Technical Abstract: 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 may provide better understanding of the presumptive pathogen and possibly aid development of effective strategies for control and management of HLB. Here, we report cloning and characterization of an additional 14.7 Kbp of new genomic sequences from three different genomic regions of Candidatus Liberibacter asiaticus (Las). Analysis of available Ca. Liberibacter species sequences, including the newly cloned 1.5 Kb of rpoB gene, identified INDELs and SNPs. Phylogenetic analysis of deduced protein sequences from the cloned regions characterized Candidatus Liberibacter as a new clade in the subdivision of the a-proteobacteria. Comparative analyses of gene cluster organization of Candidatus Liberibacter with members of the order Rhizobiales suggest overall gene structure and order conservation, albeit with minor variation. Most notably, the presence of pseudogenes suggest that genomes of Candidatus Liberibacter species have undergone gene decay.