Transovarial Transmission of Rickettsia spp. and Organ-Specific Infection of the Whitefly Bemisia tabaci

Abstract

bThe whitefly Bemisia tabaci is a cosmopolitan insect pest that harbors Portiera aleyrodidarum, the primary obligatory symbiotic bacterium, and several facultative secondary symbionts. Secondary symbionts in B. tabaci are generally associated with the bacteriome, ensuring their vertical transmission; however, Rickettsia is an exception and occupies most of the body cavity, except the bacteriome. The mode of Rickettsia transfer between generations and its subcellular localization in insect organs have not been investigated. Using electron and fluorescence microscopy, we show that Rickettsia infects the digestive, salivary, and reproductive organs of the insect; however, it was not observed in the bacteriome. Rickettsia invades the oocytes during early developmental stages and resides in follicular cells and cytoplasm; it is mostly excluded when the egg matures; however, some bacterial cells remain in the egg, ensuring their transfer to subsequent generations. Rickettsia was localized to testicles and the spermatheca, suggesting a horizontal transfer between males and females during mating. The bacterium was further observed at large amounts in midgut cells, concentrating in vacuole-like structures, and was located in the hemolymph, specifically at exceptionally large amounts around bacteriocytes and in fat bodies. Organs further infected by Rickettsia included the primary salivary glands and stylets, sites of possible secretion of the bacterium outside the whitefly body. The close association between Rickettsia and the B. tabaci digestive system might be important for digestive purposes. The vertical transmission of Rickettsia to subsequent generations occurs via the oocyte and not, like other secondary symbionts, the bacteriome.

Diversity and Localization of Bacterial Endosymbionts from Whitefly Species Collected in Brazil

“…In contrast to the rest of the detected endosymbionts in this study, only Rickettsia showed a scattered localization pattern and was observed outside the bacteriome infecting tissues in the abdomen, thorax and head as was recently shown [57]. Rickettsia was shown to manipulate host reproduction in many arthropods [50], [52], and this fits well with its localization pattern in B. tabaci.…”

Implication of the Whitefly Bemisia tabaci Cyclophilin B Protein in the Transmission of Tomato yellow leaf curl virus

“…Population of the B. tabaci B infected with the secondary symbionts Rickettsia and Hamiltonella , rearing conditions and establishment of iso-female strains of Rickettsia -free (R-) and Rickettsia -infected (R+) strains, were conducted as previously described (Brumin et al, 2012). Briefly, the populations were reared on cotton seedlings ( Gossypium hirsutum L. cv.…”

Implication of the Bacterial Endosymbiont Rickettsia spp. in Interactions of the Whitefly Bemisia tabaci with Tomato yellow leaf curl virus

“…Two methods of DNA isolation were used to confirm the presence of Rickettsia or TYLCV: one for single insects and one for pools of insects. To isolate DNA from single insects for PCR, 20 adult B. tabaci were individually homogenized in lysis buffer as previously described (22,25). The lysate was then incubated at 65°C for 15 min, followed by incubation at 95°C for 10 min.…”

“…Only Rickettsia localizes outside the bacteriocytes, appears in most of the body cavity, and infects the majority of the internal organs, excluding the bacteriocytes (22,23). Rickettsia infects B. tabaci's digestive, salivary, and reproductive organs and cells and reaches exceptionally high concentrations within the host (22). These recent findings raised the possibility that the unique localization patterns and infection of pivotal organs in the insect host may significantly influence the insect's biology.…”

“…The release of virions protected by GroEL occurs adjacent to the primary salivary glands (21). Only Rickettsia localizes outside the bacteriocytes, appears in most of the body cavity, and infects the majority of the internal organs, excluding the bacteriocytes (22,23). Rickettsia infects B. tabaci's digestive, salivary, and reproductive organs and cells and reaches exceptionally high concentrations within the host (22).…”