1,720,971 research outputs found
Revised systematics of Holospora-like bacteria and characterization of “Candidatus Gortzia infectiva”, a novel macronuclear symbiont of Paramecium jenningsi
No full textThe genus Holospora (Rickettsiales) includes highly
infectious nuclear symbionts of the ciliate Paramecium with
unique morphology and life cycle. To date, nine species have
been described, but a molecular characterization is lacking for
most of them. In this study, we have characterized a novel
Holospora-like bacterium (HLB) living in the macronuclei of
a Paramecium jenningsi population. This bacterium was morphologically
and ultrastructurally investigated in detail, and its
life cycle and infection capabilities were described. We also
obtained its 16S rRNA gene sequence and developed a specific
probe for fluorescence in situ hybridization experiments. A new
taxon, “Candidatus Gortzia infectiva”, was established for this
HLB according to its unique characteristics and the relatively
low DNA sequence similarities shared with other bacteria. The
phylogeny of the order Rickettsiales based on 16S rRNA gene
sequences has been inferred, adding to the available data the
sequence of the novel bacterium and those of two Holospora
species (Holospora obtusa and Holospora undulata) characterized
for the purpose. Our phylogenetic analysis provided molecular
support for the monophyly of HLBs and showed a
possible pattern of evolution for some of their features. We
suggested to classify inside the family Holosporaceae only
HLBs, excluding other more distantly related and phenotypically
different Paramecium endosymbionts
The Obligate Symbiont “Candidatus Megaira polyxenophila” Has Variable Effects on the Growth of Different Host Species
Get PDF“Candidatus Megaira polyxenophila” is a recently described member of Rickettsiaceae which comprises exclusively obligate intracellular bacteria. Interestingly, these bacteria can be found in a huge diversity of eukaryotic hosts (protist, green algae, metazoa) living in marine, brackish or freshwater habitats. Screening of amplicon datasets revealed a high frequency of these bacteria especially in freshwater environments, most likely associated to eukaryotic hosts. The relationship of “Ca. Megaira polyxenophila” with their hosts and their impact on host fitness have not been studied so far. Even less is known regarding the responses of these intracellular bacteria to potential stressors. In this study, we used two phylogenetically close species of the freshwater ciliate Paramecium, Paramecium primaurelia and Paramecium pentaurelia (Ciliophora, Oligohymenophorea) naturally infected by “Ca. Megaira polyxenophila”. In order to analyze the effect of the symbiont on the fitness of these two species, we compared the growth performance of both infected and aposymbiotic paramecia at different salinity levels in the range of freshwater and oligohaline brackish water i.e., at 0, 2, and 4.5 ppt. For the elimination of “Ca. Megaira polyxenophila” we established an antibiotic treatment to obtain symbiont-free lines and confirmed its success by fluorescence in situ hybridization (FISH). The population and infection dynamics during the growth experiment were observed by cell density counts and FISH. Paramecia fitness was compared applying generalized additive mixed models. Surprisingly, both infected Paramecium species showed higher densities under all salinity concentrations. The tested salinity concentrations did not significantly affect the growth of any of the two species directly, but we observed the loss of the endosymbiont after prolonged exposure to higher salinity levels. This experimental data might explain the higher frequency of “Ca. M. polyxenophila” in freshwater habitats as observed from amplicon data
Detection of a Novel Subspecies of Francisella noatunensis as Endosymbiont of the Ciliate Euplotes raikovi.
