Intracellular symbionts (endosymbiotic bacteria), either isolated or in clusters, were found within the cytoplasm and the nucleus of female germ cells and of trophocytes in nymphs and reproductives of two termite species, Kalotermes flavicollis (Isoptera: Kalotermitidae) and Reticulitermes lucifugus (Isoptera: Rhinotermitidae) , collected in the wild. This finding represents the first record of endonuclear symbiotic bacteria in a metazoan species. The bacteria reach the host ovarian cells by crossing the tunica propria. The ultrastructural morphology of the bacteria closely resembles that of cytoplasmic symbionts found in other insect orders (such as Dictyoptera and Homoptera) and their presence does not appear to be correlated with bacteriocytes (or mycetocytes) as in the more primitive termite Mastotermes darwiniensis (Isoptera: Mastotermitidae). The endonuclear symbionts, as well as the cytoplasmic ones, are enveloped by a plasma membrane, by a cell wall typical of Gram-negative bacteria and by a perisymbiotic membrane, the last two separated by an outer periplasmic space. In some of the endonuclear symbionts, however, the perisymbiotic membrane is lacking. Different kinds of inclusions, apparently unrelated to mesosomes, are visible within the endonuclear symbionts. A wide array of vesicles is found in the outer periplasmic space and inside the host chromatin, in close proximity to bacteria. Some vesicles apparently originate tram the outer layer of bacterial cell wall and are freed in the host chromatin by a further process of budding and vesiculation of the perisymbiotic membrane. These observations support the hypothesis of product exchanges between endosymbionts and the host cell. The presence of endonucIear symbionts (also seen in the act of dividing within the nucleus) does not apparently affect the meiotic processes or cause host cell degenerations, although a less dense chromatin, aggregates of granular material, thin cylindroid bodies and bundles of microfibrils are indeed observed within the nucleoplasm. A continuity between the perisymbiotic membrane and the RER is often detected in the cytoplasm and some endosymbionts appear to be closely associated with mitochondria.
Endonuclear bacterial symbionts in two termite species: an ultrastructural study.
GRANDI, Gilberto;CHICCA, Milvia
1997
Abstract
Intracellular symbionts (endosymbiotic bacteria), either isolated or in clusters, were found within the cytoplasm and the nucleus of female germ cells and of trophocytes in nymphs and reproductives of two termite species, Kalotermes flavicollis (Isoptera: Kalotermitidae) and Reticulitermes lucifugus (Isoptera: Rhinotermitidae) , collected in the wild. This finding represents the first record of endonuclear symbiotic bacteria in a metazoan species. The bacteria reach the host ovarian cells by crossing the tunica propria. The ultrastructural morphology of the bacteria closely resembles that of cytoplasmic symbionts found in other insect orders (such as Dictyoptera and Homoptera) and their presence does not appear to be correlated with bacteriocytes (or mycetocytes) as in the more primitive termite Mastotermes darwiniensis (Isoptera: Mastotermitidae). The endonuclear symbionts, as well as the cytoplasmic ones, are enveloped by a plasma membrane, by a cell wall typical of Gram-negative bacteria and by a perisymbiotic membrane, the last two separated by an outer periplasmic space. In some of the endonuclear symbionts, however, the perisymbiotic membrane is lacking. Different kinds of inclusions, apparently unrelated to mesosomes, are visible within the endonuclear symbionts. A wide array of vesicles is found in the outer periplasmic space and inside the host chromatin, in close proximity to bacteria. Some vesicles apparently originate tram the outer layer of bacterial cell wall and are freed in the host chromatin by a further process of budding and vesiculation of the perisymbiotic membrane. These observations support the hypothesis of product exchanges between endosymbionts and the host cell. The presence of endonucIear symbionts (also seen in the act of dividing within the nucleus) does not apparently affect the meiotic processes or cause host cell degenerations, although a less dense chromatin, aggregates of granular material, thin cylindroid bodies and bundles of microfibrils are indeed observed within the nucleoplasm. A continuity between the perisymbiotic membrane and the RER is often detected in the cytoplasm and some endosymbionts appear to be closely associated with mitochondria.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
