Several thermophilic members of orders Thermoanaerobacterales [31] and Clostridiales [24], class Clostridia are considered as common inhabitants of terrestrial hot springs where they most probably participate to fermentative processes of organic matter [28]. They are considered as strict anaerobes with representatives of the order Thermoanaerobacterales (e.g., Thermoanaerobacter and Thermoanaerobacterium spp.) being frequently isolated from such extreme ecosystems and having the ability to use thiosulfate as terminal electron acceptor and reduce it to sulfide or elemental sulfur