No full textFrancisella are facultative intracellular bacteria causing severe disease in a broad range of animals. Two species are notable: Francisella tularensis, the causative organism of tularemia and a putative warfare agent, and
Francisella noatunensis, an emerging fish pathogen causing
significant losses in wild and farmed fish. Although
various aspects of Francisella biology have been intensively
studied, their natural reservoir in periods between massive
outbreaks remains mysterious. Protists have been suspected
to serve as a disguised vector of Francisella and co-culturing
attempts demonstrate that some species are able to survive
and multiply within protozoan cells. Here, we report the first
finding of a natural occurrence of Francisella sp. as a protist
endosymbiont. By molecular and morphological approaches,
we identified intracellular bacteria localized in a strain of the
marine ciliate Euplotes raikovi, isolated from the coast of
Adriatic Sea. Phylogenetic analysis placed these endosymbionts within the genus Francisella, in close but distinct association with F. noatunensis. We suggest the establishment of a novel subspecies within F. noatunensis and
propose the cytoplasmatic endosymbiont of E. raikovi as “Candidatus F. noatunensis subsp. endociliophora” subsp.
nov
Response of the bacterial symbiont Holospora caryophila to different growth conditions of its host
No full textPrevious studies on bacterial symbionts of ciliates have shown that some symbionts can be maintained relatively well under standard laboratory conditions whereas others are frequently lost, especially when the host is cultivated at a high division rate. In this study, the variation in infection level by the endosymbiont Holospora caryophila within its host population Paramecium octaurelia was investigated in response to three alimentary treatments and a subsequent starvation phase. The response of the ciliates was determined as a nearly exponential growth rate with different slopes in each treatment, proportional to the amount of food received. The initial infection level was higher than 90%. After 24 days of exponential host's growth, the prevalence remained stable at approximately 90% in all treatments, even after a subsequent starvation phase of 20 days. However, at intermediate time-points in both the feeding and the starvation phase, fluctuations in the presence of the intracellular bacteria were observed. These results show that H. caryophila is able to maintain its infection under the tested range of host growth conditions, also due to the possibility of an effective re-infection in case of partial loss
Molecular characterization of the obligate endosymbiont "Caedibacter macronucleorum" Fokin and Gortz, 1993 and of its host Paramecium duboscqui strain Ku4-8
No full textAbstract: Bacterial endosymbionts of protozoa were often described as new species by protozoologists mainly on the basis of few morphological characters and partly by host specificity. Many of these species have never been validated by prokaryotic microbiologists whose taxonomic rules are quite different from those of protozoologists, who use the Zoological Code of Nomenclature. "Caedibacter macronucleorum" Fokin and Gortz 1993, an endosymbiont of Paramecium duboscqui, belongs to this category. Here we provide the molecular characterization of this organism and of its host P. duboscqui strain Ku4-8. Bacterial 16S rRNA gene sequence analysis proved that "C. macronucleorum" belongs to the Alphaproteobacteria. It is closely related to Caedibacter caryophilus but not to Caedibacter taeniospiralis, which belongs to the Gammaproteobacteria. "Caedibacter macronucleorum" and C. caryophilus 16S rRNA genes show a similarity value of 99%. This high 16S rRNA sequence similarity and the lack of ..
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Tracing the role of R-bodies in the killer trait: Absence of toxicity of R-body producing recombinant E. coli on paramecia.
No full textR-bodies are coiled proteinaceous ribbons produced by Paramecium endosymbionts belonging to the genus Caedibacter. These intracellular bacteria confer upon their hosts a phenomenon called the killer trait. It is the ability to kill symbiont-free competitors called sensitives. The R-body is the crucial element of this process, but despite many efforts, the actual role of R-bodies in killing sensitive paramecia is still not satisfactory clarified. The open question is whether the R-body acts as transmitter for a yet unidentified toxin or whether it directly kills sensitive paramecia having intrinsic cytotoxic effects. In the present study, this problem is addressed by heterologous expression of Caedibacter taeniospiralis R-body in Escherichia coli followed by a detailed analysis of its potential intrinsic toxic effect on feeding sensitive Paramecium tetraurelia. Using this approach, we can exclude any eventual effects of additional, unidentified factors produced by C. taeniospiralis and thus observe the impact of the recombinant R-body itself. No cytotoxic effects of recombinant R-bodies were detected following this approach, strengthening the hypothesis that R-bodies act as releasing system for an unidentified C. taeniospiralis toxin
- …
