Hydrogen and Carbon Monoxide-Utilizing Species From Pantelleria Island, Italy.

Volcanic and geothermal areas are hot and often acidic environments that emit geothermal gasses, including H, CO and CO. Geothermal gasses mix with air, creating conditions where thermoacidophilic aerobic H- and CO-oxidizing microorganisms could thrive. Here, we describe the isolation of two strains, which can grow autotrophically by oxidizing H and CO with oxygen. These strains, FAVT5 and COOX1, were isolated from the geothermal soils of the Favara Grande on Pantelleria Island, Italy. Extended physiology studies were performed with FAVT5, and showed that this strain grows optimally at 55°C and pH 5.0. The highest growth rate is obtained using H as energy source (μ 0.19 ± 0.02 h, doubling time 3.6 h). FAVT5 can additionally grow on a variety of organic substrates, including some alcohols, volatile fatty acids and amino acids. The genome of each strain encodes for two O-tolerant hydrogenases belonging to [NiFe] group 2a hydrogenases and transcriptome studies using FAVT5 showed that both hydrogenases are expressed under H limiting conditions. So far no Firmicutes except FAVT5 have been reported to exhibit a high affinity for H, with a K of 327 ± 24 nM. The genomes of each strain encode for one putative CO dehydrogenase, belonging to Form II aerobic CO dehydrogenases. The genomic potential and physiological properties of these strains seem to be quite well adapted to thrive in the harsh environmental volcanic conditions.