Publications

4474

ABSTRACT Two novel methanesulfonate-degrading bacterial strains of “ Candidatus Filomicrobium marinum” (strains Y and W) were isolated from a marine water enrichment, and their complete genome sequences are presented here. These are the first full genomes reported for the genus Filomicrobium and for methanesulfonate (MSA)-degrading bacteria.

ABSTRACT Huanglongbing, or citrus greening, is a devastating disease of citrus plants recently spreading worldwide, which is caused by an uncultivable bacterial pathogen, “ Candidatus Liberibacter asiaticus,” and vectored by a phloem-sucking insect, Diaphorina citri . We investigated the infection density dynamics of “ Ca . Liberibacter asiaticus” in field populations of D. citri with experiments using field-collected insects to address how “ Ca . Liberibacter asiaticus” infection density in the vector insect is relevant to pathogen transmission to citrus plants. Of 500 insects continuously collected from “ Ca . Liberibacter asiaticus”-infected citrus trees with pathological symptoms in the spring and autumn of 2009, 497 (99.4%) were “ Ca . Liberibacter asiaticus” positive. The infections were systemic across head-thorax and abdomen, ranging from 10 3 to 10 7 bacteria per insect. In spring, the infection densities were low in March, at ∼10 3 bacteria per insect, increasing up to 10 6 to 10 7 bacteria per insect in April and May, and decreasing to 10 5 to 10 6 bacteria per insect in late May, whereas the infection densities were constantly ∼10 6 to 10 7 bacteria per insect in autumn. Statistical analysis suggested that several factors, such as insect sex, host trees, and collection dates, may be correlated with “ Ca . Liberibacter asiaticus” infection densities in field D. citri populations. Inoculation experiments with citrus seedlings using field-collected “ Ca . Liberibacter asiaticus”-infected insects suggested that (i) “ Ca . Liberibacter asiaticus”-transmitting insects tend to exhibit higher infection densities than do nontransmitting insects, (ii) a threshold level (∼10 6 bacteria per insect) of “ Ca . Liberibacter asiaticus” density in D. citri is required for successful transmission to citrus plants, and (iii) D. citri attaining the threshold infection level transmits “ Ca . Liberibacter asiaticus” to citrus plants in a stochastic manner. These findings provide valuable insights into understanding, predicting, and controlling this notorious citrus pathogen.