51 research outputs found
“Candidatus Hafkinia simulans” gen. nov., sp. nov., a Novel Holospora-Like Bacterium from the Macronucleus of the Rare Brackish Water Ciliate Frontonia salmastra (Oligohymenophorea, Ciliophora): Multidisciplinary Characterization of the New Endosymbiont and Its Host
No full textWe characterized a novel Holospora-like bacterium (HLB) (Alphaproteobacteria, Holosporales) living in the macronucleus of
the brackish water ciliate Frontonia salmastra. This bacterium was morphologically and ultrastructurally investigated, and its life
cycle and infection capabilities were described. We also obtained its 16S rRNA gene sequence and performed in situ hybridization experiments with a specifically-designed probe. A new taxon, BCandidatus Hafkinia simulans^, was established for this
HLB. The phylogeny of the family Holosporaceae based on 16S rRNA gene sequences was inferred, adding to the already
available data both the sequence of the novel bacterium and those of other Holospora and HLB species recently characterized.
Our phylogenetic analysis provided molecular support for the monophyly of HLBs and placed the new endosymbiont as the sister
genus ofHolospora. Additionally, the host ciliate F. salmastra, recorded in Europe for the first time, was concurrently described
through a multidisciplinary study. Frontonia salmastra’s phylogenetic position in the subclass Peniculia and the genus Frontonia
was assessed according to 18S rRNA gene sequencing. Comments on the biodiversity of this genus were added according to past
and recent literature
"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
Studio preliminare delle associazioni simbiotiche fra protisti ciliati e procarioti in un ambiente salmastro costiero: caratterizzazione morfologica e molecolare
No full textIl lavoro ha come obiettivo l’identificazione e la caratterizzazione morfologica e molecolare di protozoi ciliati mesopsammici di uno specifico ambiente salmastro confinato e dei loro eventuali batteri simbionti. L’attenzione è stata focalizzata sui ciliati quantitativamente dominanti nell’ambiente e che, ad uno screening preliminare, risultavano associati a batteri ecto- od endosimbionti. Tali caratterizzazioni rappresentano un punto di partenza indispensabile per possibili studi futuri di tipo ecologico volti a determinare la variabilità spaziale e temporale delle associazioni simbiotiche all’interno della comunità in esame.
Sono stati effettuati tentativi di coltivabilità su ciascuna specie di ciliati presa in esame, ed ove possibile sono state allestite colture monoclonali. La caratterizzazione morfologica è stata effettuata mediante osservazioni in vivo (binoculare, D.I.C.), colorazioni cellulari (Feulgen, impregnazione argentica). osservazione al S.E.M. La microscopia a trasmissione (T.E.M.) ha consentito una descrizione ultrastrutturale dei batteri simbionti.
Come marcatori molecolari sono stati impiegati il 18S rDNA per i ciliati ospiti ed il 16S rDNA per i batteri simbionti, caratterizzati tramite PCR e sequenziamento diretto (ove possibile) o PCR, clonaggio e sequenziamento dei cloni rappresentativi. Sulla base delle sequenze del 16S rRNA desunte, sono state fatte sintetizzare specifiche sonde oligonucleotidiche marcate con fluorocromi al fine di poter associare con certezza, tramite ibridazione in situ, una sequenza di 16S rRNA ad uno specifico batterio simbionte.
