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Background  Comparative analysis of gene expression among serotypes within a species can provide valuable information on important differences between related genomes. For the pig lung pathogen  Actinobacillus pleuropneumoniae , 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. We used a pan-genomic microarray to study the transcriptional response to iron restriction  in vitro  in six serotypes of  A. pleuropneumoniae  (1, 2, 3, 5b, 6, and 7), representing at least two levels of virulence.    Results  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  A. pleuropneumoniae  was the up-regulation of a putative  cirA -like siderophore in all six serotypes. Three genes, recently described in  A. pleuropneumoniae  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  A. pleuropneumoniae . The three genes share homology with the  hmbR  haemoglobin receptor of  Neisseria meningitidis , a possible virulence factor which contributes to bacterial survival in rats.    Conclusions  By comparative analysis of gene expression among 6 different serotypes of  A. pleuropneumoniae  we identified 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  A. pleuropneumoniae , 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 identical to iron restriction. One notable exception, however, is the haemoglobin-haptoglobin binding protein cluster which merits further investigation.

bmc genomics

Comparative profiling of the transcriptional response to iron restriction in six serotypes of Actinobacillus pleuropneumoniae with different virulence potential