AbstractTrypanosomatids of the genera Angomonas and Strigomonas (subfamily Strigomonadinae) have long been known to contain intracellular beta-proteobacteria, which provide them with many important nutrients such as haem, essential amino acids and vitamins. Recently, Kentomonas sorsogonicus, a divergent member of Strigomonadinae, has been described. Herein, we characterize the genome of its endosymbiont, Candidatus Kinetoplastibacterium sorsogonicusi. This genome is completely syntenic with those of other known Ca. Kinetoplastibacterium spp., but more reduced in size (~742 kb, compared with 810–833 kb, respectively). Gene losses are not concentrated in any hot-spots but are instead distributed throughout the genome. The most conspicuous loss is that of the haem-synthesis pathway. For long, removing haemin from the culture medium has been a standard procedure in cultivating trypanosomatids isolated from insects; continued growth was considered as an evidence of endosymbiont presence. However, we demonstrate that, despite bearing the endosymbiont, K. sorsogonicus cannot grow in culture without haem. Thus, the traditional test cannot be taken as a reliable criterion for the absence or presence of endosymbionts in trypanosomatid flagellates. It remains unclear why the ability to synthesize such an essential compound was lost in Ca. K. sorsogonicusi, whereas all other known bacterial endosymbionts of trypanosomatids retain them.
ABSTRACT
“
Candidatus
Liberibacter asiaticus” is the causative bacterium associated with citrus greening disease. “
Ca
. Liberibacter asiaticus” is transmitted by
Diaphorina citri
more efficiently when it is acquired by nymphs rather than adults. Why this occurs is not known. We compared midguts of
D. citri
insects reared on healthy or “
Ca
. Liberibacter asiaticus”-infected citrus trees using quantitative PCR, confocal microscopy, and mitochondrial superoxide staining for evidence of oxidative stress. Consistent with its classification as propagative, “
Ca
. Liberibacter asiaticus” titers were higher in adults than in nymphs. Our previous work showed that adult
D. citri
insects have basal levels of karyorrhexis (fragmentation of the nucleus) in midgut epithelial cells, which is increased in severity and frequency in response to “
Ca
. Liberibacter asiaticus.” Here, we show that nymphs exhibit lower levels of early-stage karyorrhexis than adults and are refractory to the induction of advanced karyorrhexis by “
Ca
. Liberibacter asiaticus” in the midgut epithelium. MitoSox Red staining showed that guts of infected adults, particularly males, experienced oxidative stress in response to “
Ca
. Liberibacter asiaticus.” A positive correlation between the titers of “
Ca
. Liberibacter asiaticus” and the
Wolbachia
endosymbiont was observed in adult and nymph midguts, suggesting an interplay between these bacteria during development. We hypothesize that the resistance of the nymph midgut to late-stage karyorrhexis through as yet unknown molecular mechanisms benefits “
Ca
. Liberibacter asiaticus” for efficient invasion of midgut epithelial cells, which may be a factor explaining the developmental dependency of “
Ca
. Liberibacter asiaticus” acquisition by the vector.