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

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 (Bogatic, Metkovic and Belotic in the Macva 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 (Bogatic and Belotic) and an intergranular aquifer (Metkovic). 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. Key words: Serbia, mineral waters, phototrophic microorganisms, biofilm. Mineralne vode v Srbiji in razvoj fototrofnih mikrobnih združb na mestih izvirov in na ustjih vrtin Fototrofni mikroorganizmi v oblogah termalnih izvirov v Srbiji v preteklosti niso bili deležni posebne pozornosti. V clanku predstavljena raziskava je prva, ki obravnava biofilme na izbranih mestih izvirov mineralnih vod v Srbiji (Bogatic, Metkovic in Belotic v Macvi ter Radaljska Banja, Lukovska Banja in Vranjska Banja) (v srbskem jeziku je banja izraz za toplice). Preucevanje je potekalo med letoma 2014 in 2016. Temperature obravnavanih voda se gibljejo med 30 in 93,9 °C, glede na kemijsko sestavo pa jih uvrscamo v HCO3 − – Na++ K+ in SO4 2−, HCO3 − – Na++K+ tipe mineralne vode. Eden od ciljev raziskave je bil proucevati razmere na ustjih vrtin (inkrustacija, obrast in korozija) in se se posebej posvetiti navzocnosti fototrofnih mikroorganizmov, katerih metaboliti lahko spremenijo kakovost, izdatnost in kemizem mineralnih vod. Z analizo slik s svetlobnim in vrsticnim elektronskim mikroskopom lahko podrobneje spoznamo raznolikost fototrofnih organizmov, ki sestavljajo biofilme na mestih izvirov in na ustjih vrtin. Raziskava je pokazala obstoj predstavnikov treh skupin fototrofnih mikroorganizmov: cianobakterij ter predstavnikov debel Chlorophyta in Bacillariophyta. Cianobakterije so bile najbolj stevilcne, prevladovali so osebki reda Oscillatoriales z desetimi ugotovljenimi rodovi, od katerih je bilo najvecje stevilo vrst iz rodov Leptolynbgya in Phormidium. Red Chroococcales je bil s sedmimi zabeleženimi rodovi drugi najbolj stevilcen, prevladovala sta Gloeocapsa in Synechocystis. Najvecreprezentativnih taksonov je bilo v Radaljski Banji in Vranjski Banji, kjer mineralne vode izvirajo iz litostratigrafskih enot vulkanskega izvora, sledijo mineralne vode iz kraskega (Bogatic in Belotic) in medzrnskega vodonosnika (Metkovic). Najmanjfototrofnih organizmov je bilo v vzorcu iz Lukovske Banje, kjer vode izvirajo iz razpoklinskih vodonosnikov v sedimentnih in metamorfnih kamninah z vmesnimi lecami diabaza. Ceprav sostevilne reprezentativne taksone nasli le na eni od proucevanih lokacij, kot na primer Synechococcus bigranulatus in Pseudanabaena thermalis, se tisti iz rodu Leptolyngbya, Phormidium in Cosmarium laeve in predstavniki vec rodov, ki pripadajo deblu Bacillariophyta, pojavljajo na vec vzorcnih mestih. Za ugotavljanje odvisnosti med taksoni cianobakterij in alg ter okoljskimi parametri so uporabili analizo glavnih komponent. Kljucne besede: Srbija, mineralne vode, fototrofni mikroorganizmi, biofilm.