Submitted to: Journal of Bacteriology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 6/25/2013
Publication Date: 8/12/2013
Citation: Wang, X., Tan, J., Bai, Z., Su, H., Deng, X., Li, Z., Zhou, C., Chen, J. 2013. Detection and characterization of miniature inverted-repeat transposable elements in “Candidatus Liberibacter asiaticus”. Journal of Bacteriology. 195:3979-3986. Interpretive Summary: Transposons are small segments of DNA, jumping around a bacterial genome and causing mutations. “Candidatus Liberibacter asiaticus” is a bacterium associated with citrus Huanglongbing (HLB), which is highly destructive to the world citrus production. No transposon has been found in the HLB bacterium. In this study, a total of 326 bacterial isolates collected in China and Florida were examined. Two transposons, MCLas-A and MCLas-B, were detected and characterized. While the main structures remain, both transposons have variants. MCLas-A is highly active in the Florida bacterial population. On the bacterial genome, excision of transposon left behind remnant DNA. Remnant types could be used to separate the “Ca. L. asiaticus” populations between Florida and China. This is the first observation and characterization of transposons in “Ca. L. asiaticus”.
Technical Abstract: Miniature inverted-repeat transposable elements (MITEs) are non-autonomous transposons (devoid a transposase gene, tps) involving insertion/deletion of genomic DNA in bacterial genomes influencing gene functions. No transposon has yet been reported in “Candidatus Liberibacter asiaticus”, an alpha-proteobacterium associated with citrus Huanglongbing, which is highly destructive to the world citrus production. In this study, MITEs in “Ca. L. asiaticus” were detected and characterized through a pan-genomic analysis. A total of 326 isolates collected in China and Florida were examined for variations in a genomic locus, flanked by primer set LapPF1-f/LapPF1-r. Three PCR amplicons, B-SC1 (~720bp), B-SC2 (~640 bp) and B-CH1 (~300 bp), were observed. B-SC2 was found to be identical to B-CH1except for a DNA insertion characterized as a MITE, named as MCLas-A, based on the presence of terminal inverted repeats (TIRs), small size (<500 bp), a non-coding central region (CR) and evidence of mobility. B-SC1 contained a different MITE, MCLas-B. Both MITEs had variants, used phages / prophages as hosts and were found in both China and Florida. The representative variant, MCLas-A1, had a pair of 54-bp TIRs, a 217 bp CR and a pair of 6 bp direct repeats (DRs). Upstream 230 bp on its host was a putative tps. MITE mobility was evidenced by the presence of “full” (with MITE) / “empty” (without MITE) isolates in the bacterial pan-genome. All “empty” isolates had TIR remnants at the excision sites. Remnant types varied according to geographical origins. This is the first observation and characterization of MITEs or transposons in “Ca. L. asiaticus”.