Mucus Glycoproteins Selectively Secreted from Bacteriocytes in Gill Filaments of the Deep-Sea Clam <i>Calyptogena okutanii</i>

The deep-sea clam Calyptogena okutanii possesses a large gill containing vertically transmitted symbiotic sulfur-oxidizing bacteria. It produces large amounts of highly viscoelastic mucus from the gill, which is thought to be a physical and chemical barrier. The mucus collected from the gill was shown to be composed of glycoproteins having the following sugar composition: Man (17.4%), GlcNAc (16.6%), GalNAc (15%), Glc (1.1%), Gal (29.9%), Xyl (3.0%), Fuc (14.4%), and unknown (2.6%), indicating that it contained mucin-like glycoproteins. In a monoclonal antibody library against the gill tissue, we found a monoclonal antibody (mAb), CokG-B3C10, reacting to the mucus. Western blot analysis using the mAb showed that it reacted to several glycoproteins in the mucus from the gill tissue, but not with those of other tissues such as the mantle, foot, and ovary, where mucus production has been reported in bivalves. Further, immunohistochemical analysis showed the CokG-B3C10 mAb reacting to glycoproteins was detected in the inner area of the gill, which was occupied by many bacteriocytes in the row of gill filaments. Strong mAb signals were found on the outer surface of the bacteriocytes facing the interfilamental space, and in the interfilamental spaces between filaments. Weaker signals were also observed in the bacteriocyte cells. These results indicate that the CokG-B3C10 mAbbinding mucus glycoproteins were produced from cells including bacteriocytes and nonbacteriocyte cells in the inner area of the gill filaments.

Patterns of host cell inheritance in the bacterial symbiosis of whiteflies

Whiteflies possess bacterial symbionts Candidatus Portiera aleyrodidium that are housed in specialized cells called bacteriocytes and are faithfully transmitted via the ovary to insect offspring.In one whitefly species studied previously,Bemisia tabaci MEAMI,transmission is mediated by somatic inheritance of bacteriocytes,with a single bacteriocyte transferred to each oocyte and persisting through embryogenesis to the next generation.Here,we investigate the mode of bacteriocyte transmission in two whiefly species,B.tabaci MED,the sister species of MEAM1,and the phylogenetically distant species Trialeurodes vaporariorum.Microsatllite analysis supported by microscopical studies demonstrates that B.tabaci MED bacteriocytes are genetically different from other somatic cells and persist through embryogenesis,as for MEAMI,but T.vaporariorum bacteriocytes are genetically identical to other somatic cells of the insect,likely mediated by the degradation of maternal bacteriocytes in the embryo.These two alternative modes of transmission provide a first demonstration among insect symbioses that the cellular processes underlying vertical transmission of bacterial symbionts can diversify among related host species associated with a single lineage of symbiotic bacteria.