F. PALMIERI¹, S. FILIPPIDOU¹, P. JUNIER<sup>1

1</sup>Laboratory of Microbiology, University of Neuchâtel, Neuchâtel, Switzerland

Volcanos are extreme environments with elevated temperatures, low pH, high pressure and high concentration of heavy metals. In order to thrive in these environments and to withstand unfavourable conditions, microorganisms have developed adaptations and survival strategies. One of these strategies is endospore formation. Thanks to their structure, endospores are highly resistant to heat, UV radiation, chemicals and other stressors. The aim of this study was to assess the role of endospore formation as a survival strategy along a temperature gradient in volcanic fumaroles. We hypothesize that endospore-forming Firmicutes (EFF) are predominant in the higher temperature sites as they withstand harsher environmental conditions. In order to address this hypothesis, soil was sampled across two thermal gradients from two different fumaroles in Nisyros volcano. Soil across a macrogradient from the crater to the vegetation was also sampled. The total bacterial community was assessed by qPCR of the 16S rRNA gene, while the endospore-forming community was assessed by qPCR of the spo0A (sporulation transcriptional factor) gene. Dipicolinic acid (DPA) will be also quantified as a proxy to endospores. The results showed that endospore-formers dominate the community at high temperature sites. The relative proportion of EFF compared to the total community decreases further away from the fumaroles. Similarly, endospore-formers are supposed to be predominant in the crater sample compared to the other soil samples in the macrogradient towards vegetation. DPA quantification should show the same tendency. These results suggest that bacterial communities stratify across a thermal gradient, with a dominance of EFF at higher temperatures. This study is the first to give an insight into the role of endospore-formation as a survival strategy in volcanic habitats.