engleski

Microbial diversity of Croatian thermal waters

Croatian thermal waters represent a poorly investigated microbial habitat. This type of environment is challenging for microbial survival. Temperature and chemical composition usually present the main driving force of microbial community assembly. The primary objective was to characterize microbial communities of Croatia's most important thermal waters. Furthermore, we were interested in identifying the abiotic factors that affect the community structure, detecting spatio-temporal variability across three seasons, and exploring the effects of different aquifer types. A total of 19 thermal waters located in central, eastern, and northern coastal Croatia were sampled. After DNA extraction, samples were amplified and sequenced on an Illumina MiSeq platform. The microbial community was highly site- specific and often dominated by a single genus such as Hydrogenophilus, Sulfuricurvum, Sulfurovum, Thiofaba, and Nitrospira, while ammonia-oxidizing archaea Candidatus Nitrosotenuis and Candidatus Nitrososphaera were the main archaeal representatives. The combination of temperature and pH, together with oxygen and nutrient availability, determined distinct development patterns of microbial communities. Little to no effect of aquifer type was detected to drive microbial community changes, while longitudinal sample collection showed that thermal waters were highly temporally stable, as their physio-chemical parameters. Our study is the first to provide a cultivation-independent overview of the microbial communities in Croatian thermal waters, currently used for balneology, agricultural and district heating, and electricity production. Our results highlight microbial communities' high level of endemism and underline the large and still underexplored diversity of genetic resources in these waters, which can now be further mined for their biotechnological potential.

hot springs, 16S rRNA gene sequencing, extremophiles, aquifers

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