Submitted to: Current Microbiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/16/2014
Publication Date: 6/10/2014
Citation: Deng, X., Chen, J., Lopes, S., Wang, X., Sun, X., Jones, D., Irey, M., Civerolo, E.L. 2014. Diversity of “Candidatus Liberibacter asiaticus” strains from Brazil, China, and United States at two hyper-variable genomic loci. Current Microbiology. Available:http://dx.doi.org/10.1007/s00284-014-0621-9. Interpretive Summary: Huanglongbing (HLB, yellow shoot disease) is a highly destructive disease of citrus production worldwide. A bacterium, called “Candidatus Liberibacter asiaticus”(CLas), is associated with HLB. Characterization of the diversity of CLas strains from different geographical regions will facilitate development of HLB control strategies. In this study, CLas strains were collected from Brazil, China and the United States and evaluated using two DNA markers, which are highly sensitive in detecting CLas variation. Although the two markers are different in their variation mechanisms, analyses using the two markers complimented each other and concluded that CLas strains grouped according to geographical origins but overlapping strains also occurred. This is also the first to reveal that the CLas strains from Brazil are unique and recently introduced. The results of this research will lead to development of improved diagnostic capabilities, and improved understanding of the ecology of CLas and epidemiology of HLB.
Technical Abstract: Huanglongbing (HLB, yellow shoot disease) is a highly destructive disease of citrus production worldwide. “Candidatus Liberibacter asiaticus” is associated with HLB. In this study, the diversity of “Ca. L. asiaticus” populations from Brazil, China and the United States was evaluated using two hyper-variable genomic loci, CLIBASIA_01645 and CLIBASIA_05610. The former has a region with variable tandem repeat numbers (TRNs) and the latter has single nucleotide polymorphisms (SNPs). At the CLIBASIA_01645 locus, “Ca. L. asiaticus” strains fell into TRN<10 and TRN>10 groups. Strain of TRN<10 group dominated the China and U.S. bacterial populations as previously reported (Phytopathology 100:567-572) and were not found in Brazil. TRN>10 group included all Brazil strains and occurred at low frequencies in China (3%) and U.S. (6%). Analyses at the CLIBASIA_05610 locus established two groups with 9 SNPs: Term-A and Term-G, namely. All Brazil and China strains were in Term-A group, covering both TRN<10 and TRN>10 strains. A few Term-A strains were found in the U.S. and they were also TRN>10 strains. Term-G strains were only detected in U.S. analyses of data from the two genomic loci indicated that “Ca. L. asiaticus” strains clustered according to geographical origin but overlapping genotypes occurred. The dominance of TRN>10:Term-A strains also suggested the recent introduction of “Ca. L. asiaticus” in Brazil.