A New Species of the γ-Proteobacterium Francisella, F. adeliensis Sp. Nov., Endocytobiont in an Antarctic Marine Ciliate and Potential Evolutionary Forerunner of Pathogenic Species

• Published in: Microbial Ecology
• Main Authors: Vallesi, Adriana, Sjödin, Andreas, Petrelli, Dezemona, Luporini, Pierangelo, Taddei, Anna Rita, Thelaus, Johanna, Öhrman, Caroline, Nilsson, Elin, Di Giuseppe, Graziano, Gutiérrez, Gabriel, Villalobo, Eduardo
• Other Authors: Sjödin, Andrea
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2018
• Subjects: Endosymbiosi; Environmental Francisella; Euplote; Francisella phylogeny; Microbial association; Polar microbiology; Ecology; Evolution; Behavior and Systematic; Soil Science; Antarctic; Antarc*
• Online Access: https://hdl.handle.net/11568/953065; https://doi.org/10.1007/s00248-018-1256-3

The study of the draft genome of an Antarctic marine ciliate, Euplotes petzi, revealed foreign sequences of bacterial origin belonging to the γ-proteobacterium Francisella that includes pathogenic and environmental species. TEM and FISH analyses confirmed the presence of a Francisella endocytobiont in E. petzi. This endocytobiont was 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 new early branching clade, basal to the evolution of pathogenic species. The correlations of this clade with the other clades raise doubts about a genuine free-living nature of the environmental Francisella species isolated from natural and man-made environments, and suggest to look atF. adeliensis asa pioneer in the Francisella colonization of eukaryotic organisms.