Abstract
The Euganean Thermal District has been known since Roman times for the therapeutic properties of peloids, obtained from natural clays that have undergone a traditional maturation process. This leads to the growth of a green microbial biofilm with Cyanobacteria and the target species Phormidium sp. ETS-05 as fundamental components for their ability to synthetize anti-inflammatory molecules. Currently, in-depth studies on the microbiota colonizing Euganean peloids, as in general on peloids utilized worldwide, are missing. This is the first characterization of the microbial community of Euganean thermal muds, also investigating the effects of environmental factors on its composition. We analysed 53 muds from 29 sites (Spas) using a polyphasic approach, finding a stable microbiota peculiar to the area. Differences among mud samples mainly depended on two parameters: water temperature and shading of mud maturation plants. In the range 37–47 °C and in the case of irradiance attenuation due to the presence of protective roofs, a statistically significant higher mud Chl a content was detected. Moreover, in these conditions, a characteristic microbial and Cyanobacteria population composition dominated by Phormidium sp. ETS-05 was observed. We also obtained the complete genome sequence of this target species using a mixed sequencing approach based on Illumina and Nanopore sequencing.
Highlights
Peloids are special muds or clays consisting of mineral and organic components generated by geological and biological, chemical and physical processes
53 samples were collected from 29 thermal spas situated in Abano, Montegrotto and Battaglia Terme (Figure 1A). pH, electric conductivity (EC), total dissolved solids (TDS) and temperature (T) of thermal waters flowing on the mature mud surface were measured during mud sampling at two time points (May 2017 and 2018, Table S1)
T data distribution showed minimum and maximum values at 33.8 and 54.6 ◦ C respectively, and two outliers at 21.5 and 60.3 ◦ C. We investigated how these variations in environmental and operating conditions were affecting the mud maturation process and the development of the green microbial biofilm and the Cyanobacteria growth
Summary
Peloids are special muds or clays consisting of mineral and organic components generated by geological and biological, chemical and physical processes. The use of peloids, for baths or packs, is called pelotherapy and shows beneficial effects in the healing of rheumatic disorders, osteoarthritis, skin diseases and other pathologic afflictions [1,2,3]. This is a common practice all over the world and has been used in Europe for 200 years. It includes the Euganean Hills of volcanic origin and the surrounding plain with the thermal localities of Abano, Montegrotto, Battaglia Terme and Galzignano (Figure 1)
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