ARS | Publication request: Molecular Characterization of the Citrus Huanglongbing (HLB) associated bacterium Candidatus Liberibacter

Submitted to: International Citrus Congress Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: August 15, 2008
Publication Date: October 26, 2008
Citation: Doddapaneni, H., Lin, H., Liao, H., Bai, X., Zhao, X., Civerolo, E.L. 2008. Molecular Characterization of the Citrus Huanglongbing (HLB) associated bacterium Candidatus Liberibacter. International Citrus Congress Proceedings: Pg. 53.

Technical Abstract: Candidatus Liberibacter is a a-protobacterium associated with citrus Huanglongbing (HLB), a serious threat to citrus production world-wide. We have developed a modified technique to acquire uncharacterized genomic sequences of Candidatus Liberibacter asiaticus (Las), Ca. L. africanus and Ca. L. americanus. Here, we present comparative phylogenomic analyses of newly cloned sequences from these species. In addition, analyses of sequence data from pyrosequencing studies of Ca. Liberibacter were used to predict a possible structure of the Liberibacter genome and identify several genes that have common and distinctive features to taxonomically related bacteria from Rhizobiales and Rickettsiales. Multiple polymorphisms in 16S and other gene regions were identified among Ca. Las strains from China, Brazil, Florida and Japan, Ca. L. africanus (Laf) strains from South Africa and Ca. L. americanus (Lam) strains from Brazil. Phylogenetic analyses of deduced protein sequences from the cloned regions characterize Candidatus Liberibacter as a new clade in the sub-division of the a-proteobacteria, consistent with the 16S rRNA gene analyses. Molecular evolutionary clock analyses estimated evolutionary time based on full-length 16S rRNA gene sequences from multiple strains of three species of Liberibacter. This study suggested that monophyletic origin of Candidatus Liberibacter and subsequent speciation occurred in the last 110-120 million years, a time scale coincident with the breakup of the supercontinent Gondwana.