Abstract
In recent years, natural thermal mineral waters have been gaining the special attention of the scientific community, namely in the prevention and treatment of some diseases, due to the microbial properties that exist in these habitats. The aim of this work was to characterize the physicochemical composition and the microbial taxonomic communities present in three thermal waters of the Galician region in Spain and two samples of the northern region in Portugal. These collected water samples were analyzed for physicochemical characterization and the respective hydrogenome of the waters using next generation sequencing together with 16S rRNA gene sequencing. The sequencing showed a high diversity of microorganisms in all analyzed waters; however, there is a clear bacterial predominance of Proteobacteria phylum, followed by Firmicutes, Deinococcus-Thermus, Aquificae and Nitrospira. The main physicochemical parameters responsible for the clustering within the Spanish waters were sulfur compounds (SO32− and S2−), CO32− and neutral pH, and in the Portuguese waters were Mg, Ca and Sr, nitrogen compounds (NO3− and NH4+), Na, Rb, conductivity and dry residue. This work will allow for a better understanding of the microbial community’s composition and how these microorganisms interfere in the physicochemical constitution of these waters often associated with medicinal properties. Furthermore, the hydrogenome may be used as an auxiliary tool in the practice of medical hydrology, increasing the likelihood of safe use of these unique water types.
Highlights
Water is considered the basis for biodiversity on our planet, it is part of all life processes and it has a primordial function in the existence of life as we know it [1]
Higher temperatures favor the appearance of more mineralized water [7], water PT_SA has very high mineralization values even though it is a water with a low emergency temperature (15 ◦C), which may be related to the fact that emergency temperature is often much lower than the maximum temperature reached in the reservoir, as it decreases along the ascending hydraulic circuit [33,53]
According to European legislation, water with a ≤50 mg/L dry residue is classified as hyposaline or very little mineralized, 50–500 mg/L is low mineralized, 500–1500 mg/L is classified as mineralized water and water with dry residue above 1500 mg/L is classified as hypersaline, presenting strong mineralization [54]
Summary
Water is considered the basis for biodiversity on our planet, it is part of all life processes and it has a primordial function in the existence of life as we know it [1]. Over time, humans began to observe the beneficial effects that some waters had on health, these waters became known as the thermal waters and some civilizations even attributed to them a strong religious and sacred character [5,6,7]. According to the European Directive 2009/54/EC, natural mineral waters are defined as microbiologically wholesome and originated from an underground water table or deposit, emerging from a natural spring or bore These waters are characterized by nature (mineral content and trace elements, among others) and original purity. These water characteristics can confer beneficial effects to health, considering the assessment of the main following parameters, such as physicochemical, microbiological (absence of pathogenic microorganisms and parasites), hydrological and geological [11]
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