None of the Tn916 insertion sites identified in this study were adjacent to neighbouring genes with a convergent orientation, selleck but 23 (67%) were adjacent to neighbouring genes with a tandem orientation ( or ) and 12 (33%) to genes with a divergent () orientation (Table 1). The frequency of neighbouring gene orientation (NGO) was performed for the fully annotated core genome of B316T (Table 1) and was found to be significantly different from the NGO of the Tn916 insertion sites (χ2=94.75, df=2, P-value <0.001) (Table 2). The same analysis of the distribution of tandem, convergent
and divergent neighbouring genes within the completed B316T genome was also significantly different (χ2=13.25, df=2, P-value <0.05) when compared with the NGO of other insertion sequences, such as transposases (n=35), associated with the fully annotated core genome of B316T (Kelly et al., 2010). Similarly, the NGO were significantly different (χ2=28.22, df=2, P-value <0.001) when the Tn916 insertion
sites and insertion sequences from the B316T core genome were compared (Table 1). Transcription termination sites were identified from the annotated B316T genome, and in addition to having a high G+C percentage (Table 1), the long runs of A or T nucleotides associated with the Tn916 insertion consensus site were not apparent. These regions of higher G+C percentage may direct small molecule library screening Tn916 insertion away Etofibrate from gene termini. Additionally, selection using tetracycline may influence the maintenance of Tn916 insertion sites where the transposon would be lost in the absence of antibiotic. This study has been the first to comprehensively examine the insertion of Tn916 in a bacterial genome with multiple replicons. Furthermore, we were able to demonstrate
variations in transpositional frequency in megaplasmids having specific characteristics (copy number and stability) and unexpected NGO frequencies that did not correlate with the likelihood of disruption, but appeared to correlate negatively with proximity to gene termini. These data suggest that the presence of a consensus sequence for transposon insertion is biased towards intergenic regions that constitute only 10% of the B316T genome. Although the presence of transposon insertions in intergenic regions may appear to be of limited value for assessing changes in phenotype commonly associated with insertions in ORFs, insertions between ORFs may still provide useful insights into gene function.