Characterization of the type I secretion system of the RTX toxin ApxII in "Actinobacillus porcitonsillarum"

Kuhnert, Peter; Schlatter, Yvonne; Frey, Joachim (2005). Characterization of the type I secretion system of the RTX toxin ApxII in "Actinobacillus porcitonsillarum". Veterinary microbiology, 107(3-4), pp. 225-232. Amsterdam: Elsevier 10.1016/j.vetmic.2005.01.020

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Strains of Actinobacillus porcitonsillarum are regularly isolated from the tonsils of healthy pigs. A. porcitonsillarum is non pathogenic but phenotypically it strongly resembles the pathogenic species Actinobacillus pleuropneumoniae, thereby interfering with the diagnosis of the latter. A. porcitonsillarum is hemolytic but unlike A. pleuropneumoniae, it contains only apxII genes and not apxI or apxIII genes. In contrast to the truncated apxII operon of A. pleuropneumoniae, which lacks the type I secretion genes BD, characterization of the apxII operon in A. porcitonsillarum revealed that it contains an intact and complete apxII operon. This shows a typical RTX operon structure with the gene arrangement apxIICABD. The region upstream of the apxII operon is also different from that in A. pleuropneumoniae and contains an additional gene, aspC, encoding a putative aspartate aminotransferase. Trans-complementation experiments in Escherichia coli and A. pleuropneumoniae indicated that the entire apxII operon of A. porcitonsillarum is sufficient to express and secrete the ApxIIA toxin and that the ApxIIA toxin of A. pleuropneumoniae can be secreted by the type I secretion system encoded by apxIIBD. These findings suggest that the complete apxII operon found in A. porcitonsillarum might be an ancestor of the truncated homologue found in A. pleuropneumoniae. The genetic context of the apxII locus in A. porcitonsillarum and A. pleuropneumoniae suggests that in the latter, the contemporary truncated operon is the result of a recombination event within the species, rather than a horizontal transfer of an incomplete operon.

Item Type:

Journal Article (Original Article)


05 Veterinary Medicine > Department of Infectious Diseases and Pathobiology (DIP) > Institute of Veterinary Bacteriology

UniBE Contributor:

Kuhnert, Peter; Schlatter, Yvonne and Frey, Joachim


500 Science
500 Science > 570 Life sciences; biology
600 Technology > 630 Agriculture








Peter Kuhnert-Ryser

Date Deposited:

24 Jan 2014 08:54

Last Modified:

20 Dec 2014 02:26

Publisher DOI:


PubMed ID:


Uncontrolled Keywords:

Apx toxin, Secretion, Porcine pleuropneumonia, Actinobacillus pleuropneumoniae




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