title: Prophage-mediated dynamics of 'Candidatus Liberibacter asiaticus' populations, the destructive bacterial pathogens of citrus huanglongbing.
abstract: Prophages are highly dynamic components in the bacterial genome and play an important role in intraspecies variations. There are at least two prophages in the chromosomes of Candidatus Liberibacter asiaticus' (Las) Floridian isolates. Las is both unculturable and the most prevalent species of Liberibacter pathogens that cause huanglongbing (HLB), a worldwide destructive disease of citrus. In this study, seven new prophage variants resulting from two hyper-variable regions were identified by screening clone libraries of infected citrus, periwinkle and psyllids. Among them, Types A and B share highly conserved sequences and localize within the two prophages, FP1 and FP2, respectively. Although Types B and C were abundant in all three libraries, Type A was much more abundant in the libraries from the Las-infected psyllids than from the Las-infected plants, and Type D was only identified in libraries from the infected host plants but not from the infected psyllids. Sequence analysis of these variants revealed that the variations may result from recombination and rearrangement events. Conventional PCR results using type-specific molecular markers indicated that A, B, C and D are the four most abundant types in Las-infected citrus and periwinkle. However, only three types, A, B and C are abundant in Las-infected psyllids. Typing results for Las-infected citrus field samples indicated that mixed populations of Las bacteria present in Floridian isolates, but only the Type D population was correlated with the blotchy mottle symptom. Extended cloning and sequencing of the Type D region revealed a third prophage/phage in the Las genome, which may derive from the recombination of FP1 and FP2. Dramatic variations in these prophage regions were also found among the global Las isolates. These results are the first to demonstrate the prophage/phage-mediated dynamics of Las populations in plant and insect hosts, and their correlation with insect transmission and disease development.
authors.affiliation: Horticultural Research Laboratory, Agricultural Research Service, US Department of Agriculture, Fort Pierce, Florida, United States of America ; Indian River Research and Education Center, University of Florida, Fort Pierce, Florida, United States of America.
authors.forename: Lijuan
authors.initials: L
authors.lastname: Zhou
authors.affiliation: Indian River Research and Education Center, University of Florida, Fort Pierce, Florida, United States of America.
authors.forename: Charles A
authors.initials: CA
authors.lastname: Powell
authors.affiliation: Center for Plant Health, Science and Technology, Animal and Plant health Inspection Service, US Department of Agriculture, Beltsville, Maryland, United States of America.
authors.forename: Wenbin
authors.initials: W
authors.lastname: Li
authors.affiliation: Southern Garden Citrus, U. S. Sugar Corp., Clewiston, Florida, United States of America.
authors.forename: Mike
authors.initials: M
authors.lastname: Irey
authors.affiliation: Horticultural Research Laboratory, Agricultural Research Service, US Department of Agriculture, Fort Pierce, Florida, United States of America.
authors.forename: Yongping
authors.initials: Y
authors.lastname: Duan
mesh_terms: D020561:Alphaproteobacteria / Q000502:physiology* / Q000821:virology*; D000818:Animals; D044822:Biodiversity; D030008:Catharanthus / Q000382:microbiology; D002957:Citrus / Q000382:microbiology*; D005431:Florida; D015723:Gene Library; D015321:Gene Rearrangement; D005843:Geography; D006430:Hemiptera / Q000382:microbiology; D054884:Host-Pathogen Interactions; D008969:Molecular Sequence Data; D016133:Polymerase Chain Reaction; D039002:Prophages / Q000502:physiology*; D011995:Recombination, Genetic / Q000235:genetics; D015203:Reproducibility of Results