Kirstine Klitgaard and co-workers at the Technical University of Denmark in Copenhagen have published a paper in a recent issue of BMC Genomics into their studies on the virulence potential of Actinobacillus pleuropneumoniae (App).

Comparative analysis of gene expression among serotypes within a species can provide valuable information on important differences between related genomes, they explained. For the pig lung pathogen, App, 15 serotypes with a considerable variation in virulence potential and immunogenicity have been identified. This serotypic diversity can only partly be explained by amount of capsule and differences in the RTX toxin genes in their genomes. Iron acquisition in vivo is an important bacterial function and in pathogenic bacteria, iron-limitation is often a signal for the induction of virulence genes. The Danish group used a pan-genomic microarray to study the transcriptional response to iron restriction in vitro in six serotypes of App (1, 2, 3, 5b, 6 and 7), representing at least two levels of virulence.

They found that, in total, 45 genes were significantly (p<0.0001) up-regulated and 67 genes significantly down-regulated in response to iron limitation. Not previously observed in App was the up-regulation of a putative cirA-like siderophore in all six serotypes. Three genes, recently described in App as possibly coding for haemoglobin-haptoglobin binding proteins, displayed significant serotype-related up-regulation to iron limitation. For all three genes, the expression appeared at its lowest in serotype 3, which is generally considered one of the least virulent serotypes of App. The three genes share homology with the hmbR haemoglobin receptor of Neisseria meningitidis, a possible virulence factor which contributes to bacterial survival in rats.

Klitgaard and colleagues conclude that by comparative analysis of gene expression of six different serotypes of App, they were able to identify a common set of presumably essential core genes involved in iron regulation. The results support and expand previous observations concerning the identification of new potential iron acquisition systems in App, showing that this bacterium has evolved several strategies for scavenging the limited iron resources of the host.

The combined effect of iron-depletion and serotype proved to be modest, indicating that serotypes of both moderate and high virulence at least in vitro are reacting almost identically to iron restriction, they say. One notable exception, however, is the haemoglobin-haptoglobin binding protein cluster, which merits further investigation.

Reference

Klitgaard K., C. Friis, Ø. Angen and M. Boye. 2010. Comparative profiling of the transcriptional response to iron restriction in six serotypes of Actinobacillus pleuropneumoniae with different virulence potential. BMC Genomics, 11:698. doi:10.1186/1471-2164-11-698.

Further Reading

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Further Reading

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Find out more information on App by clicking here.