Molecular characterization of a mosaic locus in the genome of 'Candidatus Liberibacter asiaticus'

doi:10.1186/1471-2180-12-18

BMC Microbiol. 2012; 12: 18.

Published online 2012 January 26. doi: 10.1186/1471-2180-12-18

PMCID: PMC3296602

Molecular characterization of a mosaic locus in the genome of 'Candidatus Liberibacter asiaticus'

Xuefeng Wang,¹ Changyong Zhou,¹ Xiaoling Deng,² Huanan Su,¹ and Jianchi Chen³

¹National Engineering Research Center for Citrus, Citrus Research Institute, Southwest University, Chongqing 400712, People's Republic of China

²Citrus Huanglongbing Research Center, South China Agricultural University, Guangzhou 510642, People's Republic of China

³San Joaquin Valley Agricultural Sciences Center, United States Department of Agriculture-Agricultural Research Service, Parlier, CA 93648, USA

Corresponding author.

Xuefeng Wang: xfwang/at/swu.edu.cn; Changyong Zhou: changyong/at/hotmail.com; Xiaoling Deng: xldeng/at/scau.edu.cn; Huanan Su: huanansu211/at/163.com; Jianchi Chen: jianchi.chen/at/ars.usda.gov

Received July 19, 2011; Accepted January 26, 2012.

This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Background

Huanglongbing (HLB) is a highly destructive disease of citrus production worldwide. 'Candidatus Liberibacter asiaticus', an unculturable alpha proteobacterium, is a putative pathogen of HLB. Information about the biology and strain diversity of 'Ca. L. asiaticus' is currently limited, inhibiting the scope of HLB research and control.

Results

A genomic region (CLIBASIA_05640 to CLIBASIA_05650) of 'Ca. L. asiaticus' showing hyper-sequence variation or locus mosaicism was identified and investigated using 262 bacterial strains (188 from China and 74 from Florida). Based on the characteristic electrophoretic profiles of PCR amplicons generated by a specific primer set, eight electrophoretic types (E-types) were identified, six E-types (A, B, C, D, E, and F) in China and four E-types (A, C, G, and H) in Florida. The 'Ca. L. asiaticus' strains from China consisted predominately of E-type A (71.3%) and E-type B (19.7%). In contrast, the 'Ca. L. asiaticus' strains from Florida was predominated by E-type G (82.4%). Diversity of 'Ca. L. asiaticus' in China was also evidenced. Strains from the high altitude Yunnan Province consisted of five E-types with E-type B being the majority (62.8%), whereas strains from the low altitude coastal Guangdong Province consisted of only two E-types with E-type A as the majority (97.0%). Sequence analyses revealed that variation of DNA amplicons was due to insertion/deletion events at CLIBASIA_05650 and the downstream intergenic region.

Conclusions

This study demonstrated the genomic mosaicism of 'Ca. L. asiaticus' resulted from active DNA insertion/deletion activities. Analyses of strain variation depicted the significant inter- and intra-continent diversity of 'Ca. L. asiaticus'.

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