AUTHOR=Picone Nunzia , Blom Pieter , Wallenius Anna J. , Hogendoorn Carmen , Mesman Rob , Cremers Geert , Gagliano Antonina L. , D’Alessandro Walter , Quatrini Paola , Jetten Mike S. M. , Pol Arjan , Op den Camp Huub J. M. 

TITLE=Methylacidimicrobium thermophilum AP8, a Novel Methane- and Hydrogen-Oxidizing Bacterium Isolated From Volcanic Soil on Pantelleria Island, Italy

JOURNAL=Frontiers in Microbiology

VOLUME=12

YEAR=2021

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2021.637762

DOI=10.3389/fmicb.2021.637762

ISSN=1664-302X

ABSTRACT=<p>The Favara Grande is a geothermal area located on Pantelleria Island, Italy. The area is characterized high temperatures in the top layer of the soil (60°C), low pH (3–5) and hydrothermal gas emissions mainly composed of carbon dioxide (CO<sub>2</sub>), methane (CH<sub>4</sub>), and hydrogen (H<sub>2</sub>). These geothermal features may provide a suitable niche for the growth of chemolithotrophic thermoacidophiles, including the lanthanide-dependent methanotrophs of the phylum Verrucomicrobia. In this study, we started enrichment cultures inoculated with soil of the Favara Grande at 50 and 60°C with CH<sub>4</sub> as energy source and medium containing sufficient lanthanides at pH 3 and 5. From these cultures, a verrucomicrobial methanotroph could be isolated <italic>via</italic> serial dilution and floating filters techniques. The genome of strain AP8 was sequenced and based on phylogenetic analysis we propose to name this new species <italic>Methylacidimicrobium thermophilum</italic> AP8. The transcriptome data at μ<sub>max</sub> (0.051 ± 0.001 h<sup>−1</sup>, doubling time ~14 h) of the new strain showed a high expression of the <italic>pmoCAB</italic>2 operon encoding the membrane-bound methane monooxygenase and of the gene <italic>xoxF</italic>1, encoding the lanthanide-dependent methanol dehydrogenase. A second <italic>pmoCAB</italic> operon and <italic>xoxF</italic>2 gene were not expressed. The physiology of strain AP8 was further investigated and revealed an optimal growth in a pH range of 3–5 at 50°C, representing the first thermophilic strain of the genus <italic>Methylacidimicrobium</italic>. Moreover, strain AP8 had a K<sub>S(app)</sub> for methane of 8 ± 1 μM. Beside methane, a type 1b [NiFe] hydrogenase enabled hydrogen oxidation at oxygen concentrations up to 1%. Taken together, our results expand the knowledge on the characteristics and adaptations of verrucomicrobial methanotrophs in hydrothermal environments and add a new thermophilic strain to the genus <italic>Methylacidimicrobium</italic>.</p>