Investigation of genome sequences within the family Pasteurellaceae

Introduction The bacterial genome sequences are now available for an increasing number of strains within the family Pasteurellaceae. At present, 24 Pasteurellaceae genomes are publicly available through internet databases, and another 40 genomes are being sequenced. This investigation will describe the core genome for both the family Pasteurellaceae and for the species Haemophilus influenzae. Methods Twenty genome sequences from the following species were included: Haemophilus influenzae (11 strains), Haemophilus ducreyi (1 strain), Histophilus somni (2 strains), Haemophilus parasuis (1 strain), Actinobacillus pleuropneumoniae (2 strains), Actinobacillus succinogenes (1 strain), Mannheimia succiniciproducens (1 strain), and Pasteurella multocida (1 strain). The predicted proteins for each genome were BLASTed against each other, and a set of conserved core gene families was determined as described previously (P.F. Hallin, T.T. Binnewies and D.W. Ussery: "The genome BLASTatlas-a GeneWiz extension for visualization of whole-genome homology", Molecular BioSystems, 4:363-371, 2008). Results and discussion The genome sizes ranged from 1.2 to 1.7 Kbp with a gene content ranging from 1619 to 2307 genes. The homology between genomes ranged from 47.2% to 94.1%. The number of genes found increased steadily for each sequence added to the analysis and the pan-genome of all 20 sequences consisted of around 8500 genes. On the other hand, the number of genes found in all strains steadily decreased when adding additional sequences to the analysis and constituted less than a thousand genes when all 20 sequences were included (~10% of all genes described in the family so far). Within H. influenzae the pan genome consisted of about 4200 genes and the core genome of about 1000 genes (23%). The present investigation shows that the genomic diversity within species of Pasteurellaceae is a bit lower than the level which has been found for E. coli and B. cereus. This might reflect that most members of Pasteurellaecae have relatively small genomes and that the species of the family often are adapted to host specific niches as pathogens in animals or commensals on mucosal surfaces.