94 research outputs found
Characterization of a novel Holospora-like symbiont from Frontonia (Ciliophora, Oligohymenophorea)
No full textThe existence of symbiotic relationships between prokaryotes
and ciliate protozoa is known from over a century. Most studies
concerned obligatory mutualistic symbiosis, whereas there is little
knowledge about facultative non-mutualistic symbiotic relationships,
mainly because these associations can be spatially and temporally
variable in natural populations and are especially difficult
to maintain in lab conditions. Nevertheless, they seem to be more
widespread among ciliates than so far supposed. A research
project was recently started in order to get data about such kind
of association in ciliate populations living in a coastal brackish
environment. During this study, we observed some individuals
from a population of Frontonia sp. (Oligohymenophorea, Peniculia)
showing roundish macronuclei instead of ellipsoidal ones.
Observation at DIC microscope revealed the presence of some
relatively large spindle-shaped objects in all macronuclei. According
to the general shape and morphological features, the identification
of these objects as Holospora infectious forms was
hypothesized. The genus Holospora (Alphaproteobacteria, Rickettsiales)
comprises bacterial endosymbionts, which are resident
in the nuclear apparatus of ciliates belonging to the genus Paramecium
(Oligohymenophorea, Peniculia). Their life cycle presents
two different forms: a large infectious form and a smaller
reproductive form. Experiments of in situ hybridization using a
genus-specific probe confirmed the identification of the observed
endonuclear objects as Holospora infectious forms; it made also
possible to observe even the smaller reproductive forms in macronuclei
that were not clearly visible at DIC observation. To further
characterize this symbiont, bacterial DNA was extracted from a
population of infected Frontonia sp. cells. The 16S rRNA gene
sequence was obtained by touchdown PCR reaction with a-proteobacteria-
specific primers and direct sequencing of reaction
product. The new sequence shows a similarity value of about
95% with that of H. obtusa. Indeed, analysis of phylogenetic relationships
revealed that the two sequences are firmly associated.
Molecular data obtained up to now suggest the belonging of this
organism to a novel species of Holospora
Betaproteobacterial symbionts of the ciliate Euplotes: origin and tangled evolutionary path of an obligate microbial association.
No full textThe Polynucleobacter-Euplotes association is an obligatory symbiotic system between a monophyletic group of ciliate species belonging to the genus Euplotes and bacteria of the species Polynucleobacter necessarius (Betaproteobacteria). Both organisms are unable to survive independently. Several studies revealed the existence of free-living populations of Polynucleobacter bacteria which are phylogenetically closely related to the endosymbiotic ones, but never share associations with Euplotes in the natural environment. Hence, following the most parsimonious explanation on the origin of the association, this symbiosis should represent a synapomorphic character for the hosts’ clade. Nevertheless, phylogenetic analyses performed on an increased number of strains here presented suggest that Euplotes species, during their evolution, recruited Polynucleobacter bacteria as symbionts more than once. Moreover, in three cases, we observed different bacteria as obligate symbionts. These symbionts are the first characterized representatives of a phylogenetic lineage branching in a basal position with respect to the genus Polynucleobacter. The hypothesis that the original obligate symbionts belonged to this newly discovered clade, and that, only subsequently, in most cases they have been replaced by Polynucleobacter bacteria recruited from the environment is proposed and discussed. The evolutionary path of this association seems anyway to have been more complex than so far supposed
A new obligate bacterial symbiont colonizing the ciliate Euplotes in brackish and freshwater: "Candidatus Protistobacter heckmanni"
No full textA monophyletic group of freshwater and brackish ciliate species belonging to the
genus Euplotes is known to harbor bacterial endosymbionts of the class Betaproteobacteria permanently
in the natural environment. One or other of 2 different species of bacteria have been
shown to be present: the obligate symbiont Polynucleobacter necessarius or a recently described
betaproteobacterium. While the association between P. necessarius and its Euplotes hosts has
been well studied in the past, knowledge about the relationship between the newly discovered
symbiont and its Euplotes hosts is still very poor. Here we present the SSUrRNA gene characterization
of both host and symbiont for an additional brackish-water population of Euplotes hosting
the newly discovered symbiont. We also provide the symbiont genome size determination and
ultrastructural description. Attempts to cultivate the new symbiont outside its host, using many
different methods, failed. This result indicates that, as in the case of the symbiotic P. necessarius,
we are probably dealing with an obligate symbiont, unable to grow outside the cytoplasm of its
natural host. On the basis of the results obtained we propose the new symbiont as a candidate new
species with the name of ‘Candidatus Protistobacter heckmanni’, according to the current rules of
