56 research outputs found
Phylogenetic relationships among endosymbiotic R-body producer: Bacteria providing their host the killer trait
No full textR-body producing bacterial endosymbionts of Paramecium spp. transform their hosts into “killer” paramecia and provide them a selective advantage. This killer trait is connected to the presence of R-bodies, which are peculiar, tightly coiled protein ribbons capable of rapid unrolling. Based mainly on those two characteristics the respective obligate intracellular bacteria have been comprised in the genus Caedibacter and additional traits such as host species, subcellular localization, and R-body dimensions and mode of unrolling were used for species discrimination. Previous studies applying the full-cycle rRNA approach demonstrated the polyphyly of this assemblage. Following this approach, we obtained new sequences and in situ hybridizations for five strains of Caedibacter taeniospiralis and four strains associated to Caedibacter varicaedens and Caedibacter caryophilus. Detailed phylogenetic reconstructions confirm the association of C. taeniospiralis to Fastidiosibacteraceae and to Holosporales in case of the others. Therefore, we critically revise the taxonomy of the latter group. The high 16S rRNA gene sequence similarity among the type strains of Caedibacter varicaedens and C. caryophilus indicate that they should be classified within a single species for which we propose Caedimonas varicaedens comb. nov. owing to the priority of Caedibacter varicaedens. Moreover, we propose to establish the new family Caedimonadaceae fam. nov. to encompass Caedimonas varicaedens, “Ca. Paracaedimonas acanthamoebae” comb. nov. and “Ca. Nucleicultrix amoebiphila” within the order Holosporales
Free-living ciliates as potential reservoirs for eukaryotic parasites: Occurrence of a trypanosomatid in the macronucleus of Euplotes encysticus
No full textBackground: Flagellates of the family Trypanosomatidae are obligate endoparasites, which can be found in various hosts. Several genera infect insects and occur as monoxenous parasites especially in representatives of Diptera and Hemiptera. These trypanosomatid flagellates probably share the worldwide distribution of their hosts, which are often infested by large numbers of endoparasites. Traditionally, their taxonomy was based on morphology, host origin, and life cycle. Here we report the characterization of a trypanosomatid infection detected in a protozoan, a ciliate collected from a polluted freshwater pond in a suburb of New Delhi (India). Methods. Live observations and morphological studies applying light, fluorescence and transmission electron microscopy were conducted. Molecular analyses of host and parasite were performed and used for phylogenetic reconstructions and species (host) or genus level (parasite) identification. Results: Although the morphological characteristics were not revealing, a high similarity of the trypanosomatids 18S rRNA gene sequence to Herpetomonas ztiplika and Herpetomonas trimorpha (Kinetoplastida, Trypanosomatidae), both parasites of biting midges (Culicoides kibunensis and Culicoides truncorum, respectively) allowed the assignment to this genus. The majority of the host population displayed a heavy infection that significantly affected the shape of the host macronucleus, which was the main site of parasite localization. In addition, the growth rate of host cultures, identified as Euplotes encysticus according to cell morphology and 18S rRNA gene sequence, was severely impacted by the infection. Conclusions: The host-parasite system described here represents a recent example of free-living protists acting as environmental reservoirs for parasitic eukaryotic microorganisms
Fitness Impact of Obligate Intranuclear Bacterial Symbionts Depends on Host Growth Phase
No full textAccording to text book definition, parasites reduce the fitness of their hosts whereas mutualists provide benefits. But biotic and abiotic factors influence symbiotic interactions, thus under certain circumstances parasites can provide benefits and mutualists can harm their host. Here we addressed the question which intrinsic biotic factors shape a symbiosis and are crucial for the outcome of the interaction between the obligate intranuclear bacterium Holospora caryophila (Alphaproteobacteria; Rickettsiales) and its unicellular eukaryotic host Paramecium biaurelia (Alveolata; Ciliophora). The virulence of H. caryophila, i.e., the negative fitness effect on host division and cell number, was determined by growth assays of several P. biaurelia strains. The performances of genetically identical lines either infected with H. caryophila or symbiont-free were compared. Following factors were considered as potentially influencing the outcome of the interaction: (1) host strain, (2) parasite strain, and (3) growth phases of the host. All three factors revealed a strong effect on the symbiosis. In presence of H. caryophila, the Paramecium density in the stationary growth phase decreased. Conversely, a positive effect of the bacteria during the exponential phase was observed for several host × parasite combinations resulting in an increased growth rate of infected P. biaurelia. Furthermore, the fitness impact of the tested endosymbionts on different P. biaurelia lines was not only dependent on one of the two involved strains but distinct for the specific combination. Depending on the current host growth phase, the presence of H. caryophila can be harmful or advantageous for P. biaurelia. Thus, under the tested experimental conditions, the symbionts can switch from the provision of benefits to the exploitation of host resources within the same host population and a time-span of less than 6 days
Microbial Consortium Associated with the Antarctic Marine Ciliate Euplotes focardii: An Investigation from Genomic Sequences
