Genome characteristics and type IV effector protein repertoire of Coxiella burnetii depend rather on Genomic Groups than on host species

Background Q fever is a zoonotic disease with virtually worldwide dissemination. Its bacterial agent, Coxiella burnetii , is primarily found in cattle and small ruminants. Disease manifestation is highly variable, i.e. asymptomatic, acute or chronic in humans, and subclinical or present as reproductive disorders in ruminants. Different genomic lineages of C. burnetii have been recognized and are considered to show host preferences and influence the disease outcome. The virulence of C. burnetii is essentially determined by effector proteins that modulate host cell processes, allowing the bacterium to persist and proliferate in the host. Thus, these effectors have been suggested to play a role in the presumed host specificity and disease manifestation. Results In the present study, a comprehensive set of 140 C. burnetii genomes from ten Genomic Groups (GGs) and various hosts was studied bioinformatically to determine if there was an association between their genomic characteristics, including the effector protein repertoire, and their isolation source. The differences in genome size, IS1111 count, number of coding sequences, accessory genome and others observed could be attributed to lineage-specific traits. Likewise, the GGs showed conserved sets of effector proteins, although intra-lineage variances were high in GGIV. Several effector proteins, e.g. Cem8 (CBU_1634a) and CBU_0469, were highly conserved, while CBU_2007 showed a remarkably high number of sequence variants. Conclusions C. burnetii exhibits genomic diversity that aligns with phylotypes rather than host species, suggesting that genomic traits as well as host factors influence disease outcome rather than a host species specific adaptation.