Sei tipi di batteri simbionti sono stati ritrovati in quattro diversi ciliati: Euplotes parawoodruffi (Spirotrichea, Hypotrichia), che ne contiene due, Frontonia salmastra (Oligohymenophorea, Peniculia), anch’esso contenente due simbionti, Sonderia cfr. vorax (Plagiopylea, Plagiopylida), Pseudomicrothorax dubius (Nassophorea, Microthoracida). Sono state messe a punto specifiche tecniche per il mantenimento di colture monoclonali di F. salmastra e di popolazioni di Sonderia cfr. vorax e P. dubius. Gli organismi sono stati caratterizzati morfologicamente e molecolarmente. La scarsità di letteratura e l’ambiguità di interpretazione di alcune caratteristiche morfologiche non ha consentito di poter giungere in tutti i casi alla determinazione della specie. Sono state ottenute le sequenze del 16S rDNA del simbionte principale di E. parawoodruffi, un β-proteobatterio vicino al gen. Polynucleobacter, del simbionte di F. salmastra., un β-proteobatterio vicino al gen. Holospora, e del simbionte di P. dubius., un β-proteobatterio vicino al gen. Rickettsia; tali risultati sono stati confermati da esperimenti di ibridazione in situ utilizzando sonde genere-specifiche. La caratterizzazione dei simbionti di Sonderia sp. e del simbionte secondario di E. parawoodruffi, appartenenti alla cl. Gammaproteobacteria, è tuttora in corso
Facultative Associations between Protists and Rickettsial Symbionts: Morphological and Molecular Characterization Functional Implications, and Insights on Emerging Intracellular Parasites
No full textRickettsiae and Rickettsia-like organisms (RLOs) are Gram-negative prokaryotes known as obligate intracellular parasites of a variety of eukaryotic hosts, including humans. Recent studies reported the presence of these organisms also in protists, although no specific researches were accomplished. This work was aimed to investigate the diffusion of RLOs among protists, and to get insights about their host range and host shift capabilities. The first goal was achieved by systematical screenings of natural populations of ciliated protists from different habitats trough the “full-cycle rRNA approach” (individuation of symbionts through FISH, 16S rDNA characterization and use of specifically designed oligonucleotide probes for in situ detection). Descriptions of symbionts were refined through electron microscopy techniques and phylogenetic analysis. Six novel species of RLOs were identified in five different ciliates, namely Pseudomicrothorax dubius (Nassophorea), Spirostomum minus (Heterotrichea), Euplotes octocarinatus (Spirotrichea), Paramecium multimicronucleatum (Oligohymenophorea) and Diophrys oligothrix (Spirotrichea), which harbours two different symbionts. Phylogenetic inferences supported their belonging to the family Rickettsiaceae as candidate novel genera, except for symbionts of S. minus and P. multimicronucleatum that branches within the genus Rickettsia. These latter also share motile flagella, which were never reported among Rickettsiaceae. Analysis revealed the belonging of symbionts of E. octocarinatus and of one of that of D. oligothrix to the same novel species, which was further retrieved in three unrelated ciliate hosts. The finding accounted for possible host shifts through horizontal transfer. Both inter- and intraspecific transmissibility were tested using the other symbiont of D. oligotrix as infector and uninfected conspecific and allospecific (E. harpa) strains as hosts. Experiments evidenced its capability to undergo horizontal host shifts at both levels. Preliminary results indicate that some RLOs (symbionts of P. multimicronucleatum and one of that of D. oligothrix) can survive in association with lab-cultured metazoan cell lines. The present work contributed to reveal an unexpected, intriguing phylogenetic and morphological diversity among ciliate-borne Rickettsiaceae. The frequency of occurrence of symbioses between these latter and protists, together with the retrieval of the same RLO species from different hosts and the capability of horizontal shift (in case of symbionts of D. oligothrix) account for their polyxenic and likely opportunistic nature. Given the parasitic/pathogenic nature of the majority of known Rickettsiaceae, ciliated protists could effectively play the role of both natural reservoir and vectors for potentially hazardous rickettsial pathogens
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.
Morphology, ultrastructure, and molecular phylogeny of the ciliate Sonderia vorax with insights into the systematics of order Plagiopylida.
No full textBackground: Ciliates of the family Sonderiidae are common members of the eukaryotic communities in various
anoxic environments. They host both ecto- and endosymbiotic prokaryotes (the latter associated with
hydrogenosomes) and possess peculiar morpho-ultrastructural features, whose functions and homologies are not
known. Their phylogenetic relationships with other ciliates are not completely resolved and the available literature,
especially concerning electron microscopy and molecular studies, is quite scarce.