prokaryotic nomenclature
Molecular phylogeny of unculturable Kariorelictea (Alveolata Ciliophora)
No full textKaryorelictea is a class of traditionally unculturable ciliates characterized by a non-dividing macronucleus. Their classification has been recently revised and morphological redescription
of many species has been performed as well. On the contrary, molecular data of karyorelictean ciliates are largely underrepresented in public databases. In the present article we resumed and
improved a method to characterize 18S rRNA gene sequences through direct amplification and sequencing of single cells. Using this approach, we characterized 12 different karyorelictean
molecular operational taxonomic units (MOTUs: nine trachelocercids, one Geleia
, one Remanella and one
Loxodes ), most of which were also photo-recorded. These molecular data were used to reconstruct phylogenetic relationships among the three orders (Protostomatida,
Loxodida and rotoheterotrichida) in which the class is traditionally subdivided. The most
supported tree topology shows an association between orders Loxodida (Loxodes,Remanella)
and Protoheterotrichida(Geleia
), in contrast with previous works associating orders Loxodida and Protostomatida (trachelocercids) on a morphological basis
Candidatus Anadelfobacter veles" and "Candidatus Cyrtobacter comes," Two New Rickettsiales Species Hosted by the Protist Ciliate Euplotes harpa (Ciliophora, Spirotrichea)
No full textThe order Rickettsiales (Alphaproteobacteria) is a well-known group containing obligate endocellular prokaryotes. The order encompasses three families (Rickettsiaceae, Anaplasmataceae, and Holosporaceae) and a fourth, family-level cluster, which includes only one candidate species, “Candidatus Midichloria mitochondrii,” as well as several unnamed bacterial symbionts. The broad host range exhibited by the members of the “Candidatus Midichloria” clade suggests their eventual relevance for a better understanding of the evolution of symbiosis and host specificity of Rickettsiales. In this paper, two new bacteria belonging to the “Candidatus Midichloria” clade, hosted by two different strains of the ciliate protist Euplotes harpa, are described on the basis of ultrastructural observations, comparative 16S rRNA gene sequence analysis, and an estimation of the percentage of infection. Ultrastructure of these bacteria shows some unusual features: one has an electron-dense cytoplasm, and the other one lacks a symbiosomal membrane. The latter was up to now considered an exclusive feature of bacteria belonging to the family Rickettsiaceae. 16S rRNA gene phylogenetic analysis unambiguously places the new bacteria in the “Candidatus Midichloria” clade, although their phylogenetic relationships with other members of the clade are not clearly resolved. This is the first report of a ciliate-borne bacterium belonging to the “Candidatus Midichloria” clade. On the basis of the data obtained, the two bacteria are proposed as two new candidate genera and species, “Candidatus Anadelfobacter veles” and “Candidatus Cyrtobacter comes.
Interferon-alpha enhances cross-presentation in human dendritic cells by modulating antigen survival, endocytic routing and processing.
No full textMultivalent presentation of saccharide fragments related to streptococcus pneumoniae 19F serotype
No full textThe polysaccharide encapsulated bacteria Streptococcus pneumonia (SP) is one of the leading causes of bacterial infections in young children. The capsular polysaccharides (CPS) are virulence factors, and their chemical structure defines the different bacterial serotypes. One of the most virulent SP serotype is the 19F, which is characterized by the trisaccharide repeating unit (4)--D-ManpNAc-(14)--D-Glcp-(12)--L-Rhap-(1-OPO3-), with a phosphodiester bridge connecting a residue of rhamnose at the reducing end of one unit to the non-reducing end of the following unit. It has been demonstrated that there is an evident effect of the pneumococcal polysaccharide chain length on the immunogenicity. We have observed for SP 19F that even the single trisaccharide repeating unit shows a good ability to inhibit the binding between the 19F polysaccharide and the anti-19F human polyclonal antibody, with efficacy and affinity lower than the natural polysaccharide. The lower activity of the monomer can be ascribed to the absence of the multivalent presentation of the epitope, that on the contrary is present in the natural polysaccharide chain. In this context, a multivalent scaffold which act as the core for the multivalent resentation of biological ligands is a strategy to positively affect the immunological potential of the saccharide antigen. Herein we will describe our ongoing work toward the preparation of a multivalent system based on a calixarene scaffold for the multivalent presentation of the trisaccharide repeating unit of SP 19F. A set of calix[4]arenes decorated with 3-amino-propyl N-acetyl-Dmannosamine, i.e. the immunodominant residue of the trisaccharide SP 19F repeating unit, have been prepared. The systems show different conformational properties, that reflect in different orientation of the saccharide antigens toward the protein receptor, and have been biologically evaluated to select the more promising calixarene platform for the conjugation of the SP 19F trisaccharide repeating unit
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