No full textWe report the characterization of the bacterial consortium associated to Euplotes focardii, a strictly psychrophilic marine ciliate that was maintained in laboratory cultures at 4 °C after its first isolation from Terra Nova Bay, in Antarctica. By Illumina genome analyser, we obtained 11,179 contigs of potential prokaryotic origin and classified them according to the NCBI's prokaryotic attributes table. The majority of these sequences correspond to either Bacteroidetes (16 %) or Proteobacteria (78 %). The latter were dominated by gamma- (39 %, including sequences related to the pathogenic genus Francisella), and alpha-proteobacterial (30 %) sequences. Analysis of the Pfam domain family and Gene Ontology term variation revealed that the most frequent terms that appear unique to this consortium correspond to proteins involved in "transmembrane transporter activity" and "oxidoreductase activity". Furthermore, we identified genes that encode for enzymes involved in the catabolism of complex substance for energy reserves. We also characterized members of the transposase and integrase superfamilies, whose role in bacterial evolution is well documented, as well as putative antifreeze proteins. Antibiotic treatments of E. focardii cultures delayed the cell division of the ciliate. To conclude, our results indicate that this consortium is largely represented by bacteria derived from the original Antarctic sample and may contribute to the survival of E. focardii in laboratory condition. Furthermore, our results suggest that these bacteria may have a more general role in E. focardii survival in its natural cold and oxidative environment
Evaluation of Enrichment Protocols for Bacterial Endosymbionts of Ciliates by Real-Time PCR
No full textLarge-scale studies on obligate bacterial endosymbionts may frequently require preliminary purification and enrichment protocols, which are often elaborate to set up and to evaluate, especially if the host organism is a protist. The purpose of this study was to develop a real-time PCR-based strategy and employ it for assessing two of such enrichment protocols for Holospora caryophila, hosted by the ciliate Paramecium. Four SSU rRNA gene-targeted real-time PCR assays were designed, which allowed to compare the amount of H. caryophila to other organisms, namely the host, its food bacterium (Raoultella planticola), and free-living bacteria present in the culture medium. By the use of the real-time PCR assays in combination, it was possible to conclude that the “cell fractionation” protocol was quite successful in the enrichment of the symbiont, while the “Percoll gradient” protocol will need further refinements to be fully repeatable. The proposed approach has the potential to facilitate and encourage future studies on the yet underexplored field of bacterial endosymbionts of ciliates and other protists. It can also find valuable applications for experimental questions other than those tested, such as fast and precise assessment of symbiont abundance in natural populations and comparison among multiple coexisting symbionts
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
Isolation and characterization of bacterial strains from a consortium associated to the Antarctic ciliate Euplotes focardii
No full textCiliate (Alveolata,Ciliophora) possess a diverse association of symbiotic bacteria. They can be presenta s endosymbionts or localized in the outer as ectosymbionts. In a previous study we reported the characterization of a bacterial consortium associated to E. focardii, a strict psycrophilic ciliate isolated from the Terra nova Bay, Antarctica (Pucciarelli et al2015). This consortium is composed by Bacteroidetes (19%), Alpfa probacteria (28%), Beta protobacteria (5%) and Gamma proeobacteria (33%). In the present study, we report the isolation of bacterial strains from this consortium. In particular we were interested in the isolation of bacterial stains able to grow in the presence of pollulants, in order to verify thir potential application in bioremediation. By using culture enrichment technique with different source of pollulants such as diesel oil, methanol and cadmium chloride, we succeded to isolate tree bacterial species
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 ..
Biodiversity of Ciliates and Their Symbionts: A Special Issue
No full textInterests to estimate and assess the diversity of ciliates have a centuries-long history [...
"Candidatus Megaira polyxenophila" gen. nov., sp. nov.: Considerations on Evolutionary History, Host Range and Shift of Early Divergent Rickettsiae
No full text‘‘Neglected Rickettsiaceae’’ (i.e. those harboured by non-hematophagous eukaryotic hosts) display greater phylogenetic
variability and more widespread dispersal than pathogenic ones; yet, the knowledge about their actual host range and host
shift mechanism is scarce. The present work reports the characterization following the full-cycle rRNA approach (SSU rRNA
sequence, specific in situ hybridization, and ultrastructure) of a novel rickettsial bacterium, herewith proposed as
’Candidatus Megaira polyxenophila’ gen. nov., sp. nov. We found it in association with four different free-living ciliates
(Diophrys oligothrix, Euplotes octocarinatus, Paramecium caudatum, and Spirostomum sp., all belonging to Alveolata,
Ciliophora); furthermore it was recently observed as intracellular occurring in Carteria cerasiformis and Pleodorina japonica
(Chlorophyceae, Chlorophyta). Phylogenetic analyses demonstrated the belonging of the candidate new genus to the
family Rickettsiaceae (Alphaproteobacteria, Rickettsiales) as a sister group of the genus Rickettsia. In situ observations revealed
the ability of the candidate new species to colonize either nuclear or cytoplasmic compartments, depending on the host
organism. The presence of the same bacterial species within different, evolutionary distant, hosts indicates that ’Candidatus
Megaira polyxenophila’ recently underwent several distinct host shifts, thus suggesting the existence of horizontal
transmission pathways. We consider these findings as indicative of an unexpected spread of rickettsial infections in aquatic
communities, possibly by means of trophic interactions, and hence propose a new interpretation of the origin and
phylogenetic diversification of rickettsial bacteria
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