escadia Grande mining complex (Gois, Portugal).