Actual distribution of bacteriocytes in the trophosome of a beard worm (Oligobrachia mashikoi, Siboglinidae, Annelida): clarification using whole‐mountin situhybridization

Abstract

it is important to determine how the bacteriocytes are organised in the trophosome. As ｔhe first step of the present study, the appearance of bacteriocytes was examined in routinely stained paraffin sections.Secondly, visualisation of the actual distribution of the bacteriocytes was attempted using whole-mount in situ hybridisation with a probe of the 16S rRNA nucleotide sequence of the bacterium. After routine haematoxylin and eosin staining, the bacteriocytes appeared to be aligned in cell cords accompanied with nutrient-deposit cells that extended from both sides of the trophosome toward the dorsal side and folded up in the coelomic spaces. In whole-mount preparations, however, bacteriocytes with intense signals of 16S rRNA were seen three-dimensionally as many irregular leaves arranged from both sides of the ventral vessel toward the dorsal vessel. 2We will discuss the physiological significance of this characteristic distribution of the bacteriocytes in the present species.

Alpha-Glucosidase-like Activity Detected in a Siboglinid Polychaete, Oligobrachia mashikoi

“…On the other hand, beard worms prefer to inhabit cold seeps in which hydrogen sulfide levels are rather low compared with those in the tubeworm environment (Schulze et al, 2003). In beard worms, there is no systematic organization of the bacteriocytes in the trophosome, unlike that seen in tubeworms (Southward, 1982;Deguchi et al, 2007). Since the beard worm trophosome is limited to the posterior region of the body, bacteria occupy no more than 1% of the body volume (Southward, 1982).…”

Distribution and Population of Free-Living Cells Related to Endosymbiont A Harbored in Oligobrachia mashikoi (a Siboglinid Polychaete) Inhabiting Tsukumo Bay

“…Therefore, in addition to free-living cells of the endosymbionts, other factors may be required for the growth of O. mashikoi. Judging from the morphology of the endosymbiotic cells 11) and the existence of the extracellular giant hemoglobin, which is thought to convey sulfides to the endosymbionts 29) , the O. mashikoi endosymbionts seem to be sulfur-oxidizing bacteria. Total sulfide levels in sediment collected from a region in which O. mashikoi adults live were moderate 36) .…”

“…When the worm is pushed out of the tube, the body is about 13 cm long and 0.6-0.8 mm wide 37) . The adult worm lacks a mouth and a digestive tract, and harbors bacterial cells in its bacteriocytes, like other beard worms 11,38) . Transmission electron micrographs show that the morphology of the endosymbiotic cells is uniform 11) .…”

“…The adult worm lacks a mouth and a digestive tract, and harbors bacterial cells in its bacteriocytes, like other beard worms 11,38) . Transmission electron micrographs show that the morphology of the endosymbiotic cells is uniform 11) . Although we classified the endosymbionts into seven types (endosymbiont A-G) on the basis of the nucleotide sequences of the 16S rRNA gene, one adult worm of O. mashikoi harbors just one of the seven types 25) .…”

Direct Evidence That Extracellular Giant Hemoglobin is Produced in Chloragogen Tissues in a Beard Worm, Oligobrachia mashikoi (Frenulata, Siboglinidae, Annelida)

“…To detect the actin cDNA of O. mashikoi, primers were designed on the basis of sequence information in an O. mashikoi cDNA library (Sasayama et al, 2006, unpublished data): actin forward primer 5'-GCCCCA-GAGGAGCACCCAGT-3' and actin reverse primer 5'-CATCTCCT-GCTCGAAGTCGAG-3'. …”