Results: Sonderia vorax Kahl, 1928 is redescribed from an oxygen-deficient, brackish-water pond along the Ligurian
Sea coastlines of Italy. Data on morphology, morphometry, and ultrastructure are reported. S. vorax is ovoid-ellipsoid
in shape, dorsoventrally flattened, 130 x 69 μm (mean in vivo); it shows an almost spherical macronucleus, and one
relatively large micronucleus. The ventral kinetom has a “secant system” including fronto-ventral and fronto-lateral
kineties. A distinctive layer of bacteria laying between kineties covers the ciliate surface. Two types of extrusomes
and hydrogenosomes-endosymbiotic bacteria assemblages are present in the cytoplasm. The phylogeny based on
18S rRNA gene sequences places S. vorax among Plagiopylida; Sonderiidae clusters with Plagiopylidae, although
lower-level relationships remain uncertain. The studied population is fixed as neotype and the ciliate is established
as type species of the genus, currently lacking.
Conclusions: This is the first description of a representative of Sonderiidae performed with both morphological
and molecular data. To sum up, many previous hypotheses on this interesting, poorly known taxon are confirmed
but confusion and contradictory data are as well highlighted
‘‘Candidatus Cryptoprodotis polytropus,’’ A Novel Rickettsia-Like Organism in the Ciliated Protist Pseudomicrothorax dubius (Ciliophora, Nassophorea).
No full textRickettsia-like organisms (RLO) are obligate, often highly fastidious, intracellular bacterial parasites associated with a variety of vertebrate and invertebrate hosts. Despite their importance as causative agents of severe mortality outbreaks in farmed aquatic species, little is known about their life cycle and their host range. The present work reports the characterization of "Candidatus Cryptoprodotis polytropus," a novel Rickettsia-like bacterium associated with the common ciliate species Pseudomicrothorax dubius by means of the "Full-Cycle rRNA Approach" and ultrastructural observations. The morphological description by in vivo and scanning electron microscopy and the 18S rRNA gene sequence of the host species is provided as well. Phylogenetic analysis based on the 16S rRNA gene supports the inclusion of "Candidatus Cryptoprodotis polytropus" within the family Rickettsiaceae (cl. Alphaproteobacteria) together with the genera Rickettsia and Orientia. Observations on natural ciliate populations account for the occasional nature of this likely parasitic association. The presence of a previously unknown RLO in ciliates sheds a new light on the possible role of protists as transient hosts, vectors or natural reservoir for some economically important pathogens. © 2009 by the International Society of Protistologists
Flagellar Movement in Two Bacteria of the Family Rickettsiaceae: A Re-Evaluation of Motility in an Evolutionary Perspective
No full textBacteria of the family Rickettsiaceae have always been largely studied not only for their importance in the medical field, but
also as model systems in evolutionary biology. In fact, they share a recent common ancestor with mitochondria. The most
studied species, belonging to genera Rickettsia and Orientia, are hosted by terrestrial arthropods and include many human
pathogens. Nevertheless, recent findings show that a large part of Rickettsiaceae biodiversity actually resides outside the
group of well-known pathogenic bacteria. Collecting data on these recently described non-conventional members of the
family is crucial in order to gain information on ancestral features of the whole group. Although bacteria of the family
Rickettsiaceae, and of the whole order Rickettsiales, are formally described as non-flagellated prokaryotes, some recent
findings renewed the debate about this feature. In this paper we report the first finding of members of the family displaying
numerous flagella and active movement inside their host cells. These two new taxa are hosted in aquatic environments by
protist ciliates and are described here by means of ultrastructural and molecular characterization. Data here reported
suggest that the ancestor of Rickettsiales displayed flagellar movement and re-evaluate the hypothesis that motility played a
key-role in the origin of mitochondria. Moreover, our study highlights that the aquatic environment represents a well
exploited habitat for bacteria of the family Rickettsiaceae. Our results encourage a deep re-consideration of ecological and
morphological traits of the family and of the whole order
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