title: Structure, mineralogy, and microbial diversity of geothermal spring microbialites associated with a deep oil drilling in Romania.
abstract: Modern mineral deposits play an important role in evolutionary studies by providing clues to the formation of ancient lithified microbial communities. Here we report the presence of microbialite-forming microbial mats in different microenvironments at 32°C, 49°C, and 65°C around the geothermal spring from an abandoned oil drill in Ciocaia, Romania. The mineralogy and the macro- and microstructure of the microbialites were investigated, together with their microbial diversity based on a 16S rRNA gene amplicon sequencing approach. The calcium carbonate is deposited mainly in the form of calcite. At 32°C and 49°C, the microbialites show a laminated structure with visible microbial mat-carbonate crystal interactions. At 65°C, the mineral deposit is clotted, without obvious organic residues. Partial 16S rRNA gene amplicon sequencing showed that the relative abundance of the phylum Archaea was low at 32°C (<0.5%) but increased significantly at 65°C (36%). The bacterial diversity was either similar to other microbialites described in literature (the 32°C sample) or displayed a specific combination of phyla and classes (the 49°C and 65°C samples). Bacterial taxa were distributed among 39 phyla, out of which 14 had inferred abundances >1%. The dominant bacterial groups at 32°C were Cyanobacteria, Gammaproteobacteria, Firmicutes, Bacteroidetes, Chloroflexi, Thermi, Actinobacteria, Planctomycetes, and Defferibacteres. At 49°C, there was a striking dominance of the Gammaproteobacteria, followed by Firmicutes, Bacteroidetes, and Armantimonadetes. The 65°C sample was dominated by Betaproteobacteria, Firmicutes, [OP1], Defferibacteres, Thermi, Thermotogae, [EM3], and Nitrospirae. Several groups from Proteobacteria and Firmicutes, together with Halobacteria and Melainabacteria were described for the first time in calcium carbonate deposits. Overall, the spring from Ciocaia emerges as a valuable site to probe microbes-minerals interrelationships along thermal and geochemical gradients.
authors: Taxonomy and Ecology, Algology, National Institute of Research and Development for Biological Sciences, Institute of Biological Research Cluj-Napoca, Romania ; Molecular Biology and Biotechnology Department, Faculty of Biology and Geology, Babeş-Bolyai University Cluj-Napoca, Romania.
authors: Cristian
authors: C
authors: Coman
authors: Taxonomy and Ecology, Algology, National Institute of Research and Development for Biological Sciences, Institute of Biological Research Cluj-Napoca, Romania ; Molecular Biology and Biotechnology Department, Faculty of Biology and Geology, Babeş-Bolyai University Cluj-Napoca, Romania.
authors: Cecilia M
authors: CM
authors: Chiriac
authors: Biosciences Division, Oak Ridge National Laboratory Oak Ridge, TN, USA ; Fish, Wildlife, and Conservation Biology, Colorado State University Fort Collins, CO, USA.
authors: Michael S
authors: MS
authors: Robeson
authors: Geology Department, Faculty of Biology and Geology, Babeş-Bolyai University Cluj-Napoca, Romania ; Kazan (Volga Region) Federal University Tatarstan, Russia.
authors: Corina
authors: C
authors: Ionescu
authors: Taxonomy and Ecology, Algology, National Institute of Research and Development for Biological Sciences, Institute of Biological Research Cluj-Napoca, Romania ; Molecular Biology and Biotechnology Department, Faculty of Biology and Geology, Babeş-Bolyai University Cluj-Napoca, Romania.
authors: Nicolae
authors: N
authors: Dragos
authors: Electron Microscopy Center, Faculty of Biology and Geology, Babeş-Bolyai University Cluj-Napoca, Romania.
authors: Lucian
authors: L
authors: Barbu-Tudoran
authors: Molecular Biology and Biotechnology Department, Faculty of Biology and Geology, Babeş-Bolyai University Cluj-Napoca, Romania ; Molecular Biology Center, Institute for Interdisciplinary Research on Bio-Nano-Sciences, Babeş-Bolyai University Cluj-Napoca, Romania.
authors: Adrian-Ştefan
authors: AŞ
authors: Andrei
authors: Molecular Biology and Biotechnology Department, Faculty of Biology and Geology, Babeş-Bolyai University Cluj-Napoca, Romania ; Molecular Biology Center, Institute for Interdisciplinary Research on Bio-Nano-Sciences, Babeş-Bolyai University Cluj-Napoca, Romania.
authors: Horia L
authors: HL
authors: Banciu
authors: Biological Research Center Jibou, Romania.
authors: Cosmin
authors: C
authors: Sicora
authors: Biosciences Division, Oak Ridge National Laboratory Oak Ridge, TN, USA.
authors: Mircea
authors: M
authors: Podar
keywords: amplicon sequencing; biomineralization; carbonate; hot springs; microbial diversity; oil drill