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Description
Vulcano is the southernmost of the seven islands forming the Aeolian volcanic archipelago. This island harbors a developed hydrothermal system and is the place where the first hyperthermophilic marine archaeon, Pyrodictium occultum was isolated. Shallow hydrothermal systems have been recently the subject of numerous investigations as they constitute easy access extreme environments, and may be actual analogues of places where life appeared. Indeed, due to the mixing of hot, reduced and sometimes metal/sulfur rich fluids with oxygenated seawater, these environments are characterized by high gradients of temperature and fluid chemistry. Here we describe the taxonomic and physiological properties of strain V6Fe1T, a novel anaerobic bacterium, isolated from shallow subsurface sediments on the seashore. Cells were thin, non-motile, Gram-negative flexible rods. 16S rRNA gene sequence showed that strain V6Fe1T was a member of the unwell characterized Deferribacteraceae family. This strain showed substantial metabolic versatility, fermenting organic substrates, using various electron acceptors (ferric iron, manganese, sulfur, nitrate, nitrous oxide) to perform respiration, growing autotrophically (e.g without organic carbon sources) with molecular hydrogen as an electron donor and Fe(III), Mn(IV), S° or NO3- as electron acceptors. Thermodynamical calculation demonstrated that among terminal electron acceptors, nitrate may be the most suitable for anaerobic chemolithotrophic and chemoorganotrophic lifestyles in Vulcano hydrothermal systems. Nitrate reduction pathways were investigated according to the growth conditions. Unlike the most closely related strains, strain V6Fe1T performed both dissimilatory nitrate reduction to ammonium (DNRA) and denitrification, nitrate being reduced to dinitrogen. The genome consisted of a 2,358 kbp long chromosome. Genomic data were used to decipher which genes were involved when nitrate reduction took place. Comparison with genomes of closely related strains suggested that DNRA and denitrification pathways should be leveraged by cyclic AMP receptor protein (CRP) paralogues according to electron donor/acceptor availability.