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Diversity of “Candidatus Liberibacter asiaticus” strains in California

Jianchi Chen: USDA, ARS, SJVASC

<div>Citrus Huanglongbing (HLB) is a highly destructive disease and associated with a non-culturable bacterium, “<em>Candidatus</em> Liberibacter asiaticus” (<em>C</em>Las). Characterization of <em>C</em>Las strains is critical for HLB management. HLB was found in Florida in 2005 and now is endemic there. In California, <em>C</em>Las was first detected in Los Angeles County in 2012. Since then, the bacterium has been detected in multiple urban locations in southern California. Little is known about the diversity and biology of these <em>C</em>Las strains. In this study, nine <em>C</em>Las strains from six southern California cities were analyzed targeting chromosomal loci and prophage regions based on next generation sequencing (Illumina MiSeq and HiSeq). No variation was detected in 16S rRNA and <em>nrd</em>B gene sequences. All California <em>C</em>Las strains were of Asiatic origin, rather than Florida, based on <em>ter</em>L gene grouping. Single Type 1 prophages were found in <em>C</em>Las strains from Anaheim, Cerritos, San Gabriel, and Riverside; Single Type 2 prophage was found in a Hacienda Heights strain; Type 1 and 3 prophages were found in a Cerritos strain, and Type 1 and 2 prophages were found in a La Habra strain. All prophages harbored Miniature Inverted-Repeat Transposable Elements (MITEs) with Type B MITEs associated to Type 1 and Type 3 prophages and Type A MITEs associated with Type 2 prophages. This information provides data useful to track the origin and pathway of <em>C</em>Las strains and is critical for the management of the disease.</div>