Short Report

Comparative phylogenomics and multi-gene cluster analyses of the Citrus Huanglongbing (HLB)-associated bacterium Candidatus Liberibacter

Harshavardhan Doddapaneni^1,2 , Huihong Liao^3,4 , Hong Lin¹ , Xianjin Bai³ , Xiaolong Zhao⁵ , Edwin L Civerolo¹ , Michael Irey⁶ , Helvecio Coletta-Filho⁷ and Gerhard Pietersen⁸

¹USDA-ARS. San Joaquin Valley Agricultural Science Center, 9611 So. Riverbend Avenue, Parlier, CA 93648, USA

²University of California Davis, Department of Viticulture and Enology, Davis, CA 95616, USA

³Guangxi Academy of Agricultural Sciences, Nanning, PR China

⁴Agricultural College, Guangxi University, Nanning, 530004, PR China

⁵Guangxi Citrus Research Institute, Guilin, PR China

⁶United States Sugar Corporation, Clewiston, Fl 33440, USA

⁷Instituto Agronémico de Campinas, Cordeirópolis, Brazil

⁸Citrus Research International c/o University of Pretoria, Pretoria, Republic of South Africa

author email corresponding author email

BMC Research Notes 2008, 1:72doi:10.1186/1756-0500-1-72

Published:	28 August 2008

Abstract

Background

Huanglongbing (HLB, previously known as citrus greening), is associated with Candidatus Liberibacter species and is a serious threat to citrus production world-wide. The pathogen is a Gram negative, unculturable, phloem-limited bacterium with limited known genomic information. Expanding the genetic knowledge of this organism may provide better understanding of the pathogen and possibly develop effective strategies for control and management of HLB.

Results

Here, we report cloning and characterization of an additional 14.7 Kb of new genomic sequences from three different genomic regions of the Candidatus Liberibacter asiaticus (Las). Sequence variation analyses among the available Ca. Liberibacter species sequences as well as the newly cloned 1.5 Kb of rpoB gene from different Ca. Liberibacter strains have identified INDELs and SNPs. Phylogenetic analysis of the deduced protein sequences from the cloned regions characterizes the HLB-associated Candidatus Liberibacter as a new clade in the sub-division of the α-proteobacteria.

Conclusion

Comparative analyses of the cloned gene regions of Candidatus Liberibacter with members of the order Rhizobiales suggest overall gene structure and order conservation, albeit with minor variations including gene decay due to the identified pseudogenes. The newly cloned gene regions contribute to our understanding of the molecular aspects of genomic evolution of Ca. Liberibacter.