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Almost there: transmission routes of bacterial symbionts between trophic levels.

Chiel E, Zchori-Fein E, Inbar M, Gottlieb Y, Adachi-Hagimori T, Kelly SE, Asplen MK, Hunter MS - PLoS ONE (2009)

Bottom Line: Using florescence in situ hybridization (FISH) and transmission electron microscopy we found that Rickettsia invades Eretmocerus larvae during development in a Rickettsia-infected host, persists in adults and in females, reaches the ovaries.However, Rickettsia does not appear to penetrate the oocytes, but instead is localized in the follicular epithelial cells only.In contrast with Rickettsia, Hamiltonella did not establish in any of the parasitoids tested, and none of the parasitoids acquired Hamiltonella by host feeding.

View Article: PubMed Central - PubMed

Affiliation: Department of Evolutionary and Environmental Biology, University of Haifa, Haifa, Israel. chiel@email.arizona.edu

ABSTRACT
Many intracellular microbial symbionts of arthropods are strictly vertically transmitted and manipulate their host's reproduction in ways that enhance their own transmission. Rare horizontal transmission events are nonetheless necessary for symbiont spread to novel host lineages. Horizontal transmission has been mostly inferred from phylogenetic studies but the mechanisms of spread are still largely a mystery. Here, we investigated transmission of two distantly related bacterial symbionts--Rickettsia and Hamiltonella--from their host, the sweet potato whitefly, Bemisia tabaci, to three species of whitefly parasitoids: Eretmocerus emiratus, Eretmocerus eremicus and Encarsia pergandiella. We also examined the potential for vertical transmission of these whitefly symbionts between parasitoid generations. Using florescence in situ hybridization (FISH) and transmission electron microscopy we found that Rickettsia invades Eretmocerus larvae during development in a Rickettsia-infected host, persists in adults and in females, reaches the ovaries. However, Rickettsia does not appear to penetrate the oocytes, but instead is localized in the follicular epithelial cells only. Consequently, Rickettsia is not vertically transmitted in Eretmocerus wasps, a result supported by diagnostic polymerase chain reaction (PCR). In contrast, Rickettsia proved to be merely transient in the digestive tract of Encarsia and was excreted with the meconia before wasp pupation. Adults of all three parasitoid species frequently acquired Rickettsia via contact with infected whiteflies, most likely by feeding on the host hemolymph (host feeding), but the rate of infection declined sharply within a few days of wasps being removed from infected whiteflies. In contrast with Rickettsia, Hamiltonella did not establish in any of the parasitoids tested, and none of the parasitoids acquired Hamiltonella by host feeding. This study demonstrates potential routes and barriers to horizontal transmission of symbionts across trophic levels. The possible mechanisms that lead to the differences in transmission of species of symbionts among species of hosts are discussed.

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FISH of En. pergandiella stained with Rickettisa specific probe (blue).Left panel-Rickettsia probe fluorescent channel; right panel- overlay of fluorescent and brightfield channels. A- parasitoid larvae, arrow points to specific signal inside the larva body. B- parasitoid pupa, arrows pointing to the meconia deposited outside the parasitoid's body.
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pone-0004767-g003: FISH of En. pergandiella stained with Rickettisa specific probe (blue).Left panel-Rickettsia probe fluorescent channel; right panel- overlay of fluorescent and brightfield channels. A- parasitoid larvae, arrow points to specific signal inside the larva body. B- parasitoid pupa, arrows pointing to the meconia deposited outside the parasitoid's body.

Mentions: Examination of the symbionts' localization by means of FISH shows a concentration of Rickettsia in the center of the Eretmocerus spp larval body in what seems to be the parasitoid's digestive tract, as well as scattered signals outside of the larval body in the remaining whitefly hemolymph (Fig. 2A). Later on, in the pupal stage, Rickettsia is aggregated in a kidney (or oval) shape within the wasp larva, and is more distal, toward the tip of the abdomen (Fig. 2B). Looking at an image without fluorescence shows an identical kidney-shaped concentration of small, dark spheres that are likely meconia (fecal material, typically retained within the wasp body until late in development) (Fig. 2C). In En. pergandiella, Rickettsia signals can be seen along the digestive tract of the crescent-shaped third instar larva as well as outside of the larva (Fig. 3A). In the pupal stage, however, Rickettsia is clearly present only in the meconia, deposited before pupation on both sides of the pre-pupal wasp (Fig. 3B). These FISH results are consistent with the results of the acquisition and sustainability experiment. In particular, they support the finding that adult En. pergandiella that developed on R+ whiteflies are not infected, and suggest that the detection of Rickettsia in pupal En. pergandiella by PCR is likely due to an extraction method that includes the whitefly cuticle and meconial pellets that surrounds the pupal wasp.


