Genômica comparativa de Francisella noatunensis subsp. orientalis

Abstract

The Francisella species are intracellular facultative bacteria that cause a variety of infections in terrestrial and aquatic animals. In this genus, F. noatunensis subsp. orientalis (FNO) has a remarked importance as an emergent fish pathogen associated with outbreaks in Nile tilapia farms. Although the disease caused by FNO presents a high mortality rate during outbreaks and has been reported in several countries, the phylogenomic relationships among isolates from different countries, the evolutionary history of this pathogen and other aspects still are poorly characterized. In this context, comparative genomic analyzes were performed in order to assist in better understanding this species of great epidemiologic interest. Thus, 18 strains of F. noatunensis subsp. orientalis isolated from outbreaks in Brazilian Nile tilapia farms were sequenced, assembled and manually curated. Then, the Gegenes, Mauve, BRIG and Gipsy softwares, and the Genome Comparator module of the BIGsdb database were used to perform phylogeny, synteny, genomic plasticity and polymorphisms analyzes. Other Francisella subspecies and FNO strains available in the NCBI were included in all of these analyzes. Additionally, searches were made for genes possibly involved in the response to environmental stresses. Therefore, it was observed that the FNO strains are highly clonal and that the arrival of the disease in Brazil is probably due to the entrance of a single strain. Eight genomic islands were also predicted, six being considered pathogenicity islands. Finally, the search for genes potentially involved in the response to environmental stresses indicated a number of candidate genes for a more detailed study for the development of drugs.