Functional and comparative genomic analysis of integrated prophage-like sequences inCandidatus Liberibacter asiaticus

Huanglongbing (HLB; yellow shoot disease) is a severe worldwide infectious disease for citrus family plants. The pathogen Candidatus Liberibacter asiaticus (CLas) is an alphapro-teobacterium of the Rhizobiaceae family that has been identified as the cause. The virulence of CLas has been attributed, in part, to prophage encoded genes. Prophage and prophage like elements have been identified in 12 of the 15 CLas available genomes, and are classified into three prophage types. Here, we re-examined all 15 CLas genomes using a de novo prediction approach and expanded the number of prophage like elements from 16 to 33. Further, we find that all CLas contain at least one prophage-like sequence. Comparative analysis reveals a prevalent, albeit previously unknown, prophage-like sequence type that is a remnant of an integrated prophage. Notably, this remnant prophage is found in the Ishi-1 CLas strain that had previously been reported as lacking prophages. Our findings provide both a resource and new insights into the evolutionary relationship between phage and CLas pathogenicity.