Almost there: transmission routes of bacterial symbionts between trophic levels.

Chiel E, Zchori-Fein E, Inbar M, Gottlieb Y, Adachi-Hagimori T, Kelly SE, Asplen MK, Hunter MS - PLoS ONE (2009)

FISH of En. pergandiella stained with Rickettisa specific probe (blue).Left panel-Rickettsia probe fluorescent channel; right panel- overlay of fluorescent and brightfield channels. A- parasitoid larvae, arrow points to specific signal inside the larva body. B- parasitoid pupa, arrows pointing to the meconia deposited outside the parasitoid's body.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2651630&req=5

pone-0004767-g003: FISH of En. pergandiella stained with Rickettisa specific probe (blue).Left panel-Rickettsia probe fluorescent channel; right panel- overlay of fluorescent and brightfield channels. A- parasitoid larvae, arrow points to specific signal inside the larva body. B- parasitoid pupa, arrows pointing to the meconia deposited outside the parasitoid's body.
Mentions: Examination of the symbionts' localization by means of FISH shows a concentration of Rickettsia in the center of the Eretmocerus spp larval body in what seems to be the parasitoid's digestive tract, as well as scattered signals outside of the larval body in the remaining whitefly hemolymph (Fig. 2A). Later on, in the pupal stage, Rickettsia is aggregated in a kidney (or oval) shape within the wasp larva, and is more distal, toward the tip of the abdomen (Fig. 2B). Looking at an image without fluorescence shows an identical kidney-shaped concentration of small, dark spheres that are likely meconia (fecal material, typically retained within the wasp body until late in development) (Fig. 2C). In En. pergandiella, Rickettsia signals can be seen along the digestive tract of the crescent-shaped third instar larva as well as outside of the larva (Fig. 3A). In the pupal stage, however, Rickettsia is clearly present only in the meconia, deposited before pupation on both sides of the pre-pupal wasp (Fig. 3B). These FISH results are consistent with the results of the acquisition and sustainability experiment. In particular, they support the finding that adult En. pergandiella that developed on R+ whiteflies are not infected, and suggest that the detection of Rickettsia in pupal En. pergandiella by PCR is likely due to an extraction method that includes the whitefly cuticle and meconial pellets that surrounds the pupal wasp.

Bottom Line: Using florescence in situ hybridization (FISH) and transmission electron microscopy we found that Rickettsia invades Eretmocerus larvae during development in a Rickettsia-infected host, persists in adults and in females, reaches the ovaries.However, Rickettsia does not appear to penetrate the oocytes, but instead is localized in the follicular epithelial cells only.In contrast with Rickettsia, Hamiltonella did not establish in any of the parasitoids tested, and none of the parasitoids acquired Hamiltonella by host feeding.

View Article: PubMed Central - PubMed

Affiliation: Department of Evolutionary and Environmental Biology, University of Haifa, Haifa, Israel. chiel@email.arizona.edu

ABSTRACT
Many intracellular microbial symbionts of arthropods are strictly vertically transmitted and manipulate their host's reproduction in ways that enhance their own transmission. Rare horizontal transmission events are nonetheless necessary for symbiont spread to novel host lineages. Horizontal transmission has been mostly inferred from phylogenetic studies but the mechanisms of spread are still largely a mystery. Here, we investigated transmission of two distantly related bacterial symbionts--Rickettsia and Hamiltonella--from their host, the sweet potato whitefly, Bemisia tabaci, to three species of whitefly parasitoids: Eretmocerus emiratus, Eretmocerus eremicus and Encarsia pergandiella. We also examined the potential for vertical transmission of these whitefly symbionts between parasitoid generations. Using florescence in situ hybridization (FISH) and transmission electron microscopy we found that Rickettsia invades Eretmocerus larvae during development in a Rickettsia-infected host, persists in adults and in females, reaches the ovaries. However, Rickettsia does not appear to penetrate the oocytes, but instead is localized in the follicular epithelial cells only. Consequently, Rickettsia is not vertically transmitted in Eretmocerus wasps, a result supported by diagnostic polymerase chain reaction (PCR). In contrast, Rickettsia proved to be merely transient in the digestive tract of Encarsia and was excreted with the meconia before wasp pupation. Adults of all three parasitoid species frequently acquired Rickettsia via contact with infected whiteflies, most likely by feeding on the host hemolymph (host feeding), but the rate of infection declined sharply within a few days of wasps being removed from infected whiteflies. In contrast with Rickettsia, Hamiltonella did not establish in any of the parasitoids tested, and none of the parasitoids acquired Hamiltonella by host feeding. This study demonstrates potential routes and barriers to horizontal transmission of symbionts across trophic levels. The possible mechanisms that lead to the differences in transmission of species of symbionts among species of hosts are discussed.

Show MeSH
Related in: MedlinePlus