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. 2006 Jan;72(1):769-75.
doi: 10.1128/AEM.72.1.769-775.2006.

Transmission of nephridial bacteria of the earthworm Eisenia fetida

Seana K Davidson  1 , David A Stahl
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Transmission of nephridial bacteria of the earthworm Eisenia fetida (V体育官网入口)

Seana K Davidson et al. Appl Environ Microbiol. 2006 Jan.

"VSports在线直播" Abstract

The lumbricid earthworms (annelid family Lumbricidae) harbor gram-negative bacteria in their excretory organs, the nephridia. Comparative 16S rRNA gene sequencing of bacteria associated with the nephridia of several earthworm species has shown that each species of worm harbors a distinct bacterial species and that the bacteria from different species form a monophyletic cluster within the genus Acidovorax, suggesting that there is a specific association resulting from radiation from a common bacterial ancestor. Previous microscopy and culture studies revealed the presence of bacteria within the egg capsules and on the surface of embryos but did not demonstrate that the bacteria within the egg capsule were the same bacteria that colonized the nephridia. We present evidence, based on curing experiments, in situ hybridizations with Acidovorax-specific probes, and 16S rRNA gene sequence analysis, that the egg capsules contain high numbers of the bacterial symbiont and that juveniles are colonized during development within the egg capsule VSports手机版. Studies exposing aposymbiotic hatchlings to colonized adults and their bedding material suggested that juvenile earthworms do not readily acquire bacteria from the soil after hatching but must be colonized during development by bacteria deposited in the egg capsule. Whether this is due to the developmental stage of the host or the physiological state of the symbiont remains to be investigated. .

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Figures

FIG. 1.
FIG. 1.
Anatomy of earthworm nephridia and location of the associated bacteria. (Left) Schematic diagram of an earthworm (dorsal) with enlargement of one half of the body, showing the location of nephridia within the segments. The numbers indicate the loops. (Right) Schematic drawing of a nephridium, showing the arrangement of the three loops. The arrowheads indicate the direction of flow.
FIG. 2.
FIG. 2.
Earthworm mating and egg capsule formation. (Diagram 1) The worms adhere to each other on the ventral side. A nephridium is shown for a single segment to illustrate the orientation of the nephridia. (Diagram 2) The precapsule forms around the clitellum and slides off the anterior end of the worm. (Diagram 3) The capsule chitinous shell matures. D, dorsal; V, ventral; n, nephridium; p, nephridial pore.
FIG. 3.
FIG. 3.
False color images of bacterial cells detected by FISH in egg capsules of E. fetida using both Cy3-LSB 145 and FL-Eub 338. (A) laser scanning confocal microscope image of a large aggregate representative of aggregates detected in the egg capsule albumin. (B to D) Yellow cells, Acidovorax; red cells, Eub 338 only. (B) Enlargement of the area in the box in panel A. (C) Acidovorax cells, showing morphology similar to the morphology of cells observed in ampullas of E. fetida nephridia. (D) Abundant cells labeled with only Eub 338.
FIG. 4.
FIG. 4.
Proportion of nephridia containing bacteria after 10-day antibiotic treatments of E. fetida egg capsules as detected by FISH. The percentages of infected worms indicate the percentages of nephridia that were colonized by bacteria within a worm.
FIG. 5.
FIG. 5.
Detection of bacteria in juvenile earthworm nephridia by FISH using the Acidovorax-specific Cy3-LSB 145 probe and the FL-Eub 338 probe. (A) Six segments of a hatchling with Acidovorax cells (yellow) detected in ampullas (arrow). (B) Nephridia of adjacent segments in a partially cured juvenile, one colonized (arrow) and the other not colonized. (Inset) Cross section of a colonized ampulla.
FIG. 6.
FIG. 6.
Phylogenetic relationships among earthworm symbionts, E. fetida capsule bacteria, and other members of the genus Acidovorax. The maximum-likelihood topology was determined from sequences aligned with the ARB software package (www.arb-home.de) and analyzed with PAUP V. 4.0beta 10 (30). Bootstrap values (1,000× sampling) are indicated at the nodes. Unsupported branch patterns have been collapsed. C. testeroni was used as the outgroup. The bracket indicates the earthworm nephridial bacterium cluster.
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References

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