Mineral waters of Serbia and development of phototrophic microbial communities near points of emergence and on wellheads

Abstract

Phototropic microorganisms in thermal mats had not attracted enough attention in Serbia in the past. The research presented in this paper is the first to address biofilms at selected occurrences of mineral water in Serbia (Bogatić, Metković and Belotić in the Mačva District as well as Radaljska Banja, Lukovska Banja and Vranjska Banja) (in Serbian, banja denotes a spa town). The study period is from 2014 to 2016. The temperatures of the studied occurrences are in the 30-93.9 °C range and the chemical composition corresponds to the HCO3--Na++K+ and SO4 2-, HCO3--Na++K+ types of mineral water. One of the objectives was to examine the condition of wellheads (incrustation, biofouling and corrosion), focusing on the presence of phototrophic microorganisms whose metabolites may lead to changes in mineral water quality, yield and chemistry. Analysis by light and scanning electron microscopy provides insight into the diversity of phototrophic microorganisms that populate biofilms near the points of emergence and on wellhead. The research reveals the presence of representatives of three groups of phototrophic microorganisms: Cyanobacteria, Chlorophyta and Bacillariophyta. Cyanobacteria were the most numerous, dominated by the order Oscillatoriales with ten recorded genera, of which Leptolynbgya and Phormidium feature the largest numbers of species. The order Chroococcales are the second most numerous, with seven recorded genera, of which Gloeocapsa and Synechocystisare the most noteworthy. The largest numbers of representative taxa were noted at Radaljska Banja and Vranjska Banja, where mineral waters originate from Encrustalithostratigraphic units of igneous origin, followed by mineral water occurrences in karst aquifers (Bogatić and Belotić) and an intergranular aquifer (Metković). The smallest number of identified phototrophic microorganisms is noted at Lukovska Banja, where the origin is associated with a fractured aquifer formed in sedimentary and metamorphic rocks, with occasional diabase interbeds. Although many representative taxa are found on only one of the studied localities, such as Synechococcus bigranulatus and Pseudanabaena thermalis, those of the genera Leptolyngbya, Phormidium and Cosmarium laeve, as well as genera of the phylum Bacillariophyta, occur at several sampling sites. Principal component analysis (PCA) was used to show the relationship between documented cyanobacterial and algal taxa and environmental parameters.