Holosporaceae Gortz and Schmidt 2006
General information
Description and emendation
Bacteria are present specifically in the micronucleus or macronucleus of Paramecium species. Exists in two forms: the reproductive form is a short rod 1.0-3.0 × 0.5 μm. It undergoes binary fission and may give rise to the long infectious form, measuring 5.0-20.0 μm with rounded or tapered ends, that can infect Paramecium and become established in the nucleus. The infectious form has a voluminous periplasm filled with fine, granular material with a less electron-dense pale tip, called the special tip. The condensed-looking bacterial protoplasm of the infectious form contains ribosomes and mesosome-like structures. The cytoplasm is polarly positioned opposite to the special tip in one half of the cell (Figure 1). The cytoplasm stains with DNA-specific dyes. Gram-negative, nonmotile, obligate symbiont. No toxic effects of Holospora-bearing paramecia on paramecia lacking the symbiont were observed. Paramecia can outgrow Holospora species, but reinfection occurs readily; mass cultures show up to 100% infection.
1: Basis of assignment to this family is a stable clustering in phylogenetic trees with the type genus Holospora and not with the Caedibacter-Nucleicultrix clade; showing a prokaryotic SSU rRNA identity with Holospora higher than 81%. All described members of this family are obligate intracellular bacteria. Several possess two morphologically distinct forms and/or life cycles. The family currently comprises the genera Holospora, 'Candidatus Gortzia', 'Candidatus Paraholospora', 'Candidatus Hepatobacter', 'Candidatus Bealeia', and several sequences from uncultured organisms.
Subdivision(s)
MID | Name | Rank | Taxon ID |
---|---|---|---|
M022502130201 | Holospora | Genus | 44747 |