Microbial Ecology A new species of the γ-protobacterium Francisella, F. adeliensis sp. nov., endocytobiont in an Antarctic marine ciliate and potential evolutionary forerunner of pathogenic species

Manuscript Number: MECO-D-17-00706R1 Full Title: A new species of the γ-protobacterium Francisella, F. adeliensis sp. nov., endocytobiont in an Antarctic marine ciliate and potential evolutionary forerunner of pathogenic species Article Type: Original Article Section/Category: Microbiology of Aquatic Systems Order of Authors: Adriana Vallesi Andreas Sjödin Dezemona Petrelli Pierangelo Luporini Anna Rita Taddei Johanna Thelaus Caroline Öhrman Elin Nilsson Graziano Di Giuseppe Gabriel Gutiérrez Eduardo Villalobo Corresponding Author: Adriana Vallesi University of Camerino ITALY Corresponding Author Secondary Information: Corresponding Author's Institution: University of Camerino Corresponding Author's Secondary Institution: First Author: Adriana Vallesi First Author Secondary Information: Order of Authors Secondary Information: Funding Information: Abstract: The study of the draft genome of an Antarctic marine ciliate, Euplotes petzi, revealed foreign sequences of bacterial origin belonging to, and implying symbiotic relationships with the γ-proteobacterium Francisella that includes pathogenic and environmental species. TEM and FISH analyses confirmed the presence of a Francisella endocytobiont in E. petzi, which we then isolated and found to be a new species, named F. adeliensis sp. nov.. F. adeliensis grows well at wide ranges of temperature, salinity, and carbon dioxide concentrations implying that it may colonize new organisms living in deeply diversified habitats. The F. adeliensis genome includes the igl and pdp gene sets (pdpC and pdpE excepted) of the Francisella pathogenicity island needed for intracellular growth. Consistently with an F. adeliensis ancient symbiotic lifestyle, it also contains a single insertion-sequence element. Instead, it lacks genes for the biosynthesis of essential amino acids such as cysteine, lysine, methionine and tyrosine. In a genome-based phylogenetic tree, F. adeliensis forms a