Identification and characterization of regions of difference between the Salmonella Gallinarum biovar Gallinarum and the Salmonella Gallinarum biovar Pullorum genomes.

Salmonella Gallinarum is the causative agent of fowl typhoid, a severe septicaemic disease that affects birds of all ages, whereas S. Pullorum causes pullorum disease, a systemic disorder affecting primarily young birds. A proportion of birds with pullorum disease become carriers and are thereby able to transmit S. Pullorum vertically. Although these two pathogens cause distinct diseases, they are otherwise phenotypically and genetically similar. Therefore, the small variations that lead to the differences in virulence must have a genetic basis which currently is unknown. In the present study, we compared the genome sequences of S. Gallinarum (strains: SG287/91 and SG9) and S. Pullorum (strains: SP_CDC, SP_RKS, SP_FCAV, SP_S06) and identified 223 regions of difference (RODs), characterized by indels which were detected by using the software Artemis Comparison Tool. Some of the RODs led to pseudogenes frequently formed by frameshifts and premature stop codons in genes primarily involved in virulence and metabolism. We further verified the presence of some conserved RODs by PCR in 26 isolates of S. Gallinarum and 17 of S. Pullorum in order to extrapolate data analyses from genome comparison to field strains. The variations observed in virulence-related genes of S. Gallinarum and S. Pullorum appear not to be sufficient to explain the differences between the distinct biology of infection of fowl typhoid and pullorum disease. Thus, we suggest that the identified pseudogenes affecting metabolism might play a greater role during infection than previously thought.

Evolutionary and structural analysis of the cytochrome c oxidase subunit I (COI) gene from Haematobia irritans, Stomoxys calcitrans and Musca domestica (Diptera: Muscidae) mitochondrial DNA.

This work describes the molecular characterization of the cytochrome c oxidase subunit I (COI) gene of the mitochondrial DNA from three species of great medical and veterinary importance: the horn fly, Haematobia irritans, the stable fly, Stomoxys calcitrans and the house fly, Musca domestica (Diptera: Muscidae) (Linnaeus). The nucleotide sequence in all species was 1536 bp in size and coded for a 512 amino acid peptide. The nucleotide bias for an A+T-rich sequence is linked to three features: a high A+T content throughout the entire gene, a high A+T content in the third codon position, and a predominance of A+T-rich codons. An anomalous TCG (serine) start codon was identified. Comparative analysis among members of the Muscidae, Scatophagidae, Calliphoridae and Drosophilidae showed high levels of nucleotide sequence conservation. Analysis of the divergent amino acids and COI protein topologies among these three Muscidae species agreed with the evolutionary model suggested for the insect mitochondrial COI protein. The characterization of the structure and evolution of this gene could be informative for further evolutionary analysis of dipteran species.