National Engineering Research Center for Citrus, Citrus Research Institute, Southwest University, Chongqing 400712, People's Republic of China.
BMC Microbiol. 2012 Jan 26;12:18. doi: 10.1186/1471-2180-12-18.
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.
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.
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'.
黄龙病（HLB）是世界范围内对柑橘生产具有高度破坏性的疾病。“亚洲韧皮杆菌”（Ca. Liberibacter asiaticus），一种不可培养的α变形菌，是 HLB 的假定病原体。目前，有关“Ca. L. asiaticus”的生物学和菌株多样性的信息有限，这限制了 HLB 的研究和控制范围。
鉴定并研究了“Ca. L. asiaticus”的一个基因组区域（CLIBASIA_05640 到 CLIBASIA_05650），该区域显示出超序列变异或基因座镶嵌现象。使用 262 株细菌菌株（188 株来自中国，74 株来自佛罗里达州）进行了研究。基于特定引物对产生的 PCR 扩增子的特征电泳图谱，鉴定出了 8 种电泳类型（E 型），其中 6 种 E 型（A、B、C、D、E 和 F）在中国，4 种 E 型（A、C、G 和 H）在佛罗里达州。中国的“Ca. L. asiaticus”菌株主要由 E 型 A（71.3%）和 E 型 B（19.7%）组成。相比之下，佛罗里达州的“Ca. L. asiaticus”菌株则主要由 E 型 G（82.4%）组成。中国“Ca. L. asiaticus”的多样性也得到了证实。来自高海拔云南省的菌株包含 5 种 E 型，其中 E 型 B 占多数（62.8%），而来自低海拔沿海广东省的菌株仅包含 2 种 E 型，其中 E 型 A 占多数（97.0%）。序列分析表明，DNA 扩增子的变异是由于 CLIBASIA_05650 和下游基因间区的插入/缺失事件引起的。
本研究表明，“Ca. L. asiaticus”的基因组镶嵌是由活跃的 DNA 插入/缺失活动引起的。菌株变异分析描绘了“Ca. L. asiaticus”在洲际间和洲内的显著多样性。
