Characterization of ISApl1, an insertion element identified from Actinobacillus pleuropneumoniae field isolate in China

An insertion sequence (IS), designated ISApl1, was identified in Actinobacillus pleuropneumoniae. It was 1072 bp in length, and contained a large open reading frame (ORF), which encoded a putative transposase whose sequence was similar to that of transposases of various IS elements of the IS30 family. Another small ORF, a putative antisense repressor of transposase, was located in the opposite direction of transposase. ISApl1 generated a 3-bp duplication of the target DNA and carried 24-bp inverted repeats sequence. ISApl1 was identified in the genome of a biofilm-formation negative A. pleuropneumoniae strain field isolate HB04 and inserted into an A/T rich region of the ORF of pgaC, which encoded the PGA [N-acetyl-d-glucosamine residues in β(1,6) linkage] synthesizing N-glycosyltransferase. The genotype of the pgaC−/IS+ was not altered after re-isolation from challenged mice, which indicated that this IS element was relatively stable in A. pleuropneumoniae during infection.