Complete Genome Sequence of Citrus Huanglongbing Bacterium, 'Candidatus Liberibacter asiaticus' Obtained Through Metagenomics

• Published in: Molecular plant-microbe interactions Vol. 22; no. 8; pp. 1011 - 1020
• Main Authors: Duan, Yongping, Zhou, Lijuan, Hall, David G, Li, Wenbin, Doddapaneni, Harshavardhan, Lin, Hong, Liu, Li, Vahling, Cheryl M, Gabriel, Dean W, Williams, Kelly P, Dickerman, Allan, Sun, Yijun, Gottwald,Tim
• Format: Journal Article
• Language: English
• Published: St. Paul, MN APS Press 01.08.2009; The American Phytopathological Society
• Subjects: active transport; Animals; bacterial proteins; Bacterial Proteins - genetics; Biological and medical sciences; Candidatus Liberibacter asiaticus; Carrier Proteins - genetics; cell motility; cell respiration; Citrus - microbiology; DNA; Fundamental and applied biological sciences. Psychology; genome; Genome, Bacterial; genomics; Genomics - methods; Hemiptera - microbiology; metagenomics; microbial genetics; Molecular Sequence Data; nucleotide sequences; Phylogeny; Phytopathology. Animal pests. Plant and forest protection; plant pathogenic bacteria; Psyllidae; Rhizobiaceae - genetics; Rhizobiaceae - isolation & purification; Rhizobiaceae - metabolism; Sequence Analysis, DNA; symbionts; Symbiosis; transport proteins; Type III secretion system; Citrus; Plant; Microbiology; Nucleotide sequence; Citrus fruit; Dicotyledones; Angiospermae; Rutaceae; Spermatophyta; Metagenome
• ISSN: 0894-0282; 1943-7706
• DOI: 10.1094/MPMI-22-8-1011

Citrus huanglongbing is the most destructive disease of citrus worldwide. It is spread by citrus psyllids and is associated with a low-titer, phloem-limited infection by any of three uncultured species of α-Proteobacteria, 'Candidatus Liberibacter asiaticus', 'Ca. L. americanus', and 'Ca. L. africanus'. A complete circular 'Ca. L. asiaticus' genome has been obtained by metagenomics, using the DNA extracted from a single 'Ca. L. asiaticus'-infected psyllid. The 1.23-Mb genome has an average 36.5% GC content. Annotation revealed a high percentage of genes involved in both cell motility (4.5%) and active transport in general (8.0%), which may contribute to its virulence. 'Ca. L. asiaticus' appears to have a limited ability for aerobic respiration and is likely auxotrophic for at least five amino acids. Consistent with its intracellular nature, 'Ca. L. asiaticus' lacks type III and type IV secretion systems as well as typical free-living or plant-colonizing extracellular degradative enzymes. 'Ca. L. asiaticus' appears to have all type I secretion system genes needed for both multidrug efflux and toxin effector secretion. Multi-protein phylogenetic analysis confirmed 'Ca. L. asiaticus' as an early-branching and highly divergent member of the family Rhizobiaceae. This is the first genome sequence of an uncultured α-proteobacteria that is both an intracellular plant pathogen and insect symbiont.