Time series metagenomic sampling of the Thermopyles, Greece, geothermal springs reveals stable microbial communities dominated by novel sulfur-oxidizing chemoautotrophs

Abstract

Geothermal springs are barely affected by environmental conditions aboveground as they are continuously supplied with subsurface water with little variability in chemistry. Therefore, changes in their microbial community composition and function, especially over a long period, are expected to be limited but this assumption has not yet been rigorously tested. Toward closing this knowledge gap, we applied whole metagenome sequencing to 17 water samples collected between 2010 and 2016 (two to four samples per year) from the Thermopyles sulfur geothermal springs in central Greece. As revealed by 16S rRNA gene fragments recovered in the metagenomes, Epsilonproteobacteria-related operational taxonomic units (OTUs) dominated most samples, while grouping of samples based on OTU abundances exhibited no apparent seasonal pattern. Similarities between samples regarding functional gene content were high, especially in comparison to other surface water systems in Greece, with all samples sharing >70% similarity in functional pathways. These community-wide patterns were further confirmed by analysis of metagenome-assembled genomes (MAGs), which showed -in addition- that novel species and genera of the chemoautotrophic Campylobacterales order dominated the springs. These MAGs carried different pathways for thiosulfate and/or sulfide oxidation coupled to carbon fixation pathways. Overall, our study showed that even in the long term, functions of microbial communities in a moderately hot terrestrial spring remain stable, driving presumably the corresponding stability in community structure.

Autotrophic biofilms sustained by deeply-sourced groundwater host diverse CPR bacteria implicated in sulfur and hydrogen metabolism

“…are gliding bacteria that can grow as long filaments (cells in a microtubular sheath) and are known to accumulate S 0 spherical granules when in the presence of reduced sulfur[13,19] and organics (energy and carbon source) [14]. Prior work[20–24] indicate that sulfur-oxidizing bacteria support communities by providing resources such as fixed carbon and nitrogen.…”

Exploring the Bacterial Communities of the Kaiafas Thermal Spring Anigrides Nymphes in Greece Prior to Rehabilitation Actions

“…Additionally, Arcobacter was the most commonly detected species in this study, being a potential risk factor for foodborne or waterborne human illness [43]. In several studies, Arcobacter was isolated from drinking, spring, lake water, and seawater [43][44][45][46][47][48][49]. Moreover, Arcobacter cryaerophilus and Arcobacter butzleri were isolated from patients with diarrhea [50,51] and spring water [43,52], respectively.…”

Metagenomic Thermometer

“…Hot springs are a suitable environment for confirming the effectiveness of Metagenomic Thermometer because of their wide temperature range. Also, both the temperature and microbiome of a hot spring are generally stable throughout the year 21 . However, the microbial community of a hot spring can be affected by characteristics other than temperature, such as pH 19 and chemical composition 22,23 .…”